Re: [CAD_CAM_EDM_DRO] part holding

Rick,

Thats the $64,000 dollar question for the day. And not one that can be answered in a few paragraphs. There are whole books devoted to the subject of set-up. With an infinite amount of methods and factors that come into play. The desire to machine a whole part in its entirety with just one setup operation is what every machinist strives for. However, often times it just doesn't work out that way. Experience is the best asset. Your broken end-mill and ruined parts are the cost of learning. I've been slingin' chips for over twenty years and I still have things move during setup. Still forget to add my edge-finder when moving to zero zero reference. and so-on
Some parts may spend a little time in the vise then go on an angle plate or sine plate. Often many,many steps. Anything you can machine in the vise is the best way to go. If you wish to machine a thin part in its entirety and it has holes in it, then bolt it to a plate secured in the vise or to the table. If it doesnt have holes in it, put some in it. Often times it doesnt matter if the holes are small. Even an 8-32 screw will hold a part securely. And its all just judgement call, the more material you are attempting to remove the better securing of your workpiece must be obtained. Sometimes I even tack-weld thin pieces to a larger block then just make the last step the perimiter and machine out the welds, Thats a great trick for bandsawing large diameter tubing thats too short to hold. Explain to your customer that you have no other way of securing it. Prior to machining it of course. Think about how many production parts you've seen with holes that were merely placed there for
the aid of manufacture.
As far as machining through your clamps (chuckling...sorry) One needs to make sure the safe Z is set to clear all clamps and fixture. And thats generally done by knowing the general path of entry and traverses and just use a scale. If you have a 3D toolpath and can see that there are no erroneous moves. There is no sin in dry running the routine with no part in the set-up. Running the old tape readers if we didnt dry run, the outcome was disasterous. Even now if I'm machining something and only have one shot at it, I still dry run.

Ron

skykotech <rick@...> wrote:
The hardest part about cnc is not the electronics, the servos, the
ballscrews. The hardest part is holding down the friggen part! I
just ruined yet another brand new 1/2" made-in-usa endmill when my
program had a rapid that went .010 too close to a holddown clamp at
120IPM. Doh! I wouldn't have had things so close to the clamps if
it were not for the fact that I wanted to machine everything at once
without remounting the part. How do you guys hold down a part when
you want to machine 5 surfaces on it? Vacuum table? Glue? :-)

Good thing Enco still has that free shipping going on...sigh




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