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PStechPaul
03-11-2015, 05:36 PM
(From my thread on shop class):

I had to tap a 1/4-20 hole that I drilled with the specified #7 drill (0.201") to about 3/4" deep, and after a few turns the tap it became very hard to turn, in spite of liberal use of Tap-Magic and backing out 1/2 turn occasionally. It is a full taper 3 flute alloy steel tap from a HF set, but seems good quality and I just used it with no problem to tap 12 holes in my parting tool post. That was easy-to-machine 1215 steel, however, and were through holes in 0.3" to 0.4" material, while the manifold is 1018. I was able to tap it deeper by using a 4 flute carbon steel tap I reground to an almost bottom or plug tap, but each time I could only get about 1/2 more turn before switching.

I had a similar problem with the two mounting holes on the bottom, which I drilled to a depth of 1" with a slightly larger 13/64" (0.203") drill. The drills seemed to be 0.195" to 0.199" diameter, but they usually drill a few thousandths over. My buddy in the shop class broke a tap when he tried to tap the bottom holes, so the common element is the steel, although I don't know for certain if he took the same precautions as I did. I was able to get usable threads to a depth of 0.5", which should be enough, but the drawing calls for 0.6 min.

A search of the forum turned up some threads from 2010 and earlier, and of course the advice is to buy high quality taps, especially with spiral points and spiral flutes. But I want to find out why I had so much trouble. I will see if I can use a spiral tap at school tomorrow, and maybe it will work just fine and tell me that my taps are the problem.

KJ1I
03-11-2015, 05:45 PM
My reference table shows a #1 (0.228") pilot for 1/2" thick steel.

Paul Alciatore
03-11-2015, 06:06 PM
1. It is a blind hole, so the chips are likely building up in it. You have to remove them. One way is a cotton swab: stick it in and rotate it as you retract it. Another way is a can of compressed air with a straw. Insert the straw. PROTECT YOUR EYES and blast away.

2. The chips can also build up in the flutes of the tap. I find that after 1 or 2 turns in a blind hole that I must withdraw the tap and clean it. I use a toothbrush.

3. Harbor freight taps are not the best quality. You can get good ones from McMaster (any that they sell) or look for name brands from other suppliers. That being said, if the tap did not break, it is probably not your problem.

If you are going to to to tap to the bottom of a blind hole, you will need a set of three taps: taper, plug, and bottom styles. However, if you have the room, it is usually better to drill the hole deeper and not tap it all the way down. That also allows some room for the chips to accumulate, making clean-out less necessary.

TN Pat
03-11-2015, 06:16 PM
Yes - tapping a blind hole in steel, a quality spiral-flute tap is the bee's knees. Honestly, spiral flute taps are great all around if you just want one type of tap.

At the shop I work at, we regularly tap any and all materials using the normal 75% thread tap drill - mild steel, A2, 304 stainless, etc.. We use normal OSG black oxide HSS taps, typically spiral point, for some reason. I believe it really all comes down to the tap...

oxford
03-11-2015, 07:08 PM
My first suggestion is get a known good quality tap and see if you have the same problem. With that being said even good taps don't last forever, they will dull to the point that you will have trouble tapping some material before it breaks.

Like the others said, make sure you are taking care of the chip accumulation issue as well.

kf2qd
03-11-2015, 07:09 PM
One machine shop I used to work for had Tapping Wax. They were sticks of a soft yellow wax that you would stick down a blind hole and then run the tap to the bottom. The wax pushed the chips up the flutes and provided some lubrication. And the wax would stick to the tip of the tap (always used a spiral point tap) and the hole would be clean when you finished. Have not seen tapping wax since but it was a great way to tap a blind hole.

P.S. As far as I am concerned, small 3 or 4 flute taps are only good for chasing threads, A 2 flute spiral point is much stronger and gives better, faster results.

Bob Fisher
03-11-2015, 07:21 PM
Already mentioned, but get rid of the HF taps. When you use a good quality tap from McMaster or elsewhere, you will FEEL the difference. If you cannot drill deeper and still have a blind hole, you best get a quality tap. Bob.

PixMan
03-11-2015, 07:40 PM
My reference table shows a #1 (0.228") pilot for 1/2" thick steel.

If that's the case then you either have a really crappy chart or are looking at the wrong pitch (threads per inch.) That drill size is for a 1/4-28 UNF, and only f you want a scant 50% of thread.

http://www.physics.ncsu.edu/pearl/Tap_Drill_Chart.html

This is the type of tap which should be used in a blind hole, a spiral flute tap. The one on the left would be for short-chipping materials such as brass, cast iron, bronze. The one on the right can do steels and stainless steels.

The only ones if this style that I've ever broken were the cheap crap. Never use anything less than a name brand HSS, HSS-E or HSS-Co tap. Threading is most often the last step in a workpiece, so why take a chance that it'll be the start of a whole 'nuther job of getting the broken POS tap out, cleaning the hole and trying to get it done with a good one.

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/DSC_0510-r_zpsf86334d7.jpg

For through holes, a spiral point tap is the choice. Here's an example of a top quality one, in this case one for austenitic stainless steels.

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/IMG_2547-r_zps90ea6df0.jpg

garyhlucas
03-11-2015, 08:19 PM
Say what? That second picture is NOT a spiral point tap! That's a starter or maybe a plug tap. It doesn't have the tapered lead in that cause the chip to spiral forward of the tap and out the back side of the hole instead of traveling up the flutes.

Willy
03-11-2015, 08:45 PM
Something most folks do not realize is that 55-65 percent threads are only a few percent less strong than 75% threads and they are oh so much easier to tap due to dramatically less torque requirement.
Tooling lasts longer and tap breakage is virtually eliminated. The crests of the thread do not add significantly to the threads strength.
For all but the most demanding applications I usually aim for a 60-65% percent thread rather than what most tap/drill charts recommend. Quite often lately I've even used 55% threads and have been amazed both by their strength and the ease of tapping the hole.
Below some info that may make your day less stressful.:)

http://tapmatic.com/tapping-questions/tapping-torque-vs

http://tapmatic.com/images/technical_images/torque4.gif


http://blog.cnccookbook.com/2012/06/14/tap-drill-size-whats-the-right-one-aka-planning-ahead-to-reduce-broken-taps/



-
OSG suggests 55-65% threads for most applications. The force required to drive a tap is way less than for 75%. This is the range I use most of the time unless I’m really worried about strength. If the length of the threaded hole is more than about 3x the diameter of the fastener, 55-65% threads are very likely going to be stronger than the fastener itself anyway.

Willy
03-11-2015, 08:52 PM
Say what? That second picture is NOT a spiral point tap! That's a starter or maybe a plug tap. It doesn't have the tapered lead in that cause the chip to spiral forward of the tap and out the back side of the hole instead of traveling up the flutes.

The lighting in PixMan's pic may not be the best as I think the details are hidden in the shadows but it shares the same profile as the spiral point tap below.

http://www.maritool.com/images/Spiral-Point-Plug-Tap-Bright-Finish-1.jpg

Rosco-P
03-11-2015, 08:53 PM
For through holes, a spiral point tap is the choice. Here's an example of a top quality one, in this case one for austenitic stainless steels.



IMHO the word spiral was typed when the word gun was meant. Gun taps shoot the chips forward.

