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Forum topic by MrRon posted 06-18-2019 04:48 PM 432 views 0 times favorited 17 replies Add to Favorites Watch
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MrRon

5572 posts in 3665 days


06-18-2019 04:48 PM

Topic tags/keywords: question

I need to drill some 3/4” holes in plastic, specifically 3/8” thick UHMW polyethylene. The only bits I have that can drill a 3/4” hole are spade bits and forstener bits. I have drilled 1/2” holes before using straight drill bits without any problem, but I’m concerned that either of the 2 bits mentioned may not work. What say you? Would a 3/4” straight router bit or an end mill work?


17 replies so far

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Nubsnstubs

1584 posts in 2152 days


#1 posted 06-18-2019 05:02 PM

If the router bit or end mill is for through holes, why not? Either way, you are going to need to clamp them in a vice/vise or to the table to get it done. If they don’t do through holes, drill a pilot hole with the 1/2” bit, change to the larger bit mentioned and finish the hole. Repeat until all are done.. How many holes are you gonna drill? ............. Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

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HokieKen

9974 posts in 1560 days


#2 posted 06-18-2019 05:11 PM

I’ve drilled UHMW with Forstner bits many times with no problems. Just clear the long stringy chips a couple of times. The UHMW has a high enough melting point that heat won’t be an issue.

-- Kenny, SW VA, Go Hokies!!!

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MrRon

5572 posts in 3665 days


#3 posted 06-18-2019 05:12 PM

84 holes.

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Fred Hargis

5595 posts in 2915 days


#4 posted 06-18-2019 05:28 PM

Like HokieKen, I’ve used forstners that size on UHMW with no problems.

-- Our village hasn't lost it's idiot, he was elected to congress.

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SMP

1199 posts in 328 days


#5 posted 06-18-2019 05:36 PM

Forstner should be fine, but give it time to cool regularly if doing 84.

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HokieKen

9974 posts in 1560 days


#6 posted 06-18-2019 05:46 PM

For that many holes, I’d invest in a reduced shank twist bit. Gonna be slow going with anything else.

-- Kenny, SW VA, Go Hokies!!!

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CaptainKlutz

1507 posts in 1916 days


#7 posted 06-18-2019 06:02 PM

+1 forstner bits work in UHMW PE.

When drilling UHMW the bit center tends to wonder. Need to use high enough speed that cut smoothly, but not so high that it melts instantly. Machinist guide will have suggested starting speeds. Use of a drill guide bushing works best to avoid wondering. Can also reduce movement by using wood plate on top, and then wood plate on bottom for tear out and helped avoid heat induced deformation. We used to drill round UHMW stock inside matching ID metal or wood tube.

UHMW also grabs bit and tends to act like screw, so use a rigid drill head with good feed rate control (Drill press or vertical mill) – not hand drill. Step drilling with small hole, then bigger one will make large bit grab and drive down even worse. Forstner bit does not have this problem.

Always challenge to maintain tolerances with UHMW plastic. It will deform under high clamping pressure, and expansion due excess heating can increase hole size once it cools. Can use compressed air (or any other standard method) for cooling during machining.

Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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bilyo

746 posts in 1524 days


#8 posted 06-19-2019 12:59 AM


+1 forstner bits work in UHMW PE.

UHMW also grabs bit and tends to act like screw, so use a rigid drill head with good feed rate control (Drill press or vertical mill) – not hand drill. Step drilling with small hole, then bigger one will make large bit grab and drive down even worse. Forstner bit does not have this problem

- CaptainKlutz


I concur. I have had good results using a forstner bit in UHMW. But, I strongly recommend you use a drill press and clamp your work down securely. I also use a fairly slow speed.

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Redoak49

4051 posts in 2411 days


#9 posted 06-19-2019 11:12 AM

I would use a hole saw drill. I have cut a lot this way to make washers for bolts.

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ChefHDAN

1417 posts in 3271 days


#10 posted 06-19-2019 11:50 AM

+1 for a hole saw

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

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Heyoka

17 posts in 274 days


#11 posted 06-19-2019 12:45 PM

+2 hole saw

-- Heyoka

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farmfromkansas

56 posts in 36 days


#12 posted 06-21-2019 01:23 AM

Think the secret to working with plastic, is keeping your speed down. I tried cutting a piece of plexiglass in my tablesaw, just melted the plastic and stuck to the blade. But a hand saw worked fine.

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MrRon

5572 posts in 3665 days


#13 posted 06-21-2019 08:25 PM

I tried different bits on a scrap piece of .417” UHMW. The forstner bit required a lot of feed pressure, but it produced a clean hole. A 3/4” 2-flute end mill in my vertical mill worked great. The holes were clean and done quickly.

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HokieKen

9974 posts in 1560 days


#14 posted 06-21-2019 08:41 PM

Oh heck, I didn’t know you had a mill MrRon! You have your answer now ;-P FWIW, On CNCs for plastics, I would typically rough the holes with a twist drill and follow with a boring bar. If you’re positioning manually though, that would be FAR less efficient with the tool change.

-- Kenny, SW VA, Go Hokies!!!

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WhyMe

1160 posts in 1983 days


#15 posted 06-22-2019 01:16 AM

I use a step drill bit to drill plastic. It works great.

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