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Elninio
09-09-2010, 08:08 PM
I have to tap 6 8NC32 holes, about 3/4" deep. My tap broke three times and I had to extract the broken fragment twice with a dremel (I've interest in removal the third time). I was tapping in the small drill-press with the spring of the spindle completely dis-engaged (the one that pulls the spindle up). I was going real slow and backing out the chips every 1/4 turns.

The tap is CHINESE.

BMSS
09-09-2010, 08:19 PM
I have to tap 6 8NC32 holes, about 3/4" deep. My tap broke three times and I had to extract the broken fragment twice with a dremel (I've interest in removal the third time). I was tapping in the small drill-press with the spring of the spindle completely dis-engaged (the one that pulls the spindle up). I was going real slow and backing out the chips every 1/4 turns.

The tap is CHINESE.

First off, why would you ever try to tap an 8-32 hole 3/4" deep? The old rule is maximum holding power is attained at 1 1/2 times the diameter of the tap. For an 8-32 that would be something less than 1/4" depth.
Second off, using Chinese taps for any kind of deep hole tapping is a real mistake.

Back bore your holes, so that you only have to tap 1/4" deep,and you will be fine.

radkins
09-09-2010, 08:26 PM
Which tap are you using? You need to start the hole and go as far as you can with a taper tap then use a plug tap, the taper tap will cut with much less resistance and is a lot easier to use without breaking. It seems taper taps are hard to find at most stores and usually plug taps are all most places have, some of them do have bottom taps sometimes, but for whatever reason plug types are the most common.

Liger Zero
09-09-2010, 08:29 PM
I use Chinese taps to fill in unwanted holes. Simply crank the sucker in, snap it off and grind flush.


Seriously... Don't waste your time with that junk. You can follow proper tapping process but it's all for naught if you use junk "Snap-Off(tm)" taps.

daveo
09-09-2010, 08:31 PM
Back bore your holes, so that you only have to tap 1/4" deep,and you will be fine.

How do you back bore a blind hole.... Especially on a hole that small?

Dr Stan
09-09-2010, 08:31 PM
BMSS & Liger are spot on.

BMSS
09-09-2010, 08:35 PM
How do you back bore a blind hole.... Especially on a hole that small?

He never said anything about them being a blind holes. Guess you read something that I didn't.

Elninio
09-09-2010, 08:36 PM
How do you know if a tap is 'Snap-Off' brand?

Liger Zero
09-09-2010, 08:39 PM
How do you know if a tap is 'Snap-Off' brand?

My pet nickname for junk Chinese tools. :D

Elninio
09-09-2010, 08:40 PM
My pet nickname for junk Chinese tools. :D

I know - but not all taps are advertised as MADE IN USA or something like that

wierdscience
09-09-2010, 08:44 PM
If your tapping a hole more than 2x's the diameter in depth the tap drill size can be increased since you will have more threads engaged.The increase in tap drill size means a slightly larger hole and a reduction in the amount of torque required to thread it.

Liger Zero
09-09-2010, 08:45 PM
I know - but not all taps are advertised as MADE IN USA or something like that

To be fair I've had American and French made taps snap off on me. That was mostly my fault as I was still learning how to use them properly. "Cranky Old Machinist In The Corner" showed me the right way... after he bit my head off for ruining his expensive French tap. :D (I paid to replace it out of my pocket A) because he took the time to teach me the right way and B) that's just how I roll. I break it I replace it.)


I had a set of Chinese Taps I got at a flea-market. Complete with Chinese paperwork! They were less than useless for metal I broke most of the smaller diameter ones.

wierdscience
09-09-2010, 08:49 PM
I know - but not all taps are advertised as MADE IN USA or something like that

They don't have to be made in USA to be good and not all US made taps are good.

Some brand names to look for-OSG,Nachi,Greenfield,TRW,TMX,Excello.

High Speed steel is best for longevity and for my own personal preference 3 flute taps work best for me when hand tapping,especially spiral point "gun" taps.

Elninio
09-09-2010, 08:49 PM
Why do the chinese tap suck more --- do they start with a weaker metal, or do they get the heat-treatment wrong?

Elninio
09-09-2010, 08:51 PM
They don't have to be made in USA to be good and not all US made taps are good.

Some brand names to look for-OSG,Nachi,Greenfield,TRW,TMX,Excello.

High Speed steel is best for longevity and for my own personal preference 3 flute taps work best for me when hand tapping,especially spiral point "gun" taps.

Are those brands to watch out for in a negative way? Or as those brand I would want to buy? Do they make taps out of carbide?

Liger Zero
09-09-2010, 08:54 PM
Why do the chinese tap suck more --- do they start with a weaker metal, or do they get the heat-treatment wrong?

