Guard around milling table

I wanted to make a guard around the milling table, so that chips and coolant would not be strewn all over the shop.
I want to make something like what I saw on the web:
http://machineability.com/Bridgeport_series_II.html
My first question is what material to use? Acrylic? Lexan?
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For a lot of the mini mills they have prefab cabinets available. Acrylic is supposedly more scratch resistant, but if you think you might have a cutter break and fly off the mill several hundred feet per second Lexan will stop it without cracking. I have never had the pieces of a broken cutter go flying, but you never know, and I have not been milling all that long. I suspect most home built cabinets are made with whatever the builder was able to find at Home Depot.
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wrote:

defiantly $LEXAN$
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wrote:

Lexan :== Tuffak :== polycarbonate is shatter resistant Acrylic:== plexiglas :== Lucite is less so, but less expensive.
I'd be somewhat concerned with compatibility with your cutting lubricant, as well; neither will do well with trichlor.
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whit3rd wrote:

I can't imagine anybody using trichloroethane today. Acrylic - Plexiglas - seems to handle oil and typical coolants just fine.
Jon
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    IIRC, the original formula of TapMagic still has it, and you can (by jumping through hoops) still get it.
    But you are not going to be spraying it around on a CNC mill anyway. :-)

    Yes -- but given the application I would not want it because it is so much more brittle.
    Enjoy,         DoN.
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Ignoramus8473 wrote:

I just put up a page on my own take on a coolant shield. It is decidedly low-tech, but works well. http://jelinux.pico-systems.com/shield.html
Jon
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wrote:

I believe I'd make one from tempered hardboard with hinges on the back corners first, just to see how big of a pain it was going to be to live with. If you like it you can always make another more permanent one from plastic or 16ga sheetmetal. The one shown looks to be clear plastic and also looks like it will constantly be in the way on a manual machine
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    *Thick* Lexan -- not Plexiglass, because that is too brittle. If you have something heavier than a chip (e.g. a broken HSS or carbide mill half), you want something more likely to keep it away from you.
    When I was first learning CNC, I fast moved a workpiece though a solid carbide end mill -- and spent the next eternity ducking it bouncing off hard plaster walls. :-)
    Enjoy,         DoN.
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1/4 inch?

Yea, that's fun, I had this experience at 15 when I crashed a lathe carriage into the chuck. The lathe was 10 kW, like this one:
http://uaprom-image.s3.amazonaws.com/138857_w640_h640_dsc07722.jpg
i
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wrote:

1/4" Lexan will return .22 mag bullets from a revolver w/ a 6 1/4" barrel. We tried it on an old smoky Jeep windshield when we replaced it with a new panel years ago. I suspect that is more energy than a broken cutter.
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    1/4" or perhaps 5/16" for the size of mill you are using. For some machines, you would want something 1" thick or so -- like what is used to bulletproof the tellers at some banks. :-)

    Looks like a nice machine.
    Must have felt really bad at 15 to crash that.
    Enjoy,         DoN.
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How high do you think it should go above the cutting point? I mean, I am sure that the higher, the better, but at some point the height will interfere with the ram and table movement. So if I could get some idea like "4 inches above the point of cutting" it would be nice. Just want to find a way to think properly about that.

It still feels bad.
i
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I think we are going overboard with the guard. A flexible curtain will work to catch spay and chips, and will stop a flying cutter by deflecting. These are not bullets.
For the record, the Flexbar guard on my lathe is made of 3/16" thick lexan, and the backshield (which I made) is a sheet of 1/8" plexiglass hanging from the Flexbar's axle.
As for height above the cutting point, whatever is needed to make the edge at least 45 degrees angle from wherever the chips and spray come from will catch most of it. But you will not get all of it unless there is complete enclosure. Bottom line is to make things easily adjustable, so you can adapt to various setups.
Joe Gwinn
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I agree, but I think that it will be messier.
I may get away with using Luan plywood for rear and sides.

That would certainly be cheaper.

Yeah. I am not losing sleep over this, but if I really use this mill seriously, a good guard will save a good deal of grief from just chips, coolant, and other messy stuff.
3/16" ;lexan seems to be completely adequate.
i
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I would certainly think so. How fast does your mill turn?
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up to 4.2k RPM, but I was told to run it under 3K RPM.
i
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On 7/26/2010 8:41 AM, Joseph Gwinn wrote:

What size machine is under discussion? I would think that that would have some relation to the required robustness of the guard.
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2 HP CNC knee mill with 3 HP peak HP (makes it sound like it was sold by Sears, but the 3 peak HP rating is for up to 30 minutes). Max spindle speed 4,200 RPM, but I would probably run it under 3,000 RPM.
i
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I have the Flexbar guard on a Clausing 5914 with a ~2 HP motor, and a max speed of 1900 rpm.
Iggy has posted the details of his mill.
Joe Gwinn
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