UHMW vs Delrin vs HDPE rail slides

[Rance]

So will any of these work for a 1st (read: simple, cheap) machine? More specifically, is there a really good reason to stay away from HDPE? Thanks all.

Rance

[joecnc2006]

On my machine i used UHMW to start with, but switched to bearings for more acuracy, if you can not machine the UHMW percisely than you will have play in it.

[signIT]

Hi,

I have a Zoltar router with plastic rails i don't like it as it has to high friction I will try a material that is made for low friction it's called Robalon-RM, another nice material is Oilon that has oil in its material structure, here is a link to Christian Berner I think you can find a english site from this company. http://www.cbab.se/pdf/tp.pdf

Although my Zoltar router has rather high friction it works pretty well and I have done some small job in aluminium and brass.

Signit

[amen23]

i know this is an old thread ..but i have a question for those who might know..

what about the use of delrin for linear rails aswell as making carriges. Is there any fundametal reason why this cannot be used??

couplings could aslo be made ...and at the far end of the spectrum acme/lead screws

[sansbury]

A good rule of thumb is to have a softer material riding on a harder material and make the softer contact parts adjustable to take any play out. Delrin riding on aluminum is a good example. If you have Delrin against itself, both parts will wear, and in a linear bearing, you will get more wear at the center than at the ends, or at one end than at the other, etc. I -think- you also have more chance of binding with like against like but that's kind of a WAG on my part.

[DSL PWR]

UHMW is very slippery, which makes it a good bearing material, but it's a bugger to hold onto for machining. I've found to hold this stuff you need to clamp it quite hard, usually deforming it in the process, this makes it hard to do any thing to a tolerance.

If possible mount the UHMW to what ever you are going to mount it to (hopefully steel or alum) and then machine it out. I did this on my z axis slides for my pasma table and it worked out well.

[amen23]

Originally Posted by sansbury A good rule of thumb is to have a softer material riding on a harder material and make the softer contact parts adjustable to take any play out. Delrin riding on aluminum is a good example. If you have Delrin against itself, both parts will wear, and in a linear bearing, you will get more wear at the center than at the ends, or at one end than at the other, etc. I -think- you also have more chance of binding with like against like but that's kind of a WAG on my part.

i agree with that statement ...and was thinking along the lines of delrin against itself. I'm sure over time it would wear ...but how long would it take?
20mm dia delrin rod goes for around £10 a 3 meter length(drilling and tapping for support is a matter of minutes) .......hardened 12mm rail at the same length pre drilled and tapped costs in the region of £150 (£50 a meter).

for someone building thier first machine i'd say this would be ideal......for a hobby machine being used on week-ends. I'd imagine these rails lasting for some time - long enough to iron out all the kinks and design your second machine (which you know is inevitable).

I think a good indicator would be to find out how long a delrin antibacklash nut would last - against a acme/trapezoidal screw. has anyone had to replace one recently ??? how long did the old one last???

carriage could be contructed using skateboard bearings instead of linear bearing increasing surface contact area , just an idea!

[amen23]

Originally Posted by DSL PWR UHMW is very slippery, which makes it a good bearing material, but it's a bugger to hold onto for machining. I've found to hold this stuff you need to clamp it quite hard, usually deforming it in the process, this makes it hard to do any thing to a tolerance. If possible mount the UHMW to what ever you are going to mount it to (hopefully steel or alum) and then machine it out. I did this on my z axis slides for my pasma table and it worked out well.

Looks good --heres what they say:

Ultra High Molecular Weight Polyethylene (UHMWPE/PE1000)

Having the highest molecular weight of our standard range of Polyethylene, PE1000 ultra high molecular weight polyethylene is the most wear resistant. Particularly suited to applications such as chain guides, star wheels, wear strips etc. It remains the typical impact resistance of Polyethylene and can operate as low as -270ºC.

[DareBee]

I agree that UHMW is the best material. It is sooo commonly used that it is close to half the price of Delrin at my plastic suppliers.

[amen23]

Been doing more research on UHMW ....was surprised to see this...

UHMW-PE a unique combination of high impact strength, low co-efficient of friction and abrasion resistance that outwears carbon steel 10 to 1

thinking about building a little test machine!

[sansbury]

Originally Posted by amen23 20mm dia delrin rod goes for around £10 a 3 meter length(drilling and tapping for support is a matter of minutes) .......hardened 12mm rail at the same length pre drilled and tapped costs in the region of £150 (£50 a meter). for someone building thier first machine i'd say this would be ideal......for a hobby machine being used on week-ends.

What are you doing using hardened 12mm rail? For a hobby machine you can use aluminum channel or gas pipe and get great results. Economizing is one thing, but Delrin rails just seem like the wrong way to do this to me. You can do it a much better way for the same or less cost.

Originally Posted by amen23 carriage could be contructed using skateboard bearings instead of linear bearing increasing surface contact area , just an idea!

Why is increasing contact area a benefit? It seems like all it would add is friction. You need bearings if you want to move faster, but they make building more complicated and add lots of opportunities for slop, misalignment, etc. Depending on what you're building they're overkill.

[woodworker2]

I have been looking at some of the same material for several different reasons, but here is some info that I have discovered for the better this week: uhmw is very soft material, and is hard to machine as stated, Delrin is very strong, it machines well, and it is hard enough that you can tap it with a manual tool. HDPE is also very strong, and it machines well, but it is just a touch softer, just enough that you can't tap it manually, but you can pre-drill a hole and a screw will bite and stay in place. cost wise on 1/2" thick material, Delrin-most expensive at about $30 plus a square foot, HDPE was about $8-$10 per square foot. Don't know if HDPE is available where you are, but check it out. High density polyethylene.