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View Full Version : what's the largest TPI thread you've ever cut?



Elninio
09-15-2010, 05:03 AM
I cut a 64 TPI as a test today, and I can't imagine how people make use of the ability of lathes -such as monarch EE- that are able to cut 184TPI. I think the hardinge HLV can cut 224 TPI, why would you need such a fine thread (even in optics it doesn't make sense)

Arcane
09-15-2010, 05:24 AM
When they built the Synchrotron here in Saskatoon a few years ago, the leveling blocks for the light beam were built by a local machine shop. One of the shop owners was a brother to a friend I worked with who had been given one as a souvenir and he brought it to work. AFAIR, the threaded block was roughly 1 1/4" thick by 2 1/4" square, threaded completely through, and the "weight jack" part of it was about an inch, maybe 1 1/8" in diameter. I do remember that the tpi was 180 and it turned as smooth as anything I have every seen.

Elninio
09-15-2010, 05:59 AM
When they built the Synchrotron here in Saskatoon a few years ago, the leveling blocks for the light beam were built by a local machine shop. One of the shop owners was a brother to a friend I worked with who had been given one as a souvenir and he brought it to work. AFAIR, the threaded block was roughly 1 1/4" thick by 2 1/4" square, threaded completely through, and the "weight jack" part of it was about an inch, maybe 1 1/8" in diameter. I do remember that the tpi was 180 and it turned as smooth as anything I have every seen.

Does adding more threads per inch increase or decrease the load capability for the bore sustaining?

Your Old Dog
09-15-2010, 08:33 AM
Does adding more threads per inch increase or decrease the load capability for the bore sustaining?

You just struck a nerve :D This topic came up once before and the general consensus was that fine threads were stronger then coarse threads. There must be a cross-over point because I speculated that if you carried this theory out all the way you would end up with next to no thread depth and hence the bolt would fall through the nut. The thread ended abruptly as I remember and I was left holding the bag and feeling like a jerk :D

wierdscience
09-15-2010, 10:04 AM
Largest I have ever cut 8"- 2tpi,smallest 1.220"-72.

Spin Doctor
09-15-2010, 10:09 AM
Coarsest, 2toi Buttress, finest. probably 64tpi. Although I did do some 5/16th-40 internal single point for some inside mic extentions.

Deja Vu
09-15-2010, 12:03 PM
Your Old Dog posed this with quote:
Quote:
Originally Posted by Elninio
Does adding more threads per inch increase or decrease the load capability for the bore sustaining?


You just struck a nerve :D This topic came up once before and the general consensus was that fine threads were stronger then coarse threads. There must be a cross-over point because I speculated that if you carried this theory out all the way you would end up with next to no thread depth and hence the bolt would fall through the nut. The thread ended abruptly as I remember and I was left holding the bag and feeling like a jerk :D

But wouldn't it be the same as lowering the TPI to 0? I.e., they both become nonfunctional.
Without going to extremes, i myself feel(no math here) that because of the surface area of large TPIs, they would be the stongest, with the added ability to make fine adjutments.
__________________

hitnmiss
09-15-2010, 12:06 PM
Fine threads may be theoretically stronger I don't know but I never had a problem with the bolts on my old chevy, nice course american threads.

My suzuki samurai with metric fine threads is a different story. It's virtually impossible to remove a bolt and reinstall with out cross threading. Now I resort to chasing every thread with a tap knowing it will save me time in the long run.

Just last week I single pointed some 6-48 screws for a scope block mount on the lathe. Smallest and highest pitch I've ever single pointed.

I dropped one in the lathe removing it and never found it. Had to make another.

Paul Alciatore
09-15-2010, 12:13 PM
I did some experimenting with some high TPI threads once. At some point, you stop thinking about TPI and start thinking in terms of feed rate.

On high TPI threads the material becomes a real important factor. Many common (cheap) steel alloys will just have too rough of a finish and the actual thread disappears in the surface roughness. You need a clean cutting (leaded?) alloy or perhaps 360 brass. And real sharp tools. REAL sharp. I have done 64 and 72 TPI with a fair amount of care. Over 100 TPI would get harder but could be done. I am not so sure about 200 TPI: that is only a 0.005" lead. You would need a magnifier just to see it. Infeed would be only 0.004".

At 100 TPI and higher, I would definitely want to use a die to finish the thread. Probably better at lower numbers too.

Forestgnome
09-15-2010, 04:19 PM
Better to use a differential thread adjuster, although that would be difficult in some optical applications.

Elninio
09-15-2010, 05:20 PM
But wouldn't it be the same as lowering the TPI to 0? I.e., they both become nonfunctional.
Without going to extremes, i myself feel(no math here) that because of the surface area of large TPIs, they would be the stongest, with the added ability to make fine adjutments.
__________________

I don't think the analogy works. Consider ratchet mechanisms - have you seen "one way ball bearings" ?

Elninio
09-15-2010, 05:22 PM
I did some experimenting with some high TPI threads once. At some point, you stop thinking about TPI and start thinking in terms of feed rate.

On high TPI threads the material becomes a real important factor. Many common (cheap) steel alloys will just have too rough of a finish and the actual thread disappears in the surface roughness. You need a clean cutting (leaded?) alloy or perhaps 360 brass. And real sharp tools. REAL sharp. I have done 64 and 72 TPI with a fair amount of care. Over 100 TPI would get harder but could be done. I am not so sure about 200 TPI: that is only a 0.005" lead. You would need a magnifier just to see it. Infeed would be only 0.004".

At 100 TPI and higher, I would definitely want to use a die to finish the thread. Probably better at lower numbers too.

My sharpened tool had no radius and it was barely enough for the 64TPI thread I cut, I sharpened it on a medium-grit 8" benchgrinder.

