# Acme Threading



## devils4ever (Nov 5, 2020)

I plan on building a drill press vice as my next project. I could probably buy one cheaper than making it, but I want the experience and fun of making it myself.

I would like to use a 1/2"-10 Acme thread in my design. I've never cut an Acme thread before. My mini-lathe is probably not up to the task. I don't think it's rigid enough for such a big cut for either internal or external Acme thread cutting. So, I'm planning of buying an Acme threaded rod which is fairly cheap rather than machine it on my lathe. 

However, I'll need to tap a 1.25" thick piece of mild steel for the rod to go through. I've seen various taps available for Acme threads, some are tandem. Would this be the preferred way to go about this? I imagine the cutting forces are much higher with Acme threads since much more material needs to be removed.

Another option is to buy a brass flanged nut and fit it into my steel block. This is a fairly expensive option. Is brass okay for a vise or will it wear out quickly from the higher forces?

The last option is to just use a standard 60* V-thread. I can cut either 1/2-13 or 1/2-20 easily. I've done this many times and have no issue doing this. I'm not sure a V-thread is the best option for a vise though.

Comments? Opinions?


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## projectnut (Nov 5, 2020)

I would go with a single lead tap.  Multiple leads are generally used where the parts are regularly disassembled and reassembled.  The multiple leads aid in the speed of reassembly. The screw on a vise is permanently captured.  Since it (almost) never disengages the "nut" there is no need for multiple leads.

As for the internal thread I would go with your first option.  Brass would be a poor choice of material given the clamping forces likely involved.  They wear over time with even light pressures.  Think of a milling machine vise versus a table.  The table generally uses a brass nut, and the only forces applied are the resistance of the table being moved and the cutter against the material.  Even then they wear over time as can be witnessed by the play in the handle.  A vise on the other hand sees clamping pressures multiple times that of the table lead screw.  They rarely wear. 

I have a Bridgeport mill and vise that were purchased together by a local high school in the early 1970's.  The vise still works fine.  There's probably some wear, but nothing that renders it unusable.  The table on the other hand had nearly .030" of play when I got it.  I was lucky in that it had a split nut configuration rather than 2 individual nuts for the lead screw.  I was able to cut the nut in half (as recommended) to remove the play.  If I had the dual nut configuration I would have had to replace both since there is no provision for tightening them due to wear.

A 60* thread will likely not last long  you will either strip or disfigure the thread with the forces needed to solidly clamp material in the vise.


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## devils4ever (Nov 5, 2020)

So, you're recommending I go with a tandem tap?


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## SLK001 (Nov 5, 2020)

If you take small bites when threading, there is no reason why you can't single point the nut.  If you're not sure on your abilities, single point to about 90% then finish with a tap.  This also helps if your tool isn't exactly on spec for threading.  If you try to tap the entire thing, just know that the tapping forces are HUGE.


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## projectnut (Nov 5, 2020)

My error.  By tandem I thought you were referring to a "multiple lead" tap.  In this case I would think the "tandem" as in combination roughing/finishing tap would be appropriate IF you don't feel you can turn the profile on your lathe AND have the means to hold the stock accurately and securely.


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## devils4ever (Nov 5, 2020)

Yes,  the tandem tap is a combination roughing/finishing tap in one. See this.

My mini-lathe seems to struggle cutting V threads on a course pitch near the end of the cut. I typically take 1 thou cuts after about 30-40% of the way through. I can't imagine cutting an Acme thread on it. I'd be taking a 1 thou cut and a spring pass every time and I'm not sure it would work. I'd love to try, but I'm not sure I want to invest in the tooling for it if I can't get it to work.


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## MrWhoopee (Nov 5, 2020)

Get a steel acme coupling nut, turn it round (not full cleanup) with a shoulder and press/weld it in.








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That's what I did on my table/verti-vise.


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## devils4ever (Nov 5, 2020)

Interesting idea. I can't weld, but I could press it in. When you say, "not full cleanup", do you mean don't make it completely round?


