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21
CamBam help (General usage) / Re: Machining Polycarbonate
« Last post by airnocker on November 26, 2022, 02:31:15 am »
So, Dave, is the test you did a profile (edge) cut of the full thickness of this material?

It isn't clear to me, and there is no pun intended.
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CamBam help (General usage) / Re: Machining Polycarbonate
« Last post by dave benson on November 26, 2022, 01:47:02 am »
This has been an interesting and informative thread.
I made this test to demonstrate what a bit of lube can do. (Mainly for my on edification).

I found a piece of material (a cover from an old machine bought at auction).
I did not machine the securing holes or pocket.
It has crazing on both the top and bottom faces, and the holes and pocket are opaque.

I did everything wrong to make an acceptable cut.

Wrong speeds and feeds.
Crappy work holding (sitting on parallels in the vice) so no support at all.
Wrong type of endmill (it was a well-used one for cutting AL, four flute).
No air blast.
Short of spinning the endmill in reverse, I could not think of anything else
to do wrong. ;D

The only thing I did was lubricate the cut with straight dish washing liquid at
the start of the cut with my finger.

Tooling marks aside, the piece came out optically clear, I can see straight through it
(40 mm) to the woodgrain of the table.
I can even see the crazing from the top and bottom faces reflected in the side face I milled.
This is why it was hard to get a decent pic.

I’m not suggesting that you use the dish washing liquid, just that if you are still struggling
to get an optically clear surface to your satisfaction, after taking all of the above
advice (which is good) then it’s well worth considering.

Dave
23
Members Projects / Re: 'Got it done, even though the body is weak!
« Last post by Bob La Londe on November 25, 2022, 15:02:40 pm »
Two carts five inches different in height. 

Rollers on the bottom edge.

Something to hook them together in the door way.

Alternatively collapsible ambulance gurney setup.
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CamBam help (General usage) / Re: Machining Polycarbonate
« Last post by Chip Owner on November 25, 2022, 14:49:53 pm »

The chips must cool the cut. Therefore, one mills with extremely sharp polished cutters with one flute. Good straight cutters for PMMA with one cutting edge are necessary for milling. We mostly use the ACRYLIC SINGLE FLUTE ROUTING TOOLS GENERATION 2 from crown-norge.no For diameters over 6mm we use the BALANCED single flute routing tools.


ralf

Can't speak for polycarbonate but on any plastic I cut, these are the same bits I use and would be reluctant to swap for anything else. I source them in the uk from LKHtools, slightly more expensive than most from the big online stores, but typically better value than many popular named brands. The latest GEN2 type is brilliant.
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Members Projects / Re: 'Got it done, even though the body is weak!
« Last post by lloydsp on November 25, 2022, 12:47:04 pm »
I guess you'd have to see the setup, Bob.  There's a 5" step UP from the main bay into the router bay, and really no room for a ramp.  Even 36" wheels wouldn't navigate that step.  At least one end's wheels have to caster, and the top tray of the tilt table must lower to about 16" off the floor.

I wish you were here, so you could just 'fix it'! <grin>

Lloyd
26
CamBam help (General usage) / Re: STEP Transform
« Last post by Chip Owner on November 25, 2022, 12:08:25 pm »
Quote
Stupidly added some positive clearance on the lower part pocket trying to clear it with an 8mm tool when
 I should have reverted to the 3mm and couldn't do the chamfer edge as all my v bits were to big to get
 round the lower part.

It looks good, there is a property in the side panel called cut width, where you can cut wider
than the width of the tool, I used this to clear out some extra material for clearance for reasons.
For example If you use a  6 mm tool but set the cut width to 8 mm then you would get an 8 mm
wide cut.
The cut width property is not the same as a roughing clearance property where you want to cut
or leave a little extra material.

Dave

Now that is interesting, I need to play with that it could come in handy.

I was in the end in a hurry between paid jobs to get this done just to confirm I had fully understood the step file process.  I've just run caliper over it and it is out, but can see where this happened.

