[a_johnson]

Hi

I am new with CNC and have a safety / cutting question.

I have been cutting 0.15" aluminum plates on my little CNC, various cuts and shapes from small holes to about a 1" hole using a 1/8" upcut bit.

Now when I cut, I always 'pocket' which takes a lot of time. I have been scared to cut as an example a 1" hole just by just cutting the inside profile since I imagine the left over metal in the center of the hole could catch the cutter and fly off (towards me) at 500 mph. Now is that the case or when cutting a inside profile of a large hole does the left over metal just fall away?

Thanks

[tony978]

that is what plexiglass if for to slow down things like that . get a pice 1/4 thk. from the local hardware store . also the pices have such low mass they don't fly too fare but if caught right they will , no that is with a standard endmill . Inserted tooling can and will make things fly faster . you can slow your feed down to 25-50 % of what your running and the slug will drop .

[neilw20]

Make a big hole, like 3/6" at the end of where the cut will be and when it breaks through, there will be nothing to react against.
The cutter will just push it aside, that is, if where you have been cutting is not full of chips.
Never let the cutter eat it's own chips, for good cutter life.

[dertsap]

imagine the left over metal in the center of the hole could catch the cutter and fly off (towards me) at 500 mph.

Thanks

at such a low rpm you don't need to worry about the slug flying at you but it is possible for it to get caught up and break your tool , a good thing to do with plate is to use a sub plate and drill and tap holes where the slugs are going to be , then once you clamp your plate down(the one to be cut) , drill holes at those tapped locations and bolt down the slug before cutting it

[InnovativeMach]

It's better to worry than not to worry around machinery. Lots of older guys in shops I go to have a couple less digits than they should. I've never had chunks of material fly at me like you are saying, but those hot chips that fall down your shirt always make me jump around. Good luck, after awhile you will get a feel for things and it will get less "scary".

Used CNC

[roninB4]

Safety should always be a concern so you're smart to ask before trying something that you think might cause an accident.

As the cutter works it's way around the circle it will leave less support/attachment to the rest of the plate. If there's a center "slug" it will begin to vibrate when the remaining "bridge" decreases. There's a good chance that the vibration/deflection from the "center slug" can/will affect the cutting action on the ID if you have surface finish requirements. Where possible, I'll try to put a hole through the center of the slug and bolt it down so it doesn't move. If not possible, I'll use the eraser on a pencil (wood) to dampen vibration and influence the direction the slug will take when it breaks free. You can use a hole saw to remove the excess material and then go in for the finish cut with a regular cutter. You can also leave the "bridge" and plunge cut the attachment so the plug falls out of the hole rather than being in contact with the side of the cutter. Sometimes I'll plunge cut the entire circle/pocket, leaving some material for the finish profile cut. You can also do almost the entire profile, stop the program to twist out the slug, then finish the cylce. I'm not very fond of the last method but there's several suggestions you can try and pick one of mine or from the other posters. Good luck, err on the side of safety.


OBTW- The other posters were correct about having machine guards (like plexiglass) in place. I've been doing machine work for 25 years, ALWAYS wore my safety glasses and STILL occasionaly had chips get past my safety glasses. It burns, can cause loss of your eye(s), and makes you dance at inopportune moments (the machine is still running....). There's also the old diemaker adage of losing one finger for every ten years of service. Please be careful.