# machining delrin/acetal?



## adrenalnjunky (Jul 28, 2007)

For one of my projects, I need to make a flat mount out of a block of what was called Delrin/Acetal

I don't have any milling machines or fun stuff like that. I do have nice router/table, benchtop drill press, scroll saw & belt sander. 

I need to machine a grove across this plate, and I'm thinking my router table with a straight cut or round nose bit is the ticket. 

Has anyone tried working with this stuff before, am I going to have issues with the plastic melting instead of cutting? Low RPM vs. high RPM?

Tips/Tricks/Thoughts appreciated before I go and foul up this relatively pricey piece of plastic.


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## mattthemuppet (Jul 16, 2004)

not sure about delrin, but I've cut a lot of lexan with a dremel/plastic cut off disk and I always have to make several light cuts at the slowest rpm, otherwise it just melts and balls up.

Pretty sure Golddigger has machined a lot of delrin, might be worth asking him


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## troutie-mtb (Sep 20, 2007)

I don't know the rules for delrin 
But I have lathed and milled some and slow or fast made not a lot of difference
fast in the lathe gave a better finish 

great to machine real easy .

you should have no problems with a router might get some f
iffy bits at the edges. but they trim off easy.


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## chaos lodge (Oct 15, 2009)

I have a fair amount of experience machining Delrin. (used to build prototypes at SRAM)

Delrin machines very nicely and you'll get a fine quality finish with it. I wouldn't recommend the router ,though, as the rpm's are too high -well, unless you matched the feed rate to the rpm's but the logistics of getting the chips out of the way, safe cutting practices...

As a reference, I used to run a 3/32 end mill at 2200 rpm at pretty slow feed rates. Just don't take too much of a cut (I'd keep it at no more than 60% the depth of the flutes of the end mill) and make sure to have clear path for the chips to leave the workpiece (it's the chips that carry away much of your heat). 

I'd also recommend cutting uphill (having the flutes of the cutter moving opposite the direction of feed). This leaves a very clean finish, particularly if you'll be using a thinner end mill. Running it the other way will cause the cutter to 'climb' up the workpiece resulting in a very ridged/choppy finish. Feed rates can affect finish also.

Play with it a bit and get a feel for how it responds. It is very forgiving. Remember to reduce your rpm's as the cutter diameter increases -it's the speed at the cutting surface of the mill that matters.

Hope that helps!


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## wquiles (Aug 22, 2010)

I have done a lot of machining on Delrin, and it is a great material to work with. As long as the cutters/inserts are sharp, Delrin machines like if it were a metal. Even though I have done a lot of work with Delrin, it always has been on the lathe or milling machine, but I have not gone higher than about 1300rpm's with it. I suspect that the router will be moving too fast, and that in fact it might tend to soften/melt the Delrin.

Here in this page of my website I am making a custom heatsink for a customer, and in video #13 you can see me working on the lathe with a Delrin piece - in this video I am taking a 0.100" cut (0.2" reduction in diameter) at about 900 rpms, and moving the carriage as fast as possible (I am using a carriage stop!) - you can see from the shower of chips how easily the Delrin cuts - it is awesome!

Custom parts - page 2

Will


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## brad72 (Jun 12, 2009)

Like the other guys I have worked extensively with Acetal making machine parts etc and it is a pleasure to machine, holding tolerances really well and any shapes being possible. 

If you want a really smooth surface finish use a nice sharp tool, but if you start to smell something weird, slow down as you are overheating the Acetal. By a weird smell you will now it when it happens. To me it reminds me of the digestive biscuits smell, which the Pom's will be all to familiar with.


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## Magnum9 (Jun 8, 2011)

Only really one rule with acetal, if it melts slow down or add coolant! And as mentioned use sharp tools with plenty of rake.

Oh and that smell is extremely toxic and has been known to knock people out.


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## mattthemuppet (Jul 16, 2004)

brad72 said:


> To me it reminds me of the digestive biscuits smell, which the Pom's will be all to familiar with.


mmm, digestives. How you can call that a weird smell I don't know - it's like the smell of dew on grass on a fresh sunny morning. Then again, this is from someone who's country thinks a bucket of shrimp left in the sun all day is the height of culinary excellence


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## Vancbiker (May 25, 2005)

One thing to keep in mind when using Delrin/acetal, is there are few glues that work well with it. I use acetal for the handlebar remote switch housings I make since they are just one machined piece and it cuts so well. I use ABS plastic or polycarbonate/Lexan if I am building something that is going to be glued together.


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## adrenalnjunky (Jul 28, 2007)

Thanks all,

The only tool I could get with that sort of RPM was my bench drill press, but when I got everything set up I found that my cross-slide vise had suffered a spill off the workbench and the casting broke. Now with it non-functional, I went back to my router table and experimented with the router dialed down as low as it could go - 10,000 rpm.

Using a 1/4" straight cut bit, I made a couple of test passes and was very impressed with how it was cutting. Was more like working with hardwoods. Nice, clean shaving, and no "gumming up" at all.

Here's was the mount I was making in mid-build:









And with the housings mocked up. Going for a dual XM-L Bar light. L-flex in one side, power socket and mom switch in the other - or maybe a PG-7 gland - not 100% sure yet. Status LED will be in the mount - wiring runs from one side to the other on the bottom of the mount to keep it hidden and neat and will enter the housings from the bottom through a grommet.


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## brad72 (Jun 12, 2009)

Nice work mate. Acetal is lovely to machine


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## wquiles (Aug 22, 2010)

brad72 said:


> Nice work mate. Acetal is lovely to machine


+1 on both counts


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## prostheticsarefun (Nov 22, 2013)

Does anyone have experience cutting delrin with a much larger cut? We're trying to cut a 1" deep and 1/2" wide cut with a router. I'm assuming multiple passes would be the way to go.


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## wquiles (Aug 22, 2010)

prostheticsarefun said:


> Does anyone have experience cutting delrin with a much larger cut? We're trying to cut a 1" deep and 1/2" wide cut with a router. I'm assuming multiple passes would be the way to go.


As was mentioned above, the problem is the "relatively" low melting point for Acetal/Delrin. A router spins simply too fast, so melting might be a problem. Even on light passes, the edge of the cutting bit is still rubbing against the soft material , so you might have to just try it and see how it goes.

Will


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## El34 (Jan 11, 2009)

I have machined Delrin and other plastics like HDPE and UHMW plastics

You can use a router table, just feed it at a proper rate and cut the proper amount of material per pass so as *not to produce excessive heat*. Making sure your bit is really sharp will make a world of difference

And you found out that it *did *work on your router table.
You have to take internet opinions with a grain of salt on matters like this

What looks like it won't work on paper works just fine if you adjust your method properly.


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## Vancbiker (May 25, 2005)

I have found that directing my air gun at the cut gets the chips clear of the cut and reduces the tendency for the heat of the cutting to cause the chips to melt back onto the part giving a "fuzzy" surface.


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