Delrin Cross Slide Nut

coherent said:
In the very first small home built CNC router I made I used acme threaded rod and blocks of delrin (which I threaded) for the nuts and bearing mounts they worked surprisingly well. They were easy to machine with basic tools and held up pretty well considering. If nothing else they would be cheap and easy to replace when they wear and the backlash becomes excessive. I've seen some very simple "double nuts" which were made with two blocks with a spring compressed between them on the screw. The tension of the spring pushing the nuts apart reduce play/backlash even more.
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I did the double nut trick on my old Atlas/Craftsman. I used a previously replaced lead screw nut which floats on the lead screw. The channel in the cross feed saddle prevents it from rotating. It reduced the usable cross feed travel but reduced backlash to a thou or two.

One concern when using such a system is although backlash is effectively removed, a lead screw does not wear evenly along its entire length. On a properly cut screw, the leading edges of the threads are a fixed, consistent distance from thread to thread. As the thread wears in the heavily used region, that leading edge will move back several thousandths. While the effect won't be that great over one or two turns, if you zero your dial and then move some distance, your dial reading may not be accurate. Additionally, depending upon whether you are moving intoi or out of a worn region, the error can go either way.

The are two workarounds to this problem. The first is to stop short of your intended position and make a cut and remeasure. This is good practice anyway. The second is to install a DRO. The DRO records actual position so any wear is removed from the equation.
 
Mazak is a zinc alloy. i have used it heaps of times for a quick fix.

car door handles normally use mazak alloy. Easy to melt and cast ,

maybe called another name in the USA.
 
"RJSakowski, said: The second is to install a DRO. The DRO records actual position so any wear is removed from the equation.

I suppose in my case since it was on a CNC machine it had a DRO in a sense. I just checked it every now and then and entered the backlash compensation in the driver software. Made new ones if it got too excessive but the delrin wears pretty well considering and it's low friction helps. I've also heard of using other types of polys with lower friction properties, but some of them can get pricey and it seems using delrin is generally done to keep machining easy and cost low.
 
You shouldnt be just relying on a DRO for tool placement. If you fail to remove the backlash from your feed then the tool can move inadvertantly when it contacts the work.
It is good work practice to wind out, (or in) past any backlash and then reverse direction so the tool contacts the work in such a way the pressure is against the direction of feed.

Cheers Phil
 
didtas said:
Mazak is a zinc alloy. i have used it heaps of times for a quick fix.

car door handles normally use mazak alloy. Easy to melt and cast ,

maybe called another name in the USA.
Click to expand...

Yeah, here that is called Zamak aka "pot metal". Mazak here, is a machine tool corporation.
 
I've read a couple of oldish threads on other forums where people have successfully used
Delrin for both feedscrew nuts and gears. Apparently it wears very well and has a long life.

Also, Replacement bronze feed screw nuts, even the screws themselves are readily available from Latheman, Miller Machine and Fabrication, several eBay vendors . Current pricing for bronze nuts is $55 to $65 or thereabouts. Seems like a reasonable cost for new replacement parts.

Glenn
 
I would not use plastic. It adds another layer of potential tool pressure deflection. Bronze.

Sent from my Moto G Play using Tapatalk
 
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