# Machining polypropylene for the best finish.



## picclock (Apr 25, 2012)

Hi

Does anyone have any info on how to achieve a very high finish on this material ? First attempts are not encouraging. I was wondering about going over it with a hot air gun or some sort of solvent. It just needs to be very smooth rather than dimensionally critical.

Many Thanks

picclock


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## Tin Falcon (Apr 25, 2012)

check boedeker plastics web page usualy very helpful.

http://www.boedeker.com/fabtip.htm


Tin


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## ProdEng (Apr 25, 2012)

Polypropylene is not the best choice for finish but it does machine well with very sharp tools. If turning, an HSS tool with no top rate works well. PP is resistant to solvents but a hot air gun will produce a waxy surface if you get it hot enough, but too hot and it melts. Acrylic and PVC are better choices for good finish and PVC takes paint well. Hope that helps.


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## Darren English (Apr 28, 2012)

Hi Picclock, normally for finish cuts on PP I use the highest speed possible with a depth of cut around .1mm/.2mm and a feed rate of about .1mm per rev and make sure to use coolant or lubricant (WD40 works). Just make sure you feed at a good rate when machining. 

For hand finishing I've tried many things, Scotchbrite or abrasive pads soaked in WD40 or oil seems to work but it does take time.
Hope this helps.


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## picclock (Apr 28, 2012)

Thanks for the info. I think its just tricky stuff to finish. I was hoping someone had cracked it but it seems that its just a bit difficult. 

@ Tin
checked out the boedeker site but couldn't find any info on polypropylene, although the generic stuff was interesting.

@ ProdEng
I am using sharp HSS tools. Tried 0 rake but did not seem much different. Heating was interesting. The underlying irregularities were still there and didn't flatten as expected, however the peaks of the roughness do round down so the surface feel is smoother.

@ Darren
I haven't tried turning with a lube, and have generally turned slowly figuring the plastic would melt - so I will give that a try on Monday

Many Thanks

picclock


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## Omnimill (Apr 28, 2012)

Some plastics are just a pain to turn as you've found out. It's often the fine finishing cuts that ruin a piece. Another thing you can try is to put the material in the freezer and cool it down before turning it but what's going to happen to dimensional accuracy is anyone's guess ... :-\


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## peatoluser (Apr 28, 2012)

I buy my plastics from here 
http://www.directplasticsonline.co.uk/machining_guidelines.html
gives some guide lines on machining
yours
peter


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## doc1955 (Apr 28, 2012)

I have done machining in poly and I shoot for the best finish I can and when finished I give it a wipe down with some acetone and it will get rid of the cloudiness and make it clear. Same principal used to clear the head light lenses on the new cars that have cloudy lenses.

 PS: Don't throw out your small pieces of poly you can weld them together with acetone just dampen the surfaces of the pieces being welded together and lightly clamp together and let set for 5 or 6 hours and you will have a large piece made from smaller pieces. The following pic was made with 3/8 thick pieces welded together.


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## picclock (Apr 28, 2012)

@ Peatoluser - me too although I have other suppliers their prices are good and delivery fast.

@doc1955 I think your referring to polycarbonate, I'm using polypropylene which appears to be completely unaffected by Acetone. Liked the piccy though.

Best Regards

picclock


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