Threading on a lathe when you cannot set up 29.5 degree compound

[benmychree]

Most my threading I only use the cross slide for feed.

If can not use compound it is not problem.

FYI Turret lathes don't have a compound and some have threading.

Dave

I have yet to see a turret lathe with a lead screw and gearing, Some use a single thread pitch attachment that fits over the feed rod, these types are generally used for following a die head for multiple cuts to finish size to avoid "shaving " of the threads and control of lead, not for cutting threads from scratch.

 

[francist]

Reminds me of a Breville (sp?) spring.

Are you by any chance thinking of a Belleville washer...?

 

[koenbro]

Are you by any chance thinking of a Belleville washer...?

View attachment 496612

Haha yes, you’re right. My correct spelling of the wrong word reminds me of “There is nothing worse than a sharp image of a fuzzy concept.” Variously attributed to Jean-Luc Godard, Anselm Adams, and, no doubt, many others.


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[Ischgl99]

An alternative to turning the compound to 29.5 degrees for threading is to use the method taught in Europe which you describe in your OP. You don’t need to worry about feeding in at 29.5 degrees, it just needs to be 30 or less. With the European method, you keep the compound at 90 degrees to the cross slide. To cut a thread, you advance the cross slide, and then the compound half of the depth you did on the cross slide. If you go in 0.005” with the cross slide, you want to go in about 0.0025” with the compound. That gives you an infeed angle of 26.6 degrees. This will cut a bit more on the trailing side of the threading tool, but that doesn’t really matter much. If you are finding it is chattering and you need to be closer to no cutting on the trailing edge, advance the compound up to 0.577X the cross slide infeed for a 60 degree thread. These numbers are for the depth of cut, not the diameter. As long as you don’t advance your compound an amount that would give the equivalent of infeeding at more than 30 degrees, you are good. Limiting it to half the cross slide infeed, you are good for both standard V threads and Whitworth threads that are 55 degrees.

Personally, I'm at a loss as to why the pins are even there.

For a manual lathe, it makes no sense to have them on a compound, but these are also used on some CNC machines where you would want pins so that the tool post does not move at all. If it moves, all your tool positions are wrong. I wasn’t clear if it came that way from the factory, or if he added those, if from the factory, the T nut might have been intended for a CNC installation.

 

[Shiseiji]

I have yet to see a turret lathe with a lead screw and gearing, Some use a single thread pitch attachment that fits over the feed rod, these types are generally used for following a die head for multiple cuts to finish size to avoid "shaving " of the threads and control of lead, not for cutting threads from scratch.

Logan 10, 11 & 12" turret lathes have a lead screw and gearing. No feed rods. The turret/tailstock is the only difference between the models.

 

[koenbro]

@Ischgl99 :
"For a manual lathe, it makes no sense to have them on a compound, but these are also used on some CNC machines where you would want pins so that the tool post does not move at all. If it moves, all your tool positions are wrong. I wasn’t clear if it came that way from the factory, or if he added those, if from the factory, the T nut might have been intended for a CNC installation."

Came with the pins from the factory. I have all my tools aligned in the SDM memory of my DRO so can easily switch and maintain alignment. As a learner it is not essential to have the pins but will consider replacing them in the future.


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[koenbro]

An alternative to turning the compound to 29.5 degrees for threading is to use the method taught in Europe which you describe in your OP. You don’t need to worry about feeding in at 29.5 degrees, it just needs to be 30 or less. With the European method, you keep the compound at 90 degrees to the cross slide. To cut a thread, you advance the cross slide, and then the compound half of the depth you did on the cross slide. If you go in 0.005” with the cross slide, you want to go in about 0.0025” with the compound. That gives you an infeed angle of 26.6 degrees. This will cut a bit more on the trailing side of the threading tool, but that doesn’t really matter much. If you are finding it is chattering and you need to be closer to no cutting on the trailing edge, advance the compound up to 0.577X the cross slide infeed for a 60 degree thread.

Yea the 0.577 ratio is the limit case for 60degrees, same as my calculations of tan(60deg) = 1.73 which is 1/0.577. Kind of awkward to calculate this ratio at every step, then dial it in.

 

[Ischgl99]

@Ischgl99 :
"For a manual lathe, it makes no sense to have them on a compound, but these are also used on some CNC machines where you would want pins so that the tool post does not move at all. If it moves, all your tool positions are wrong. I wasn’t clear if it came that way from the factory, or if he added those, if from the factory, the T nut might have been intended for a CNC installation."

Came with the pins from the factory. I have all my tools aligned in the SDM memory of my DRO so can easily switch and maintain alignment. As a learner it is not essential to have the pins but will consider replacing them in the future.


Sent from my iPhone using Tapatalk Pro

I use tool offsets as well, but I took my compound off and use a solid plinth, so no worries about losing the offsets. I haven’t had any issues threading with the cross slide, so only use the compound whenI need to turn a taper.

 

[timmeh]

I learned the angled compound method for threading at TAFE(technical college).
First time on the job, foreman had a giggle, said "nah, wasting time, DOC with cross slide and advance compound as needed(always left parallel to spindle axis). Did the math to figure a close relational ratio between the two axes.
All that's needed is to keep one of the tip flanks doing litte to no actual cutting.
Last cut, back compound up to shave the "other" flank if required.
Can't ever recall actually doing angled compound threading on the job.

 

[savarin]

I removed the pins on my qctp very early on and used a brown paper shim underneath. That stopped all rotation creep.
Lately I added a thrust washer under the top nut and cannot believe how much tighter it clamps now.

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