threading thread...

[charleyy]

a couple of questions regarding the drive nut material...

it appears that the material of choice would be delrin; in reading through a bunch of posts, i found one or two questions asking about using nylon nuts (like you could find at the ace hardware wall-o-nuts-and-stuff), but don't recall seeing any answers pro or con...

since all the posts appear to be about using delrin nuts, i guess i can infer that the nylon nuts are not suitable for whatever reason; is that a correct assumption ?

*besides* delrin or nylon, are there other materials that have been found to be usable, or just that delrin is the combination of most economical, most available, most machinable material, most suitable for the job ? (i'm thinking of using some of the scrap starboard or other high density plastic stuff i have in hand...)

now, for a mechanical question...
*if* at least part of the reason that 'regular' steel nuts are not used, is that there is too much tolerance in their machining such that they slop back and forth on the threads, how is it tapping threads in (fill in the blank material) doesn't produce the same situation ?
...are the threads cut by a hand tap to closer tolerances than mass produced nuts, or something ?
...or is it just the nature of the plastic-like materials that they 'rebound'/'swell' after the threads are cut, such as to produce a tighter mating of rod and nut ?

i guess this is mostly just curiousity, since i imagine i will end up using the tried and true delrin, as you experienced CNC-ers and machinists have found it to be a suitable material for the task...

oh yeah, one last one, assuming delrin is the material, do you lubricate the threaded rod with something, or does it run 'dry' ?

thoughts and speculations are appreciated...

charley
charleyy@alltel.net

eof

[chuckknigh]

Plastic, especially high density "waxy" plastics are inherently self lubricating. Plus, they are inherently softer than the lead screw, which means that they, and not the far more expensive screw, will be the part to show wear.

You can actually use any plastic, but make sure it's hard, resilient, and somewhat slippery...those are the desirable traits.

Basically, it comes down to the fact that plastics are easy to come by, cheap, and easily workable without a machine shop. And, they actually have a few benefits, like their slipperiness! No lubricants needed, in most cases.

-- Chuck Knight

[Ken_Shea]

or is it just the nature of the plastic-like materials that they 'rebound'/'swell' after the threads are cut, such as to produce a tighter mating of rod and nut ?

You are correct.

[Moondog]

I am also going to use Delrin Nuts. I made one last weekend for a 25mm screw and I machined a flange onto the nut. Now I have the nut I just have to work out the best method of attaching the nut to the Y carriage.

For those that use the Delrin type of nut, what method/system do you use to attach the nut to the carriage?...

Would really appreciate some ideas here?..

cheers

[Ken_Shea]

Probably not much easier or better then good old bolting on, minimum of 3 bolts if a round flange, preferably 4.

Ken

[Moondog]

Ken.. thanks...

But what bolting method and what type of bracket and or mounting system.

What bracket design to fit from the round nut to the back of the Alum Y axis carriage?...ie, angle barckets, solid alum machined?...

[Ken_Shea]

With out seeing the design I am unable to offer any suggestions other then it would make sense to bolt directly to the frame, a machined flange recess pocket could be of value if it were precisely centered.

Could be I am not thinking parallel with your thoughts.

Ken

[Moondog]

Ken we might be thinking differently....

Like when you see the pics of the flanged Ball Nuts there has to be a preferred method of attachment from the flanged nut to the back of Y or Z carriage.

On my Z axis I bought an Isel Ball Nut set in a housing with a 2 hole flange that will bolt onto the Z carriage.

But for the Y axis where I am using a Delrin flange nut there is no housing assembly etc, so I need to make something to move the Y axis.

does this make sense?..

[cbcnc]

Moondog,

Here are some pictures of what you are talking about.
Go to the very bottom of the page and you will see.
http://www.cnconabudget.com/stuff.html
If you haven't seen his site it's worth a look at the rest of it.

Chris

[Moondog]

Thanks CBCNC...

That's the type of fitting I am leaning towards. Are there other similar types maybe utilising Alum plate etc... On most machines posted here that have been built, what do they use?

cheers

[cbcnc]

I did mine a bit different. I happened to have some 2" diameter delrin rod. I bored a hole with my lathe and ran the tap in. Then I milled a flat into it which screws to the bottom of my axis. There is no backlash adjustment.
Works so far.

Chris

[Jim Stein]

I just used a chunk of leaded bronze for my X and Y axis .I machined it to size then driled and tapped it.I used some brass for my Z axis. No backlash compensation or adjustment.