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## MrWhoopee (Nov 5, 2020)

devils4ever said:


> Interesting idea. I can't weld, but I could press it in. When you say, "not full cleanup", do you mean don't make it completely round?


Yes, the distance across the flats is 5/8, leaving 1/16 wall thickness if turned fully round. I just turned off the points to make it round enough to press into a hole, leaving about 1/4 in. full hex to create a shoulder which gets recessed into a counterbore. Be sure to put the shoulder on the right side of the jaw to take the thrust and prevent the nut from pushing out.


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## devils4ever (Nov 5, 2020)

How tight a fit is required so it doesn't spin?


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## markba633csi (Nov 5, 2020)

You could do a light press fit with epoxy or loctite, it will stay put
-Mark


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## Technical Ted (Nov 5, 2020)

I suggest you go for it and take a crack at threading both on your lathe! What do you have to lose? You certainly have a lot of knowledge and experience to gain. Don't be afraid to try new things. We've all been there.... the experienced guys wouldn't be experienced if they didn't try new things. It would be a great learning project for you and you have nothing to lose.

Ted


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## SLK001 (Nov 5, 2020)

Remember, since this is going to be a leadscrew for a vise, you're going to need LEFT HAND threaded versions of both.  

Left hand would be standard, but if you can live with your vise going "the wrong way" when you try to use it, then you can use RIGHT HAND threads


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## pacifica (Nov 5, 2020)

Kurt vises are not acme thread.
 In use acme threads have lower friction than 60 degree threads and acme work better in the presence of debris or dust. 

Russ


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## SLK001 (Nov 5, 2020)

pacifica said:


> Kurt vises are not acme thread.
> In use acme threads have lower friction than 60 degree threads and acme work better in the presence of debris or dust.
> 
> Russ



What are they, square threaded?

ACME and square threads are used when very large forces are needed to be transmitted.


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## Weldingrod1 (Nov 5, 2020)

Yes, 10 pitch acme is quite deep. Lots of metal to take off. It was more than my Hardinge could retract... And 1/2" is a pretty small hole to work into.
Worth a try for fun factor! I've done them. Stub acme is a bit easier. You may want to gash the thread with an internal grooving tool before you start the threading tool.

Oh, gauging the internal thread is hard... you will do some "cut to fit" at the end.

I think you would find both a brass and a steel nut perfectly acceptable. All Bridgeports have brass nuts on the acme table screws, and they last a looong time. Lubed, the steel will hold up too.

Sent from my SM-G892A using Tapatalk


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## devils4ever (Nov 6, 2020)

SLK001 said:


> Remember, since this is going to be a leadscrew for a vise, you're going to need LEFT HAND threaded versions of both.
> 
> Left hand would be standard, but if you can live with your vise going "the wrong way" when you try to use it, then you can use RIGHT HAND threads



I plan on making something along these lines. I _think _they are right hand threads.


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## devils4ever (Nov 6, 2020)

pacifica said:


> Kurt vises are not acme thread.



Yes, I was surprised to find my Kurt vise is not Acme or square threaded. It looks like a V thread to me and I think it is left handed. Maybe, it's a custom form of thread to give more precision and lots of force?


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## addertooth (Nov 6, 2020)

Acme is undeniably stronger, provided you are comparing threads made out of the same material with the same heat treating process (and the same O.D.).  Although it is obvious, I will still say it, a properly heat treated 60 degree thread on O1, D2, A2, 154CM steel will be very strong, certainly stronger than a similarly sized Acme thread of annealed 1018 steel.  The softer steel will have the advantage of being more "chewey" or tougher to withstanding sharp shock.


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## JohnG (Nov 6, 2020)

I'm confused here.  My understanding is that Acme screws are designed to transmit motion, and so they develop less friction than V threads.  This makes them less useful for clamping.  Also, I've read that an Acme screw and nut should be dissimilar materials to minimize wear--steel screw and bronze nut is common.
I turned this left hand Acme screw to replace the worn cross feed screw on a surface grinder.  I bought a pair of bronze Acme nuts and turned external threads on them to assemble a double nut with more bearing area and a slight tension between the nuts to minimize backlash.
Turning Acme threads develops much higher lateral force.  If you are turning a left hand Acme screw between centers, tighten the tailstock extra tight.  A single point tool for turning small diameter inside Acme threads is the hardest lathe tool to grind for my money.


