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How To Thread Inside Diameter Polycarbonate Pipe
I have picked so many machinists' brains trying to find a solution for threading inside diameter 4" O.D. x 3.5" I.D. x 36" length polycarbonate pipe and have come up with a design that I think will work.I am using a 3.5" wooden mandrel with a 7/8" hollow shaft then mounting Acme standard thread flanges on each end.I will then insert into the hollow shaft mandrel an Acme screw shaft with a rotary cutting tool attached at the end of the pipe with a hand crank.The cutting tool can be adjusted for several shallow passes for a desired depth.The pipe will be sealed with threaded pvc end-plugs for a water tight container for scuba camera gear.This is a copy of a 2-1/8" diameter x 9" length scuba container.Image is attached.:confused:
Re: Machining Polycarbonate
Quote:
Originally Posted by
shearder
Anyhow: it was too fast and instead of chips i got melted bits of PC all over. Long story short i was bust milling small nano tank lid struts. So the BEST finish i got - smooth and slightly smokey - i ran at 12000 rpm @ 200mm/min. May be a bit slow for some BUT let me tell you it was spewing chips for 14 hours non stop. The finish was excellent and the end mill held out to the point that it is still sharp enough for more work.
If i was brave enough i would have maybe played around more - any end mill sponsors out there?? LOL
I machined my first piece of polycarbonate this morning using a new 1/4" Onsrud bit intended for PC. I was trying 15-RPM and 15-IPM, and was getting a lot of chattering and shaking on my little CNC router. I'm not sure if the PC will work for me in the long run, but it will be interesting to try slowing my feed rate further and seeing if I get better results. I suspect I would, but was afraid of chips melting to my cutter.
Re: Machining Polycarbonate
Well just a follow-up, I tried reducing my speed to 7.5 ipm (.125" depth) and it was still grabby and didn't cut so great. After some experimentation, I discovered that as long as I kept my passes to .05" or less, I could cut at 14k at up to 60-IPM, which is really the limit for my machine anyhow.
Re: Machining Polycarbonate
Well another follow-up to my follow-up. I tried .04" per pass and found out also that normal milling (as opposed to climb milling) isn't a great option, the bit wants to grab into the material too much and I get chatter and gouges into my walls. Climb milling works a ton better. So I was running .04" per pass and about 50-IPM but I think the 50-IPM was too fast, too, as the polycarbonate is very grabby and I got a couple of more gouges in my walls at 50-IPM. So I slowed down to a crawl, 15-IPM, climb cut, .04" per pass, and got real nice results. No melting plastic as my reading would have caused me to believe.
Oh, and I would normally do a .01" clean-up pass at full depth, but even with a climb cut, I got some chatter and found that I didn't really need a clean-up pass anyhow, I had no ridges in my walls or anything from my dozen passes at .04".
Just thought I'd provide the update. In a nutshell, climb cut, slow down (15-IPM feed and plunge), no clean-up pass.
My router is a table-top CNC router from K2, and my spindle is a Bosch Colt running at the lowest speed (about 15k). I was using a new Onsrud spiral upcut double flute intended for hard and soft plastics.
Re: Machining Polycarbonate
Has anyone tried a cold gun to avoid the melting? I cut a lot of small parts out of 3/16" PC with a 1/16" 2 flute spiral end mill at 23,000 RPM and 8 IPM with no cleanup pass. I've had pretty good luck with mostly straight lines but the set of parts I am working on now has all curves and I am getting build up on the blade that turns into big melted blob that ruins the cut. ( The bits are 130007 1/16” 2 Flute End Mill bits from American-carbide.com )
Sounds like I should slow down to 15000 RPM and possibly go back to multiple passes. Also maybe try climb cut.
Re: Machining Polycarbonate
I would say climb cut for sure.
I cut a lot of PC and the best bits I have found are the Onsrud 2 straight flute solid carbide type. They are designed for soft plastics and have no spiral, so no lifting or pushing properties.
I get clean dado's, holes etc and no melting with a standard PC router.
Re: Machining Polycarbonate
If you are running @ 8 ipm you can slow the spindle to 8000-10000rpm or speed up more on your feed. You can add a air blast to keep things cool but I never do. But try 8000rpm first. AH but just remembered you can only drop to 15k. Maybe speed up to 12ipm multiple passes
Quote:
Originally Posted by
rdlohr
Has anyone tried a cold gun to avoid the melting? I cut a lot of small parts out of 3/16" PC with a 1/16" 2 flute spiral end mill at 23,000 RPM and 8 IPM with no cleanup pass. I've had pretty good luck with mostly straight lines but the set of parts I am working on now has all curves and I am getting build up on the blade that turns into big melted blob that ruins the cut. ( The bits are 130007 1/16” 2 Flute End Mill bits from American-carbide.com )
Sounds like I should slow down to 15000 RPM and possibly go back to multiple passes. Also maybe try climb cut.
Re: Machining Polycarbonate
Speed way up on the feed.
I probably cut at 40 to 80 IPM depending on the type of cut. Sometimes as much as 150 IPM.
Re: Machining Polycarbonate
I would speed up little by little. A 1/16 end mill is not that strong. You may need a few to find that sweet spot.
Re: Machining Polycarbonate
Good suggestion. I use 1/8", 3/16" and 1/4" bits. Feed rate does vary depending on which is chucked up and the type of cut.
Re: Machining Polycarbonate
Yeah I typically use 1/8" when machining acrylic or PC
Re: Machining Polycarbonate
Thanks. All good suggestions. I use a 1/16" bit because I do some intricate cuts. I'm currently cutting through in one pass so I think I will try multiple passes then a finish pass full depth.
Re: Machining Polycarbonate
What depth are your cuts currently?
Quote:
Originally Posted by
rdlohr
Thanks. All good suggestions. I use a 1/16" bit because I do some intricate cuts. I'm currently cutting through in one pass so I think I will try multiple passes then a finish pass full depth.
Re: Machining Polycarbonate
Quote:
Originally Posted by
shearder
What depth are your cuts currently?
Its 3/16" Lexan and I was cutting it with one cut. I'm doing 2 cuts and a final finish pass now at 15 IPM and 23000 RPM and its working well even with a bit that I have quite a few cuts on.
Climb out vs. traditional didn't matter much.
Lower speed (10,000) produced a rough finish. I didn't try any intermediate speeds.
Not sure I even need the Cold Gun now.
Re: Machining Polycarbonate
That's great news :) like I said I don't use any air though I have it. If it is moving fast enough it doesn't get tine to heat the material. You should be ok now 👍
Quote:
Originally Posted by
rdlohr
Its 3/16" Lexan and I was cutting it with one cut. I'm doing 2 cuts and a final finish pass now at 15 IPM and 23000 RPM and its working well even with a bit that I have quite a few cuts on.
Climb out vs. traditional did matter much.
Lower speed (10,000) produced a rough finish. I didn't try any intermediate speeds.
Now sure I even need the Cold Gun now.