AD5MB
03-11-2015, 09:11 PM
I frequently have the pleasure of tapping 1/2" armor plating with the cheap TiN taps. new guys break ten taps before noon, and spend hours grinding broken taps flush and trying to tap two more holes somewhere other than where the customer specified.

meanwhile the GHOGs ( grey haired old geezers ) have the other door tapped and the accelerometers mounted before noon. the young guys ask the old guys what they are doing wrong. a 60 year old high school graduate who was doing a thing before a college guy was born can't tell that college boy a thing until college boy asks.

the gray haired old geezers figured out a long time ago:

Its' called a tap for a reason.

It isn't called a "put that puppy in a drill and spin it up to 1,000 RPM. puh-DUKSHUN, son, that's what it's all about!"
It isn't called a "put a cheater bar on that sumbatch and teach it the meaning of torque!"
and it isn't called a Timex because you wind it like a watch.

if you apply the tiniest bit of reason, you can see that the only part of the tap that removes material is the one to 5 tapered threads at the front. all the rest of the threads guide, support, and get jammed up with the crud the one to 5 tapered threads at the front break loose. do not apply torque at the tip of a brittle steel rod by twisting.

you operate a tap by tapping. when you remove the tap to blow the crud out with compressed air, you back it out until it binds, then you tap until it turns. don't torque, don't twist, tap.

there are pockets of even harder steel in armor plated steel. you can feel them when your tap hits them. when you get to the point where you feel one at the edge of your tap, you don't break taps.

side note: drilling armor plated steel: Norseman jobber AG 190s. keep plenty of spares on hand. when someone working for another contractor tries drilling armor plated steel with HSS bits, hand them an AG 190 with a drill stop made of duct tape and tell them not to punch through the steel and hit the 30,000 PSI concrete inside, because the drill is instantly ruined. they give you a goofy look, stare in amazement as the drill goes through the armor plate like it's brass, and tell you they broke all the bits you loaned them and where can I get these?

Doozer
03-11-2015, 09:40 PM
There are spiral point taps (sometimes called gun taps)
and there are spiral flute taps. Some noobs think all
spiral taps have to look like a twisted roller coaster.
Spiral points often are miscategorized or go unnoticed.
Don't be a noob, learn your taps.
Also, a 2 flute gun tap is the strongest (against breakage)
when tapping tough material. This is because less meat is
ground away to form the flutes.
--Doozer

oxford
03-11-2015, 09:56 PM
P.S. As far as I am concerned, small 3 or 4 flute taps are only good for chasing threads, A 2 flute spiral point is much stronger and gives better, faster results.

I have to agree with this. On the smaller taps I do much better with a 2 flute.

wierdscience
03-11-2015, 10:18 PM
There is really no good reason to run 70% threads when the threaded hole is more than 2xs the bolt diameter.Instead of a #7 drill,try a #5.

And I agree 100% buy quality taps from an industrial supplier,that really also applies to all cutting tools.

PixMan
03-11-2015, 10:47 PM
IMHO the word spiral was typed when the word gun was meant. Gun taps shoot the chips forward.

You are using the old, original or colloquial term for a spiral point tap when you say "gun tap". A gun tap is a spiral point tap and all of them push the chip ahead of the tap as it goes through the hole. Furthermore, it is not recommended to stop and break chips when using a spiral point tap. They have more radial back relief than a spiral flute tap which is specifically designed to have to back out of a hole and break the chips upon reversal.

Willy is right. Unless your eyes are sharp and you know taps (as I do), that photo may not show it's a spiral point tap all that well. Here's a better photo of a cheaper Greenfield tap I have:

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/IMG_1147-r.jpg

And here's a few more spiral flute taps, for blind holes. The one on the left is a DIN (ISO) standard shank and length. The one on the right is a DIN-ANSI shank, meaning it's ANSI diameter shank and square drive, but DIN length. The one in the middle is an old American design spiral flute, ANSI shank, and they are the most prone to breaking deep inside a hole. You can have it if you want, I'd only use it for cleaning dirty crap out of an already tapped hole.

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/IMG_1161-r.jpg

PStechPaul
03-11-2015, 11:07 PM
Although I agree that good quality taps are best, I think my main problem was using the #7 drill for 75% threads, and I see that the NCSU chart uses that for aluminum and plastic, while for steel it calls for 50% threads and a 7/32" (0.2188") drill. Most likely a #5 (0.2055") or #4 (0.209") would have been fine. The 0.6" minimum depth may refer to the hole, while the usable threads only really need 5 to 8 turns which is 0.25" to 0.4".

There was also a blind hole for a 1/4-18 NPT 2B thread and it calls for a flat bottom 0.5" deep (in 1.0" stock) that cannot break into a 0.156" diameter hole (exhaust port) that is drilled 0.125" from center. So that is a clearance of only 0.047". I decided to make this for a 1/8-27 thread because I have a couple of taps that size as well as a hose fitting, and I figured I could always drill it out for the larger size if needed. So I carefully drilled with an 11/32" drill, and then tried to bore the bottom flat (with a crappy boring bar holder). As I got close to the ID it deflected because it was impinging on part of the other half-thru hole (intake port). So I used a two-flute 5/16" end mill and got as close as I dared, a measured depth of 0.450".

I was able to turn the pipe tap about 4 turns before meeting resistance that I figured was from the tip bottoming out. Then I ground the tip of my other (lower quality black oxide carbon steel) tap and I got maybe another turn or so. The brass fitting only went in about 1-1/2 turns but it seems airtight. I think there would be less than one turn with a 1/4-18 tap. The pilot hole for 1/4-18 is 7/16" and I probably have an end mill that size. But I don't think having the hole bottom totally flat will help get any more depth on the tap because of the tip being tapered.

Thanks for the information and advice. :D

thaiguzzi
03-11-2015, 11:18 PM
HSS. Only.

PixMan
03-11-2015, 11:54 PM
HSS. Only.

?? HSS-E (5% cobalt) is a little better in taps because it adds just enough toughness to the shanks to keep them from being so brittle they break.

Euph0ny
03-12-2015, 04:30 AM
?? HSS-E (5% cobalt) is a little better in taps because it adds just enough toughness to the shanks to keep them from being so brittle they break.

The right composition of a tap also depends on the application. In gunsmithing work, there are a lot of tiny holes to tap in very tough steel. Because they are tiny, they love to break. When they break, it's often easier to get the HSS ones out without ruining the gun than the tough cobalt-enhanced ones.

DATo
03-12-2015, 06:53 AM
There is really no good reason to run 70% threads when the threaded hole is more than 2xs the bolt diameter.Instead of a #7 drill,try a #5.

And I agree 100% buy quality taps from an industrial supplier,that really also applies to all cutting tools.

+1

I routinely drill holes oversize before tapping regardless of whether the material is aluminum or stainless steel. In most cases the required strength of the thread does not need to be maximized. In the event the assembled parts will be under stress or if a safety issue is at stake such as a high-pressure chamber, then, of course, you want a full 75% thread (or better), but if all you are doing is joining two parts together such as a couple of brackets you can take considerable liberties with the tap drill size. Obviously, the less material the tap is trying to cut the less pressure will be required to cut it. This having been said I strongly agree with those who say to purchase quality taps.

Below may be the best advice I have ever offered on this website in the last four years.

