Hello.

I am curious as to how a vacuum chuck holds down the workpiece efficiently if the workpiece is not big enough to cover all the holes that the vacuum is applied to ?

Can someone please explain ?

I've never actually seen one physically, to get to play around with it and try find out, poor deprived child that I am !

They don't.....In order for a chuck/fixture to pull a vac. all holes must be covered and sealed. Think about pouring water into a bucket with holes in it...if the holes aren't plugged the water will leak. Maybe I'm not fully understanding your question....:confused:

Usually it's a grid and each square in the grid has a hole in it and between each square (the grid lines) are grooves cut into the base. THere is a rubber like gasket material that is just a long string and you put it in the grooves to make a sealed area of the size you need. Then, when you turn on the vacuum, it sucks down and the seal is good.

If you don't get what I'm saying, let me know and I will take a pic of one I have in the shop to show you.

you can use check valves and different grid sections to make the remaining holes seal up. and when the stock is placed on the table the stock will push open the check valves and you will have the vacume in that area only.

Thanks guys.

I think I get it now.

I thought the holes needed to be blocked, but just didn't know how.

Cheers !

:banana:

The vaccuum table we had at school had a sub-layer with channels in it, on top of which you put a sacraficial piece of 1/4" mdf. the vaccuum was strong enough to pull air through the mdf. Any size piece of wood set on it would be held securely. A vaccuum system with that power isn't cheap though.

I think a lot of vacuum systems pull enough air that some holes can be open

You can have different zones, with a shutoff valve for each zone. So you don't have to plug un-used holes.


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I'd want to plug any unused holes so chips don't get in them potentially messing up your pump. Check out http://www.nemi.com/grid_table_fixturing.htm
It's a cool modualr system that I saw at IMTS.

Hope this helps y'all out.

I have heard of putting plastic wrap over the whole chuck with the part loaded on a surface grinder and then grinding away. I suppose the plastic would have to be several mils thick.