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woodnerd
09-30-2010, 07:47 AM
I'm just learning to thread with my old Craftsman 101 lathe. I'm having a couple of problems ...

One, the finish on the threads seems rather rough. I'm taking very small final cuts, but I get a lot of burrs and the surface of the threads is "flaky" looking. I'm using a 60* carbide insert tool in a quick change tool post. There's no way to adjust this to get a back rake, is this the wrong tool to use? Also, should it be on the centerline of the spindle or higher/lower?

Two, the lathe is cutting exactly half the TPI I'm selecting. According to the chart on the front, it appears that I need to disengage the "slide gear" but there's nothing in the manual showing where this thing is. Any ideas?

Tony Ennis
09-30-2010, 07:50 AM
re: side gear - try pulling/pushing one of the QCGB's handles. I think the left one.

woodnerd
09-30-2010, 08:36 AM
OK, I solved the TPI issue, the owners manual calls it a "sliding gear" instead of a slide gear. It's located at the back of the side gears, you have to loosen a bolt and swing the plate with all the gears mounted on it down, then one gear slides out on it's shaft. Kind of a pain, but it stays "out" for all but the smallest threads.

Thanks Tony. While it wasn't what you thought, it pointed me in the right direction.

Boot
09-30-2010, 08:46 AM
Do you have your compound set at 29 1/2 degrees. You want to be cutting with only one side of the tool until the very last cuts. You should always be on center. Plus it is always best to consider the type of material and to use a suitable cutting fluid accordingly. Some steel will do what you ar saying if not any cutting fluid is being used. Very important to set compound at 29 1/2 degrees. All my years in a machine shop (37) I never plunged straight into parts with threading tool.

luthor
09-30-2010, 09:09 AM
Is this 60 degree tool a screwcutting tool or a normal turning tool? A turning tool will not have sufficient clearance to allow for the lead angle of the thread unless you are cutting a fine thread on a large diameter.

Boot
09-30-2010, 09:09 AM
Go to the Practical Machinist site . Then go to South Bend forum and you will see about half way down the page a fellow asks about threading. The fellows on there explain all there is about what to look for and do when you thread single tool on a lathe.

Bill Pace
09-30-2010, 09:25 AM
About the ragged edge -- Its highly likely its the metal youve chosen, (though the tool/shape) is secondly possible. Do you know what the metal is that youre threading?

I'm a home shopper and 98% of my work stock is scrap yard or cast off/finds from here or there so I rarely know what it is and some times I cant get a good finish no mater what. I was just threading a piece of 3/4" hardware store black pipe for a non critical 'filler' piece and I was about to think it wasnt gonna work because the crappy threads, - what I call "lottsa whiskers". But I ran several 'clean up' passes over it, ran a stiff wire brush over them and lightly filled the tops and it was useable. The piece I was mating it to - "unknownium" threaded up very nicely.

woodnerd
09-30-2010, 09:27 AM
Yes, I have the compound set to a little under 30* and using a cutting fluid. I make a pass, use the crossfeed to back it out, move the carriage back, put the crossfeed back, then feed the compound for the next cut.

I see in the other thread some people suggesting using the back gear for the slowest possible speed. Really? I'll be here all day if I cut that slow.

I'm using a generic 60* uncoated carbide insert. I didn't see a special threading insert, is there such a thing? Or do I need to get a special cutter or grind a HSS one?

woodnerd
09-30-2010, 09:30 AM
At this point I'm just experimenting with whatever I have lying around :)

I got some pretty decent threads on chunk of 2" stuff that I think is brass. When I try steel is when I get the raggedy stuff. What I was playing with this morning was a piece of allthread, just trying to turn down the end and thread it to 1/4-20

Lew Hartswick
09-30-2010, 09:42 AM
First I'd suggest a HSS bit with a bit of top rake. But plain old "steel"
is going to do that. Higher speed will reduce the effect but then you
have the problem of stoping the cut. :-) Try it to an extra large stop
groove and see.
...lew...

rkepler
09-30-2010, 09:42 AM
At this point I'm just experimenting with whatever I have lying around :)

I got some pretty decent threads on chunk of 2" stuff that I think is brass. When I try steel is when I get the raggedy stuff. What I was playing with this morning was a piece of allthread, just trying to turn down the end and thread it to 1/4-20

First: you're going to have trouble getting clean looking threads using a tool with no rake as the chip doesn't have time to form. You'd be a lot better off experimenting with some HSS tooling so you could put in some rake and hone the edge fine for the final cuts.

Second: "all thread" is rolled, not cut, and the steel isn't really all that great for cutting. The rolling will also leave some residual stresses in the steel that'll make it fun to try and cut decent threads.

If you want to experiment threading in steel try getting something like 12L14 - leaded steels are made for turning and threading. If you can't get that try some 1144, it's common as shafting and turns and threads very nicely. If you can try and get a threading tool with some rake, it'll make a big difference in the threading (I like the laydown threading inserts myself, but take the time to find bargains on eBay rather than pay list).

Boucher
09-30-2010, 12:43 PM
I would suggest that you put the carbide cutter away to start with. If you are going to try to use it you need to determine whether it is a threading tool. If it is a chamfer tool you need to sharpen it to produce a good sharp cutting edge and to establish side relief on both sides of the point.