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## Papa Charlie (Nov 6, 2020)

JohnG said:


> I'm confused here.  My understanding is that Acme screws are designed to transmit motion, and so they develop less friction than V threads.  This makes them less useful for clamping.  Also, I've read that an Acme screw and nut should be dissimilar materials to minimize wear--steel screw and bronze nut is common.
> I turned this left hand Acme screw to replace the worn cross feed screw on a surface grinder.  I bought a pair of bronze Acme nuts and turned external threads on them to assemble a double nut with more bearing area and a slight tension between the nuts to minimize backlash.
> Turning Acme threads develops much higher lateral force.  If you are turning a left hand Acme screw between centers, tighten the tailstock extra tight.  A single point tool for turning small diameter inside Acme threads is the hardest lathe tool to grind for my money.
> View attachment 343344



Correct, ACME is for motion and do not have the holding properties that a 60 degree thread would.


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## RandyWilson (Nov 6, 2020)

Acme threads do not have the wedging self locking tendencies of a standard 60 degree thread. Thus they can still turn while under high load. You can apply more clamping load for a given screw force, and more importantly, you can loosen it back up without a large hammer.


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## Larry$ (Nov 6, 2020)

So inconclusion, take your pick. If you buy a V thread & Coupling nut try to get a grade 8. Better precision, stronger and the screw will have been rolled rather than cut. You can do the threading in tool steel and then harden and temper. O1 is supposed to be less inclined to warp than W1. Air hardening might be a good bet if you can cover it to cool slowly. 
As to why right or left hand, depends on which part the nut is in. A drill press vice takes a right hand because the nut ins in the frame. A mill vice like Kurt has the nut in the moving jaw.


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## pacifica (Nov 6, 2020)

If you're worried about thread strength on v threads make the screw a larger diameter and the nut longer( since it's your design you can make it as hefty as you want) The nut on a 6" kurt vise is over 5" long. 
With a 2' cheater bar on my 8" kurt I am pretty sure the pressure generated is well over 5 tons ( f_rom the vise testing video on you tube it may be between 30.000 and 40,000 pound_s) no bending or movement at all,rock-steady.


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## MrWhoopee (Nov 6, 2020)

And I can see we are well down in the weeds now. It's a drill press vise, not for a horizontal mill or shaper.



devils4ever said:


> How tight a fit is required so it doesn't spin?



If you are going for a press fit, I'd go .0003 to .0008 interference. @markba633csi 's suggestion for a slip fit with Loctite is a good one. The fit will be less critical, assembly will be easier and the holding power more than sufficient.


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## devils4ever (Nov 6, 2020)

I was going to comment that this if for a drill press. So, I'm not looking for maximum clamping force.


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## devils4ever (Nov 7, 2020)

I think I might try using the lathe to create the internal Acme thread in the steel block. It sounds like a good experience to have. 

If I have trouble, I have a few options:

finish the hole with a tap
bore it out and use a premade bronze nut/flange
bore it out and make a bronze insert (I'm assuming cutting a thread in bronze is easier than steel?)
use a V-thread instead since I already have 1/2-13 and 1/2-20 taps and dies


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## Weldingrod1 (Nov 7, 2020)

The angle of the thread contact face couples bolt tension to hoop stress in the nut. Shallower angles than 60 degrees mean the nut stretches less. With highly loaded shallow threads in thin nuts (think oilfield downhole tools) this can end in unexpected nut popping off thread failure.

For our purposes, acme, square, and buttress threads all have a bit less friction, are less self-centering, more wear resistant, more power efficient, and more irritating to cut ;-) 

Buttress threads are the ultimate for one-directional loading, but super irritating to cut and gauge. And there are no taps or dies... there are, however, inserts available! In the oilfield, the suction covers on frac pump fluid ends are held on with buttress threads. BIG ones.

