Backlash nut whats the best material?

[DomB]

Hi there,

I am trying to make an anti backlash nut for a fairly simple machine. I was wondering if there was a general agreement what relative materials should be used between the nut and the leadscrew.

Should the leadscrew be hard steel and the nut be soft plastic. (could this squash in milling operations with a lot of force)

Or should the leadscrew be normal low carbon or stainless steel and the nut be case hardened for example.

Any ideas

Dom

[jerber]

I don't think you want your a/b nuts case hardened.
The nuts are easier/cheaper to replace then the leadscrew.

I use a/b nuts made made out of delrin (aka acetal).
There's some squashing but it's fairly constant.
From what I can measure it's under 0.05 mm under "heavy" load.

There are some pictures in my thread.
http://www.cnczone.com/forums/showthread.php?t=23180

[Zumba]

Bronze or Delrin for an ACME.

If you plan on motorizing it, it may be counter productive to use anything other than a ballscrew. Friction is a killer in CNC machines.

[cncuser1]

Originally Posted by DomB Hi there, I am trying to make an anti backlash nut for a fairly simple machine. I was wondering if there was a general agreement what relative materials should be used between the nut and the leadscrew. Should the leadscrew be hard steel and the nut be soft plastic. (could this squash in milling operations with a lot of force) Or should the leadscrew be normal low carbon or stainless steel and the nut be case hardened for example. Any ideas Dom

a basic rule is to make the nut softer than the screw.
Use a screw as hard ,accurate, and polished as you can afford.

Most users tend to work in the middle of the table. If the nut is MORE resistant to wear, the the screw would wear first, and only in one area. So what would happen when you go to tighten the nut to eliminate the slop created from the worn screw? You would be O.K. in the worn area of the screw, but tooooo tight at the unworn screw areas.

On the other hand, if the screw wears first, when you tighten it up, it'll be O.K. over the entire screw.

If you are making a machine that will consistently travel the entire length of the stroke at relatively low forces, Delrin would be O.K.

Moving up the force scale would take you to a metal. Brass is cheapish, machinable.

Bronze, possibly lubricated, is better.

Consider the popular tabletop mill alot of home hobbiests have, the Sieg X2.

It uses a brass nut on the leads screw. I use bronze gibbs in mine

So for you machine you can use the X2 as a guide. do you expect more or less forces and hours of use?

Higher working loads would take you to mild steel, like on a lathe cross slide.

good luck

[DomB]

Hi thanks for the info everybody.

I expect the machine will be more like a hobby router than a heavy machine like the Sieg.

However I do want to machine aluminium with as little chatter as my budget will allow.

Hours of use, i plan for the machine to do several hours each day.

I like the idea of a brass nut, which is not something I had previously considered.

I am initially trying to use threaded rod to keep build costs and replacement costs low. But it looks like I will have to do some testing for friction losses.

Is there ayy clever way to cut the nut so less area of the nut hits the threaded rod? to possible reduce friction, perhaps grind a 65degrees thread tool to make different parts of the thread hit.

Many thanks
Dom

[cncuser1]

Originally Posted by DomB Hi thanks for the info everybody. I expect the machine will be more like a hobby router than a heavy machine like the Sieg. However I do want to machine aluminium with as little chatter as my budget will allow. Hours of use, i plan for the machine to do several hours each day. I like the idea of a brass nut, which is not something I had previously considered. I am initially trying to use threaded rod to keep build costs and replacement costs low. But it looks like I will have to do some testing for friction losses. Is there ayy clever way to cut the nut so less area of the nut hits the threaded rod? to possible reduce friction, perhaps grind a 65degrees thread tool to make different parts of the thread hit. Many thanks Dom

The actual threads on a threaded rod are not accurate enough to allow you to reduce thread height. The threaded rod, this is standard threaded stud right?, not an acme thread.


If friction is a concern, try delrin or oiled bronze.
Once you have the rod and a tap to cut the threads, you can play around with Delrin or brass or oiled bronze.


but in my opinion, not knowing about the specifics of your prooject, to my mind, the distance and accuracy implied by the word "router" don't fit with threaded rod.

ballpark, what is the travel of the table?
will you actually be cutting material?

[DomB]

Hi,

yes I was planning to try and use stainless threaded rod as I have found some that seems to be much higher quality than the normal rod you get with very clean threads.

I want to be able to cut aluminium.

I would like the accuracy to be perhaps 0.05mm if possible.

The acme threads I have seen wold blow the leadscrew part of the budget. I also intend to make my own anti backlash nut, the acme screws often seem to just have a tight fixed nut and no anti backlash mechanism. Are taps for acme threads hard to find?

Dom

[cncuser1]

Originally Posted by DomB Hi, yes I was planning to try and use stainless threaded rod as I have found some that seems to be much higher quality than the normal rod you get with very clean threads. I want to be able to cut aluminium. I would like the accuracy to be perhaps 0.05mm if possible. The acme threads I have seen wold blow the leadscrew part of the budget. I also intend to make my own anti backlash nut, the acme screws often seem to just have a tight fixed nut and no anti backlash mechanism. Are taps for acme threads hard to find? Dom

0.05mm is difficullt for commercial threaded rod. I suggest to have the motor attached with belts, not direct drive, so you can achieve a large steps per revolution.

Of course I say this withoout knowing thhe size of the work.
What size cutters will you use?


Acme taps are available from the supplly houses that cater to the professional mmachinsts, like Manhhattan suppply, possibly Enco.


But if you are using an acme tap, what will the opposite part be( the rod)? it must also be acme. so along with an acme tap would go an acme rod or cut an acme thread on a rod. if you are cuttinng a long acme rod, it would be hard to keep the rod straight.

This is doable, but a bit hard.