This is what I'm finding, I've cut sheet stuff (99.9% thin alu) using the settings for so long, understanding the broader scope of what the software can do escaped me also learning what my machine can do.

Looking at this from a commercial perspective as a type of machining itself, (which is what so far has stopped me finishing any arty 3d carves),  in this instance, despite making a fixture plate some time ago to test something like this, the set up took as long as the cut if not longer, I'm not sure it's anything I'm ever likely to develop.

I have some ideas to make smaller vacuum beds that I can lift on an off my main bed and use as required for small parts, perhaps as an when I get this done, if they perform, I may play more.


 
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CamBam help (General usage) / Re: Machining Polycarbonate
« Last post by pixelmaker on November 25, 2022, 11:51:47 am »
Hello
sawing and milling polycarbonate is daily work for me.

All I can see from the pictures is that the cutter is not suitable for polycarbonate. It is not sharp enough.
You can already see this with the holes, the hole is not straight and throws up the edge on the top.
The fact that you can see the individual depth increments also shows that the milling cutter is bent away here.
By the way, spiral drilling is the better choice.
Polycarbonate must be processed as cold as possible.
The chips must cool the cut. Therefore, one mills with extremely sharp polished cutters with one flute. Good straight cutters for PMMA with one cutting edge are necessary for milling. We mostly use the ACRYLIC SINGLE FLUTE ROUTING TOOLS GENERATION 2 from crown-norge.no For diameters over 6mm we use the BALANCED single flute routing tools.
Radius or ball cutters have hardly any cutting edge towards the tip. More frictional heat is generated there, which cannot be removed due to the lack of chip size.
For such drawings you need very expensive ballnose cutters with only one flute and and a shank with reduced diameter.
However, the cut is not clean at the top. So you only cut radii with it and clear pockets with straight cutters.

A little explanation.
Polycarbonate is an extremely impact-resistant thermoplastic. Cold, the material does not break, it deforms, because of the impact strength, the material is difficult to cut and mill.
If the material becomes warm, it softens abruptly. With a very small margin, the material then becomes white and foamy, also due to the high water absorption. This is why polycarbonate is better formed cold and not under heat, as is the case with PMMA.
The small margin of heat tolerance goes together with the high water absorption. It is 12 times higher than PMMA. The material must be dried if it is to be processed hot. The material gets a white surface when it gets hot because it is milled with blunt cutters.

For all these reasons, PC is not well suited for such milling work.
Cooling with mist can only assist, as with all thermoplastics. But if the tool is not right, it will not help.
Cutting under water is also not a solution because of the high water absorption. The material will be damaged. Only if you can dry it professionally afterwards (12 hours at 105°C) would you think about it.
Since the light transmission is much lower than PMMA, PC always has gray edges. Polishing is also difficult with PC as it also generates heat.

If the impact strength is the reason for the material, use impact resistant PMMA.

ralf
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Members Projects / Re: 'Got it done, even though the body is weak!
« Last post by Bob La Londe on November 25, 2022, 03:39:06 am »
Make one with pnuematic tires. 
29
CamBam help (General usage) / Re: Machining Polycarbonate
« Last post by Tool-n-Around on November 25, 2022, 02:38:38 am »
There is a vid on Utube where the people from carbide create cut out some polycarbonate
and give the feeds and speeds for various tool diameters.

I always forget YouTube. Upon quick search I see there’s tons there.

He does lament that his software doesn’t have a spiral lead in’s, CB does though.
This is important is can help a lot, is for example in your Logo where you are using a
ball end endmill, it’s a good idea to use the leadins as plunging straight down into the material
is not a ball end mill’s superpower, (typically the plunge feed rate is less than a center cutting endmill) and as this is the start of the cut and if you get chip welding it’s hard to recover from.

My palm is on my forehead. In fact I could see this happening upon the plunge. I will incorporate lead ins.