Sent from my SM-G892A using Tapatalk


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## Bi11Hudson (Nov 8, 2020)

A few comments, if I may. Nothing to add, just a few points to clarify things. First off, there are several thread forms for motion and load carrying. 60* such as bolt threads have the highest torque capacity. ACME is the most common motion transmission, with moderate load carrying. Square threads are the strongest in that respect but are hard to cut on external threads and a bear to cut internally. Butress threads are sort of a mix between ACME and square. They are essentially square on the load carrying side and ACME on the "off" side. Most often seen on big screw jacks, like a house jack or a railroad jack.  For Square and Butress threads there are no "common" taps for doing inside threads. Although there must be somewhere for commercial producers.

Tandem taps now, I have a few. At one time I was building 5/8x8 Left Hand followers for a friend in the commercial ceramics industry. That has gone by now, but I still have the taps. I used a tap because my lathe is fairly light and holding the piece to be tapped was near impossible. The tandem tap for 5/8" is about 3-1/2 inches of a "V-sharp" 60* thread, followed by about 3 inches of the ACME. The taper for the starter portion is long, like a "starter" tap for bolts. The transition from V-sharp to ACME is shorter, sort of like a "plug" tap.

*Tandem taps are pricey!* I would hesitate to suggest one for one or two uses. I have both 1/2-10 and 5/8-8, right and left hand pitch. I bought them when times were flush, so the price didn't hurt too much. But they do exist, albeit costly. I have an Atlas lathe, MF-C milling machine and an S-7 shaper, that was the reason for acquiring the 1/2-10s. I haven't used them much, haven't needed them. I also have a few smaller sizes, down to 1/4 inch. They were salvage from an aircraft repair source. Never used them but they were cheap and I could foresee uses "down the road" for them.

In use, I would start the starter thread in the lathe to maintain concentricity. When the brass started to slip in the chuck, about 4-5 pitches, I would remove the entire assembly to a vise and cut the rest by hand. With a *very large* tap wrench. They do not cut easily, even in soft metal like brass. Precutting with a boring bar and then finishing with the tap would take a lot longer but much less work.
.


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## devils4ever (Nov 9, 2020)

I decided to order a Tandem tap to cut this thread. It is very $$$, but I think my chances for success are greater.

I've read that cutting internal Acme thread on the lathe with a small diameter (<= 1/2") is tricky because the tool can't be thick/stiff enough to cut well.

I may start the thread in the lathe and cut a 1/2-10 V-thread first. It may help remove some metal first and start the tap squarely. The largest tap wrench I have is a Starrett 91B which is 9" long. Do I need a larger one?

Also, remember this is being tapped in 1.2" of 1018 steel. If I run into trouble, I may bore it out and use a brass or bronze insert.


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## MrWhoopee (Nov 9, 2020)

You will probably need a bigger tap handle. I've seen one or two tandem taps broken when hand tapping, they snap right between the roughing and finishing sections. Be sure to do this in the mill with a pilot in the quill.


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## ericc (Nov 9, 2020)

I would just give the single point lathe threading a try in a piece of junk brass.  If it worked, it could come in useful in the future.  When I tried acme threading for the first time, I did not practice but went straight to the cross slide nut which I had put a lot of time in to.  It worked pretty well even though I made the same mistake that Abom79 made in his video.  I watched the video and made the mistake anyway.  Fortunately, I was able to recover as soon as I heard the squeak.


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## BGHansen (Nov 9, 2020)

Here's a thread of me cutting a 7/8" x 6 ACME thread into a CRS bushing.  I don't recall having any issues other than pucker factor of of a fast-moving carriage.  My Grizzly's minimum speed is 70 RPM, so at 6 threads per inch it's moving about 12" every minute or an inch every 5 seconds.  

All you'll need is a boring bar and a HSS bit for grinding the profile.  It helps to have an Acme thread for getting the 29 deg. correct and the tip width.  Other than that, it's no different than conventional 60 degree threading.

