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Beginner's Guide to Machining Plastics

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OP
Captain Slug

Captain Slug

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Asteroid B-612
I got a rather strange response to this same guide in another forum so I would like to add the following clarifications as to why there are certain techniques and materials omitted from this guide.

Waterjet Cutting
Plastics are very receptive to waterjet cutting. The cut edges will have beveled edges and you can get an extremely high level of detail, provided you keep thickness tolerances in mind. Since few people have access to these services and enough experience with them to understand the Pros or Cons I didn't feel it was pertinent to include this as an option. In most applications waterjet cutting will end up being more time-consuming to implement than much simpler tooling combinations such as a drillpress and tablesaw.

Laser-Cutting
I don't recommend using laser-cutting for plastics. Most of the machine shops I've talked to that offer laser cutting simply won't do that kind of work with anything other than aluminum, steel, or titanium. It's also just not a cost effective method and in most cases takes more time to do correctly than it would with standard tools. Laser-cutting simply present too many safety concerns so the average person SHOULD NEVER consider this an option without extensive research and clarification.

Acetal, Nylon, And Delrin
I have extremely limited experience with Acetal, Delrin, and Nylon. I left them it out since they are considerably more expensive than the other materials listed due to their density. It's not something I felt I should include in a beginner's guide. They are ideal materials for load-bearing or frequent wear applications. Neither of which instances an entry-level machinist would presumably be capable of designing said parts.

Flame-Polishing
An inexperienced plastics machinist SHOULD NOT be considering flame-polishing as a primary means for finishing the edges of machined pieces. Polycarbonate beyond 400 degrees fahrenheit leeches hazardous fumes. Acrylic is equally as dangerous when it comes to fume production at certain temperature ranges. It also begins producing fumes at a lower temperature than polycarbonate.
Don't use flame polishing unless you have a serious filtration mask, a ventilated work area, and have thoroughly researched the hazards involved. As a standard it's best for most people to simply use sanding and polishing since the more "convenient" methods required exprienced hands and controlled environments in order to be safe.
 

Benvanz

Member
Joined
May 9, 2005
What about using a mill/cnc mill or a lathe to work on plastics....any special bits needed? etc.
 
OP
Captain Slug

Captain Slug

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Location
Asteroid B-612
Benvanz said:
What about using a mill/cnc mill or a lathe to work on plastics....any special bits needed? etc.
When it comes to milling standard grade bits work fine. Shallow bite angle (plastic specific) bits might be more reliable but they're not exactly required.

And standard lathing equipment for soft metals work just fine with plastics.
 

Benvanz

Member
Joined
May 9, 2005
When it comes to milling standard grade bits work fine. Shallow bite angle (plastic specific) bits might be more reliable but they're not exactly required.

And standard lathing equipment for soft metals work just fine with plastics.

cool, now I know what to use when my school strike ends :p
 

alinosa

Member
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Feb 18, 2002
Location
San Antonio, TX
Benvanz said:
What about using this process instead of using JPS


wow, i didn't know you could do that... i had a huge mound of shavings leftover from building a (now defunct) radbox... i could have used those to glue it all together...

thnx for posting this.
 
OP
Captain Slug

Captain Slug

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Benvanz said:
What about a higher acetone to acrylic ratio?
Acetone, as it is applied, will dissolve most plastics and I doubt that it will set as solidly as IPS will but it's worth a try if you have some scraps laying around.

However, since everything I work with are machined parts that I need to reliably and predictably meld together into an assembly I will continue using the product I know I can trust.
 

gvblake22

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Dec 13, 2003
Location
Tempe Desert
Ok, quick Q. How strong is that JPS Weld-On? Like, is it strong enough to hold up a PSU if there was only about a 1" by 4" area that was secured to the side of the panel and then went out like a shelf that the PSU sat on top of?
 
OP
Captain Slug

Captain Slug

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gvblake22 said:
Ok, quick Q. How strong is that JPS Weld-On?
80-90% fusion so it's 80-90% the strength of the base material. Remember that shape determines strength more than that material itself so if you need something to be rigid add cross-members to it.
 
Last edited:

gvblake22

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Dec 13, 2003
Location
Tempe Desert
Captain Slug said:
80-90% fusion so it's 80-90% the strength of the base material. Remember that shape determines strength more than that material itself so you you need something to be rigid add cross-members to it.
Cool, thanks :thup:
 

EvilT

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Dec 17, 2005
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In Your MiNd
when im milling plastics (mostly abs and derlin) i got to the max mill speed on my mill which is about 3000rpms and use a 3/8 2 fluke mill bit and anything smaller in size i turn the rpms down because the smaller ones tend to clog up.
 
OP
Captain Slug

Captain Slug

Helpful Senior Member
Joined
May 23, 2001
Location
Asteroid B-612
EvilT said:
when im milling plastics (mostly abs and derlin) i got to the max mill speed on my mill which is about 3000rpms and use a 3/8 2 fluke mill bit and anything smaller in size i turn the rpms down because the smaller ones tend to clog up.
I can finally reply to this now.

The speed you use will be heavily dependent upon the plastic you are machining. And yes fewer flukes are generally better for all plastics.

For ABS, Acrylic, and other relatively lower temperature plastics it's best to use as low of a speed as possible when lathing to prevent cracks and warping. It's sad to say, but acrylic is being safely lathed whenever it's making the most annoying noise possible.

For milling the speed seems to be less important then they are when lathing and each plastic will have it's own optimal speed that will allow for efficient chip removal.
 

cruzer

New Member
Joined
Feb 19, 2017
I know this is topic is 11 years old. Why is it not a sticky?

Anyways, does anyone know what type of plastic the xbox 360 case is made of?