Threading Question.

Fldvr

Fldvr

H-M Supporter - Gold Member
H-M Supporter Gold Member
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Hi everyone, I've done a little threading on non critical parts using the cross slide. Now
that I'm ready to move on to the compound I find myself wondering about the depth of cut.
When using the cross slide and I wanted to make a thread with say a depth of .100 then I would
gradually move the cross slide in until I had a total of .100

Now my question is, when using the compound there must be some difference in the depth of
cut due to the angle/movement of the slide. Is there a correction factor that seems to be eluding me
here? I have read and looked on you tube but do not see any references.
 
The movement is the sine of whatever angle you have the compound set. At 30 degrees (assuming it is exactly 30 degrees) the movement is 0.5 for every compound increment. For all practical purposes, assume the .5 movement. I am a total newbie myself, and I experiment with different ways to get the job done. On threading I stick a dial indicator on the tool post with the mag base on the saddle, square it and level it and I just use it to measure the cut since I normally use the cross slide for the last couple of thou.

I may be out of my league here, the pros can chime in and correct me please.
 
Professionally, I've never concerned myself with Depth of Cut while threading, other than individual cuts. There are thread mikes or PD Thread wires to tell you when you're deep enough. Anything else is guesswork.

I always use the compound for increment the cut, the cross slide is for backing out at the end and returning to datum before starting the next pass
 
My thread specification software shows the compound infeed amount.
Beyond that , in my very unprofessional guesswork :) is to use the nut I am going to use to check fit when it gets close.

Just being practical TB, you are of course correct in all that you say but most hobby machinist do not have thread mikes or thread wires.

Ken
 
T Bredehoft said:
Professionally, I've never concerned myself with Depth of Cut while threading, other than individual cuts. There are thread mikes or PD Thread wires to tell you when you're deep enough. Anything else is guesswork.

I always use the compound for increment the cut, the cross slide is for backing out at the end and returning to datum before starting the next pass
Click to expand...
What he said!!!
Turn close, measure, turn finish pass to desired size (repeat as needed), all of the folklore, how to guides, text books, rules of thumb and downright misinformation will only get you close. If you are a hobbyist buy a thread wire set and learn to use it, as unpleasant as that is. I do this for a living and use wires when we don't have any other way to measure a particular thread, very accurate in skilled hands yet cumbersome to use at best.
Good Luck
 
Ken_Shea said:
... most hobby machinist do not have thread mikes or thread wires. Ken
Click to expand...

Ken, you're probably right about thread micrometers and maybe even regarding thread wires but there's really NO reason for not owning a set of thread wires ($7 from CDCO, for example). Takes a little practice to use the wires but some pitch diameter measurement capability beats none, right ?
 
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randyc said:
Ken, you're probably right about thread micrometers and maybe even regarding thread wires but there's really NO reason for not owning a set of thread wires ($7 from CDCO, for example). Takes a little practice to use the wires but some pitch diameter measurement capability beats none, right ?
Click to expand...
Measurement over wires is extremely accurate, think of it as a sine bar for compound angles.

I did a thread 2 weeks ago that isn't even listed in MH, 2 15/16-8 X 5 LH (the left handedness is meaningless since it measures the same) fortunately the Customer had a sample that I could measure over wires because it had to fit an existing component of unknown age and condition. Hasn't come back yet but time will tell.
 
If a particular class fit was required then I'd be all over a set of thread mikes and wires, when it's not you just do not need them and a good thread job would be done by the time I was done finding, selecting and fiddling around with a set of thread wires.

Don't take me wrong, and I certainly made no argument against the proper method/s nor would even the thought of suggesting other wise cross my mind to one who wanted to use/learn them. That said, in 50 + on/off years of hobby machining I've managed well with out either and I do not put out junk sloppy jobs. Professionally, that senario would be a much different.

Ken
 
Wreck™Wreck said:
Measurement over wires is extremely accurate, think of it as a sine bar for compound angles...
Click to expand...

I agree and used wires + masking tape for years. I have a hereditary motor movement problem that causes severe tremors in both hands (it has gotten worse as I age). After dropping a wire three times before getting a measurement, I gave up and got thread micrometers :)
 
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