Is UHMW a good choice for this part?

[martin_05]

I have to make a bunch of these little parts (roughly 2 x 0.4 x 0.4 in).







I was thinking UHMW. It's a glorified spacer, so, no serious mechanical requirements. It should do well when exposed to water and the usual household cleaning chemicals.

I have never machined UHMW. I wonder if there might be something that's a better choice.

I was thinking of buying something like a 6 x 24 x 0.5 sheet to make a bunch in one pass. Lay them flat, with the slot facing up. The contoured cutouts can be cut from that side also, not critical, they'll just have a radius somewhere else.

I figured I just drill a bunch of 1/4 holes for clamping down onto either a piece of MDF, plywood or aluminum plate. I would imagine edge clamping this on a Kurt vice isn't going to work. In case it's relevant, this will be done on a VF2.

I'd have to face it to thickness from 1/2 to about 0.4. Not sure how well UHMW takes facing. Does it end-up with a rough surface?

Acrylic would be fine too, although I'd prefer the part to be black (without having to paint/coat).

I imagine I can use almost any kind of tool to cut it. Plain carbide?


Thanks,

-Martin

 

[MaxPrairie]

Black delrin/acetal. Watch those thin walls.

 

[chip_maker]

Uhmw sucks to machine.

Not sure of it's resistance to households cleaners, but black delrin or black acetal would be much easier to machine.

Sent from my SM-G991U using Tapatalk

 

[CalG]

that slot would make heat in UHMW . And not a good kind of heat.

Regardless of material, Use a saw for that slot.

 

[13engines]

You might try HDPE. Low water absorption, and easy to machine like Delrin/Acetyl. I believe it is lower cost too.

 

[Garwood]

I can't think of anything else I'd like to make parts from less than UHMW.

That slot could be an ass kicker. UHMW tries to grab the tool AND it's impossible to hold onto because it's slick.

My experience with UHMW is mostly with big parts (Like 50+ lbs each), but no other material has kicked my ass so unexpectedly.

 

[CalG]

You might try HDPE. Low water absorption, and easy to machine like Delrin/Acetyl. I believe it is lower cost too.

High density PE IS UHMW!

UHMW Plastic | UHMWPE Properties & Material Uses | Curbell Plastics

 

[john.k]

Id say its super resistant to chemicals....used to make the pistons and glands in Graco airless HP (up to 7000psi) paint pumps using paint like putty at times,and also pump various solvents like epoxy thinners ,polycyclics,aromatics,organic peroxides etc.

 

[jwmelvin]

High density PE IS UHMW!

UHMW Plastic | UHMWPE Properties & Material Uses | Curbell Plastics

UHMW is polyethylene, but UHMW != HDPE

HDPE vs UHMW - Physical Attributes - Polymershapes

 

[13engines]

High density PE IS UHMW!

Not even...

 

[CalG]

"Basically, both of these materials are useful in a variety of instances. But UHMW tends to be better suited for industrial or manufacturing applications where friction or wear may be a concern. However, HDPE is often performed for items that need to be shaped using techniques like welding or 3D printing, especially in tanks or vessels that need to hold chemicals or other fluids."

Yaaa, For this application, they are the same material. Sheet or bar, it's all a matter of degree.

High or ultra high. Where so you get to draw the line?

 

[martin_05]

I knew it was a good idea to ask. So a definite "no" on UHWM. Got it.

It looks like the best options so far are:

Acetal
Object moved
$600 for 12 x 24 x 0.5 in



HDPE
Object moved
Object moved
$16 to $20 for 12 x 12 x 0.5 in squares

That's a massive difference in cost. Being that this is just a spacer, I think I'll get some HDPE and see what it's like to machine.

I could actually 3D print these using PETG. I have tested it that way. The solution would be vastly more robust with a machined plastic.

My spindle maxes out at 8100 RPM. The slot is 2 mm wide and about 0.3 in deep. My speed/feed calculator says 37 IPM with a depth of cut of 0.025. I was hoping to be able to go faster than that.


Thanks,

-Martin

 

[gregormarwick]

I can't think of anything else I'd like to make parts from less than UHMW.

That slot could be an ass kicker. UHMW tries to grab the tool AND it's impossible to hold onto because it's slick.

My experience with UHMW is mostly with big parts (Like 50+ lbs each), but no other material has kicked my ass so unexpectedly.

Yes.

And don't forget that it moves around like crazy.

Years ago I lost hard on some thin wall UHMW sleeves, ~200mm diameter, ~1.5mm wall thickness, ~25mm long, turned from a solid bar and parted off. Stupid tolerances from the client, and I was too green to know better. Cutting the OD and the ID separately made it curl like a bell no matter what. Ended up making a ID/OD HSS box tool to cut both simultaneously, which worked pretty well actually.

