acme threads

[Don Huseman]

I have a friend that is building an elevator form his garage up to his living room that is right over the garage. he wants to use four acme 1.125, 4tpi screws 10 ft long to go form the garage up to the living room. I said I would machine some of the parts for him. I have never machined a acme nut or screw before. I have an acme thread gage. He is going to use four threads per inch. I would assume that we would use some kind of bronze nuts. what experience does any body have making acme nuts? also should I use a spring loaded grease cup to force the grease on the male acme shaft. What kind of grease should I use.
I have so many questions if I only new how to read.

 

[DickDastardly40]

10 Feet of acme thread on an inch and an eighth diameter at 4 TPI, Hmmm :-\

First up, can you get 10 feet in one go anywhere near your lathe, if it's in a corner you may be SOL. Actually re-reading did you say you were doing the rod or is he buying that in and you are 'just' making nuts to match?

If you are doing the rod, can it be made in sections?

4 TPI will need some serious helix angle + clearance ground onto the leading edge of your tool, say about 13 deg. You could cut a square thread first, then angle the flanks afterwards with a 29 deg V shaped tool with the compound parallel to the bed, cutting by advancing and retarding the compound to do the flanks separately.

Years ago, i cut matching internal and external acme threads using a tool ground from 3/16" round section HSS which fitted in both a boring bar holder and tool holder which saved grinding two tools and the resulting threads had matching angles.

Hope this is of some help

Al

 

[DickDastardly40]

Just saw this on HSM regarding manufacture of bronze and acetal nuts for a leadscrew using a tap made from acme leadscrew barstock:

http://bbs.homeshopmachinist.net/showthread.php?t=27927

Might make the job a bit easier?

Al

 

[rake60]

I cut ACME threads about once a week on average at work.
I've cut 2 pitch (.500 lead) threads there.
There, I have the advantage of the CNC machine that advances the tool
down the 14-1/2 degree angle of the the thread form so the tool doesn't
take a full pressure cut until the finish pass.

Of course they can be cut on a manual machine, but it's one of those
charactor building experiences.

With the 29 degree included angle and flat bottom of the thread form, it can
be difficult to keep it from chattering.

Rick

 

[Stan]

My experience may or may not be useful to you. I built an elevator for my wife's wheelchair at out back entrance way. I used a different concept than your friend. Mine resembles a forklift with linear bearings running on 4140 guide rods.

The acme screw is available in almost any material and the company I bought from could supply in lengths up to 40'. I used eight pitch driven by a 250 RPM gear motor which gives 2.6'/min (fast enough for an old lady in a wheelchair).

I made one nut mounted on the back of the platform out of 660 bronze. I just ground a HSS tool for a boring bar to the shape on the Acme tread gauge for 8 TPI and went at it. I am no professional, but it works fine. I put a zerk in the side of the nut and use ordinary chassis grease but that got too stiff in cold weather so I went to synthetic grease from the auto parts store that comes in a grease gun cartridge. HTH