Why 29.5 degrees

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Bill Shields
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Re: Why 29.5 degrees

Post by Bill Shields »

of course there is also the 'stagger cut' method used by newer controls...

cut on the left flank
next cut on the right flank
next cut on the left flank
next cut on the right flank
get to bottom...eventually

depths calculated based on constant volume of metal removal based on volume to be removed by first infeed.
Too many things going on to bother listing them.
LouStule
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Re: Why 29.5 degrees

Post by LouStule »

I still hear my shop teacher (Mr.K) drumming it into our heads back in the early 70's "Set the compound rest at 29.5 deg. towards the tailstock to cut threads" I've been doing it ever since. I miss that guy.
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Harold_V
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Re: Why 29.5 degrees

Post by Harold_V »

LouStule wrote: Tue Feb 15, 2022 8:06 pm I still hear my shop teacher (Mr.K) drumming it into our heads back in the early 70's "Set the compound rest at 29.5 deg. towards the tailstock to cut threads" I've been doing it ever since. I miss that guy.
Because threads can be generated with the tool upside down or right side up, with the machine operated in forward or reverse, depending on the thread in question, it's NOT a good idea to set the compound towards the tailstock for all occasions. It's also a good idea to make reference to the location as if viewing hands of a clock, to avoid choosing the wrong markings. Not all lathes are marked such that the proper angle is 29°30'. The marking may read 60°30' when you are set properly.

When feeding with the compound in machining threads, the important message should be that the compound should feed the tool in the direction of the cut. That means that the compound may be set at either 5:00 or 7:00, depending on whether you are cutting towards the tailstock or the headstock.

If the improper location is chosen, you run the risk of cutting pressure moving the carriage away from the leadscrew. If it remains there constantly, no big deal, but if it wanders between the two flanks, a drunken thread is the usual outcome. The ideal situation is that the cutting pressure keeps the leadscrew loaded, and that is accomplished by feeding the threading tool in the same direction the carriage is propelled in the cut.

H
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atunguyd
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Re: Why 29.5 degrees

Post by atunguyd »

Joe Pieczynski did a great video explaining this

https://youtu.be/PnH_oeOUps4

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earlgo
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Re: Why 29.5 degrees

Post by earlgo »

Harold wrote:
When feeding with the compound in machining threads, the important message should be that the compound should feed the tool in the direction of the cut. That means that the compound may be set at either 5:00 or 7:00, depending on whether you are cutting towards the tailstock or the headstock.
This setup worked for me while threading toward the tailstock with spindle reversed.
reverse threading.JPG
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
LouStule
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Re: Why 29.5 degrees

Post by LouStule »

Harold_V wrote: Wed Feb 16, 2022 4:38 pm
LouStule wrote: Tue Feb 15, 2022 8:06 pm I still hear my shop teacher (Mr.K) drumming it into our heads back in the early 70's "Set the compound rest at 29.5 deg. towards the tailstock to cut threads" I've been doing it ever since. I miss that guy.
When feeding with the compound in machining threads, the important message should be that the compound should feed the tool in the direction of the cut. That means that the compound may be set at either 5:00 or 7:00, depending on whether you are cutting towards the tailstock or the headstock.
H
Our shop lathes did not have reverse and neither does my home lathe. 29.5deg. towards the tailstock still holds true 60 years later. :)





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armscor 1
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Re: Why 29.5 degrees

Post by armscor 1 »

Hi Guys, made this new spindle today for my cross slide on my lathe, original was worn where I use it most.
Used 14mm drill rod, aka silver steel and ground the profile 30 degree trapezoidal thread.
Used the tool upside down and lathe in reverse, only downside I could not use travelling steady, tool forces the work piece down so took small cuts.
Silver Steel machines nicely and achieved a nice finish and accurate.
My compound graduations only go to 45 degrees each way so I used my vernier protractor to set the compound at 14 degrees from chuck face
I bored out my cross slide nut and silver soldered and aluminium bronze slug which I bored to size and tapped with a 14mm x 3mm LH tap.
Next time I will use phosphor bronze ,aluminium bronze is extremely hard to tap but long lasting, thought I was going to break the tap but got it through in the end.
armscor 1
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Re: Why 29.5 degrees

Post by armscor 1 »

From previous post.
armscor 1
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Re: Why 29.5 degrees

Post by armscor 1 »

Won't let me attach photos.
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Harold_V
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Re: Why 29.5 degrees

Post by Harold_V »

LouStule wrote: Sun Feb 20, 2022 8:09 pm Our shop lathes did not have reverse and neither does my home lathe. 29.5deg. towards the tailstock still holds true 60 years later.
Yes, it does. So long as the cut in question is taken towards the spindle. If it is taken towards the tailstock, you are not using acceptable procedure, and that's fact. Generate a left hand thread that way and tell me how it goes. Shift the compound to 5:00 and I agree with you.

Like it or not, if you advance the tool in the opposite direction of the feed of the carriage, you are subject to a drunken thread.

Industrial machines without reverse? Are you sure? What period of time would that be? I started in the shop (in industry) in 1957 and do not recall ever seeing a lathe that didn't have reverse capability. I do admit, the vast majority of the machines in question did NOT have threaded spindles, although even the threaded spindle lathes in the shop in high school had reverse. A shop full of old LeBlond short bed lathes.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Harold_V
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Re: Why 29.5 degrees

Post by Harold_V »

armscor 1 wrote: Mon Feb 21, 2022 3:31 am Won't let me attach photos.
How large are they? You must use good judgment in posting picture. They are best posted no larger than 1024 x 768 pixels. If yours are larger, yeah, the board will reject them, just as it should.

If your pictures are not unreasonably sized, please detail the problem you're having. We'll try to help.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
armscor 1
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Re: Why 29.5 degrees

Post by armscor 1 »

Hi Harold, 9.7 MB, one photo.
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