[Zumba]

I'm thinking about making a 2-axis CNC profile knife grinder for use in shaper cutterheads or a W&H molder. Sure would be nice to be able to grind a pair of 6" crown molding knives out of tool steel for $20.

Has anyone seen something like this done? I'm thinking about utilizing a 4.5" angle grinder, ball screws actuators and stepper motors.

[wizard]

There is another guy who just posted about a similar issue in another thread. In his case he wants to grind knives that you cut meat with. So his interest is similar atleast to yours.

As for your grinding I would suggest that what you really need is a grinder or grinder arbor set up that takes 1-1/4 inch wheels. Mainly this size ardor provides access to many types of wheels that may be suitable for your idea. As to the actual grinding with CNC I'm not sure there is a low cost CNC option for that right now. You are in the area of experimentation here.

If you don't find the other thread post back. It is only about a day or so old so there is a good chance some more info might drop in soon.

Dave

[Smackre]

You are going to have trouble finding software for it. Problem is to grind knives like you are talking about it requires more axis. You look at a set of molder knives or W&H knives and they look like 2 axis. But the side clearance that you half to put on it are also axis. To grind effectively you need 4 axis at least i beleive. Thus why most cnc profile grinders are 5 axis. At work we have a Walter 5 axis Power R. A better option to you may be a used profile grinder and a cnc router to make the templates for the profile grinder.

[Jim Estes]

I have made a few sets of cutter knives for a molding cutter. I made mine from D-2 toolsteel and rough milled them with a tapered cutter. Then after heat treat and flat grinding, I re-cut the profile with a fresh sharp carbide cutter, they worked great.

Jim

[Zumba]

Thanks, all.

Jim, that is a great idea. I've been holding off on converting my industrial hobbies mill to CNC... I think I'll have to bite the bullet now.

How does D-2 compare to A-2? All I know is that A-2 is used in handplanes. For your flat grinding, do you do it by hand on a stone or do you use a surface grinder?

[Jim Estes]

Zumba,

D-2 is a bit harder to grind, I use a surface grinder, and when grinding D-2 I have to re-dress my wheel much more often, but I use D-2 flat ground so there really isn't a lot of grinding to do. I basically finish mill everything and after heat treat I just take enough of a cut to remove the scale and get a nice sharp edge. D-2 can be heat treated to a much harder Rockwell hardness, but I draw it back to basically where A-2 would be 58-60c. You could even use S-7 which typically treats to 52-54c. I don't use the cutters myself I have a friend who is a cabinetmaker and he wanted some special cutters made, so I did them for him. I had the D-2 laying around so that's what I used. In the future I will use A-2 which is much less expensive and easier to use. He is talking about making several more sets, so I was considering making up several "blanks" and then WIRE EDMing the profile after heat treat.

I was talking to him about how the first set was holding up compared to the "factory made" sets he has, and he said that he couldn't see any difference in the quality of the cut now compared to when he first got them. Sharpening them is as easy as grinding off 0.005" of the thickness, although I haven't sharpened any yet.

The tough part of making the cutters was getting the back cutters (that cut the 45 degree angles on the back side of the crown molding) to be at very close to the proper level to cut the back without adjusting the cut height with every board. The first set I made, the back cutters had to be lowered way down close to the table in order to cut enough of the board. This was a problem because he had to raise and lower the cutter blades every time he went to cut more molding. I solved this problem with the second set of back cutters I made. I drew the back cutters and the profile cutter together in my CAD software and then I used this drawing to locate the distance to the spindle so that they would be at the same height when cutting. This makes each set of back cutters only work this way with the set of profile cutters they were designed for. But he won't be mixing and matching a lot of moldings. He said it was well worth the little bit of time it takes to raise and lower the cutters for a molding that might cost $50.00-$75.00 for a 12 ft length.

Jim