I always use dish washing detergent for polycarbonate\Acrylic.

Will do so after some more (dry) experimentation.

Without the cutting surface speed for the material or the chipload from the endmills manufacturer data sheet your feed and speeds cannot be calculated, so it’s a guesstimate at best.

Well, I searched my memory, poked around, and low and behold found the O-Flute data. The feederate for the ¼”D bit is making my eyes pop a bit. My router is only 1.25HP and at lowest speed, will be a fraction of that. Will need modest DOC for what the chart suggests. See attached.

When I machine polycarbonate, I always use single flute endmill (have better success with HS .25"EM vs carbide. Use lots of compressed air directed where endmill engages piece. Because I have PID spindle control, run the spindle at 9000 rpm, and high feedrate, and .25 deep. The feedrate most often is set at 45 ipm. Hopefully this will give you idea. Get scrap piece, set the rpm's to low end and make cuts varying the feed rate. When cuts the best it sound/feel like the endmill will break any moment. That where you will see nice cut. Good luck.

Thanks Bubba, wont be able to get quite that low rpm but have been in that 45 ipm range. Only carbide at the moment, but anxious to try the single O-Flute. The chart I posted seems to suggest 150-200ipm…..dont know that I’ll have the courage.

My router also originally came with its own "dial" speed control in a similar rpm range like yours and could not go below 14K rpm either.  With this PID controller it can now go down far further, like 5K rpm, under complete control by Mach3.  My acrylic milling/engraving speeds are usually in the 10-12K range, feeds in the 30-45 ips range. .......Their website is https://www.precisebits.com/.

Thanks for that airnocker and for the source. Similar to other feedrates mentioned but cant quite dial that low rpm. May need a little more feedrate and less DOC.

Thanks for replies guys.

Best,
Kelly
30
CamBam help (General usage) / Re: Machining Polycarbonate
« Last post by airnocker on November 25, 2022, 01:24:18 am »

What cutters and speed did you use?

The .25D cute was a low helix angle spiral which according to the manufacturer is designed for hard plastics, which may be the case but even though its upcut, probably doesn’t eject chips as well, especially on the two sided cut. I have a single O-flute cutter in that .25D which is supposed to be better, and thinking with a little shallower depth increment and more federate may do the trick dry.
The .031 cutter I was using to cut the logo is actually a single O-flute not round nose. I had to look at that thing under high magnification to confirm such.

My Porter Cable router 890 is my "spindle" and is modified to be controlled by a Super-PID speed controller.  I've used this combination now for close to 9 years.  https://www.vhipe.com/product-private/SuperPID-Home.htm

My router also originally came with its own "dial" speed control in a similar rpm range like yours and could not go below 14K rpm either.  With this PID controller it can now go down far further, like 5K rpm, under complete control by Mach3.  My acrylic milling/engraving speeds are usually in the 10-12K range, feeds in the 30-45 ips range.  The largest bit I use is a 1 or 2-flute .125".  I've grown to prefer doing parts cut-outs using a .0625" diameter bit just to minimize stock waste, but have also used a .0313" 2-flute.  If waste isn't a concern then I use a .125" 1 flute upcut bit.  But my preference is a .0625" 1 flute, fish-tail with an .125" shank.  I also use the same size in an upcut fish-tail, both with a .25" flute length.  My depths of cuts are usually from half the diameter of the bit and occasionally up to the diameter of the bit.  I buy bits that are expressly optimized for thermoplastics and get them from Think & Tinker, Ltd. in Colorado.  Their website is https://www.precisebits.com/.

My machine is made from polyurethane'd MDO with the waste board made of polyurethane'd MDF, except for the worksurface.  I've added the capability to use small amounts of liquid lubricant by screwing down a piece of HPDE, surfaced so it has about .125" raised edges, for a spoil board that's about 12" x 22".  But for most of my acrylic milling and engraving I've not needed it.

Happy TurkeyDay!





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