Errol Groff
09-15-2010, 05:39 PM
When I read the subject line "largest thread" I thought of the
3 3/4" x .875 pitch L.H. Brown and Sharpe worm thread (similar to an Acme thread but different) I made some years back. I did it on the CNC lathe as no other lathe in our shop would make that coarse a thread. Because our CNC lathe will not allow one to feed toward the tailstock I had to make an adapter that let me mount the cutting tool on the back side of the cross slide, run the spindle in reverse and thread toward the headstock to make the LH thread. All in all a very interesting project.

It was a repair job for a friend who is active in the Punkin Chunkin contests and
was used in the winch they used to haul back the draw string of their ballista.

Then I re-read the line and realized that you meant the "finest" thread you ever made. oops.

The Fixer
09-15-2010, 05:41 PM
At the risk of side tracking the thread, I would add that IMHO the coarse thread is used for strength and the fine thread for power. For example if you look at a stud used in an aluminum cylinder head you will see both fine and coarse threads. the coarse end is threaded into the aluminum and the fine thread is fitted with the nut. this provides strength (shearing) in the aluminum given a larger cross-section and yet provides for a more even torque with the fastener.

al

jdunmyer
09-15-2010, 09:19 PM
Jerry Kieffer makes taps that are 300 tpi and finer, IIRC. He wrote an article for HSM back in 2006 or thereabouts on using optics for micro machining and has a pic of some of his "fine" work. He also has had other articles in magazines such as Model Engine Builder on this sort of work. Most of his small work is done on Sherline equipment; he told me that my HF 7X10 isn't worth a darn for that sort of thing because the headstock bearings simply aren't good enough.

Jerry also did a seminar at one of the N.A.M.E.S. conferences on the making of very small, fine thread taps. Hardening them is kinda tricky. :-)

Arcane
09-15-2010, 10:07 PM
I knew that name sounded familiar. A friend, who is into old John Deeres, sent me this url (http://www.craftsmanshipmuseum.com/images/DeereFinal1m.jpg) to a site about Jerry Kieffer. Here's a pic of his 1/8 scale 1936 John Deere "D" tractor.
http://www.craftsmanshipmuseum.com/images/DeereFinal1m.jpg

Evan
09-15-2010, 10:29 PM
How about 160 tpi in stainless steel using my SB9?

http://ixian.ca/pics7/160tpi.jpg

http://ixian.ca/pics7/160tpi2.jpg

darryl
09-16-2010, 01:24 AM
A good point has been raised, and that is the ability of the machine to work that finely. If the machine is 'tight', it should be no big deal to make threads with a count over 100 or more. I did a test one day and got a pretty good looking thread at about 150 or so TPI. Sure, the tool has to be sharp and all plays controlled, etc, but it's not rocket science. Another good point was made, and that is the material being threaded. It has to be capable of a fine turned finish, otherwise decent threads will be limited to a lower TPI.

I used a rod from a printer and got a very nice result. I don't recall the depth of the threads, but it was only a few thou, six or seven I think.

By the way, what is the least TPI any of you have done? Mine would be 1/4, or in other words 4 inches per thread. Had to do it on the mill.

Elninio
09-16-2010, 01:24 AM
I knew that name sounded familiar. A friend, who is into old John Deeres, sent me this url (http://www.craftsmanshipmuseum.com/images/DeereFinal1m.jpg) to a site about Jerry Kieffer. Here's a pic of his 1/8 scale 1936 John Deere "D" tractor.
http://www.craftsmanshipmuseum.com/images/DeereFinal1m.jpg
http://www.craftsmanshipmuseum.com/Kieffer.htm

That's a nice thread, Evan. Did you polish it?

Evan
09-16-2010, 01:56 AM
I just barely touched it to the red rouge buffer to clean up any microscopic burrs. Cutting those threads wasn't particularly challenging. The real challenge is in cutting the mating threads. Ultra fine thread cutting is the province of the master optician, lens makers, telescopes and microscopes, other fine optical instruments. Master opticians would commonly show off their thread cutting skills on the outermost retaining ring thread on the objective lens cell of various instruments. Chief among those were large refracting telescopes where the objective lens cell might be 8 inches diametre and threaded to 120 tpi. Not only is such a large diametre thread incredibly difficult to cut it is nearly impossible to start the mating retaining ring without crossthreading it.

Forrest Addy
09-16-2010, 02:38 AM
Um. I cut a 22 1/2" 5/8" pitch 3 1/8" lead 5 start Acme timed to a part feature in a nickel aluminum bronze casting. Does that count?

On the other end, probably 40 TPI for some transit adjustment parts. I think it was 40. Machined them from gunmetal bronze. Wonderful stuff to machine. Bee-youtiful finishes. Come to think of it I cut a 5/16 56 and a 1/4 64 on to same shank for a fine adjuster. One turn advanced the mechanism 0.0022". Fancy optical gedget of some kind. I think it tilted a mirror.

I didn't last long in the instrument shop. Worked all week busting my butt and made a teapoon of chips. I could fit all the parts I made that week into a coffee cup. The microscopic pace drove me nuts. I went back to the big machines as soon as they let me.

Forestgnome
09-16-2010, 10:35 AM
At the risk of side tracking the thread, I would add that IMHO the coarse thread is used for strength and the fine thread for power. For example if you look at a stud used in an aluminum cylinder head you will see both fine and coarse threads. the coarse end is threaded into the aluminum and the fine thread is fitted with the nut. this provides strength (shearing) in the aluminum given a larger cross-section and yet provides for a more even torque with the fastener.

al
I suspect the fines threads are for accuracy in setting the final tension in the bolt. Those are "torque-to-yield" bolts and are adjusted using degrees of rotation. You would choose the pitch of the thread based on a reasonably achievable accuracy in degrees of rotation.