Also, try putting a little regular cutting oil in a small amount of that Tap-Magic (about 50-50 mix). Years ago we had some Mobile cutting oil and at the time we also had Tapmatic (not Tap-Magic) cutting fluid for tapping (It's pretty much the same stuff). I had to tap some really stubborn stainless (24 holes which had become work-hardened) plate. I applied the Mobile oil with a paste brush: didn't work - got that chattering type of cutting action which precedes a broken tap, same thing with the Tapmatic cutting fluid. Tried several new taps .. nothing doing. But with the brush still wet from the Mobile AND the Tapmatic I got the best cutting results of my entire life. I even called a doubter over to try for himself with and without the concoction. His response ... "Oh my God! It cut like butter". I wisely mixed up a quart of this solution and it's a good thing I did because you can no longer buy the Tapmatic (EPA strikes again). I have been using the solution sparingly for the last ten years and still have about 80% left. Best stuff I've ever used and I got it quite by accident. Same thing may work with your Tap-Magic ... wouldn't hurt to try.

Black Forest
03-12-2015, 07:12 AM
+1

I routinely drill holes oversize before tapping regardless of whether the material is aluminum or stainless steel. In most cases the required strength of the thread does not need to be maximized. In the event the assembled parts will be under stress or if a safety issue is at stake such as a high-pressure chamber, then, of course, you want a full 75% thread (or better), but if all you are doing is joining two parts together such as a couple of brackets you can take considerable liberties with the tap drill size. Obviously, the less material the tap is trying to cut the less pressure will be required to cut it. This having been said I strongly agree with those who say to purchase quality taps.

Below may be the best advice I have ever offered on this website in the last four years.

Also, try putting a little regular cutting oil in a small amount of that Tap-Magic (about 50-50 mix). Years ago we had some Mobile cutting oil and at the time we also had Tapmatic (not Tap-Magic) cutting fluid for tapping. I had to tap some really stubborn stainless (24 holes which had become work-hardened) plate. I applied the Mobile oil with a paste brush: didn't work - got that chattering type of cutting action which precedes a broken tap, same thing with the Tapmatic cutting fluid. Tried several new taps .. nothing doing. But with the brush still wet from the Mobile AND the Tapmatic I got the best cutting results of my entire life. I even called a doubter over to try for himself. His response ... "Oh my God!" It cut like butter. I wisely mixed up a quart of this solution and it's a good thing I did because you can no longer buy the Tapmatic (EPA strikes again). I have been using the solution sparingly for the last ten years and still have about 80% left. Best stuff I've ever used and I got it quite by accident. Same thing may work with your Tap-Magic ... wouldn't hurt to try.


That sounds very good.

So what is your address and do you have a burglar alarm protecting your shop! :cool:

DATo
03-12-2015, 07:54 AM
That sounds very good.

So what is your address and do you have a burglar alarm protecting your shop! :cool:

Not kidding Blackie ... it really did work unbelievably well. In fact, I just made up my mind before submitting this post to tell our supervisor to order a small can of Tap-Magic so I can try it out for myself. We don't have the Mobile cutting oil anymore but we have other stuff which is much like it. I'm going to retire in a couple of years but I'd like to leave this stuff as a final legacy to the guys in the shop I will be leaving behind.

PS: It won't help to break in .... I have it locked in a safe *LOL*

PixMan
03-12-2015, 08:05 AM
Those older tapping fluids had one ingredient as an extreme pressure additive which worked the best and is the one that the EPA here forced out. 1,1,1 tricholorethane.

It's just another of the best working materials that either kill you or give you three-headed children and our governments have to take it away lest we keep eating and drinking it.

Toolguy
03-12-2015, 10:24 AM
I still have 6 new old stock cans of the Tap Magic with 1,1,1 Trichlor. I will try that with some cutting oil and see how it does. I don't have anything difficult to tap at the moment, but will try it eventually.

Black Forest
03-12-2015, 11:08 AM
I still have 6 new old stock cans of the Tap Magic with 1,1,1 Trichlor. I will try that with some cutting oil and see how it does. I don't have anything difficult to tap at the moment, but will try it eventually.

So what is your address!

Toolguy
03-12-2015, 12:17 PM
I could probably spare a can or 2, but I don't think they would let me send it to Germany!

ironmonger
03-12-2015, 02:10 PM
Something most folks do not realize is that 55-65 percent threads are only a few percent less strong than 75% threads and they are oh so much easier to tap due to dramatically less torque requirement.
Tooling lasts longer and tap breakage is virtually eliminated. The crests of the thread do not add significantly to the threads strength.
For all but the most demanding applications I usually aim for a 60-65% percent thread rather than what most tap/drill charts recommend. Quite often lately I've even used 55% threads and have been amazed both by their strength and the ease of tapping the hole.
Below some info that may make your day less stressful.:)

<<snip>>-

+1 Willy

I had to tap 50+ holes for a grinder project a few years ago, and after I broke a tap (in the third hole...) my brother in law/machinist asked what tap drill I was using and laughed at the #7. That's fine for sheet metal and thin steel but a killer on deep holes. If the holding strength of a 50% thread exceeds the tensile strength of the bolt, tighter fitting threads are meaningless.

I would also add that the addition of a decent hand tap machine will reduce the tap breakage immensely on deep holes. It's hard to align taps by eye, and I no longer even try.
see:
http://cdn0.grizzly.com/pics/jpeg1000/g/g8748-60c90184049d23e76852604f7a7bdadc.jpg

paul

PStechPaul
03-12-2015, 02:18 PM
I have been using synthetic cutting fluid (Aqua-Cut) and I don't think it will mix with the oil of Tap-Magic. I'm sure my problems are a combination of low quality taps and an unnecessarily small hole. The steel may also be a factor, as I had no problem with the 1215, but I should be able to tap plain steel. And I also tapped some 4140, although it was 1/4-28 UNF, and a through hole, and had nowhere near the problem. Is it possible that I used too much tapping fluid and the tap was actually compressing it? I think the flutes would prevent that from happening.

The tapping machine might help somewhat, although it might not be tall enough for the 4.25" long manifold. I thought maybe the tap was going in crooked, but it seemed OK using a square. I also tried applying some side pressure to loosen up the first few threads and helping the alignment, but that didn't seem to help, and the shoulder bolt went in and seated nicely and the cylinder seems to ride on it properly.

The tapered pipe thread is a little bit different, and I may need to use/make a bottoming tap to get full depth, although that would mean the bottom threads would be cutting into a smaller hole. Maybe I should use a slightly bigger drill, but it would really require an end mill or boring tool to make the flat bottom.

I'll find out more in class today. I hope to complete the things that I can't do with the tools I have, such as the rounded contour on the cylinder, the special shape of the crank, surface grinding the manifold, and flycutting the surfaces of the cylinder and the base.

Thanks.

PStechPaul
03-13-2015, 12:20 AM
Well, I left about 10 minutes later than usual and instead of arriving 10-15 minutes early, I hit some slow traffic, and then could not find any parking in the usual lot and I had to park in the next lot, which meant at least a 1/4 mile hike with my bad back and creaky knees, so I was 15 minutes late. I only missed some review for mid-terms next week, but I was unable to spend much time asking about tapping the holes. However, he insisted that, for the purpose of the class and NIMS certification, only 75% threads would be considered. He did not agree to use a larger drill for steel, but he said he uses spiral flute taps which should work fine. However, I have mostly decided that I will to some extent follow my own instincts and do what "works". I'll discuss more of the class in that thread.

ironmonger
03-13-2015, 12:29 AM
<<snip>>

The tapered pipe thread is a little bit different, and I may need to use/make a bottoming tap to get full depth, although that would mean the bottom threads would be cutting into a smaller hole. Maybe I should use a slightly bigger drill, but it would really require an end mill or boring tool to make the flat bottom.

