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We have a 4x8’ bed CNC machine at work for cutting plywood and have been looking at ways to reduce man-hours running it. At the moment we have screw clamps around the perimeter and then once the machine has drilled the holes in the ply we drop M5 bolts through them and screw them into threaded inserts that are on the underside of the bed. This works fine but takes time, especially as the bolts and t-nuts (threaded inserts) wear and then cross thread due to the sawdust.
I’m 95% certain our ply is too porous and our patterns too full of small parts for a vacuum bed to work.
Bright idea is to fit air core coils underneath each hole, power them with a low voltage DC supply and use the electromagnetic field to pull the bolts into the cores. We don’t need tons of clamping force, just enough to resist plywood warping/lifting as the sheet is machined and to stop lateral movement as the cutter works.
Started looking into the sums for this but as this forum seems to always have someone who knows tech stuff in every niche I thought I might as well ask!
Gut feeling is you'll need a really big coil and a big piece of steel. A bit like a magnetic sheet metal folder but with less force. Which is lucky as the force goes down rapidly with distance between the magnet and the metal. If you want to DIY it try this video:
Have you thought about pneumatic clamps? They're not that expensive and probably easier for your application
As now but machine two quarters on the bolts and nuts flat so the bolt drops in and a quarter turn later is secure?
edit - maybe not if wear is a problem
Our machine had a vac bed and it worked really well. You needed to fill the bed to cover all the holes, so if the material was less than 8x4 you had to add some scrap pieces. Once cutting it stayed very well stuck down. Had a pretty massive pump. Vacuum force is surprisingly powerful, I wouldn't write it off
That's good to know about the vacuum bed - maybe it could work for us? What material were you usually cutting on it? What did you do for the sacrificial bed?
I'm now wondering if there's some potential man-hour wins if we could take advantage of a tool changer to allow us to remove the tabs between parts with a small diameter peck drill, as well as saving on clamping time with the vacuum system...
If anyone's curious this has rather escalated and it looks like we're probably buying a hefty new CNC machine. Any had any experience getting three phase installed, or running off a phase converter?
If you’re in any sort of industrial kind of unit I’d be amazed if you haven’t got a three phase head installed already. Using a single to three phase inverter will obviously work but you do lose some top end speed and torque of any motors. They work well for hobbyists in a shed with a small lathe etc but not sure it’s the right solution for a work environment
"If you’re in any sort of industrial kind of unit I’d be amazed if you haven’t got a three phase head installed already."
Pretty certain it's a single phase head as there's just one fuse. Have just been to inspect and looked at the unit next door but one (there's five terraced together) and that has three fuses but they upgraded to three phase power in 2019 at a cost of about £5.5k. Seems an odd oversight but down here it feels like everyone has forgotten that manufacturing still exists!
We're looking at adding a compressor, air tools and a spray booth which will all work better on three phase so I think we're going to need to upgrade too.
Seems an odd oversight but down here it feels like everyone has forgotten that manufacturing still exists!
At least you’ve got electricity, and not using steam…