Miter-Fold Methods for P-lam on MDF

CNC pros discuss tool choices and cutting and assembly techniques for miter-fold cabinet box construction. May 15, 2008

I have a job where I think miter folding will speed things up greatly. I purchased a Vortex insert cutter at AWFS and have done some testing with straight MDF. We have a large run of 5 sided open boxes approximately 24x24 with 5" sides. Do I cut all the way through the plam, or leave enough of an onion skin for glue up and then clean it up with an air file? If I cut all the way through I'll have 5 separate pieces and would need to make a jig for glue up. I've read about using a tape for the joint. Is this being applied before cutting or after cutting?

Forum Responses
(CNC Forum)
From contributor K:
The preferred method would be to tape the lam side first and then cut most of the way through, leaving about .005"-.010". This works best with an aggregate and 4th axis. You can do it with your cutter, but more than likely it will be difficult to maintain a clean edge. That type of cutter has no tip speed so you will wear the tip off quickly and end up with a blunt edge. You would be better off cutting .062"-.125" past the surface and then taping the parts together. You should not need a jig for glue up. Tape, flip, glue and fold.

From contributor M:
Contributor K's method may work for some, but I have never had good luck with it. What works best for me is cutting all the way through, even if just by a very small amount. This gives the benefit of actually having a small but finite radius on the tool with which to cut the abrasive plastic skin. Then I turn the parts over and tape them with clear plastic packing tape. This is better than masking tape, since you can see the joint alignment clearly, and also because the packing tape does not stretch at all. You also don't have to lay out all of your cuts on nested sheets from the back, which is a pain in the butt.

There is a lot of debate on whether to use a true 90 degree cutter, or a 90.5. It is actually difficult to find a true 90. Vortex's bit is 90.25 to 90.5. Most others are 90.5 plus. That's okay for a fold that is not seen from both sides, but it is really aggravating for one that has to be seen from the back as well, as for upturned wing shelves on commercial jobs. 1/2 degree off on a 6" upturn looks bad. I see no use for anything other than a true 90, but a lot of people will argue with me on the point, especially the tool salesmen. They cite the need of space for glue often, but anyone who has worked with glue knows that no space is a very good thing, otherwise we would be slightly mitering all of our edge set boards.