It's a bit of both.

They cut costs anyway they can, to keep prices down.

fishfrnzy
09-09-2010, 08:57 PM
Plus one on the spiral point taps. Way easier and you don't have to back them up. Seems like they turn easier so they don't always feel like they're just about ready to break. Of course as others have mentioned they should be high quality HSS or you're trying to fight with one arm tied behind your back.

Weston Bye
09-09-2010, 09:07 PM
I have to tap 6 8NC32 holes, about 3/4" deep. My tap broke three times and I had to extract the broken fragment twice with a dremel (I've interest in removal the third time). I was tapping in the small drill-press with the spring of the spindle completely dis-engaged (the one that pulls the spindle up). I was going real slow and backing out the chips every 1/4 turns.

The tap is CHINESE.

Small Tap? I consider anything smaller than a 4-40 as a small tap. I once had to listen to a machine shop owner whine about small taps - in his case, anything smaller than 1/4-20 was small and difficult. Using the drill press spindle adds a lot of inertia and reduces sensitivity. A better option would be a t-shaped tap handle with a shaft on the back that can be held loosely to turn free in the drill chuck. If you need a picture I can put one up here tomorrow.

Elninio
09-09-2010, 09:11 PM
Small Tap? I consider anything smaller than a 4-40 as a small tap. I once had to listen to a machine shop owner whine about small taps - in his case, anything smaller than 1/4-20 was small and difficult. Using the drill press spindle adds a lot of inertia and reduces sensitivity. A better option would be a t-shaped tap handle with a shaft on the back that can be held loosely to turn free in the drill chuck. If you need a picture I can put one up here tomorrow.

How do you know when it's going to snap? I couldn't even see it flexing (and i'm not vision impaired)!

macona
09-09-2010, 09:12 PM
Are those brands to watch out for in a negative way? Or as those brand I would want to buy? Do they make taps out of carbide?


Those are the ones to buy.

I also like thread form taps. They do titanium real nice.

wierdscience
09-09-2010, 09:16 PM
Are those brands to watch out for in a negative way? Or as those brand I would want to buy? Do they make taps out of carbide?

No,those are top of the line name brands.OSG,Greenfield,Nachi,TRW,excellent,but pricey.Those are made in the US and Japan.

The Excello and TMX are made in Spain and Poland,still very good taps,but not as expensive.

There are places to try and save money and places where it pays to spend extra to get top quality.

Taps,dies and reamers are three items where buying one high quality tool will save you money in the long run.

I buy US and Japanese taps for production,Spanish and Polish for day to day jobs.

I buy Chinese taps and dies for dirty work,thread chasing,cleaning out damaged holes that sort of work where I don't want to risk a high dollar tool.

Rusty Marlin
09-09-2010, 09:26 PM
I have to tap 6 8NC32 holes, about 3/4" deep. My tap broke three times and I had to extract the broken fragment twice with a dremel (I've interest in removal the third time). I was tapping in the small drill-press with the spring of the spindle completely dis-engaged (the one that pulls the spindle up). I was going real slow and backing out the chips every 1/4 turns.

The tap is CHINESE.

I think the Chicom dogchit tap is the problem, and has been beat to death.
What material are you tapping? You can improve your luck with the correct lubricant for the material.

RKW
09-09-2010, 09:27 PM
You did not mention the material you are trying to tap and what sort of tap lube you are using. These can make a big difference. As for Chinese taps, just say no. I only buy good USA taps and drills. Sure they cost a lot more, but they are generally worth it.

I agree with Wes ... anything smaller than 4-40 is small. I have only gone down to 2-56 myself and did not have any problems tapping several dozen holes.

Keith


I have to tap 6 8NC32 holes, about 3/4" deep. My tap broke three times and I had to extract the broken fragment twice with a dremel (I've interest in removal the third time). I was tapping in the small drill-press with the spring of the spindle completely dis-engaged (the one that pulls the spindle up). I was going real slow and backing out the chips every 1/4 turns.

The tap is CHINESE.

Paul Alciatore
09-09-2010, 09:36 PM
Good brands are Cleveland, Greenlee, and I am sure there are others. The Acme taps sold in hardware stores and taps sold in places like Sears, TSC, etc. are generally only OK for restoring damaged threads, not for cutting new ones.

I would be very cautious about using any Chinese import, no-name taps for any reason. That being said, I do have a very nice set of metric taps from Grizzly that are quite good. I took a chance and it worked out.

You can also have a trusted source. I have purchased many tap sets from McMaster. They do not specify what brand they will have in stock, but I have never gotten a bad one from them.