<<snip>>

Thanks.

McMaster carries pipe taper reamers that are used to pre-form the holes before tapping. We use them when tapping ductile iron and they do make life easier...

see:
http://www.mcmaster.com/#pipe-reamers/=waai0a

Bottoming pipe taps are a great use for older taps. An abrasive cut off saw and a water spray to keep every thing cool while cutting is messy but effective.

The great thing about the hand tapping machine for me is perfect alignment all the way in. I don't often do well on larger sizes with side thrust, and the machine keeps me aligned...Can't always use it, but I try hard to find a way...

paul

PStechPaul
03-13-2015, 04:13 AM
I had thought about getting a pipe tap reamer, and I also considered boring a tapered hole by putting the part in the four-jaw chuck on the lathe and using the compound at the taper angle. But because of the intake port hole, a boring bar does not work very well. However, when discussing the flat bottomed hole problem in class, someone brought up the idea of using an end mill as a boring bar, and that should work for the tapered hole as well. If I decide to use the specified 1/4-18 pipe fitting, I may try that. But I'll practice first on a scrap piece. ;)

McMaster also has bottoming pipe taps:
http://www.mcmaster.com/#standard-taps/=wadb6m

http://images1.mcmaster.com/Contents/gfx/large/2553a14p1-a02cl.png?ver=3941206

The instructor said he liked my outline of operations to make the parts, and thought it might be a good exam question to show the details of a part in a drawing and have the student write up a sequence of operations to make the part. :cool:

legendboy
03-13-2015, 11:38 AM
What about a form tap? I have been using Balax form taps with factional metric drills, tapping 1" (14-20) deep blind holes in aluminum round bar
Nothing I tried works as well as these, and they are far stronger than any fluted tap.

Juergenwt
03-13-2015, 03:51 PM
Paul - you should have no problem tapping 1/4 - 20 thread 1/2" deep in 1018 using a straight flute, spiral point, SHARP, HSS tap.
.201 drill is correct. Industry taps millions of holes 1/4-20 using a #7 (.201) drill. How are you drilling the holes? Free hand? How are you tapping or starting your tap? Free hand?
If that is the case you will have a breaking problem. Your tap must be in line with the drilled hole. Do not use carbon steel taps but use only good quality HSS taps.
I must have tapped thousands of blind hole in anything from aluminum to brass to 1018 to all types of tool steels (O-1, O-6, A-2, D-2, T-1, M-2)
In 1018 a good quality HSS tap will tap hundreds and hundreds of holes. Fact is - any tap will eventually break but usually for a reason. Dull, no lube, not guided straight, not having a straight tap hole, chips etc..

PStechPaul
03-13-2015, 05:57 PM
I'm drilling the hole with a milling machine, but I am tapping by hand. The tap appears to be perfectly vertical as checked with a square. I don't normally need to tap many blind holes, and if I do, the taps I have are perfectly adequate. And I don't need 75% threads, so I can use the larger tap drill as shown in the chart for 50%-60%. I may replace some often-used taps with better ones as needed, and if so I would probably get a spiral flute bottoming tap, and just start the hole with the taps I have. Good quality 1/4-20 taps are about $12-$16 from McMaster (http://www.mcmaster.com/#standard-taps/=wanj0k). They say that the uncoated taps are only for non-ferrous metals and plastics, while the TiN coated long-life taps are for steel. I couldn't search for taps on the Enco site because of that recurring cookie problem, so I sent them a complaint. Hopefully they will fix that or they may lose a customer.

HSS taps (straight flute uncoated) are about $5 each from the company where I purchased my reamers, which seem to work well:
http://buydrillbits.com/products/hss/taps.php?c=TAP-HSS-PLUG

Their HSS spiral point straight flute "gun taps" are only a little more expensive:
http://buydrillbits.com/products/hss/taps.php?c=TAP-HSS-GUN

Zoro Tools has some spiral flute HSS taps for $11-$22:
http://www.zoro.com/g/HSS%20Spiral%20Flute%20Taps%20HSS%20Spiral%20Flute %20Taps/00054870/

This is supposed to be a two-flute spiral point tap for $10:
http://www.zoro.com/i/G0507823/

This looks like a good spiral flute TiN bottoming tap for $15:
http://www.zoro.com/i/G3246196/

http://d2pbmlo3fglvvr.cloudfront.net/product/full/2LYD1_AS01.JPG

Here is a Guhring cobalt modified bottom tap, with H4 pitch diameter limits, for about $18:
http://www.zoro.com/i/G0420366/

http://d2pbmlo3fglvvr.cloudfront.net/product/full/2VXD4_AS01.JPG

I've never heard of the H4 pitch diameter limit. There are certainly lots of different tap types, material, coating, quality, etc.

The spiral flute taps may actually expand in size slightly as they are forced into the work and the spiral tends to unwind. This should also cause it to contract as it is reversed to make its removal easier.

Juergenwt
03-13-2015, 08:35 PM
Paul - I looked at the charts you posted and it looks like these distributors have no clue about taps. A lot of what they post is complete garbage.
What you need is a HSS tap, two (or four) straight flutes, spiral point, Plug, H-3 limit. You don't need TIN or any other coating - does not hurt -if you have extra money laying around. You don't need spiral or high spiral flutes. They are not for steel. Guehring is a good brand. I believe so is OSG.
Btw - if it does not say HSS - than it is not.

PixMan
03-13-2015, 08:39 PM
I would NEVER, EVER buy so much as a speck of sand for Zoro Tool!

Thieves! They sell at OVER list price. Run, don't walk.

PixMan
03-13-2015, 08:51 PM
Paul - I looked at the charts you posted and it looks like these distributors have no clue about taps. A lot of what they post is complete garbage.
What you need is a HSS tap, two (or four) straight flutes, spiral point. You don't need TIN or any other coating - does not hurt if you have extra money laying around. You don't need spiral or high spiral flutes. They are not for steel. Guehring is a good brand.

You may not be familiar with what good taps do. I have spiral flute taps made specifically for steel, some specifically for stainless steel, and all are for blind holes in those materials. I also have high quality spiral point taps for "general purpose" as well as material-specific taps.

This is an example of a tap that I would not hesitate one second to use for blind holes on any of the ISO material classes listed on the box, including carbon steels (P), austensitic stainless steels (M), cast irons (K), and non-ferrous metals (N.) It is "THL" (technical hard lube) coated and works like you would not believe.

Using a spiral point tap for a blind hole can work, but is inviting disaster. Because they are designed for through holes and push the chip ahead of the tap, they have high radial relief and are not engineered for breaking a chip as you reverse rotation. I have used them, don't get me wrong, but the difference between using the proper tap and getting by with using the inappropriate one can be dramatic.