Bruce











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A while back I got stupid and jammed up my power feed on my South Bend lathe. In my panic to unstick it, I broke the screw head off the apron screw. I know this is a left hand thread screw , so I thought if I drill a small whole in the center of it the piece would come out of the clutch shaft...




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## devils4ever (Nov 9, 2020)

ericc said:


> It worked pretty well even though I made the same mistake that Abom79 made in his video.  I watched the video and made the mistake anyway.  Fortunately, I was able to recover as soon as I heard the squeak.



What mistake did you/Abom make?


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## ericc (Nov 9, 2020)

devils4ever said:


> What mistake did you/Abom make?



Watch the video and watch the second video in which Abom fixes the mistake.  It has to do with underestimating the front clearance angle due to the thread helix angle.  I cut a junk credit card to the correct angle to make a gauge, reground the tool, and finished successfully.


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## devils4ever (Dec 4, 2020)

I did it! Tonight I tapped my first Acme thread. It was just about as hard as I thought. The first part (roughing) of the tandem tap was the hardest. The last part (finishing) was a lot easier. I thought the tap might break on the initial threading. I had to switch from my Starrett 91B tap wrench to my 91D tap wrench after starting the thread in the mill to gain more torque. I used lots of cutting fluid, but it was still rough going. I'm not sure I'd want to tap anything too much bigger in steel. I tried to reverse the tap many times to clear the chips, but it was a lot harder going in reverse than going forward. The end result is satisfying though.


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## devils4ever (Dec 22, 2020)

So, I'm just about done with my drill press vise. One of the final steps is to add a handle to the end of the Acme threaded rod.

I want to add a cylindrical metal piece on the end to beef it up so I can add a thin rod to turn. I have a 11/32" (0.34375") reamer that I plan to use on the cylindrical steel piece and press it on the turned down Acme threaded rod. I have a 2 ton Arbor press for this. 

So, I'm wondering how much of an interference fit is needed? 2-3 tenths?


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## MrWhoopee (Dec 22, 2020)

devils4ever said:


> So, I'm just about done with my drill press vise. One of the final steps is to add a handle to the end of the Acme threaded rod.
> 
> I want to add a cylindrical metal piece on the end to beef it up so I can add a thin rod to turn. I have a 11/32" (0.34375") reamer that I plan to use on the cylindrical steel piece and press it on the turned down Acme threaded rod. I have a 2 ton Arbor press for this.
> 
> So, I'm wondering how much of an interference fit is needed? 2-3 tenths?



Assuming the "tommy bar" passes thru both pieces, yes that would be fine.


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## Technical Ted (Dec 22, 2020)

Your reamer is likely to cut oversize so be aware. Roll pins can be used in situations like this. Or tapered pins. If you do use a press fit pin you can always add some Loctite if it is a little loose fitting.

Ted


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## devils4ever (Jan 3, 2021)

I finished my drill press vise and I'm _very _pleased on how it turned out. I learned on a lot on this project which was one of the main goals. I worked with Acme threads for the first time and tapped the steel with some effort.

I was able to press fit the end of the rod with a bushing to allow a beefer rod to be used to turn the screw. The interference fit was a little intimidating since I had trouble accurately measuring the reamed hole with my telescoping snap gauges. I was able to press the bushing on the turned down rod on my 2 ton arbor press without much difficulty.

Thanks for everyone's input!


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## ericc (Jan 3, 2021)

Beautiful.  I would love to use that nice looking vise and remember the joy in making it every time.  I have one of these on my milling machine, and it is much rougher, and I still like it, although there is quite a bit of lift in it.  Eventually, I'll replace it with a vise with some down force.


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## devils4ever (Jan 4, 2021)

ericc said:


> Beautiful.  I would love to use that nice looking vise and remember the joy in making it every time.  I have one of these on my milling machine, and it is much rougher, and I still like it, although there is quite a bit of lift in it.  Eventually, I'll replace it with a vise with some down force.



Thanks!


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