I like to purchase taps in sets: taper, plug, and bottoming. I do a lot of deep holes and would not hesitate to do an 8-32 3/4" deep, which is probably just about the length of the threads on the bottoming tap. Frankly, I do not consider a #8 to be a "small" tap. For me it is run of the mill. I have and have used taps down to a #0.

When you say you were "tapping in the small drill-press" I hope you were using the drill press only as a guiding device and not attempting to tap under power. A drill press, even at it's slowest speed, is just too fast for tapping. And it is very difficult to stop when resistance begins. If you want to tap with power, you will need a tapping head. A tapping head provides a combination of a further reduction in speed, a clutch, and instant (sometimes automatic) reversing. In my opinion, it is the only way to safely tap under power.

Rules for hand (unpowered) tapping:

0. Always use the proper tap drill. ALWAYS! A hole that is even a few thousanths too big is the surest way to break a tap. Been there, done that, and there is no tee shirt for it.

1. Use a good cutting fluid like Tap Magic.

2. Start with a taper tap.

3. Use a tap block or other means of keeping the tap perpendicular to the surface. This is extremely important because if the tap is started crooked, it will NOT straighten itself out and as it goes deeper, it will surely jam and break.

Tap Blocks:
http://img.photobucket.com/albums/v55/EPAIII/TapGuideBlocks.jpg

Guided Taps:
http://img.photobucket.com/albums/v55/EPAIII/TapsUnassembled.jpg
The guide bushings are placed in a chuck in a drill press or vertical mill. The one on the left was purchased as shown and is a bit loose for accurate guidance. The one on the right was altered by me to provide much better guidance and a longer starting range.

4. Back out frequently to remove chips from blind holes. Use a small brush to clean chips off the tap. (Through holes that are short can be tapped in one pass. Best to use a spiral point tap here.)

5. When the taper tap reaches the bottom, STOP. You will know this when the resistance increases.

6. If you need the threads deeper than a taper tap will cut, then use the plug tap AFTER going as far as you can with the taper tap. If you need them all the way to the bottom (well almost), use the bottoming tap after using the taper and plug taps in succession.

J Tiers
09-09-2010, 10:21 PM
Why tap so deep?

Maybe it is for an adjustment, like a spring tension.......... there are many possible reasons why. and tapping that deep is not a reason it should break.

Dull tap, no lube, sticky material, not using a spiral POINT tap, side force, running into the pile of chips at the bottom, etc, etc.

Some of the worst tap breakage I have had was from backing OUT..... the chips, which were not that long, since I was advancing and backing up per standard procedure, apparently got stuck and jammed the tap.....

x39
09-09-2010, 10:28 PM
The tap is CHINESE.
In all seriousness, buying cheap taps is false economy at best. Is the aggravation worth the few bucks you saved initially?

airsmith282
09-09-2010, 11:56 PM
for small tap holes i buy dormer taps and dies, or butterfield, i used to use the cheaper stuff nut now its the good stuff only nowfor al my taps and dies,also make sure to use cutting/tapping fluid and keep the hole clean as much as you can

Black_Moons
09-10-2010, 12:22 AM
Eh, Don't overlook the fact that chinese can screw up on the geometry. If you don't have any/enough relief on the tap it will take wayy to much force to turn, as well as if theres no relief after the 'cutting' threads at the start of the tap. You could actualy grind away most of the threads after the first few that cut and a couple that guide, if you don't plan to resharpen the tap.

Note: I do use chinese taps. But I use a ton of cutting oil (Yea I know I should buy proper TAPING oil), Only 50~60% thread depth in steel (Love the 100+ drill bit sets), usally only 1/4" thick steel at best. (anything that needs stronger, or could oneday ever strip due to repeated insertion, I use a nut)

Also, never tryed anything smaller then the 1/4" tap yet, but so far all the taps has proformed without breaking any. The last and only tap I ever broke was in a weedwacker shaft, #10 tap, took FOREVER to get it out.. and it was because I was taping with a cordless drill.. No, it did'nt snap taping.. it snaped when it bottomed out on the other side of the tiny hollow weedwacker shaft, DOH. did'nt even think to use the torque clutch on the drill. That was oddly, the first thing I ever taped.. I vowed to learn how to do it right because removing that tap REALLY sucked and kinda messed up the shaft bad.

Mcgyver
09-10-2010, 12:26 AM
Originally Posted by Elninio
How do you know if a tap is 'Snap-Off' brand?

My pet nickname for junk Chinese tools. :D

As opposed to that shiny wrench company, Strap On?

To the OP; you need a quality tap, bit of taping oil and a guide (cylinder with a flat face and hole the dia of the tap sq to the face). Do them by hand so you can feel whats going on.

assuming the right sized hole, Taps break because

1) they're crap
2) the not started straight, use the guide
3) too much torque is applied - do the smaller ones by hand or get a tapping head where you can set the torque

I suppose being dull wold be a fourth, but with a high quality tap years if not decades might go by in the home shop before its unserviceable...remember cutter wear is largely a function of surface space and hand tapping is slow stuff.

