Finishing an edge on a polypropylene sheet.

[and12y]

Hi,
I am a total novice and do not work in the plastics industry, I am a metal machinist.
However I have designed a product which uses 5mm polypropylene sheeting.
How do I cut or finish the edge properly to look professionally done?

 

[patprimmer]

What professional finish do you want.

The biggest problem is heat generated during cutting softens the surface and the saw grabs ot gets hotter until it has a melted swarf hanging off one side of the cut.

You reduce this by using very sharp tools with high set and good back clearance on the tools to reduce friction. Also about the same rake as for soft wood so the saw does not dig to deep into the soft surface.

To get a smooth surface you can flame polish with a naked flame waved over the surface. A bit of practice will perfect the technique re flame intensity, speed and distance from the surface.

Regards
Pat
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[and12y]

Thanks for your reply Pat.
The finish I am looking for on the edge is smooth with no sign of scores or roughness.
Could I use a router following a template to cut the sheet or would the high speed tend to melt the edge?
Thanks again,
Andy.

 

[patprimmer]

You can with very good swarf removal, very sharp cutters and a way to keep the plastic cool, like blowing cold compressed air over it. I am sure there is a company who specialises in cutters for plastics. Also a very slow feed rate and stop for a cool down if the cutter starts to get warm.

Unfortunately PP is one of the more difficult plastics to machine as it is relatively soft and springy so it moves away from the cutters as you feed it and has lowish softening and melting points and when moulded it has a tough skin layer that has different cutting properties to the matrix.

I never tried it, but storing the plastic in the fridge might help. To cold in the freezer will make it hard and brittle, like at around -20 to -30 deg C depending on the grade of PP

Regards
Pat
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