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Single Point Threading on Lathe

jbacc

Hot Rolled
Joined
May 5, 2009
Location
New Jersey
Good evening and Happy New Year to all,

It's been a while since I did any single point threading on my Webb/Whacheon 17" lathe and even then, I was not that good at it before. Please forgive me if I am using improper/incorrect terminology but if you look at the attached photo of a 5/8 x11 TPI threads I cut, the crest(?) of the thread looks like it's not in the center, it looks like one side cut off center.

The compound is set to 29 1/2 degrees and I was using a 60 degree HSS lathe tool. The corresponding store bought nut threads on fine with little slop, but the thread just doesn't look right to me. BTW, it was a piece of 4140 that I threaded.

In any event, any comments, insight, advice etc. would be most appreciated.

Thank you.

Joe

.625x11 tpi.jpg
 
Assuming your tool is set to the proper angle and you're feeding with compound... perhaps a dull cutter ?
 
Thanks for your help. Tool is squared to the work using a fish tail guage and yes, feeding from the compound. Tool is sharp.

Thanks again.

Joe
 
Hi Joe:
Is your tool correctly ground?
Does it fit into your fishtail gauge properly?

If that part is OK, then most likely you have the compound slide set to the wrong angle.
Are you SURE you have it set to 30 degrees from the cross slide axis.
It looks like you have it set to 30 degrees from the spindle axis.
It's an easy mistake to make and it'll make threads like the ones in your picture.

Also, the trailing flank on those threads looks awfully rough.
Do you have side clearance on that flank of the tool?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
Good evening and Happy New Year to all,

It's been a while since I did any single point threading on my Webb/Whacheon 17" lathe and even then, I was not that good at it before. Please forgive me if I am using improper/incorrect terminology but if you look at the attached photo of a 5/8 x11 TPI threads I cut, the crest(?) of the thread looks like it's not in the center, it looks like one side cut off center.

The compound is set to 29 1/2 degrees and I was using a 60 degree HSS lathe tool. The corresponding store bought nut threads on fine with little slop, but the thread just doesn't look right to me. BTW, it was a piece of 4140 that I threaded.

In any event, any comments, insight, advice etc. would be most appreciated.

If the cutter was that dull, I'd think it would look pretty odd.

Is the half-nut slipping off the leadscrew somehow? How old and beat is the lathe?

Or, are you driving the carriage with the rack by mistake?

 
Hi Joe:
Is your tool correctly ground?
Does it fit into your fishtail gauge properly?

If that part is OK, then most likely you have the compound slide set to the wrong angle.
Are you SURE you have it set to 30 degrees from the cross slide axis instead of 30 degrees from the spindle axis.
It's an easy mistake to make and it'll make threads like the ones in your picture.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Hi Marcus,

First, thanks so much for taking the time to review and respond to my question. The tool is ground properly and fits the fishtail perfectly. As far as the compound angle, I believe I have it set correctly. The handwheel of the compound is swung over to thew right and the indicator on the scale on the compound reds 29 1/2 degrees. No doubt I must be doing something wrong which in a way makes me feel better knowing it's probably not the lathe.

Thanks again.

Joe
 
Never mind numbers. The compound MUST be at whatever angle OFF THE FACE OF THE CHUCK - not off the long ways of the lathe

Try the line in your mind's eye - a line that runs along in space, aligns exactly with one flank of the tool - and incidentally exactly with one flank of your thread. How can you POSSIBLY do it differently - and on purpose??? You know for certain the compound must follow along on the very same line

:confused:
 
Last edited:


If the cutter was that dull, I'd think it would look pretty odd.

Is the half-nut slipping off the leadscrew somehow? How old and beat is the lathe?

Or, are you driving the carriage with the rack by mistake?


Joe, thanks for your help. Lathe is vintage 1970's, not pristine but certainly not beat. Definitely threading using the half-nuts and threading dial.

Below are photos of the tool and the compound.

Thanks again.

Joe

Compound.jpg
Threading Tool.jpg
 
Hi again Joe:
Asian lathes are notorious for having compound slide swivel graduations that are wacky compared to American lathes.
Do this simple thing.
Swivel your compound so its axis is parallel to the cross slide axis.
Now swing it by eye 30 degrees toward the tailstock.
Look at the swivel graduations and see if they read close to 30 degrees of if the graduations say you're close to 60 degrees.
If it says you're close to 60 degrees you know it's one of "those"

There's not many ways you can make a thread that looks like yours.
If it's not the tool, it's the angle of advance of the tool.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Edit...I just saw your pictures...you've got a wacky Asian lathe alright...your compound angle is set wrong just as I suspected.
Try setting it to 60 degrees...all should be good.
BTW...ignore the 29 1/2 degree thing...it's supposed to permit a shaving cut with the trailing flank of the tool.
I don't find it to make enough difference to be worth the trouble.