JoeCB
09-10-2010, 12:46 AM
Another thing about tap drill sizes... most common charts seem to be based on 75% thread depth. 75 % is seldom needed, espically for a deep tapped hole.... and really not if in steel. Find a chart that gives drill sizes for both 75% and 50 %, then you can select for the application at hand.
For the 8 -32 thread at 75 % depth use #29 (.1360) but for 50 % depth use #27 (.1440) ... a LOT easier tapping.
Joe B

Elninio
09-10-2010, 03:16 AM
I think the Chicom dogchit tap is the problem, and has been beat to death.
What material are you tapping? You can improve your luck with the correct lubricant for the material.
It was some generic cold-rolled bar (don't know the grade), using wd40 oil.

Elninio
09-10-2010, 03:45 AM
Another thing about tap drill sizes... most common charts seem to be based on 75% thread depth. 75 % is seldom needed, espically for a deep tapped hole.... and really not if in steel. Find a chart that gives drill sizes for both 75% and 50 %, then you can select for the application at hand.
For the 8 -32 thread at 75 % depth use #29 (.1360) but for 50 % depth use #27 (.1440) ... a LOT easier tapping.
Joe B

Purely by chance, I used the 50% (.1440") size.

Weston Bye
09-10-2010, 05:43 AM
How do you know when it's going to snap? I couldn't even see it flexing (and i'm not vision impaired)!

Ya got me there, I can't describe it, other than to say that I somehow learned what the forces on a tap should be for the particular material.

Years ago, when I was building a lot of control panels and had hundreds of 8-32 holes to drill & tap in 12ga. backplates for mounting relays and wireways and terminal strips, I speeded up the process by tapping all my holes by holding the tap in my variable-speed reversible 1/2 inch Milwaukee Magnum Hole Shooter. I even did a lot of 6-32 and 4-40 this way. (Maximum concentration required for the latter)

I guess there was some point where tapping went by feel, and I got to where I could feel a worn out tap and retire it before I broke it. Well, most of the time - If I got greedy and tried to get "just one more hole" out of a worn tap, I usually paid the price.

Rusty Marlin
09-10-2010, 05:49 AM
WD-40.....There's part of the problem.

WD-40 works great in aluminum. Ain't worth a tinker's dam for anything else, except cleaning the swarf out of your bench stones, for that its dang near peerless.

Use some form of oil, tap magic comes in little cans, even 3-1 or 30w engine oil is better than nothing and worlds better than WD-40.

I use standard cutting oil, (CIMCOOL 6000) because that's what I have. I've never owned a bottle of Tap Magic.

JoeLee
09-10-2010, 08:23 AM
Why do the chinese tap suck more --- do they start with a weaker metal, or do they get the heat-treatment wrong?

Most all the cheap Chink import taps are not a ground tap, they are made by press forming powered metal and not sharpened, basically dull.
My be OK for chasing but not for cutting. Junk..........
You saved a few pennys but purchased hours of agrevation. Even the best US made taps of that size are not that expensive. I just can't understand why you guys keep buying that junk.

JL................

Richard-TX
09-10-2010, 09:15 AM
Why do the chinese tap suck more --- do they start with a weaker metal, or do they get the heat-treatment wrong?

It isn't the Chinese taps that are bad but the company that makes them poorly that is the problem. It is easy to make crummy taps and there are a lot a Chinese companies that make crummy taps.

Finding reasonable taps is a challenge. The MSC house brand Hertel is pretty good. I do not like the Interstate brand that MSC sells.

Pherdie
09-10-2010, 09:32 AM
If you are tapping a through hole, try using a spiral tap. It 'pushes' the chip in front of the tap as the tap threads in, keeping the tap clear. Regardless, use good HSS taps. The price difference between carbon steel junk (HD, Lowes) and quality HSS, is minimal in an 8-32 tap.

Also, I saw no mention of the material being tapped, or even more important, the use of lubricant???

Daminer
09-10-2010, 01:54 PM
Here's what you need:

http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=319-5501&PMPXNO=19508862

Jim

Elninio
09-10-2010, 02:11 PM
Most all the cheap Chink import taps are not a ground tap, they are made by press forming powered metal and not sharpened, basically dull.
My be OK for chasing but not for cutting. Junk..........
You saved a few pennys but purchased hours of agrevation. Even the best US made taps of that size are not that expensive. I just can't understand why you guys keep buying that junk.

JL................
because the store that sells the good ones is 1.5 hours away