Guard around milling table

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.

defiantly $LEXAN$

Lexan :=3D=3D Tuffak :=3D=3D polycarbonate is shatter resistant Acrylic:=3D=3D plexiglas :=3D=3D 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.

I just put up a page on my own take on a coolant shield. It is decidedly low-tech, but works well.

Jon

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

I can't imagine anybody using trichloroethane today. Acrylic - Plexiglas - seems to handle oil and typical coolants just fine.

Jon

*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.

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.

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:

i

AIR, acrylic has better clarity than polycarbonate. The Tormach CNC mill uses 3/16" acrylic guards and that has worked fine for me over the past 3 years. A word of warning though - plan on higher guards than those in your referenced picture if you plan to use coolant with face mills, flycutters, or other large diameter cutters. They really fling the coolant around.

Mike

Something that has occurred to me, but I haven't implemented it yet, is to put a lip on the top edge of the shield. What I have now tends to bounce some of the chips/spray over the shield. An inward-facing lip at the top might deflect those chips to stay inside the shield. Major flying tools might be able to break 1/4" Plexiglas, but that would absorb the energy of the projectile. We are not talking about bullets, here!

Jon

As an aside, at IMTS-2000, I think, a machining center was demonstrating a cutter turning at around 15,000 rpm (CAT-40, IIRC). One came loose and went flying out into the crowd, missed the people, but hit another machine and bent the sheet metal enclosure like it had been hit by a truck.

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.

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.

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

...

With thicker plastic, it probably would make sense to add a thin easily-replaceable layer on the inside, using eg 1/16" acrylic, which is available inexpensively at many local hardware stores.

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

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

What size machine is under discussion? I would think that that would have some relation to the required robustness of the guard.