Bad surface finish is probably partly material related and partly tool related. As noted by others some material just wants to tear ragged rather than cut smooth. Sometimes you have to work with difficult materials so you just need to learn how. When turning a surface on the lathe getting the right surface speed is important. Take the material you need to work with and the diameter of the threads you need. Play with the speeds and feeds to turn the best surface finish. You need the same speeds and feeds to thread because it is just a special case turning application. Bad threads often result from cutting too slow.

Regardless of which tool material you use it needs to be sharp and configured properly, which means it has to have some side relief. HSS takes a sharper edge than carbide and it is easier to establish back rake. If you need to purchase a threading tool, look at these:
http://www.arwarnerco.com/warner_products_kits_threading_k17.html
they are available with HSS positive rake inserts that are about the sharpest and best to start with.

HSS cutting tools are your friend when you are getting started. It is better to spend money getting setup to sharpen them than to purchase Insert type tools. Buying good quality grinding stones is imperative. Most grinders come with wheels of poor quality or the wrong grit/hardness/binder.

Bill Pace
09-30-2010, 01:10 PM
That tool Boucher's showing is what I use also, and its really nice!

You might note the minimum diameter for an inside thread - 1 3/8" (iifc) that hurts me a good bit because I do more stuff around and under an inch, but, for outside threading and over that min on inside, I love it!

woodnerd
09-30-2010, 01:58 PM
It is better to spend money getting setup to sharpen them than to purchase Insert type tools

I've already got a decent grinding setup for my HSS woodturning tools. When doing HSS bits, do you set up jigs to get the angles right? Or do you just get good at eyeballing it?

Bguns
09-30-2010, 02:07 PM
Eyeballs work fine.

Some materials/equipment combinations, will require slight adjustment of book perfect angles, for best results ....

V Threading tools need to be at least checked to ensure 60 degree angle (or 55 degrees for those odd threads :) ) Relief angles are not super critical..

Mcgyver
09-30-2010, 02:12 PM
I've already got a decent grinding setup for my HSS woodturning tools. When doing HSS bits, do you set up jigs to get the angles right? Or do you just get good at eyeballing it?

free hand, and stone after grinding. get one of those little fishtail gauges and hold the bit up to the light - you'll get it in no time. You should have the fishtail gauge anyway for setting the tool bit sq to the work

carbide can leave a fantastic finish on these gummy mild steels but only at speed, I agree for slow stuff (like threading), the superior edge you can put on hss is preferred.

Note the clearance angles as some have the guys have mentioned. The helix of the thread requires a lot more clearance on the left side than a regular tool...if the thread leans a 9 degrees, then 8 degrees on a typical tool bit isn't going to work. btw, on the clerance, anything within several degrees is fine, a super exact clearance of a specific angle is not required

Lastly, mild steel can be difficult to get a good finish on. I think its great that you're experimenting and learing, it i'll make you a better machinist....but there's only so much you can do with this material. As suggested, try some free cutting steel to see the difference. Another solution is to chase the thread with a die, it'll clean up the finish and put the right profile on if your threading bit was less than perfect. This is a perfectly acceptable approach and the advantage of threading in the lathe is not lost; that the thread is properly aligned to the work over its length

Elninio
09-30-2010, 02:16 PM
McGyver your PM inbox is full so HSM is saying you can't accept any PM's! I have some items you may be interested in that I must get rid of asap!

Dr Stan
09-30-2010, 02:22 PM
Or do I need to get a special cutter or grind a HSS one?

The short answer is yes. I highly recommend buying a copy of South Bend's How to Run a Lathe. I think Lindsay's Technical Books has reprinted it, but I could not find it in their list. Take a look at: http://www.lindsaybks.com/

You can also find numerous videos of threading on You Tube which may be of help.

Mcgyver
09-30-2010, 02:24 PM
sorry about that, like Mr. Bean I must have been sending myself too many cards! clear now

Boucher
09-30-2010, 02:43 PM
I was originally taught to grind HSS tools freehand but I have digressed to using guides to do most of my grinding. Here are some that I find usefull.
http://i109.photobucket.com/albums/n50/boucherbyron/IMG_0073.jpg

http://i109.photobucket.com/albums/n50/boucherbyron/IMG_0072.jpg
What I like most about the guides is that I can touch up/sharpen a tool with just a quick brush of the fine wheel. I actually donít remove the tool from the quick-change tool holder block. I just set the block against the guide like I would the tool.
I rough out the tools on the belt grinder because it is so much faster and cooler then finish on the white Norton stone.
.

Al Messer
09-30-2010, 05:21 PM
Yes, I have the compound set to a little under 30* and using a cutting fluid. I make a pass, use the crossfeed to back it out, move the carriage back, put the crossfeed back, then feed the compound for the next cut.

I see in the other thread some people suggesting using the back gear for the slowest possible speed. Really? I'll be here all day if I cut that slow.

I'm using a generic 60* uncoated carbide insert. I didn't see a special threading insert, is there such a thing? Or do I need to get a special cutter or grind a HSS one?


Grind one from HSS and use NEXT to slowest Back Gear.

camdigger
09-30-2010, 05:55 PM
Watch these youtube videos http://www.youtube.com/watch?v=5-bTfflIPlc for threading tips and this one for threading tools http://www.youtube.com/watch?v=HTQ46NMMc88&feature=related

A google search may turn up a site or two where the Southbend book can be downloaded...;) All disclaimers re copyright blah, blah, blah... I'm just saying it's there....