|
|
Kerfing Plywood for Bending with a CNC Router
Question
Note: I don't see the need to buy kerfed plywood when I have a router that will make it for me.  Forum Responses
From the original questioner: Well, that would be nice, but no. I can duplicate it with a router bit quite easily though. I'm just looking for guidelines that tell what spacing and depth for certain radius. From contributor S: Try "The Complete Manual of Wood Bending" by Lon Schleining. From contributor G: Practice on some drop to get the result you want. Then cut the final piece. You may find a .125 millend, while thin, won't give you the bend you want. Too much flat in between for the thickness of your material. Do they even sell bendy .750 ply? From the original questioner: Oh yes, they sell the brand name Kerfcore in pretty much all thicknesses. And yes, I could practice on some drops. I have nearly completed programming the object, and if no other information appears, will probably begin experimentation tomorrow. From contributor N: We've done a fair amount of kerfing in the past and have run into numerous problems doing it with a router bit. We've worked through most of them, but it has taken a large amount of trial and error. We started with an 1/8 bit and broken too many, so we went up to 3/16. This worked better, but two more problems arose. If we used an upshear bit, the force would cause delamination of the remaining material. If we used a downshear bit, the kerfs would be packed with chips that were a pain in the behind to remove. If we didn't remove them the piece would usually snap before fully forming it. We finally went to 1/4 downshear with 1/4 spacing and it works well for what we are doing, which is mainly starting step stair risers with 4-7" radii. Your plywood quality will play a huge role in this. We run full sheets at a time, with 4-7 risers laid out on them. Some sheets machine very well, some don't. It's not unusual for 25% of the kerfed pieces to separate between the plies. Any reason not to use two pieces of 3/8" bending ply for these?
From the original questioner: No reason other than I want to use our CNC router and not buy special material. Thank you for the information. It's good to know that I'm close to what you have. I'm using a 1/4" downshear also. I may want to make the kerfs closer together, but 3/8" spacing makes it difficult to nail without chipping out already. I cut out a piece yesterday 3/4" x 4" x 95-1/2", with 1/4" kerfs, 3/8" apart, and 1/8" left in the kerf. It didn't score the first lamination and it broke before fully formed. I think that the remainder needs to be thinner. So, I'm cutting another today only leaving 3/32" in the bottom of the kerf and see what happens.
From the original questioner: Well, that did the trick! All it took was cutting through the longitudinal lamination and scoring the cross lamination next to the veneer, and it bends like there's no tomorrow. I might have a problem with the flats telegraphing through, but one problem at a time! From contributor K: Why don't you try making plywood ribs and using layers of bending ply to build up your thickness and then veneer it with whatever wood species you need? By the time you are done experimenting with different tooling and materials, depths, spacing, etc., you should have just spent the money and bought the correct pre-kerfed material. It is more cost effective to outsource certain things than waste your valuable time, not only man hours, but machine time also. The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment). Comment from contributor R:
Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Have you reviewed the related Knowledge Base areas below? 
|