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/IMG_20150108_185044216_HDR_zps8h0yc4p0.jpg

Blackfoot
03-13-2015, 10:21 PM
One machine shop I used to work for had Tapping Wax. They were sticks of a soft yellow wax that you would stick down a blind hole and then run the tap to the bottom. The wax pushed the chips up the flutes and provided some lubrication. And the wax would stick to the tip of the tap (always used a spiral point tap) and the hole would be clean when you finished. Have not seen tapping wax since but it was a great way to tap a blind hole.

P.S. As far as I am concerned, small 3 or 4 flute taps are only good for chasing threads, A 2 flute spiral point is much stronger and gives better, faster results.

Today I went to a local supply house (they sell machine tools and machine shop supplies) to pick up a few things. They sell a variety of tapping fluid type materials. I noticed next to the "Tapmatic" fluids was "Tapmatic" wax type tapping lube. There were three different ones to choose from.
One was in a paper cylinder about 10" long X 1.5" dia. The wax inside was white. For years I have used a similar product made by Johnson's Wax, that comes in a similar "paper tube" for a use as a saw lube. The Johnson stuff is yellow.

PStechPaul
03-14-2015, 01:10 AM
I have an Enco sale catalog that has OSG HSS ElectraLube 1/4-20 spiral flute taps for $9.99 (regular $24.33).

Here are my taps, two 1/8-27 pipe taps, some 1/4-20, and a 1/4-28:

http://enginuitysystems.com/pix/tools/Taps_1806.jpg

The black oxide taps are from an old set of Harbor Freight taps that were made in Japan and are carbon steel. I ground the tips to make them more like plug or bottoming taps.

becksmachine
03-14-2015, 01:55 AM
I'm drilling the hole with a milling machine, but I am tapping by hand. The tap appears to be perfectly vertical as checked with a square.

Ok, this begs the question, are you able to at least start the tap in the hole with the milling machine?

I my experience, a spiral FLUTE tap is the most difficult style to get started square when in an unguided application. If you can at least screw the tap in 2-3 turns while lined up on the hole in the milling machine it will make subsequent hand tapping a lot easier no matter what style tap you are using.

As for modifying an existing tap to make a bottoming tap, yes it can be done, I have done it myself a number of times. And I have been scared of the results almost as many times. I would encourage you to try at least once, a quality factory ground 4 flute bottoming tap. The difference will be immediately apparent.

Dave

PixMan
03-14-2015, 08:34 AM
All those UN taps you show Paul are classic hand taps, and my favorites to use when I want to break a tap off in a hole. :D OK, they are very usable, as long as you reverse every turn or two to break the chip. If going deep you may have to retract completely and clear chips out before you get to depth.

The OSG taps with "elektraLUBE" that you see in the Enco sale flyer are the fast spiral ones which are fairly fragile. I noticed in reading the description that they are intended for non-ferrous metals, not steels. Other ones on the same page (if you're looking at the March 2015 "Hot Deals" flyer, page 34) are the OSG taps for steels. Though they are more money, those would be the better choice.

Juergenwt
03-14-2015, 02:43 PM
The question to be asked when looking at the catalog sites of some of these distributors: Can't you pay some knowledgeable person a few dollars to look it over before you print it?
I am talking about the technical details like listing metric thread pitches in 20 or so decimals, or showing a picture of a four fluted tap on the page listing two fluted taps. When I see a catalog like this than I already that this company has no clue of the product they are selling. Why would anybody buy from these people?

PixMan
03-14-2015, 03:01 PM
...Why would anybody buy from these people?

Because the tools are cheap and there are people here with the "Walmart mindset", which is pretty much nothing more than "shop with the dollar in your wallet as the only consideration."

Rosco-P
03-14-2015, 03:12 PM
Because the tools are cheap and there are people here with the "Walmart mindset."

No worries, those people aren't even shopping Enco. Their aim is set to an even lower level.

Slightly OT, slight hijack.

Other day at an early morning flea market, I see a guy selling the stuff Happy Fart gives away each month with a coupon just to get you in the door. He had a big pile of flashlights, brass "toothbrush" style cleaning brushes (5 in a pack for free), digital meter, tiny blue tarp, LED magnetic light, etc., etc. All priced at one or two dollars each. He must spend his free time traveling from store to store or he's an accomplished shoplifter with no sense of quality.

PStechPaul
03-14-2015, 04:25 PM
The catalog says that the spiral flute taps are for blind holes in aluminum, magnesium, brass, copper, and die-cast. Then it says the black oxide coating is for ferrous materials, while the ElectraLube coated versions are for SS, steel forgings, tool steel, HRS, CRS, high nickel alloys, beryllium, copper, and some Al alloys. The OSG website has the following chart for coatings:
http://www.osgtool.com/Technical.asp?tid=4&id=17




Treatment Guide



Part Number Ext
Name
Characteristics
Description


01
Steam Oxide
Prevents tools from welding.
A black surface finish is produced on the tap by means of a steam furnace. A porous coating that helps retain cutting fluid in working portion of the tap.


03
Nitride
Very hard (~69HrC) on surface of a finished tap.
Produced by means of an ion furnace. Nitride offers increased wear resistance due to the higher surface hardness. Very effective treatment for both abrasive and tough materials.


04
Nitride/ElektraLUBE (NeL)
Combination between Nitride and elektraLUBE.
Effective when both short wear life and welding are encountered. A harder coating with the benefits of the ElektraLUBE's smooth finish.


05
Titanium Nitride (TiN)
Good general purpose.
A Gold coating, which helps increase wear resistance by producing a higher surface hardness. Also helps prevent welding because of high lubricity.


07
Nitrate/Oxide
Combination between Nitride and Oxide.
It is an ideal high temperature release and lubrication agent. It has the hardness qualities from the Nitride, while keeping the porous abilities of the oxide coating.


08
Titanium Carbonitride (TiCN)
High hardness, good wear resistance, enhanced toughness.
A Blue-Gray coating that enhances high speed cutting where moderate temperatures are generated at the cutting edge.


09
Diamond-Like Coating
Added lubricity & wear resistance in non-ferrous materials.
PVD Coating, with performance similar to CVD Diamond but costs similar to other high-end PVD coatings.


11
Titanium Aluminum Nitrade (TiAIN)
Excellent oxidation resistance.
The properties of TiAlN coatings make them ideal for high temperature cutting operations in many materials. When exposed to high cutting temperature, TiAlN forms a hard aluminum oxide layer with low thermal conductivity and high chemical stability. As cutting temperatures increase, TiAlN insulates the tool and rejects heat into the chips. This allows for increased production levels with higher speeds, reduced down time, stabilized cutting forces and longer tool life.


16
CVD Diamond
High hardness, High lubricity.
Diamond coated tools have the ability to cut a speeds two to three times faster than conventional carbide tools. Extended tool life can also be expected from diamond coating. The lubricity of diamond requires less cutting force, generating less heat. Also it reduces workpiece deflection to improve workpiece machining accuracy.


18
Titanium Aluminum Nitride/Tungsten Carbide/Carbon (TiALN/WC/C)
Protects cutting edges from wear, ensures reliable chip evacuation.
Black-Gray coating. Coating of choice for machining with high demand of friction and temperature control. Coating greatly aids in chip evacuation.



They also have a tap application guide:
http://www.osgtool.com/Technical.asp?tid=1&id=3

It seems to indicate that spiral fluted and spiral point taps can be used in various common steel alloys, but it provides their own part numbers which are not given in the printed catalog. There is really a lot of information about taps and tapping, and so far it has not really been covered in much depth in the class, which may be why some students have broken taps in their work. I have developed a pretty good "feel" for tapping, perhaps even more so because I have used cheap taps and I am familiar with the amount of torque and visible twist that signals imminent breakage.

