What am I doing wrong??? (Finishing knives)

R

rangrubb

Joined
Mar 20, 2001
Messages
5
I am a new maker and just purchased my own grinder. I have a smooth 10" contact wheel that I hollow grind on.

I can rough grind the blade perfectly before heat treating. When I get the blades back, I start with a 50 grit belt, and work my way down from there.

The problem I am having is with the finish. When I go to mirror polish my blade, there are marks in my finish that I cannot get out. It looks like tiger stripes in tiger maple wood, you see them but you cannot feel them.

I have determined that it is comming from my belts. Where the belts are spliced, they are thicker than the rest. When I grind, I feel the blade almost hopping over these splices, and I feel like this is what is causing this. It seems to gets worse, or I notice it more the finer grit the belt is.

Has anyone else had this problem, or does anyone have any suggestion!
 
I don't know what grit you are finishing your pre-heat treat grinding with, but it should be at least 220, and preferably 400. After HT, start with a fresh 400 grit belt. It should make a big difference.
 
Sounds like belt chatter to me, the knife bouncing on the contact wheel when grinding.

Sometimes this happens when the contact wheel is too hard, over 60 durometer shore A scale. Fine belts like softer contact wheels in the range of 40-50 durometer.

Another cause is holding the knife improperly and a bounce results. I hold the knife close to the body with my elbows pressed into my sides this reduces movement of the workpiece. Nervous individuals try to hold the blade out in front of them at arms length or thereabouts and there is no way to prevent the arms and wrists flexing causing blade bounce.

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george
www.tichbourneknives.com
sales@tichbourneknives.com


 
Yes to all of the above.

It sounds like you may not be keeping the blade flat against the wheel and getting the "waves". The blade or blank must be flat against the wheel AT ALL TIMES or you may cut grooves in your piece. Don't get in a hurry. Take your time.....

One thing that can get you is the dreaded "2 inch grind mark". For that you may crown your wheel somewhat or wear your new belts on the edges with a crock stick or something to knock the sharp grit off of the edges.

The way to Carnegie Hall is to practice, practice, practice....

C Wilkins
 
Make sure you are using Sharp belts!!!
If you use old dull one's (Trying to make them last) you have to use more pressure.
The more pressure the less control. At this stage you should only be removing the previous grit scratches. The blade should be gliding across the contact wheel, using very little pressure.
Ask me how many blades I ruined before I learned to back off at this stage...

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RHankins Available knives
http://albums.photopoint.com/j/AlbumList?u=205453
 
beside's all of the above, again get good top notch belts it cost's less in the long run. also grinding dust can stick to a wheel giving lines and noise to the machine. use acetone to wash the crud off. happy grinding

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Laurence Segal www.RHINOKNIVES.com
 
Thanks for all of your responces so quickly. The grinder I am using is the Grizzly grinder out of there catalog. I bought it second hand and the previous owner had already stablized the arm with more brackets. I have'nt noticed the belts fluttering or anything, I feel that they are on pretty securely.

The contact wheel I am using is the 10" wheel I ordered from Grizzly. It feels pretty hard, although I do not know that this is my problem. I have always heard that the solid contact wheel is what you finish the knife on!? In the past, I have used a serrated wheel to finish on and have had no problems with my finish.

I have been extremely pleased with my abilities so far, I have made only 6 knives and have not ruined one yet! Since I have started with this grizzly with the solid wheel, I have toasted two already! Oh well, I guess I have to learn some how!
 
Ragrub: The trick to removing scratches from a previous grit is to be able to see them. You need to change the angle of the scratch pattern from the previous pattern each time you change belts. Under a strong light, the remaining scratches will show up this way, so you can keep grinding until they are gone. You can change the angle by raising/lowering the handle of your blade as you grind.
As to belts bumping, the 3M Trizact or film backed belts have flush splices.
Try some WD40 or belt grease/wax on belts finer than 220. You also have to watch the pressure-it is easy to get local overheating and orange peel/deep scratches.
The suggestions made by others regarding new belts are all valid!!

Good luck. If getting a perfect finish was easy, all us "pros" would be out of business. Keep trying!

RJ MARTIN
 
From your initial description,it sounds like you are using lap joint belts.If that is the case,switch to butt joint,or better yet,finger joint,neither of those use an overlapping joint.Tru-Grit supplies these as do most knifemaker supply co's.

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MIKE
 
Yes to all of the above and When going to the final phase I put a few drops of baby oil on the belt (slow speed). It helps.
 
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