Grinder + wood... how slow do you have to go?

Chiro75

Chiro75

Joined
Feb 4, 1999
Messages
5,786
I recently finished a knife with curly koa and even with my grinder going as slow as possible (800 RPM) the wood was scorching. What I noticed was that only the end grain, so the sides of the wood at the spine, were having problems. I could run the grinder no problem to remove wood from the surface of the scales, but the ends scorched like crazy. Is that just how it is, or do you have to go even slower than that, or do you forget the grinder altogether and just hand sand/file? It was really quite frustrating. Is this what I have to look forward to with all my wood handles in the future, or is koa just really prone to this? That was the first wood handle I've done on the new grinder and it sucked, truthfully (although it turned out really nice in the end). And using different grits, fresh belts, etc didn't make any difference. In fact it might've gotten worse with finer grits. Even using the lightest pressure and the quickest pass on the belt scorched.
 
I use fresh 60 grit to rough in at the grinder.
Then use 60 grit by hand and go to 400 grit. Oil and 0000 steel wool. Thats it.
 
I've never used Koa but used to get alot of problems with scorching wood until I started using fresh belts. Now I only use fresh belts when shaping the handle and then move those belts to the blade grinding pile once they no longer feel as sharp as new.

I use a 32 grit belt to rough shape then 60, then 120grit (I do alot more shaping at this grit), then 220, and 400. After that I hand sand up to 2500grit on the bolsters and handle.

I some times still get a light scorching on the end where you are talking about at 400 grit but it is light and easily sands off when hand sanding. Usually this is still because the belt is wearing or I've used too much pressure.

Try another wood with fresh belts only and see how things go.

Sean
 
Koa is really fragile in other ways, too, and like I said, the ends were the problem, but the surface of the wood was fine regardless of what belts I used. I have some nice cocobolo around that I might as well use because it's allergy season for me right now, so why not add insult to injury and check it out? :D I'll report back next week with my results.
 
Koa burns very easily (as you've noticed).

Brand new belts - go slow and move the piece around constantly. As soon as it starts to burn more frequently, change the belt.

Like Brian, I usually only do rough shaping at the grinder. I do the rest by hand. Usually I'll do 60 and 180. Then go back to 120 through 800 by hand.

And sand with the grain the best you can. ;)
 
Switch to a bumblebee sander and you won't have that problem (otherwise referred to as a palm sander or random orbital sander). And you'd be surprised how much wood a bumblebee can remove with a 40 grit disk.
A 40, 60 or 80 grit disk for the rough in, then a 100 or 120 grit disk, then hand sand with (220 grit optional) 400, 600, and steel wool.
 
Also use a belt cleaning stick often. if you have not heard of them they are rubber or plactic. They pull the wood out of the belt grit. I have found the end grain on all wood scorches easyier. I use belts to shape leather sheaths
also same thing new belt no scorching.

If you are just learning the tricks with belts try also not grinding on the wheel but just up from it on the slack of the belt to give a curve. watch the edge of the belt does not cut into the wood faster than the flat.

edit..... I go down to 600 on the grinder on most place on the handle. some hand sanding is required.
 
I had problems with burned handles even with fresh belts.

So I switched to 3M? 360UZ belts for roughing out and shaping handles.

They cost about 1,50 Euro per belt and last pretty long, and it sure is amazing how fast they remove the wood, even with the "smearing" and belt killing type of woods like Cocobolo and such.

I would definitely give them a try, I would never go back to regular belts for this work.

Regards, Marcus
 
Very,very slow (200-300RPM ) then hand sand the ends. Several woods burn on the end grain.As jimmi said,a vibratory sander is great (you may want to try it on flat grinds,it can take out the coarser scratches FAST).On the exotic woods there is no replacement for hand sanding.Remember that buffing can burn the grain the same way.
 
I don't know near as much about sandpaper as I should. Plenty of other subjects also?? I've found that my belt sander (before it was stolen when my shop was looted) with wood sanding belts does a much better job with wood than my 2 X 72 Coote with the good red belts. More open grain on the paper? I'm not sure why, just know that it works.
Just what I do, Lynn
 
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