PStechPaul
03-14-2015, 04:32 PM
Tap Application Guide




List No.


Style of Taps


Recommended
Application


Materials


Hardness
HRC




300, 342


Spiral Pointed Taps VA3


Stainless Steels


304, 316, A286, 17-4PH


0-35




303, 343


Spiral Fluted Taps VA3


Stainless Steels


304, 316, A286, 17-4PH


0-35




397


Spiral Pointed-Long Shank VA3


Stainless Steels


304, 316, A286, 17-4PH


0-35




398


Spiral Fluted-Long Shank VA3


Stainless Steels


304, 316, A286, 17-4PH


0-35




399


Machining Center Taps VA3


General Purpose


1018, 1045, D2, H13


0-35




308, 318


EXO Pipe Taps


Stainless Steels


304, 316


0-25




305, 328


EXOTAP-Mold 8% CO Taps


Die Mold, Tool Steels


A1, 01, D2, H13


30-45




312, 312NI, 344


Spiral Pointed Taps VC10


Heat Resistant Alloyed


TI-Alloy, Inconel


20-45




313, 313NI, 345


Spiral Fluted Taps VC10


Heat Resistant Alloyed


TI-Alloy, Inconel


20-45




301


STI Point Taps VA3


Stainless Steels


304, 316, A286, 17-4PH


0-35




302


STI Spiral Taps VA3


Stainless Steels


304, 316, A286, 17-4PH


0-35




314


STI Point Taps VC10


Heat Resistant Alloyed


TI-Alloy, Inconel


20-45




315


STI Spiral Taps VC 10


Heat Resistant Alloyed


TI-Alloy, Inconel


20-45




310


EXOTIN TRF Forming Taps


Stainless Steels


1018, 304, 390AL


0-30




320


EXOTIN Spiral Pointed Taps


Stainless Steels


390AL


0-35








List No.


Style of Taps


Recommended
Application


Materials


Hardness
HRC




240, 241


HYPRO DC Straight Fluted


Die Cast Aluminum


356AL, 390AL


-




250, 260, 259
269, 280, 289


Spiral Pointed Taps VA3


General Purpose


1045, 4140, 304, D2, H13


0-35




220, 230, 229
239, 290, 299


Spiral Fluted Taps VA3


General Purpose


1045, 4140, 304, D2, H13


0-35




295, 296


HYPRO AL Spiral Fluted


Alloyed &
Cast Aluminum


390AL, 6061T6


-




288


HYPRO 7 Spiral Pointed Taps


General Purpose


1018, 1045, Aluminum


0-25




101C


Straight Fluted Taps


Gray Cast Iron


FC25


0-25




110, 111


TRF, M-BOSS Forming Taps


General Purpose


1018, 1045, 356AL


0-25




Standard Tap Section


All Types of HSS Taps


General Purpose



0-25

PStechPaul
03-14-2015, 04:34 PM
Partial table:



Tapping Guide




Materials


Condition


Hardness


Cutting


First Choice


Alternate




BHN


HRC


Speed-FPM




Low Carbon Steels


1010
1018


Normalized


-190


-10


25-50


HYPRO-Seven
TRF Tap 110, 111
M-Boss 171


EXOTAP VA3
EXOTIN 320
EXOTAP TRF 310
Standard Taps




Medium Carbon Steels


1035
1045


Normalized


-208


-15


20-40


HYPRO-Seven
TRF Tap 110, 111
M-Boss 171


HYPRO 280, 290, 250, 260, 220, 230
EXOTIN 320
EXOTAP TRF 310
Standard Taps




High Carbon Steels


1050
1065


Normalized


-253


-25


20-30


HYPRO 280, 290, 250, 260, 220, 230
EXOTAP TRF 310


EXOTAP VA3
EXOTIN 320
TRF Tap 110, 111
M-Boss 171
Standard Taps




High Strength Steels


4140
4340


Normalized


253-301


25-32


20-30


HYPRO 280, 290, 250, 260, 220, 230


EXOTAP VC10




4140
4340


Hardened


327-390


35-42


15-20


EXOTAP VC10


HYPRO 280, 290, 250, 260, 220, 230




Tool Steels


D2
H13
P20


Annealed


190-253


10-25


15-20


HYPRO 280, 290, 250, 260, 220, 230


EXOTAP VC10
EXOTAP Mold
EXOTAP TRF 310




D2
H13
P20


Hardened


327-390


35-42


12-20


EXOTAP VC10


EXOTAP Mold




Stainless Steel


303
304
316


Annealed


-253


-25


20-30


EXOTAP VA3
EXOTIN 320
EXOTAP TRF 310


HYPRO 280, 290, 250, 260, 220, 230
TRF Tap 110, 111
M-Boss 171




410
430


Hardened


327-390


35-42


12-20


EXOTAP VC10


EXOTAP VA3
EXOTIN 320




17-4
15-5
A286


Annealed


-253


-25


15-20


EXOTAP VA3
EXOTIN 320


HYPRO 280, 290, 250, 260, 220, 230




17-4
15-5
A286


Hardened


327-390


35-42


12-20


EXOTAP VC10


EXOTAP VA3
EXOTIN 320




Titanium Alloys


6AL4V


Annealed


253-301


25-32


15-20


EXOTAP VC10


-




6AL4V
6AL6V


Hardened


327-390


35-42


8-15


EXOTAP VC10


-




Nickel Base Alloys


Inconel 718


Annealed


253-301


25-32


8-15


EXOTAP VC10


-




Inconel 718


Hardened


327-390


35-42


5-10


EXOTAP VC10


-




Aluminum Alloys


2011
6061
707


Normalized


-150


-


25-60


HYPRO-Seven
HYPRO AL 295
TRF Tap 110, 111
M-Boss 171


HYPRO DC 240
EXOTAP TRF 310
Standard Taps




Aluminum Die Cast


356AL
390AL


As Cast


-150


-


30-80


HYPRO-Seven
HYPRO AL 295
HYPRO DC 240
TRF Tap 110, 111
M-Boss 171

huntinguy
03-14-2015, 05:06 PM
Tap in the mill, it knows exactly where the hole is and by using a good quality tap guide it will keep the tap square and keep the tapping force correct for the tap. Use a good quality second gun tap. Rotate one turn, back out and clean the tap and and the hole, repeat all the way to the bottom. A sulfur based tapping fluid works well. (If this were to be a production run I might do it a little differently. )

HF taps and dies are almost good for cleaning dirt out of threads... almost.

RussZHC
03-14-2015, 06:02 PM
or he's an accomplished shoplifter with no sense of quality.

that was good for a bit of a soft drink out the nose...:rolleyes:

PStechPaul
03-14-2015, 06:05 PM
I think the opinions on HF taps are similar to those on cheap digital calipers. The first set of cheap taps I got a long time ago from HF are black oxide carbon steel, made in Japan (more like their 1950s-1960s quality), and I was not even able to start a 1/4-20 tap in the recommended 0.201" hole. My newer set of alloy steel taps are much better, and I have used them without problems on aluminum, phenolic, and steel, even 4140, but mostly thru holes or occasionally fairly shallow blind holes.

