Acetal gibs?

[nateman_doo]

Has anyone ever made acetal/delrin/POM TYPE gibs?
I would imagine it would would provide smoother travel, but still have enough strength to be used as gib material.

Also as a side question, has anyone used a gib strip on each side of dovetails? Like, insteade of a 0.25 inch gib on one way, dual 0.125 gib strips to reduce wear & friction?

[TXFred]

My concern is that they would be somewhat compressible. That may cause chatter problem.

Maybe a thin piece of delrin with a steel backing would work. That would provide rigidity and reduce friction. My Tormach has plastic coated ways, so there must be some advantage to it.

You will want to make your ways very smooth, otherwise they would probably eat away at the plastic.

[pete from TN]

Your tormach has turcite coated gibs.... There are a bunch of commercial machines with this feature and it is a great way to get smooth precise movement. If you are going to go thru making your own gibs and want to seriously improve the machine why don't you get yourself some of that and give it a go. It is not terribly cheap but it is worth it. Sounds like you are making quite the Frankenstein monster of a machine there man. good luck with it!! Peace

Pete

[nateman_doo]

acetal & the likes are pretty cheap, but there are different kinds. Acetal, Delrin, POM, acetal copolymer etc, not sure which one to choose?

I would make it as flat as humanly possible. I did have my Z column re-machined with a 60° dovetail bit. The ways weren't quite 60, but now the carriage box, and z column are all machined with the same bit, so i know they are true.

[rowbare]

Turcite and the like are normally scraped in when installed. I imagine the same would hold true for UHMW or Delrin.

bob

[hoss2006]

Turcite also requires an oiling system to keep oil between the turcite and the moving way
otherwise it will wear away in no time.
I'd imagine acetal or other plastic gibs strips would require the same or else suffer the same fate.
Our matsuura had to have a tech come and replace and hand scrape the turcite when an oil line failed.
The opposite surface also needs to be very smooth or it will just file away at the acetal.
Hoss

[nateman_doo]

There wouldn't be a direct oiling system, but enough oil coolant splashes on the column during general machine use that it would be lubed, on top of the regular grease that I would use on it.

I am still tossing around the dual acetal gib idea to cut down on wear and friction. I have enough scrap acetal laying around to try it, just no machine to do it on.

[RomanLini]

I use plastic linear bearings on my CNC machine, but the Iglidur bearings run in anodised aluminium rails (not against steel).

This page;
igus® iglidur® J plain bearing - Material data
has some charts etc showing the loads, speeds and (good info) the wear of Iglidur plastic bearings on different metals.

Looks like anodied aluminium and hard chrome, then stainless, had the least wear. "Machining steel" was about the worst. From my guess; the more polished the metal surface equals the least wear, although they do mention that the surface texture has something to do with it too.

I don't think you can run a plastic bearing against a plastic bearing! I think the great life of plastic bearings comes from the plastic bearing being too soft to wear the metal, and the metal is too shiny and slippery to wear the bearing.

[nateman_doo]

I think the great life of plastic bearings comes from the plastic bearing being too soft to wear the metal, and the metal is too shiny and slippery to wear the bearing.

Good point.
Looking at various materials to use at McMaster, this one seemed like it was the best:
PTFE-Filled Delrin® Acetal Resin (Delrin® AF Acetal Resin): Filled with 13% PTFE fiber to provide better wear resistance and less friction than regular Delrin® acetal resin.

BUT its not cheap. Regular acetal & Delrin is dirt cheap.

[WaveDude]

Fignoggle has done it:

http://www.fignoggle.com/machines/x2...gibsAcetal.htm

[LUCKY13]

Splitting the room up between two gibs would be a bad idea IMHO. You really need atleast the one side to help hold the possition of the table/saddle & getting the gibs to thin could also cause stability problems.



Using such products to remake the gib though could work very good. But grease should not be used on a way/slide simply because of the stick/slip effect which will be worse with grease compaired to oil.


Plastic or such will wear metal. It may seem it would not because its softer but this is not true. Even rubber can cut glass or metal clean over time.

The bottom line is no matter what is used, either the gib or the way will wear a lot if a proper bearing surface is not created, plus oil used to keep the contact to a minimum and give lubrication. Grease will not give the fluid type bearing that is needed here. Oil from within/between is what it takes., not being slpashed on it. Even though it is not a continues pressurized system there is a certian amount of hydrodynamics involved with the bearing system. That may not be the proper way to describe it but without it there will be wear.


Brass has proven to work very good on these smaller machines, but there is not doute that if done right that other products could be as good, or even better. Your results will be interesting. I would be conserned with getting swarf imbedded into a gib that was soft. Way wipers made of felt might be a good idea.



Jess

[nateman_doo]

How about rubber way wipers? I have neoprene that could work well....

actually forget that, I plan to protect the way in its entirety.