You have to mill about 100 thin slots (about 0.050 wide by 0.100 deep and 12 inches long) all on one surface. Also a dozen or so drilled and tapped holes. Plenty of clearance for conventional clamping on all sides.
If the blank is purchased already cut to size, machining only happens on one side.
What would be the best workholding options for such a job? Is this a case where vacuum fixtures are a good idea?
My thinking is that it would be good to build an indexing subplate with hard stops on two sides and clamps (mitee-bites?) on the other two sides. If done properly you could drop a blank into this, clamp it, push go and walk away for a while.
Coolant and vacuum can get ugly. The tapping would shy me away from mitee-bites. A fixture with four or more Destaco style toggle clamps and the locating pins could fly. JL
I've been running coolant and vacuum for years. Many, many tens of thousands of parts. Use a coolant seperator in the vacuum line, it drains back into the coolant tank. Made from some 4" PVC. Two seperators, with valves, one can drain, one can seperate.. in theory. In reality, only had a couple of cups of coolant into the vacuum system after a 10 hour shift. Total. The first attempts had a high leakage rate, until I got it nearly perfected. Sometimes not even a cup of coolant after a week of running.. With the right fixtures.
Cool, we'll have to try that next time around. We ran fairly small plastic parts that were hit and miss on holding. Our pump might not have sucked enough. Or it didn't like the coolant we did manage to run through it. I would still have reservations about 15" X 20" stock cut aluminum being flat enough to keep the seal. Probably wouldn't want to drill into one of the vacuum holes. Lights out unattended also a minus. Ok, I'm a wuss - throw one part at me and I'm scarred for life. JL
How many peices? are the D&T holes thru or blind? The # of parts would tell me if I wanted to make a subplate for it.
I've never used mitee-bites but your slots are small, if your d&t are small you have very little cutting forces, so I don't think you need much clamping.
A friend of mine swears by mitee-bites. Every time I've mentioned them here the reaction seems to be luke-warm. What are the issues with this clamping approach?
First, lets reverse this.. Small parts, not a great candidtate for vacuum. Figure about 10-12 lbs per square inch of downforce, planning for the routing of the gasket. Smaller parts, not enough downforce. Larger parts, No worries about being flat enough, there is Plenty of pressure to flatten it out! I've also made lots of very small platic parts, but didn't cut them all the way through. Made like a cookie sheet, cut down to .005 of going through the part. The last cut you make is around the rim of the part, and not all the way through. Parts just snap out of the sheet, and are simple to deburr.
A 15" X 20" part, you can figure at least 1.5 tons of clamping force. Through holes just need an O-Ring around the through hole area.
Parts I used to run were 12" X 12" and had about 30 through holes. There was an O-Ring around "populations" of holes. Even though that little island of holes deducted from the pull down force, there was still plenty fo downforce.
The little plastic parts were about 1" X 3" NO wheres near enough surface area to vacuum clamp. But in a 12" X 12" sheet, there was planty of force. There are tricks to play to "grab" a non-flat part too... Basicaly, I built a floating subplate under thepart, that could "rise up" to meet the non-flat part. There was a subtrate, and a floating plastic sheet above that, O-Rings on top of the plastic shet, and the part on top. The plastic sheet would pull up to meet the part if it was not flat. Being pinned out at the four corners, it was fixed in X/Y dimensions.
Finally, 500 pieces per year???? That sounds like a few days maximum of running time!! I'd really LOVE to bid on that job. With those small slots, I've got a
24,000 RPM Robodrill that will BLOW AWAY a Hass or Fadal for parts time. There could be no way to justify setting up a machine shop for that volume of parts. I can't imagine it.
In this case you are talking about a 15" X 20" sheet. Think about the opportunity for the sheet to buckle up in the middle. For small parts, they are amazing! Well not just small parts, but stiff parts relative to their dimensions. I made a bunch of cams out of D2 steel, Hogging out a slot with a
1.25" cutter, cutting a deep channel. The parts were held down with MiteeBite Pitbull clamps. Blow you away how they held. Another thing is you need some consittancy for you clamped part dimensions. The MiteeBits can have limitations in their grip range. You can make plate fixture in a few minutes that can hold 20 parts with MiteeBites, and rune them all at once. Made some fixtures to make some door lock parts, 16 parts at a time.
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