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Using UHMW for sliding bearings ??

B

Bruce Griffing

Titanium
Joined
Jan 1, 2003
Location
Temple, Texas
Does UHMW make a decent sliding bearing for light loads? I am thinking about using it to make some sliding rail bearings for a large CNC router. Something like a 1.5" rail with a pair of 1.25" sleeves spaced about 8" apart. Thoughts? Any suggestions on machining it?
 
I feel that Delrin is a higher-quality and longer-lasting choice, for marginally more money. That said, perhaps Teflon would be the very best choice for a bearing application?
 
I have a large bit of UMHW and was thinking of it for that reason. I also have some Delrin AF, but I don't have much and I would like to hoard that for other uses if possible. I also thought the Delrin would be better - but only in the AF form. Regular Delrin has a higher coefficient of friction than UHMW. My real concern was wear, and it sounds like delrin is better in that category. OTOH, I have lots of UHMW and can easily replace the bearings if they don't wear too quickly.
 
McMaster Carr sells a teflon-loaded delrin. It's ideal for this application and I
can recommend it from personal experience.

Jim
 
Delrin is a little more rigid and has a lower thermal coefficient of expansion so it can be a bit more stable; probably not a really serious advantage when working to router tolerances.

UHMW will last almost forever sliding on steel with a good finish such as C1045 ground shafting. In 1983 I made some sliding guides for a moving paddle in an aquarium tank; UHMW running on 316 SS immersed in sea water and they are still working.
 
Bruce Griffing said:
Does UHMW make a decent sliding bearing for light loads? I am thinking about using it to make some sliding rail bearings for a large CNC router. Something like a 1.5" rail with a pair of 1.25" sleeves spaced about 8" apart. Thoughts? Any suggestions on machining it?
Click to expand...

I use UHMW Tape on the soles of my dance shoes. What a difference! It takes a bit of getting use to. I wouldn't drive the car with them on though.

This is NOT a joke.

Best regards,

Stan-
 
Definitely stay away from the PTFE; it's too soft for the application, especially if there is any torque-loading from the router rotation during traversing. The UHMW has a very good low-friction characteristic, but it is softer than the Delrin AF. Obviously, what is in hand is much more attractive to use. As Lily Sami noted, Nylatron would also be a good choice, however, I note that you are in Texas, and it is possible that the humidity absorption of nylon-based materials might be a caution for any kind of close bearing fit. That is another nicety of UHMW -- almost zero water absorption.
Nit-pick question: You mention 1.5" rails, and 1.25" sleeve. Is that right? I don't understand the setup, probably.
 
What I meant about the rails and sleeves is this - I would make the sleeve out of 1.25" flat plate - I have lots on hand. This would involve my learning how to make a clean 1.5" hole in UHMW - something I have not yet done. The resulting bearings would be used in pairs for each rail. So for each rail pair I would make 4 bearings.
 
Got it. The UHMW will respond nicely to high removal rates with razor sharp HSS tools as Steve in SoCal mentioned. The one thing that I would add is that the nose of the cutting tool can have a healthy radius on it, which (if the rest of the tool is OK) will give you a finish that approaches a polish. If I were making those parts from plate, I would think how best to get them into a condition where your last op is lathe boring to finish and size the ID. Ideal application for a nicely ground HSS tool at about 1200-1500 RPM, with an air blast to clear the chip, or some other way (hand over hand maybe) to get the chip string out of the bore.
 
We used UHMW on sliding bearing surfaces in a large wood shop on everything from feed belts to miter fold lines. It lasts a good long time and is quite inert, not much affects it.

Our CNC routers were Shoda multi-spindle with moving tables but I think you are building a moving gantry? As long as the jog rate is not supper fast your bearings will be fine.

Steve
 
I am planning a moving gantry, just for space considerations. I do plan to drive the gantry at both ends. This seemed like a good idea as it should prevent binding and will allow me to make fine adjustments to orthogonality (I hope).
 
I worked with a company that used UHMW for bearings and leadscrew nuts in high precision equipment with cycle counts into the milllions so I don't see any problem for your application. The decision between UHMW and Delrin needs to be based on the load-speed product. The app notes for DelrinAF covers this. My HBM used Delrin AF because the high loads combined with the 200ipm travel could have heated the lubricant enough to deform UHMW. ( At least I think that's why the engineers put it there; it could have been just the 'cool' factor. )

Considering the cost difference I would go with the UHMW unless you have problems.

The key to clean cuts in UHMW is slow speed/high feed, sharp tools and wide gullets. You want to take a good size chip. Say 0.06" DOC at 0.02 IPT. This is a big bite and it take a deep flute to clear the chip. It means putting some HP into the cut and it also means difficulties in holding the part still. Too much speed will melt the material and ruin the finish. Usually followed by broken tools.

Drilling and boring you want to see a good chip coming out of the hole. As long as you have a good chip you're ok. If the chip starts to get thin and wavy you need to increase the feed.

Holes will drill undersize and deep holes will close up on the drill. Use the next size up number drill and deep holes may have to neck down in steps. Drilling a deep hole in a cylinder in the three jaw is a sure way to pull the part out of the chuck.
 
I am looking for a solution to a highly specialized application. A google search led me to this forum, so I apologize if this post is out of place. Please ignore if so. I need a highly durable, affordable way to direct force from a 1.5"x16" stroke hydraulic cylinder linearly. This application would encounter different surfaces at it's contact point. My intuition is to use two 1.5" stainless steel shafts parallel, connected by a steel plate, utilizing either a linear bearing (expensive), or preferably, some type of poly/UHMW/nylon lined bushing suited for linear and angular forces. I have extremely limited knowledge of machining or material. I apologize if this extremely rookie question is obvious. This forum seems very capable of pointing me in the right direction. Thanks in advance!
 
neidig_09 said:
I am looking for a solution to a highly specialized application. A google search led me to this forum, so I apologize if this post is out of place. Please ignore if so. I need a highly durable, affordable way to direct force from a 1.5"x16" stroke hydraulic cylinder linearly. This application would encounter different surfaces at it's contact point. My intuition is to use two 1.5" stainless steel shafts parallel, connected by a steel plate, utilizing either a linear bearing (expensive), or preferably, some type of poly/UHMW/nylon lined bushing suited for linear and angular forces. I have extremely limited knowledge of machining or material. I apologize if this extremely rookie question is obvious. This forum seems very capable of pointing me in the right direction. Thanks in advance!
Click to expand...

You just couldn't bother to start a new thread with your query...
..instead--tried to Hijack an existing thread as you very first post?
 
dave powelson said:
You just couldn't bother to start a new thread with your query...
..instead--tried to Hijack an existing thread as you very first post?
Click to expand...

As it is a similar concept to the OP, I wouldn't consider it hijacking. Also, who the heck calls out someone for hijacking a thread that hadn't had a post in 8 and a half years. I'm sorry if I disrupted the world's slowest developing thread. As I told you, I have zero machinist experience and was hoping not to annoy a lot of knowledgeable posters with an amateur question. But I'm sorry I offended you. You've been absolutely helpful. I'll just go start a new thread now. Please continue being rude instead of adding absolutely anything of value!
 
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