HDPE vs polystyrene

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aarvidsson
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HDPE vs polystyrene

Post by aarvidsson » Fri May 09, 2014 9:23 pm

I'm trying to come up with a good feed rate for cutting polystyrene. How close is 3mm polystyrene to HDPE? I'm using a 3.22mm 1-flute bit that came with the ShapeOko 2 kit on a Chinese 300W spindle, should I use the same speed settings as for HDPE? My completely unscientific feeling is that HDPE is tougher than polystyrene?
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Improbable Construct
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Re: HDPE vs polystyrene

Post by Improbable Construct » Fri May 09, 2014 10:18 pm

HDPE is most definitely sturdier than polystyrene.
You should be able to plow through the polystyrene about as fast as your machine can go.
On my machine I would start with a feed speed of 2500mm/min and 20000 rpm. Your results may vary. :)
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aarvidsson
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Re: HDPE vs polystyrene

Post by aarvidsson » Fri May 09, 2014 10:32 pm

Holy cr*p - 2500mm/min? O.o I'll safely increase the feed rate from 350mm/min, then :P I'll try this in increments and see where I end up... Um, should I still do about 1mm per pass? Thanks!
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Re: HDPE vs polystyrene

Post by Improbable Construct » Fri May 09, 2014 11:26 pm

If you are talking about normal expanded polystyrene then I would start at 1mm.
Its really going to depend on the density of the foam you have.
Surface finish will be the biggest speed factor.
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Shapeoko 1 # ???? Stainless plates, still in the box.
Shapeoko 2 # 3926 not stock
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aarvidsson
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Re: HDPE vs polystyrene

Post by aarvidsson » Sat May 10, 2014 8:49 am

Hm... I got in to some problems. For each pass the bit is a wee bit off, here and there. Can this mean I'm loosing steps or is it something else acting up? 1250mm/min was the feed rate I set.

*edit* Nope, seems to be related to material flex. The plastic sheet doesn't seem to want to stay flat, but if I stick my hand in during the run and keep it flat, everything works super in 2000mm/min. Time to go to work! :D
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Gadgetman!
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Re: HDPE vs polystyrene

Post by Gadgetman! » Sat May 10, 2014 11:08 am

Sounds like that stuff needs a vacuum table, or possibly a layer of double-sided tape to hold it in place...
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aarvidsson
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Re: HDPE vs polystyrene

Post by aarvidsson » Sun May 11, 2014 4:25 pm

Yes, I'm afraid so :/ As it stands now, I'm keeping the sheet flat with my hands - not something I'd like to to for more than a very short while. I'll look into double sided tape, but I have yet to find one that won't stick to the plastic as if it was fused...
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WillAdams
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Re: HDPE vs polystyrene

Post by WillAdams » Sun May 11, 2014 4:53 pm

Please don't hold it flat w/ your hands.

Other things to try:

- rubber cement (be sure to get a solvent which won't damage the plastic)
- double stick tape --- try the sort which is dispensed from a small mechanism such as one finds in a craft store
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aarvidsson
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Re: HDPE vs polystyrene

Post by aarvidsson » Sun May 11, 2014 5:57 pm

Will, I hear you. I'm both very much attached to my hands, and I'm trained as a paramedic. Hence I've seen too many a times what happens when people put their hands in where they don't belong :P

I'm looking at alternatives as we speak, and I'm also trying to find a better alternative to the spoilboard - something that is *flat*, like an extrusion bed or similar
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DanMc
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Re: HDPE vs polystyrene

Post by DanMc » Mon May 12, 2014 3:02 am

I keep a can of 3M Super 77 in my shapeoko table for stuff like this. It's nice because you can tailor the amount of adhesive you use, i.e. little squirt on one surface for something light, heavier coat on both surfaces for heavier items or more aggressive milling strategies. The only thing that sucks is the spoil board winds up getting pretty gunked up pretty quickly, also swarf winds up sticking to overspray if you have any.

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