Hollow Grinding Setup / Process

E

Edward SE

Joined
Oct 12, 2001
Messages
16
I am going to build some utility type of blades which will have hollow ground cross-sections and very utility (Ruana / Randall) finishes. I would like some input on how anyone familiar with this blade geometry and finish does it. I have bushings and flanges being built to mount both ten and twelve inch wheels (100 grit Aluminum Oxide)to an arbor which will be driven at 1725 rpm. That's as much as I know. I plan on building a platen to rest the edge of the blade on as I draw it across the face of the wheel - thinking this is how to get a very straight grind. I have seen grinds which both continue straignt (Randall) and also those that curve up to match the curvature of the cutting edge (grind lines that stay perpendicular to a tangent line of the edge). I'm getting better at freehand grinding but why make life difficult? And I have a Beartex (AlO2, 9 hardness) wheel which seems to give close to a Ruana finish on the blade, comming directly from the 100 grit wheel.
Could I get some other views on the process / tooling used?
Thanks,
Ed
 
Ed, I have been in the Ruana shop and talked to Vic Hangus and his grandson Chris. They rough grind the slighly forged blades with a 6-8" stone wheel and finish after heat-treating on a hard felt 6-8" wheel. The felt gets repeated fresh coats of melted abrasive compound called "JacksonLea Plasticlad" It is a greaseless abasive composition for satin finishing, burring buffing and polishing. I think the C grade is about 150 grit. I was amazed at how Chris could freehand for perfect grinds and finishes with this stuff. They have a belt grinder but seldom use it. All their wheels and felts are given to them by big companys as worn too small.
 
Howdy There...!
Not real sure if I understand your question correctly, but I will give some info on how I hollow grind blades. I have a 2"x72" belt grinder with an 8" contact wheel, directly in front of the contact wheel there is a "toolrest" that is approx. 2"x 3". This toolrest is is located just below the centerline of the contact wheel. I take a small block of metal and clamp it to the toolrest with the profiled blade between the block and the wheel. Push the blade against the contact wheel and tight the clamp to hold the block into place. Then adjust the toolrest back away from the contact wheel until you get the angle of grind that you want. For each diameter contact wheel the grind line will chance, in other words the depth of the grind from the cutting edge to the top of the has a max. depth. If I can be of any more help please send me any email. Good luck and just grind to get better.

Later "Possum":cool:
 
That brings up a good question Bruce. Why (or maybe you do) don't you (professional knife makers) use hard stones more. I have one on one side of the new grinder I made. I've made 4 knives now and used two belts. Aside from removing the initial scratches with my first grind with my belt, I can't see any difference in results. It eats excess steel at high speed and is easy to control at lower speed. So far the wheels have been a big money and time saver for me.:confused:
 
Peter, You are right. The stones are less money and do a good job for roughing. The trouble is they need constant attention to keep them true. They must be dressed very often to prevent overheating the steel on the regrind. I use a big stone for my damascus to remove lots of metal fast but always head for the burr-king to make things look nice. Stones also keep changing sizes because of dressing, not a problem with belts. I really like to hog off forging scale to save on belts.
 
Thanks Bruce. Glad to see you are using them also. I've found that if you aren't using something, there's a reason other than you never tried it!
 
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