Some time ago I looked at one of Tad Lynch's bowies at the monthly meeting in Little Rock. I noted how flat the blade was. I asked him how he got his blades so flat and I think he said something like,"Well, I realy don"t know what to tell you except just concentrate on it." Tad is an exceptional knifemaker, and I guess things like that just come natural for him. That's not to say he didn't have to put in a lot of time and effort perfecting his techniques like all other good makers. I've tried draw filing, but never had much luck with that. As for my order of doing things, I get off the grinder with a 120 grit grind and proceed to my hand rubbing stand and rub with 220 till I get all the 120 scratches out. After that I quench, temper and draw the spine back. But getting back to the grinder. My problem seems to be getting a flat grind. To "my" naked eye it looks flat,but if I check it with a straight edge it's always crowned a little with the center a little higher than the spine and the cutting edge. So I've decided to try and disipline myself at rubbing with 220, (I can't seem find 180 in 3M). I grip my bar with both hands on either side of the blade. I've made myself a 3/4" thick bar about 9 inches long so there is absolutely no flex. I clamp the blade down and start sanding. I try to resist the urge to rock the bar back and forth to get the scratches out at the top and bottom and just concentrate on the center of the blade and keeping the bar flat. This is very slow going because I've got to remove all that meat in the center of the blade. I keep a straight edge handy and check it every now and then to see how it's going. I rub and rub and then rub some more! If I could ever obtain a truly flat surface, I know taking it on up to 600 grit or even 800 would be no probem with cross sanding as I go to each finer grit. I'm doing this now on a bowie and it seems to be working. I'm sure I've "rubbed" everyone to death by now, but I keep telling myself, "there has to be a better way!" I would appreciate any tips. Thanks-Bill
I think you might want to look at disc grinders. Probably the best/quickest way to do a flat grind. I like the Nielsen Design that Wayne Coe offers: http://www.nielsendesigndiscgrinder.com
Hope this helps.
Hey Bill,
It seems to me you should be able to sort this out on the grinder. I don't use a disc sander--strictly a 2x72 belt grinder for me. One thing I wonder is whether you've got any kind of backing on your platen. Some makers use a graphite, ceramic, or even a canvas backing on the platen. It reduces friction, which has a whole lot of benefits, not the least of which is wear and tear on your platen. I don't use anything like that--I just run my belts directly against the platen.
At any rate, it seems to me that one of three things is causing you to finish up at the grinder with a crowned blade:
1) If you're using a soft backing like canvas, the mechanics of the grinding are going to crown your blade for you--naturally, as you press into the canvas, the edges will sort of roll out top and bottom. I'm assuming that's not what's going on.
2) If you're using a hard backing or the platen itself, it is very likely that you've worn a bit of a "dish" into the grinding surface. Chances are, you stand in the same position and hold the knife at the same place just about every time you grind. The friction from the back of the belt being pressed against a hard surface (platen or backing) will eventually wear away a shallow dish, which will then crown your blade. I'm guessing this is your culprit.
3) Lastly, you can't ignore technique. I know you know how to grind, and I know your blades don't have all kinds of weird bevels and facets on them when you come off the grinder. If your grinding passes are all at the same angle and you have a flat grinding surface, your blade should be flat. If you've got a flat grinding surface and you're coming off the grinder a blade that looks "true," and it looks as though the blade should be flat, then it's got to be #2 above.
As I think about it, one other thing to think about is the mechanics of your platen and belt. Is your platen slightly proud over the idle wheels? If not, your belt itself might be "dishing" ever so slightly between them. Just an afterthought.
Hope that's useful.
Zack
Zack Jonas
Journeyman Smith
I have to agree with Zack. A lot of blades are still ground using the flat platen and done very well. I have to take my platten off and flatten it from time to time when I use the steel platen. I do use the ceramic lining on one grinder. There is something that is fundamental to grinding that you need to tweak. Check those things Zack mentioned and see what happens. Either way, proper hand sanding sequence will catch any dips or ripples.
I also had this "bowing" problem after about a year of "learning " on my KMG. Tim Potier suggested I put a piece of tempered glass on my platen and the problem ceased for about a year or so and then re appeared. The bow was right at the level of the work platform and it has regularly appeared at 12 to 14 month intervals. this has reguired the changing of the tempered glass and I am soon going to change the platen. It has been suggested to me to stop using the work platform but I can't. Maybe some of you younger or more experienced or never self trained to use it can. I just face reality and change out the glass and my grinds flatten out. I hope the advice helps. I know it's worth just about what you pay for it. In my case I paid quite a lotin messed up blades and funky looking grind lines that had to be laboriously draw filed out.
It's a fact that you have to perform maintenance on your platen. A simple cleaning off of the gunk is an example of how it directly affects the flat grind. Your habits in grinding will affect the areas of the platen that show wear and this wear will usually, in turn, affect your platen's performance.
I keep two platens for my grinder. Both platens have their own mounting brackets.
The hot rolled platen that comes with the machine is too rough to grind well and the edges are not uniform, so do not do a good job on the plunge lines. I use the original hot rolled platen for miscellaneous grinding.
I made a second platen from a piece of surface ground O-1 steel. The O-1 platen is used ONLY for knife blades. About every six months, I will surface grind both platens to re-flatten them.
Another method of hand sanding a blade flat, is to glue a piece of sandpaper to a flat surface and then rub the blade on the sandpaper.