 

[Schjell]

Unless you require the part to be buoyant in water then UHMW / PEHD is a terrible choice compared to Acetal/POM-C for the reasons others have mentioned. Impossible to break chips when turning, it really sucks. Also it is very easily plastically deformed over time.

Different story with our Multicam sheet router though. Good vacuum and high spindle speed helps to make chips I reckon.

 

[IninefingersI]

For plastic parts, we use either acetal or nylon 6/6 exclusively. Both machine well, but they make a mess inside your mill. After a couple parts it looks like a murder of crows exploded. Use new end mills whenever possible.

 

[Scruffy887]

I knew it was a good idea to ask. So a definite "no" on UHWM. Got it.

It looks like the best options so far are:

Acetal
Object moved
$600 for 12 x 24 x 0.5 in



HDPE
Object moved
Object moved
$16 to $20 for 12 x 12 x 0.5 in squares

That's a massive difference in cost. Being that this is just a spacer, I think I'll get some HDPE and see what it's like to machine.

I could actually 3D print these using PETG. I have tested it that way. The solution would be vastly more robust with a machined plastic.

My spindle maxes out at 8100 RPM. The slot is 2 mm wide and about 0.3 in deep. My speed/feed calculator says 37 IPM with a depth of cut of 0.025. I was hoping to be able to go faster than that.


Thanks,

-Martin

Razor sharp tooling that has never been used. Low helix could help keep the part in your vise too.
You were looking at Acetal AF, not plain Acetal. AF is Teflon filled?

Object moved

 

[IninefingersI]

Acetal
Object moved
$600 for 12 x 24 x 0.5 in


My spindle maxes out at 8100 RPM. The slot is 2 mm wide and about 0.3 in deep. My speed/feed calculator says 37 IPM with a depth of cut of 0.025. I was hoping to be able to go faster than that.

You don't need, or want, the brown stuff.

Save yourself a lot of time and heartache and buy a 5/64 wheel cutter/slotting saw.

 

[rk9268vc]

I knew it was a good idea to ask. So a definite "no" on UHWM. Got it.

Acetal
$600 for 12 x 24 x 0.5 in

HDPE
$16 to $20 for 12 x 12 x 0.5 in squares

That's a massive difference in cost. Being that this is just a spacer, I think I'll get some HDPE and see what it's like to machine.

-Martin

The headache saved by spending a little more to get delrin is well worth it.
delrin is a dream to machine, nice easy chips, doesnt get all melty, holes dont close up on you, etc

I am not too familiar with HDPE, but delrin is well worth the cost compared to uhmw

The KEY to plastic is razor sharp tools, and keeping the heat down. Cut the chips and get them out.
if the endmill has ever even kissed even aluminum, it will never cut plastic again
You want super aggressive tools as well. Very sharp edges.
I have had very good luck with YG-1 "Alu-power" endmills. They are razor sharp, 3 flute jobs with a high helix. Good at getting chips out so they dont get all melty.
The key is that they are sharp, like slice your hand trying to get them in your collet sharp. With standard general purpose endmills they like to leave strings and hairs, especially on the floor of your part, because they dont cut cleanly.
I have also had very good luck using the "Super Fly" from Tormach with the aggressive aluminum insert. Just throw it in an ER32 collet to grab the tormach 3/4" shank.
Going 10 thou DOC at 7in/min leaves a mirror finish on delrin, and almost as good on uhmw running dry, no coolant just air blast.
I have found that coolant prevents the chips from escaping, just a bunch of dry air works best for me.

what you will find if you get into plastic, is that it can be very lucrative. I make way more money turning uhmw into 100 dollar bills than i do in aluminum. The key is you just need to figure out your tooling, work holding, and feeds-n-speeds and then it is simple. You can rough as fast as your mill can run, then come back and kiss it into spec.
uhmw sucks to machine, no one wants to do it, what that means is if you can figure it out, you can charge big $.

 

[NodecoMachine]

Get Acetal (copolymer) from a plastic supplier. Delrin (which is a homopolymer) from McMaster is expensive… but Acetal (similar but not the same) is less expensive. I would say they machine the same but a decent price difference. Please take note everyone, I am not mentioning anything about the differences is mechanical properties…

 

[martin_05]

You don't need, or want, the brown stuff.

Save yourself a lot of time and heartache and buy a 5/64 wheel cutter/slotting saw.

That would require a right angle head, which I don't have. I've been looking for an excuse to buy one probably going back 15 years. I remember I had to machine lots of thin slots on a plate to make a large (12 x 24 in) heat sink with epoxy-bonded fins on 1000-series aluminum. I had a VF3-SS at the time. I was blown away by how fast and deep I was able to run a 0.047 end mill without breaking it. A right angle head would have made that job a LOT less painful.

Every time this happens I look at the cost of a right angle head and the job and say something like "How many times am I going to use this thing?".