molding knife profile

I've been making custom molder knives for an older 12" Belsaw Planer/Molder. I suspect the RBI uses the same knives. (Mine are 1/4"x

1-1/2" for 3/4" stock) I also do some mini kives that mount in the center of the head, max of 1" wide, made from .134" (??) stock. These are the same knives used in the Sears molding head.

IIRC, the knife is held at 30 degrees off of tangential, the back needs at least 15 degrees of clearance so the cut angle needs to be at least

45 degrees, more is helpful for chip clearance.

To make a profile the width will be exact. The knife depth will need to be increased by the desired depth / cos 30 degrees. I am usually copying old molding so I just cut it off at 30 degrees, trace around the stock onto a piece of knife stock with layout dye, and hand grind it. If you try and EDM it, you could pluge through at the 45 degree angle but you would still need to have the EDM profile slightly different than the original since the original will be based on the 30 degrees, not the 45 degree angle.

I'm us> Having recently acquired an EDM machine, and having a RBI 816 molder,

So are you using knife stock, or just "plain" A2 bar stock and then grinding an edge?

I think what you are describing makes sense to me. I should just do the same. Take a small piece of knife stock and try to copy an existing profile and see how close I come out on it. Would be a worthwhile experiment.

My molding head uses the corrugated knife stock. I am not sure, but I think it can hold plain back with different gibs, but I like the positive holding of the corrugated.

Thanks

Jeridiah

My head uses just plain bar stock, smooth on both sides. I usually put larger knives in the surface grinder and take a finishing cut of a couple thousanths to take out any heat treat warpage. And I use just plain A2 bar stock. I've been pleased with the hardness, toughness, and low warpage. And I really tighten up my gibs!!! The knives weigh around 6 oz for the larger ones, pretty scary thought about them coming out.

For just occasional knives I rough grind in my chopsaw. I stick a slide table made of 3 pieces of 3/4" boads in the vice, and use a 4x4 wood block with a 1/4" slot in the top. Everything is sized so the angle of the blade is correct and I can clearly see the marks of the profile I want. I then head to the bench with a die grinder, air cutoff tool, V files, etc for cleanup. On a good day I can start with a sample piece of wood, be running a test piece in a couple of hours. If I only need 50 feet, I don't even bother heat treating. If it works out, I bring it over to the lab and run it thourgh the furnace and surface grinder.

FWIW: I can usually get a good knife or a good c> >

Sounds encouraging. Mine is the same. When molding it uses a single knife. When planing it uses all three.

I will order up some knife stock and take a whack at it. Probably the cheapest stuff I can find. I dont' see need for the extra special stuff available. Not looking to run several thousand feet of anything. At least at this point. For sure plan to make a few scrap knives anyway.

JW

You are correct in knife shape not being tangental from patern, although this does give you a close approximation on some contours. To create the knife shape from original pattern the knife pattern has to be drawn by projection taking into account rake angle of cutter head. Another consideration is that each time you mount the knives in the cutter block if they protrude a little less or more than previous time the shape is slightly different, although not enough to be a problem unless you are butting the two pieces together.