Jamb Hinge Machining on CNC

      Tips for a tricky CNC problem: holding down and referencing door jamb stock with a grooved back. January 10, 2006

I am having problems machining door jambs on the CNC. Because of the kerfs on the back side of the jamb, I can't get the suction to hold down the jamb. I tried using hand clamps, but I'm still not holding my tolerances. It's worse when the jamb has a twist or bow in it. Can someone help me?

Forum Responses
(Cabinetmaking Forum)
We use suck through for most of what we do. Whenever you need some additional help holding on to irregular or warped pieces, take 2" masking tape and tape to the waster and the piece. This creates a seal and helps to concentrate your suction. You should also already be masking off the rest of the table or you'll leak too much. We have scrap Sintra that we use, of various sizes. If you're using pods, I would think you could do the same thing, but it would be harder if you can't reach them with the work piece on top. Another way is to use soft foam tape and let it compress into the irregular areas.

How about a dedicated fixture that is shaped for the backside of the jamb? This and clamps on bowed parts should give you what you need.

We also tried machining hinges in jambs, but like you mention, the grooves in the back made it pretty hard. We also found we were tying up too much valuable CNC time to run jambs. We ended up buying a jamb machine to do them by hand, although some good routing jigs cut on the CNC has also worked very well using a hand router.

If the grooves on the back of your door jambs are consistently spaced the same on the different jambs that you are machining, consider making a fixture which has the same size grooves machined into it, but on a mirror image. Then place a strip of some type of non-porous material into these grooves that is exposed above the fixture to the same depth of the grooves in your door jamb. This will not only prevent the vacuum from leaking out, it will also assist you in referencing the part much easier.

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