cutting Parts from a plate... need some tips

[Bird_E]

hello,
I just finished my CNC conversion and have started to experiment by cutting some parts in 1/2 aluminum plate. The problem is, after cutting the profile of my part approx .200" deep in a 1/2 plate... what is the best way to cut the part out of the plate. I see that alot of the parts that I want to make will require some method of cutting them from a plate. I just don't know that the best way is. Anyone have any tips?
Thanks!
BOB

[Jim Estes]

I used to cut a lot of parts from plate, not much lately though. I usually would clamp the plate on top of aluminum pads. These pads were wide enough to keep the plate level and thick enough to allow the endmill to pass through the top plate without touching the table. If a part has a hole machined into it, machine the hole first and then use it to clamp the part down on top of some pads (same thickness as the pads holding the plate).
The tough part about cutting parts from plates is that you don't have places to clamp close to each part, so why not drill some holes, slip some pads with holes in them underneath, and then bolt it down there.
Another approach to this it to cut the profile of the part in steps, for example, a square part can be cut on two sides while holding the plate by the other two sides, then switch the clamp positions. Just remember to use a third clamp so that you clamp a new clamp before loosening an old one.
At a former job, we would clamp a dozen sheets of highly polished brass (with the plastic wrap still on) between two 1/4 inch plates of hot rolled plate, and then machine the whole thing in one pass at full depth, the parts looked great, and only had just a small radiused tab the had to be machined afterward.
I also remember cutting some parts that had some really intricate details, the best way for us to cut them was to actually cut two at a time and when they were finished, cut them in half, leaving two prefectly finished parts.
Another suggestion is to plan on having stock to hold a part by whenever you plan the cut at the bandsaw. I routinely cut stock for turning work with enough stock to hold it in the lathe chuck securely.
Something else I have done is, when finishing parts that need to be 1/2" thick, cut them out of 5/8" stock, machine the profile to 0.505 depth and then turn the plate over and machine the stock off of the back of the plate until the parts fall out. Be careful when machining the stock, the parts will want to jump around whenever the stock gets thin. With steel parts, the last little bit of stock can be ground off with a surface grinder.
Just some suggestions that came to mind.

Jim

[Jim Estes]

I just remembered somethign else we used to do. Say you want to machine a tuning fork with long thin forks. Machine the forks with a really long slot but without cutting out the ends seperating the forks. Then take the part (with closed end) and stick a piece of stock into the slot and clamp the whole thing up in a vise with the end to be machined sticking out one end. Now you can machine the end of the forks, seperating them without worrying about them collapsing.

Also you can machine long thin stock by holding it between two pieces of thick bar stock, this keep the part from vibrating too much.

Jim