Bevel angle seems to change when I turn the knife over and grind the opposite side.

G

griffy85b

Joined
Aug 13, 2016
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Can anyone help shed some light on this for me? Sometimes when I'm grinding my bevels the angle seems to change when I flip the knife over to grind the other side. I usually grind a full flat grind. I'll set the angle on my jig and grind one side perfect. It will be a full flat grind that was ground all the way down to a grind mark made on the knife edge. Then when I flip the knife over and begin grinding the other side, I'll reach my grind line mark on the knife edge before I have a full flat grind on the bevel.

I checked the angle of my jig with the knife in it, and the angle is exactly the same on both sides. I placed the jig on my grinder's rest and checked the angles on both sides. Again, both angles were the same.

This doesn't happen every time either. Sometimes it works out perfect on both sides. Has anyone else had this problem?

My jig is just a piece of angle iron with two threaded holes in the bottom. I screw both bolts in or out to change the angle. The sides, front, and bottom of the angle iron were machined perfectly flat with an end mill. I double checked this again today with a machinist square, and everything checked out.

The steel I use is Starrett precision ground bar stock.

My grinder is a 2x72 Pheer 427.

I also use a file guide.

Please let me know if anyone has any suggestions.

Thank you.


Ben-
 
Ben,

Be sure your steel is perfectly flat and even dimensions before you start. If it is bowed or tapered you will get a different grind side to side.
 
The steel is always perfectly flat. I usually use the Starrett precision ground bar stock. 5/32" or 3/16" For some reason I get better results on the left side of the platen then I do on the right side. It run into this problem almost every time. Do you think it's my platen or the grinder itself? Or my work rest?
 
Can you take some pics of your setup?
Platen, work rest, and jig pics in particular.
 
There can be a number of reasons this is happening.

1. even precision ground should be checked, heat treat can cause warp. you need to check the flatness at intervals.

2. check for burrs or debris on the jig and knife, a little burr can knock the angles off.

3. Check your belts, they can be uneven when you have wobble on your grinder.

4. Check your platen, they wear and have high spots and low, are you using glass?

5. check your work rest, make sure that is perfectly flat and that it is perpendicular to your platen and on the x-axis.

6. check your jig guides that you are getting the same angles x and y.
 
i used to use a jig. even a tiny piece of metal dust between the blade and jig seems to change the angle. also any dust between the bottom of the jig and the workrest will do the same. i kept a 3" wide paintbrush handy to keep the jig bottom/workrest clean and to clean the blade and where it rests on the jig clear of metal dust. a micro burr around one of your pin holes in the handle will do it also.
 
Blades warp when they are being ground due to heat buildup. You need to check the straightness of the blade from time to time during grinding and straighten them if they are bent.
 
I had this same problem when I was first trying stock removal knives. Turned out my rest was a bit off true, and it was more than enough to screw me up. I ended up just going with freehand grinding after some trial and error.
 
Shing said:
Blades warp when they are being ground due to heat buildup. You need to check the straightness of the blade from time to time during grinding and straighten them if they are bent.
Click to expand...

Do not grind one side completely , alternate your grinding to avoid what Shing is saying . Grind 1/3rd of the way up on one side then switch . Keep blade cool to avoid warp and twist .
 
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