Hold-Down Tips and Tricks

How to hold down materials that are too rough for a workable vacuum seal. February 12, 2010

Question
I need to machine 17mm thickness sheets on a CNC engraver/router and require suitable clamps which can secure the sheets down but still allow me to machine all of the top surface. Can anyone suggest the best method/item to use? I have considered Veritas Wonder Pups but the shank is slightly too long. I do own a vacuum system but the sheets are not perfectly flat each side so this method is not viable.

Forum Responses
(CNC Forum)
From contributor K:
Sheets being not flat is about the only problem I run into these days. You can fix it down on some other MDF sheet with screws is the waste part of the sheet, and have the machine drill the holes so you know where they are for avoiding. You can put weight on it - dumbbells or window counterweights. You can use (clear ) packaging tape on the edge of the sheet and spoil board so the vacuum can't leak - this is the best.

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From contributor D:
If the Wonder Pups are close, why not "kiss" them a little bit until they clear?

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From the original questioner:
I actually thought of cutting the shaft slightly shorter but if there is anything else on the market that I can buy without altering the item then that would be preferable.

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From contributor B:
For material that we cannot clamp or vacuum we use plastic nails fired by a special nail gun just for plastic nails. If they happen to be in the way your tool will harmlessly cut them but the part will still be held. To release the part, slide a very thin metal strip under it and cut the nails. It works great.