Milling UHMW Plastic

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Todd3138

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A buddy bought a 4 post lift for his shop and needs a piece milled from UHMW as that specific piece is no longer made. This is the good one on his lift and is what we need to duplicate.
IMG958121.jpg

He purchased a few rectangular blocks of the UHMW figuring we might be able to machine a new one. I believe the finished piece is around 6" long and maybe almost as wide so we will be hogging off a lot of material before dialing it in and hitting the proper dimensions. There is also a 5/16 slot running the entire length, apparently, but from the picture I'm not certain how it is oriented on the piece.

My experience in machining generally is like a 0.2 out of 10. My experience with any sort of plastic is 0 out of 10. I've done a little reading on UHMW and am seeing a generally consistent set of opinions to use a new and very sharp HSS roughing endmill and to feed a fairly fast rate with a fairly heavy bite on each pass. I am also seeing that it is apparently quite slick and somewhat soft, presenting challenges for clamping it if you have only a small section to grab onto. Many opinions seem to suggest that if there is decent mass to grab with your vise, you should be okay. It also seems to be a consistent suggestion to have steady evacuation of your "chips" to keep the endmill clean so I plan to have a vac running next to the workpiece the whole time.

What is not consistent from what I'm seeing is the spindle speed I should be seeking. There are several opinions in favor of speeds from 3000 - 4000 rpm while others are suggesting that you don't want to go with a fast spindle speed but rather use a high feed rate to prevent formation of burrs and possible melting.

I guess my main questions that I know to ask are, 1) what do you guys suggest for a spindle speed and, 2) do you suggest using a coolant and, if so, what would be suitable?

If there are questions I'm not asking, I'd appreciate your input on that as well so I can go into this as well informed as possible. We do have a an extra block or two of the material to work with so I can get a sense of how to work it and not screw up the only available piece of stock, so that's a good thing.

I appreciate any input the collective wisdom may have to share with me.

Thanks!
 
I've had good luck with Aluminum Specific Carbide End Mills and UHMW PE. The end mills need to be super sharp. Most of my Aluminum Specific End mill are Alu-Power 3 Flute. They're razor sharp. I have to be careful not to get cut them when I mount them in the mill.

Don't remember on the speeds. I want to say Med to High RPM's. Hopefully others will speak up.

Hope this helped.
 
I would be tempted to make that on a table saw, at least to rough it out. A band saw would also be a good option.

UHMW machines like butter, like cutting oil. It is oil. No coolant required. I normally use a much slower spindle speed than most people to keep from melting, pretty agressive feed. Sharp tools are a must. Woodworking router bits work well, as do high spiral aluminum bits, did I mention sharp?

Trying to set that up in a vice might be a bit of a problem, you really can't squeeze it because it is very compliant. Clamping down to a spoilboard would be a better choice. I always keep 3/4'' MDF around for spoilboard material. Emery cloth between the work and the spoilboard (rough side towards the UHMW) helps to keep things from sliding around. As does blocks screwed down around the bottom.
 
I agree with Jim about cutting the block on a table saw. I've cut a lot of HMWPE that way. I never had any trouble with melting at normal blade speeds. I would suggest cutting the mounting surface first,using the endmill, then switch to the table saw.

I'd cut in from the right-hand end first, then lay it flat to cut the big piece out. The finish should be good enough to cut to finished dimensions on the saw, or you could cut close, then finish with the endmill. I'd cut the 5/16" slot last.

The one thing that plastic won't do is sand well. It's very abrasion-resistant. That's what makes it good for that application.
 
I’ve used UHMW a lot and for those pieces in your pic(good job providing pics!) I would not use the mill at all. 99% of all our UHMW bearings and guides like those were done on the table saw. Like Jim mentioned spoil boards using the bolt pattern for the part would be the way to go.

Be careful and good luck.
 
DAT510 said:
I've had good luck with Aluminum Specific Carbide End Mills and UHMW PE. The end mills need to be super sharp. Most of my Aluminum Specific End mill are Alu-Power 3 Flute. They're razor sharp. I have to be careful not to get cut them when I mount them in the mill.

Don't remember on the speeds. I want to say Med to High RPM's. Hopefully others will speak up.

Hope this helped.
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Thanks for the input. Interesting point about aluminum specific endmills. I don't have any of those on hand yet as I'm still getting my tooling sorted and I should probably grab a few for aluminum. I primarily work with steel at this point but I know aluminum is going to come up sooner or later.

Todd
 
Wow, excellent input, guys - thank you! Reading those thoughts helps get me in a far better mindset, particularly on how using a table saw or band saw really makes a lot of sense given how you've described the characteristics of UHMW. I had no idea on any of those points.

So, dumb question time here. What is a spoil board? I can certainly come up with some thoughts on the answer, but I might as well just ask to ensure I'm not missing something I should be aware of ahead of time.
 
Sacrificial surface. Something you can attach your part to to assist with your operations but doesn’t matter if you run cutters into it, drill through it, etc. Its entire purpose in life is to support the good stuff and get ruined in the process.
 
francist said:
Sacrificial surface. Something you can attach your part to to assist with your operations but doesn’t matter if you run cutters into it, drill through it, etc. Its entire purpose in life is to support the good stuff and get ruined in the process.
Click to expand...
Thanks! I was thinking along those lines but wanted to make sure I wasn't oversimplifying it. Turns out I wasn't!

"Its entire purpose in life is to support the good stuff and get ruined in the process." - Sort of like the bank account of someone with our particular addiction to machinery! :D

Todd
 
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