Sharpmaker problem

sheltot

sheltot

Joined
Apr 23, 2003
Messages
402
I thought I was going nuts...

I bought a used BM705 on eBay for cheap to use as a beater. I liked it so much, I polished the scratches out of the blade and decided to re-profile the edge to a 30deg included angle.

The problem was when I switched to the fine stones. I worked off and on for a day and a half and noticed on the top of the bevel was getting touched. Down toward the edge was still "rough". First, I made sure that I was keeping the blade vertical. That wasn't the problem.

Long story short...
I taped a piece of paper to a wall and set the Sharpmaker up first with the brown rod and used a very sharp carpenters pencil to follow the flat of the rod on the paper. Then I did the same with the fine rod. Aha, the angle was a bit more acute with the fine rod. So, out comes the calipers and sure enough, the brown rod is about 0.007" more narrow from corner to flat than the fine stone.

I didn't take a bunch of measurements of the slots in the base to work it all out as the proof was right there on the wall, so to speak.

Up until now, I've only used it to touch up edges and hadn't seen this.

The question is, now what the heck do I do? :confused:

Thanks for any help,
Tony
 
Maybe you got a "bad" unit? I'm glad you asked this question, I've been meaning to ask the same type of question if you do not mind...does Spyderco sell "seconds" or sub par sharpening systems? I bought mine off of EBay and when I run the blade down the corners of the stones some sound like they are not taking any metal off the blade while other corners sound and feel like its like 80 grit!
 
First off you should probably never work more than about 2 minutes with the fine stones. The real work is done with the medium stones or a supplemental coarser bench hone. It sounds like your 15 degree bevel is too wide. Your cutting performance is lowered if you go from an obtuse factory bevel straight to a 15 degree edge bevel. This indicates that the blade is thick behind the edge and so you will need to wedge through material rather abruptly as you cut. If you had reprofiled down to about 12 degrees per side (or were working on a Spyderco knife) the edge bevel you are working on would be too narrow for the angle differences to be very noticeable.

Generally though you should put your big time into using the medium rods and then just a little time into smoothing that bevel using the fine rods (at this point you are not sharpening, you are just reprofiling). When you use the fine rods do NOT be so careful to hold the blade vertical. A little slop will let the rods get to all of the surface that you worked with the medium rods. Your final sharpening will be a microbevel that you put on with the rods in the 20 degree position. This will be very narrow and you won't notice the difference in the rod angles. If you prefer you could do the microbevel with just the fine rods. The final edge should take less than 5 minutes to apply.

You will get old and grey using the fine rods to do too much of the work.
 
Additional thoughts: There are lots of ways to systematically compensate for slight differences between the medium and fine grit hones. Generally you would like the angles to match when you are reprofiling (so that you get a smooth bevel) and you would like the fine rods to be at a minutely higher angle than the medium rods for your final sharpening strokes. Your current rods bias you the opposite way.

When you are reprofiling it is often convenient to work one side of the edge at a time (using the coarser hone). Since you want this to be done at a slightly lower angle than the base/medium rod combination provides when used normally you could angle the base to tilt the rod that you are using. Put a couple pieces of paper under the end of the base that is under the rod that you are working on and thereby tilt the rod slightly closer to vertical. When you work on the other side of the edge move the paper under the base on the same end as the other rod. After you have done the majority of your reprofiling one side at a time remove the paper and do some biased honing freehand. By this I mean do some alternating left/right honing on the medium rods intentionally tilting the back (top) edge of the blade towards the hones slightly as you stroke. This is to do a little final balancing of your reprofiled bevel.

Now use your white rods at 15 degrees in the normal approximately vertical manner, but don't get too precise. You are just removing scratches from your bevel surface. Finish by doing a little microbeveling at 20 degrees. If you find that you have a burr (likely after reprofiling) do a few strokes (5 or 10 per side alternating left/right) lightly on the medium rods with the back of the blade tilted significantly away from each rod as you stroke. I try and almost double the honing angle I would get if I used a vertical stroke. Then finish your edge using vertical strokes at 20 degrees using about as many strokes on the medium and fine rods as you did on your deburring step.
 
Thanks, Jeff. Pretty much what you said, I ended up doing. However, after reprofiling the blade on the medium rods, one tends to develop serious muscle memory of how to do a perfectly vertical stroke.:) I think what I shall do in the future is shim the find stones so that they form a slightly more acute angle than the mediums.
 
Your current problem is that the white stones are more nearly vertical than the brown stones. I would describe this as the white stones currently provide a more accute angle than the brown ones. The stones that need to be shimmed are the medium ones. As you described in your first post they are the ones that are too narrow. Try and shim them with aluminum foil.
 
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