Threading - Something Went Wrong Here...

[Cody Killgore]

Hey guys,

I did my first threading a couple days ago on some aluminum. It turned out great. Fit nice.

Fast forward to today. I was going to make my first useful part that I've been wanting for my belt grinder. I did not have anything very machinable in the size that I needed so I grabbed whatever I had in the right size. This happened to be D2 tool steel.

I turned part of it down to 1/2" like I wanted. I started threading the end of it and man...something just wasn't going right. Can anybody tell what I did wrong just by looking at it? It looks like it just ripped it apart. I think I did miss a bit on the last engagement of the half nut, but regardless.....

This was supposed to be 1/2" 13 TPI

Zoomed in for your viewing pleasure

 

[randyc]

Well, I'd first suspect the geometry/sharpness of your tool. Looks like a LOT of chatter took place. The workpiece may also have been extended too far from the chuck/collet. Also need to use LOTS of cutting oil. I'm like a stuck record in that I always recommend pipe threading oil which is available from almost any hardware store.

In addition to any/all of the above and based on what I see of the turned diameter at the left of the photo, the material may not have been especially cooperative (1018 sort of steel).

Sharpen the cutter, keep the work close to the chuck, make sure that the work is securely gripped, use lots of oil, run the lathe as slow as you can and practice, practice, practice.

PS: you might try setting the compound around 27-29 degrees off perpendicular to the work. Use the compound to feed the tool, not the cross slide. Take no cuts exceeding .005.

 

[Cody Killgore]

Well, I'd first suspect the geometry/sharpness of your tool. Looks like a LOT of chatter took place. The workpiece may also have been extended too far from the chuck/collet. Also need to use LOTS of cutting oil. I'm like a stuck record in that I always recommend pipe threading oil which is available from almost any hardware store.

In addition to any/all of the above and based on what I see of the turned diameter at the left of the photo, the material may not have been especially cooperative (1018 sort of steel).

Sharpen the cutter, keep the work close to the chuck, make sure that the work is securely gripped, use lots of oil, run the lathe as slow as you can and practice, practice, practice.

PS: you might try setting the compound around 27-29 degrees off perpendicular to the work. Use the compound to feed the tool, not the cross slide. Take no cuts exceeding .005.

I did not really notice any chatter. It seemed pretty smooth and I was running it really slow. It is really only 1/2" even though it is blown up big. I was using one of those triangular carbide inserts. I turned to a new corner for this thread cutting. I center drilled the end and had a live center stuck in it since it was sticking about 4 inches out of the jaws. The compound was 29.5 degrees and I did use it to feed.

I think I tried to take bigger cuts than I should have. I do probably need to use more oil. I can't remember whether I put any on there when I was threading. I used it when turning down the diameter.

Thanks for the tips!

 

[randyc]

You did nearly everything right except for the carbide cutter (and maybe DOC).

Carbide has a tendency to chip plus the manufacturing process is sintering, not cutting. The result is that the cutting edge is not very sharp, even when honed with a diamond lap. There ARE carbide tools made for threading but I suspect that you just have a standard turning tool.

Also, carbide produces a very poor finish unless it is run at high speeds. High speeds and thread cutting are not compatible as you know.

A sharp, sharp HSS tool is ALWAYS preferable to a carbide insert for threading. Even though you didn't notice chattering your photo clearly shows it. Grind/lap a sharp HSS 60 degree tool, take light cuts and you'll produce good threads in no time at all.

 

[Cody Killgore]

You did nearly everything right except for the carbide cutter (and maybe DOC).

Carbide has a tendency to chip plus the manufacturing process is sintering, not cutting. The result is that the cutting edge is not very sharp, even when honed with a diamond lap. There ARE carbide tools made for threading but I suspect that you just have a standard turning tool.

Also, carbide produces a very poor finish unless it is run at high speeds. High speeds and thread cutting are not compatible as you know.

A sharp, sharp HSS tool is ALWAYS preferable to a carbide insert for threading. Even though you didn't notice chattering your photo clearly shows it. Grind/lap a sharp HSS 60 degree tool, take light cuts and you'll produce good threads in no time at all.

I will be sure to try HSS next time! Thanks.

 

[chips&more]

I think you answered your own question when you said you missed the mark on the threading dial. In doing so you took way too big of a cut. Under certain conditions, D2 does not cut that well and that is an example of one of them. If you miss the mark it will just tear it up. Use cutting oil. If all you have is carbide, that’s fine. When you get the hang of threading. Try threading the depth of cut with just the cross feed. This method will make the threading tool cut equal amounts on both sides of the “V”. And you will not need to set the compound to 29.5° or whatever. Also, the finish on the threads can be more rewarding doing this way….Good Luck, Dave.

 

[Wreck™Wreck]

Hey guys,

I did my first threading a couple days ago on some aluminum. It turned out great. Fit nice.

Fast forward to today. I was going to make my first useful part that I've been wanting for my belt grinder. I did not have anything very machinable in the size that I needed so I grabbed whatever I had in the right size. This happened to be D2 tool steel.

I turned part of it down to 1/2" like I wanted. I started threading the end of it and man...something just wasn't going right. Can anybody tell what I did wrong just by looking at it? It looks like it just ripped it apart. I think I did miss a bit on the last engagement of the half nut, but regardless.....

This was supposed to be 1/2" 13 TPI

Zoomed in for your viewing pleasure

View attachment 97890

Without a scale in the photo for reference it looks like the tool took 2 slightly different tracks, this happens when one is is slightly off engaging the half nuts, I am assuming you are doing this manually. If it went well the first few passes and then went to hell all of a sudden at near minor diameter depth of cut that is probably what happened.

Place a 1/16" scale along the threads and take the picture again, it may help show the cause.
I imagine that it did an excellent job of destroying the insert as well.

 

[stupoty]

Take no cuts exceeding .005.

I've found recently that 005 is quite a good for most of the cut, i tend to work down to 0.002 once the thread get deeper and the width of the cut becomes very large.

Stuart

 

[randyc]

Without a scale in the photo for reference it looks like the tool took 2 slightly different tracks, this happens when one is is slightly off engaging the half nuts, I am assuming you are doing this manually...

Good call, my old eyes missed the cross-tracking !

Try threading the depth of cut with just the cross feed. This method will make the threading tool cut equal amounts on both sides of the “V”. And you will not need to set the compound to 29.5° or whatever. Also, the finish on the threads can be more rewarding doing this way….Good Luck, Dave.

No offense but the point of using the compound set at 29 degrees is NOT to cut both flanks of the thread at the same time.

The tool skims the right flank, producing a good finish, while removing most of the metal on the left flank. At least this is the way that I was taught and to the best of my memory, literature supports the method.

Here's a pretty good discussion from "Practical Machinist"

http://www.practicalmachinist.com/vb/general/setting-compound-angle-when-thread-cutting-278289/

PS: I missed the "D2" material, which changes the process a bit

 

[JimDawson]

+1 on most of the above. There are defiantly two starts, that will tear things up pretty good on the last cut. D2 is a PITA under the best of conditions. it's a balancing act between feed/speed and work hardening. You also have to maintain a pretty healthy DOC in D2. A good, sharp HSS tool would be the best here.