Just looked even more closely...you don't even HAVE a grad mark at 60 degrees...I've seen some weird shit but never THAT one before!
 
My guess is you have the compound set at the wrong 29-1/2 degrees... To set it properly, turn your compound to a right angle to the longitudinal travel (to the length of the workpiece). Turn the compound end towards you to 29 degrees from that position.

I believe you have set it to 29 degrees from when it's travel was in line with the travel of the lathe, giving you this weird result.

Edit: hahaha I just saw Marcus posted the same thing while I way typing...

Ted
 
Hi again Joe:
Asian lathes are notorious for having compound slide swivel graduations that are wacky compared to American lathes.
Do this simple thing.
Swivel your compound so its axis is parallel to the cross slide axis.
Now swing it by eye 30 degrees toward the tailstock.
Look at the swivel graduations and see if they read close to 30 degrees of if the graduations say you're close to 60 degrees.
If it says you're close to 60 degrees you know it's one of "those"

There's not many ways you can make a thread that looks like yours.
If it's not the tool, it's the angle of advance of the tool.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Marcus,

I appreciate your insight and I will most certainly do what you suggest. I attached a photo of the compound and the threading tool if it sheds any light on my issue.

Thanks again.

Joe
Compound.jpg

Threading Tool.jpg
 
You definitely have it set wrong. Start with it on your 90 degree mark and turn it 29 degrees off from that. The tool looks OK. The angle of the compound is off.

Well, hopefully you have numbers on the other side, because it looks like it only goes to 45 on this side. Turn the compound so it is at a right angle to the workpiece and move it 29 degrees from that position even if you have to use a protractor.

Ted
 
You definitely have it set wrong. Start with it on your 90 degree mark and turn it 29 degrees off from that. The tool looks OK. The angle of the compound is off.

Ted

You guys are the best, truly.

I thank all of you who had the patience and took the time to help, I am grateful.

Joe
 
Point compound knob at your bellybutton. Depending on the lathe it could be marked zero, 90 or who knows what. Rotate CCW 29 1/2 degrees from whatever reference they used.

Thanks, it seems I had it pointed in the right direction but the either the markings are off or more likely, I am reading them wrong. Not sure if I am supposed to half the number I am seeing on the scale. Setting the angle off of the face of the chuck as John Oder advised brings me to about 15 degrees on the scale.

The advice I am receiving is quite helpful and I appreciate it.

Joe
 
I have seen similar ( older Italian import) lathes with two separate sets of degree marks and indicator lines, one set on the left, and one on the front, if the set on the left is on 30°, the indicator line will be on 60° if it's set up the same way. The set on the front is the ones to use for threads. ( Could also be on the rear, as I've seen on Chinese lathes)
 
I have seen similar ( older Italian import) lathes with two separate sets of degree marks and indicator lines, one set on the left, and one on the front, if the set on the left is on 30°, the indicator line will be on 60° if it's set up the same way. The set on the front is the ones to use for threads. ( Could also be on the rear, as I've seen on Chinese lathes)

Thanks, it seems the scale gives the total angle. 30 degrees on the scale would cut a 60 degree angle. As mentioned previously, when I set the angle to 30 degrees off of the face of the chuck, the scale on the lathe reads 15 degrees... Serenity :-)
 
NO!. It is NOT ready a double angle.

You are expecting the dial to read 0 when the compound is in line with the cross slide.
Your lathe reads 90. Set the dial to 61 degrees and rock on.
 
NO!. It is NOT ready a double angle.

You are expecting the dial to read 0 when the compound is in line with the cross slide.
Your lathe reads 90. Set the dial to 61 degrees and rock on.

Thanks, the scale stops at 45 degrees and at 90 degrees there is a zero. The scale on both sides goes only to 45 degrees.
 
I have the YAM version of that lathe, the degree marks are the same, and what everyone is telling you is correct. You will need to figure out where 60 degrees is and make a mark yourself, set compound to that mark.
 








 
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