Making Acetal leadscrew nuts the easy way

[lakeside53]

I haven't done it yet,but I plan to do just that.I have the Nylatron and a plan to use it,all I need is some spare time.Watch this thread.

Can you "melt" nylatron in the same way as acetyl?

[DFMiller]

How well do the Nylatron's or HDPE hold dimension? Many of the nylons and HDPE will not hold dimension. They move all over the place with varying moisture content.
I believe that is the reason why Delrin is suggested.
Dave

[garyhlucas]

The question about Nylatron's dimensional stability is interesting. However if a nut expands and contracts what direction does it move in? I'm thinking that because the screw is inside of it and it is locked in both directions that it mostly tightens or loosens. Interesting to find out though. I am afraid it won't be me, high precision THK ball slides and ball screws on all axis on my machine, and I have a complete spare that fits any axis!

[dbs]

Pardon me if this has been covered already, I haven't read through all 20 pages of postings. Would something like Moglice be useable for the nut. I have no experience with the stuff, just remember reading about it somewhere. Dave

[elf]

Pardon me if this has been covered already, I haven't read through all 20 pages of postings. Would something like Moglice be useable for the nut. I have no experience with the stuff, just remember reading about it somewhere. Dave

It's one of the uses for Moglice. The difference between an EvaNut and a Moglice nut is the Moglice nut is cast in place and the EvaNut is formed using heat and pressure.

[Tony Ennis]

It's one of the uses for Moglice. The difference between an EvaNut and a Moglice nut is the Moglice nut is cast in place and the EvaNut is formed using heat and pressure.

The other difference is that the EvaNut is basically free. Moglice is expensive.

[Hopefuldave]

There's a DIY moglice-alike recipe on one of the fora, iirc epoxy, flake graphite, moly-slip and a solvent, I'll try it out when I get to experimenting with an Eva-ballscrew..._

[Ant]

Has anyone here used Polycaprolactone? It can be called polymorph or friendly plastic. It thermoforms at 62deg C and is tough as nylon when cold. I belive it is dimensionally stable as dental fillings are one application that has been investigated.

Just wondered if anyone had any light to shed on it's possible use in this kind of situation?

It costs about £16 a kilo and is reusable. You can always remould your mistakes, excess or old projects into something new. Widely used as feedstock for 3D printers.

[Ant]

There's a DIY moglice-alike recipe on one of the fora, iirc epoxy, flake graphite, moly-slip and a solvent..._

When you find it a link would be nice.

[rythmnbls]

Another tip

Now that my CNC conversion is done one thing I did learn when making these nuts is to use very sharp tools when chasing the threads. I used D bit style taps made from the threaded rod and honed them with a stone just like you would for HSS tooling. This worked better than freezing the nuts prior to chasing. Also, retouching the taps frequently with the stone helped a great deal, presumably if the taps are just slightly blunt they tend to rub the Acetal rather than cut it.

Using this technique I was able get smooth backlash free movement with nuts that are not too tight after just a few passes with the tap.

Regards.

Steve

[darryl]

Polycaprolactone- I've played with it a bit. I formed a nut with it and it was very tight on the acme rod. In trying to get it to move, it cracked- then I tested the pieces for toughness. It just cracked all up in my fingers. It seems dimensionally stable and fairly slippery- I just don't know if I'd trust it with high loads or impact loads.

[Ant]

Thank you Darryl. Doesn't sound as good as the acetal.

Your report prompted me to read around a bit, looking for explanations.

It seems it should not stick to smooth bare clean metal but can be like hotmelt glue and gets stickier as it gets hotter so maybe temp was a factor? One person described it as like a nylon lock nut which seems to makes sense.

It should not be as weak as you describe but it can be prone to internal bubbles and faults if you start with granules and depending on the process and temps you use to form it. Also it can be cold on the outside and still be warm enough on the inside to not be fully set. It can take seemingly forever to cool and set properly as it is very thermally insulating.

It is porous and would probably take a moly fill pretty well. Medical types use it to scaffold bone growth. It does not stick to ptfe so a layer of tape would probably ease things.

All in all though, Evan's method seems reliably superior. I was just curious. Thanks for the input.

[rowbare]

When you find it a link would be nice.

There is a recipe for moglice as well as a link to the patent here:

http://www.cnczone.com/forums/epoxy-granite/30155-epoxy-granite-machine-bases-polymer-concrete-frame-166.html#post338085

bob

[Ant]

Thank you Bob.

[alsinaj]

Just made my first successful Evanut. Here's what I learned:

1) I cross-drilled the two blank halves and drove in a couple of roll pins -- keeps the halves aligned while squeezing in a vise, and can be used later for mounting holes.

2) The nut I made is 1/2" x 10, 1.5"H x 1.5"W x 1.25" long along the axis of the screw. I couldn't get the acetal to melt using a heat gun no way no how. What did work was to heat the acme rod with a propane torch about 12 seconds on, 8 seconds off. Nothing precise -- I just counted off the seconds. The "off" time gives the heat time to travel into the nut and to even out out the temperature over the length of the rod. By the time the acetal started to melt, I began to get the feel of how much heat to add, and played it by ear.

3) The nut was tight -- no surprise there. Making a tap out of a short section of rod helped, but not enough. The amount of friction left would suck up most of the torque available with a direct-drive NEMA 23 stepper. It occurred to me that most of the friction is probably on the outside diameter of the screw. So, how to make the tap OD just slightly larger than the stock acme rod? Easy! Knurl a short section in the middle of a piece of acme rod. You don't have to knurl to full depth. Using a small file, clean up the burrs the knurling made on the top part of the thread flanks. Then chuck the rod in a drill or lathe and run the nut back and forth over the knurled section, slowly at first, then faster, taking care to clean out the knurls between runs with a brush. You can judge the remaining friction when the nut is on the un-knurled section of the rod. If the friction is still too high after the knurls stop cutting, deepen the knurling a little. It doesn't take much longer than reading this, and you can get the amount of friction you want very quickly with good control. This particular nut will continue to rotate a turn or so if spun vigorously with a finger. Next time I'll try it without using a tap first. My guess is that the knurling will do the job on its own.