The relatively deep blind holes (0.6" minimum for 1/4") were the first that gave me such problems, and I'm still not sure why they jammed up so suddenly when I got deeper than about 3/8" (which is the threshold for "deep holes"). Certainly higher quality taps would work much better, and I will very likely replace my most-often-used taps with better ones. But I still think my main problem has been the selection of a tap drill specified for 75% threads, and according to the OSG selector calculator (http://www.osgtool.com/Technical.asp?tid=1&id=1), deep holes are generally 60-70%, and even average commercial work is 65-70%. If I select 68%, the tap drill becomes 0.2058" (#5), and for 60% it is 0.211" (#4-#3).

I think it is actually an impressive accomplishment to have tapped these holes to 0.5" using the taps I have, with the 0.201" drill for 75% threads. Of course a better tap would have made it easier, but if I can do an adequate job with 65% threads with the tools I have, there is no strongly compelling reason to spend a considerable amount of money for marginal improvement. But I will try a better tap at school and at least feel the difference.

The use of a tap guide in the mill is a good idea. I have considered getting one (or making one), and it should be as simple as a cylinder with a spring and a plunder with a point (or a countersink) to match the end of the tap. Another idea I had is to use the torque limiter from an old power drill and just use the mill or drill press to drive the tap safely into the work. But my mill doesn't have a reverse, so I'd have to remove it (and back off to clear chips) by hand. It would definitely be ideal for getting it started a few turns, and then it could be completed by hand.

Thanks for the discussion. I learned a lot more about taps and tapping than I even knew was to learn. ;)

PStechPaul
03-17-2015, 05:50 PM
With Enco's 25% off deal today, I may get some good taps. The OSG ME319-7049 is an oxide-coated bottoming tap, general purpose series 107, for $8.99, and the OSG application guide (http://osgtool.com/product_list_detail.asp?list=107&tab=Application) says it is good for aluminum, carbon steel up to 1065, and cast iron. The ME327-2141 is a modified bottoming tap, high performance series 290, for $15.49, and the application guide (http://osgtool.com/product_list_detail.asp?list=290&tab=Application) says it is not for aluminum, good for cast iron, medium carbon steel, and SS, and best for high carbon and alloy steels. I probably don't really need a bottoming tap, at least not for this project, as I can drill the hole deep enough for a plug tap, which is ME319-7039. I can use my cheap taps for aluminum, so I'm leaning toward the better Hy-Pro tap which will be $11.62 with the discount.

Some other items I plan to order:



Model#

Qty.

Availability

Low Price

Extended Price

Delete



225-3035 (http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=948925&PMAKA=225-3035)


In Stock




$32.62 ea





$25.95 ea




$25.95




Line 1. Fly Cutter Sets; Minimum Head Diameter (Inch): 3/4; Maximum Head Diameter (Inch): 2-1/2; Shank Diameter (Inch): 1/2; 5/8; Minimum Tool Bit Size (Inch): 3/16; Maximum Tool Bit Size (Inch): 1/2; Number of Bits Per Cutter: 1 May we also suggest...



325-5179 (http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=5810267&PMAKA=325-5179)


In Stock




$14.44 ea





$11.95 ea




$11.95




Line 2. Tap Guides; Minimum Tap Size (Inch): #10; Maximum Tap Size (Inch): 1; Overall Length (Inch): 3; Shank Diameter (Inch): 1/2 May we also suggest...



ME327-2141 (http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=43833159&PMAKA=ME327-2141)


In Stock




$18.71 ea





$15.49 ea




$15.49




Line 3. Spiral Flute Taps; Series/List: 290; Thread Size (Inch): 1/4-20; Thread Limit: H3; Number of Flutes: 3; Chamfer: Modified Bottoming; Finish/Coating: Oxide



404-1627 (http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=30821127&PMAKA=404-1627)


In Stock

$121.55 ea

$121.55




Line 4. Machine Vises; Jaw Width (Inch): 4; Jaw Opening Capacity (Inch): 4; Throat Depth (Inch): 1-1/8; Orientation Type: Horizontal; Number of Stations: 1; Base Motion Type: Swivel



ME600-0003 (http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=43833550&PMAKA=ME600-0003)


In Stock




$36.54 ea





$32.89 ea




$32.89




Line 5. Mechanical Outside Micrometer Sets; Minimum Measurement (Inch): 0; Maximum Measurement (Inch): 3; Digital Counter (Yes/No): No; Thimble Type: Ratchet Stop; Graduation (Decimal Inch): 0.0001; Measurement Range (Inch): 0 to 3 May we also suggest...



ME615-6610 (http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=43833418&PMAKA=ME615-6610)


In Stock




$30.71 ea





$17.95 ea




$17.95




Line 6. Telescoping Gage Sets; Minimum Measurement (Inch): 5/16; Minimum Measurement (mm): 8.00; Maximum Measurement (Inch): 6; Maximum Measurement (mm): 150.00; Number of Pieces: 6; Handle Length (mm): 102.00; 127.00 May we also suggest...



630-4010 (http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=947676&PMAKA=630-4010)


In Stock




$29.62 ea





$15.95 ea




$15.95




Line 7. Setup Blocks; Type: 1-2-3 Block; Overall Width (Inch): 1; Overall Length (Inch): 2; Overall Height (Inch): 3; Squareness Per 1 Inch (Decimal Inch): 0.0003; Overall Tolerance (Decimal Inch): 0.0001 to 0.0007 May we also suggest...

Rosco-P
03-17-2015, 06:17 PM
This is a shop class project upon which you'll be graded, right? Probably graded using multiple criteria, maybe: % completion; fit; finish; adherence to size/tolerance; functionality; etc., right? Shouldn't the instructor be giving you some guidance on process and cutting tool selection, including the taps? If he isn't maybe you need to corner him, describe the problems you're encountering and get some advice. You're paying for it.

Line 6 on your order, import telescoping gages. If they are "sticky", you'll get just as accurate a measurement using broken twigs. Hunt Fleabay for a used set of Starrett, Brown and Sharpe, Mitutoyo, etc. Money well spent.

PStechPaul
03-17-2015, 07:47 PM
I have asked the instructor about the taps, and he said he usually uses spiral flute types, but I think most of the taps in the tool drawers are ordinary straight flute types, and I'm pretty sure that's the kind that my buddy broke in his manifold. The discussion mostly concerned drilling the hole deep enough, and reversing and cleaning out often. He was fairly adamant about using the 0.201 drill for 75% threads.

When I used the telescoping gauge at school for the 0.625 bore in the cylinder, I had a hard time getting a consistent reading when following up with the micrometer, and I just used the 0.625 piston as a gauge. I figure for $13.46 (price with discount) the set would be all I really need, and if I have a project that needs a more accurate bore, I think I'll just make my own go/no-go plug gauge on the lathe. I could have gotten a high quality set from someone on MEM who is selling some tools for about 25% of list, but I'd still probably be paying twice as much as these.

My expectations for this class are mostly to learn how to do basic machining tasks for my own purposes, and also to get the tooling I need for my home shop so I'll be able to use my machines to their best advantage, as well as learn their limitations. I'm not seeking a job as a machinist and I don't intend to do any high-precision work or do work for customers. I may not continue beyond this class, although it might be interesting to learn CNC, and it is probably well worth the cost of the class to have access to the larger and better machines, and materials, and advice.

Maybe I can be an assistant instructor. It pays $18/hour, and I think I know enough basic machining to help beginning students.

Tundra Twin Track
03-22-2015, 04:35 PM
I use the spiral semi bottoming and the thru taps on mill and in cordless drill on screw setting so you can use clutch setting.I buy Sowa brand here in Canada.

oldtiffie
03-23-2015, 04:53 AM
Fit a "stop" to the machine quill in conjunction with a "slipping" clutch.

Perhaps finish the tap/ped depth required by hand.

Balls of swarf in the bottom of the tapping hole are no help at all and complete PITA.

Speeding, tear-ar$ing and trying to break records are not a good way to go - just "hasten slowly".

The correct match to machine, material and type of tap are essential.

Anyone blunt taps will get you all they deserve - and perhaps of it.

PStechPaul
03-23-2015, 06:08 PM
I just got the second shipment on my order from Enco, and I tried using the telescoping gauge for the 5/8" bore in the air motor cylinder. It was a little tricky getting it properly aligned and tightened, and I found that I had to tighten it even more once removed from the bore so that my micrometers did not compress the gauge tips. But otherwise they seem OK, and worth the $13 for the set. I also got the 3 piece micrometer set which also seems OK.

I got a good OSG semi-bottoming spiral flute 1/4-20 tap, but have not tried it yet, except to thread it by hand into the tapped holes I already have. It is certainly beautiful to behold, with a smooth dark grey oxide coating and gold markings. I think I will "save it" for finishing holes that I start with my cheap taps, which are also good enough for thru holes and some blind holes up to at least about 1.5 times the diameter (0.375"). That's 7 threads, and even a depth equal to the diameter is 5 turns, which should be nearly maximum strength.

Here is one reference, which shows a linear increase in strength up to 1.5D:
http://viewmold.com/Products/Technical%20Reference%20Sheet/Screw%20Fastener%20Theory%20and%20Application/STRIPPING%20STRENGTH%20OF%20TAPPED%20HOLES.html

http://enginuitysystems.com/pix/tools/STRIPPING_STRENGTH_OF_TAPPED_HOLES_800.jpg

I found this interesting as well:
http://machinedesign.com/news/internal-thread-strip-out-tests-yield-surprising-results

http://enginuitysystems.com/pix/tools/Tap_Test.jpg

PStechPaul
03-26-2015, 09:53 PM
Just got back from class. I decided to do the only thing remaining that I could not do at home - surface grind the manifold. So I put the piece on the table, and turn the handle of the magnetic chuck to hold it - nope, it just slides around. Huh? I thought I was doing something wrong, and somebody suggested maybe it was SS. I didn't think it was, but I put some plain steel on the table and it gripped it tight. OOPS! So I asked the instructor, and he asked me where I had gotten the raw material. He showed me a rack with some 1" square stock, and said it was stainless. He asked if I had any problems drilling or milling it, and I said no, but I did have a hard time tapping it. :p

So, I guess those cheap taps weren't all that bad after all. So, I had to hold the piece in a toolmaker's vise to grind the long surfaces, and then I used two "Kant-Twist" clamps to hold it on end to grind the ends smooth. Turned out pretty good. Now all I need to do is file the 45 degree chamfers on all edges except where the piston wobbles, and the end with the mounting holes. :cool:

Rich Carlstedt
03-26-2015, 11:35 PM
Paul
You are between a rock and a hard place.
Trying to do what your instructor wants is important....very !
However, as a manufacturing engineer I see several errors in the task at hand, or the understanding.
I also realize sometimes instructors make assignments just to see your response and they may not reflect real world "standards"

First, whenever a tapped hole depth is called on the drawing, the drilled hole must be one diameter deeper. You found out when
You said you drilled 3/4 and it tapped easy to 1/2"..but you wanted .6". The print should have said to bottom tap to .6
If you look at a tap you see one diameter before full thread

Second. 1/4-20 is a terrible thread, along with 10-24. They both should be outlawed for any machine assemblies. The reason is the ratio of the threaded area to the root diameter is far too great. That means the tap is exposed to the greatest torque requirement compared to other taps and will break/fail before similar taps . For example 1/4-20 ..radius =.125 radius of root (.208/2) =.104
Area of thread root (TR) .104 x .104 x 3.14= .0339
Area of circle (C) .125 x.125 x 3.14= .0491
Area of thread C- TR = .0152
So you can see that you are removing .0152 material and have .0339 backing it up.
can you imagine using a 1/2 steel tool bit in a lathe and removing 1/4 deep (DOC) of material ?
That's what you are asking the tap to do.

That brings up % of thread. Some here have covered it in depth . In 1943 ( WW II !) Various manufacturers
got together and set industry standards , among them thread depths. They agreed that Stainless Steels and tool steel did not
require 70 % thread and made 55 % a standard for manufacturing. Unfortunately, many design engineers have no concept of this standard !
Couple this with threaded depth, where the standard is one and one half diameter as maximum engagement between fastener and tapped hole. This requires a threaded depth of 2 times diameter (1 1/2 +1/2 D) and a hole drill 3 times diameter ( 1 1/2 + 1/2 + 1)
What further complicates the above is....material and the tensile strength of the mating materials.
"Maximum Strength of a joint " when both materials are the same is "One Diameter"
So threading a hole deeper is unnecessary....unless you use a stronger bolt in a weaker base metal hole.
So if you use a grade 3 bolt in mild steel , you need 1 1/2 depth for equality.
For Aluminum threaded holes , it would take 10 times thread diameter using steel screws ! That is impractical , but I have seen 3 X diameter.

Last , the pipe tap situation .
The reason you had trouble ( only one and half turns on the fitting ) was because the tapered pipe tap is really too long for a blind hole
After you started the thread, you would need to remove maybe 25 -35% of the tap (like making a bottom tap) and then doing a second pass.
Don't forget that such taps can start in a straight hole. If you used a taper reamer first, the tap would drop in the hole about 3 threads before engaging. With a standard NPS tap the starting threads are too small for a fitting and it needs to go deeper to assure proper form

Rich
By the way, the OSG is my favorite Tap
We used their EXOtap on H 11 at 45 -48 Rc when other taps would just stall

PStechPaul
03-27-2015, 02:53 AM
There are definitely some parts of this project that were designed to learn and demonstrate certain machining operations and skills, and not the "best" way to make a functional engine. For instance, the beveled edges of the manifold are supposed to be made by hand, using a file, or possibly a belt sander. The air engine only requires 1/16 x 45 degrees, with tolerance of 1/32" and 5 degrees, so that's easy. But the other project that some students are doing for NIMS certification has much tighter tolerances for a chamfer, also done with a file using a file guide, to 1 degree and 0.010".

Here is the stainless steel manifold after grinding, showing the tapped holes. It is supposed to be 0.995" +/- 0.005" square but I took a wee bit too much off on one surface and it's 0.9883" while the other is OK at 0.9935":

http://enginuitysystems.com/files/CAMM112/Air_Engine_Manifold_1874.jpg

http://enginuitysystems.com/files/CAMM112/Air_Engine_Manifold_1876.jpg

http://enginuitysystems.com/files/CAMM112/Air_Engine_Manifold_1877.jpg

http://enginuitysystems.com/files/CAMM112/Air_Engine_Manifold_1878.jpg