Tips for belt finished knives?

kuraki

kuraki

Fimbulvetr Knifeworks
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Jun 17, 2016
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I apologize if this has been covered, I did try searching a bit, but I don't think I'm using the correct terminology.

I'm wondering if anyone could give me some tips for how to avoid hand finishing blades. I know that one might never achieve the same level results with a blade finished on their grinder that they can with a backer and paper, but I've a lot of requests from potential customers for knives that they would rather not pay for my time hand rubbing.

I am having my best results with slack belt grinding, but would like to figure out how to get a reasonably good looking blade off my flat platen. My current process is to forge or cut the profile depending on the knife, rough it in with a 36 grit ceramic or zirc belt, step up to 60, 120 ceramics, then to trizacts, I start with A300, then A160, then A45 and last A30. That gives me a pretty good looking bevel, and I could always get one or two steps finer with the trizact, but there will sometimes be perceptible waves in my bevel, or scratches that just won't seem to come out (I actually think the finer trizacts are causing these either because I contaminated them somehow or they have a bit of bigger grit in them).

Right now the best method I have to finish a knife as efficiently as possible is to grind it, blast it and parkerize it, which I personally really like, but not all people do. The blast profile hides a lot of stuff that shows on a polished blade I'd never let out of my shop with my name on it.

I'm not trying to get rich. I like doing this, that's why I do it, but in order for me to do it the way I'd like, I need to sell a few knives for cash to reinvest into abrasives if nothing else. And my customer base is not paying $250+ for a knife. And I can't bring myself to charge someone $100 for a knife that looks like hell, even if I have 4 hours of time plus materials into it.

One issue I know I have is the lack of a VFD. I feel like if I had that speed control I could slow things down and spend more time per pass with everything lined up correctly without worrying about overheating. I plan to build a second grinder with a VFD, but are there any other tips?

Maybe I just suck and need more practice :D It's definitely part of the equation.
 
if you are finding scratches, i would say you need more work with the a300 (220) grit before moving to a finer grit. with grits above 220 its harder to remove metal and scratches, they are mostly good for only removing the scratches of the grit before them. in other words, its difficult to remove 120 grit scratches with a 400 grit belt.
 
Woodster, I do know that is part of my problem. Jumping too quickly through the grits because it looks ok in the light available, then getting it in different light and finding it's not. I've had to temper my enthusiasm of grinding to near finished dimensions with 36 grit then trying to finish only to find the blade is going to be smaller than intended because I didn't leave myself enough grind stock :eek:
 
I am in a similar boat - I am having hard time removing scratches with a belt grinder (alebeit it is only a little 1x30" with quite a few defficiencies), but I have also noticed that removing scratches with low grit belts means removing noticeable amount of material. And - since one is always grinding in the same direction - it is hard to judge when the scratches from the previous belt are gone (contrary to hand sanding where one can change the directions with every grit)
 
I use a belt finish on most of my knives. I take the blades to an even grind at 320 or higher, then scotch rite, then cork with black compound. Leaves an even, bright finish that is attractive but you don't mind using.

Chris
 
I started with hand rubbing etc when I started making knives.
here's what I learned (from Murray Carter) and what I do now, it's very fast and productive and yields a very good working finish.


rough bevel grind as desired
belt remove scratches with 120 grit belt
flap sand 240
flap sand 320
buff polish with green compound.

This takes but a few minutes and I can do the last 3 steps in less than 60 seconds.
and if you ever need to refurbish a knife you can do it quickly and easily.

I don't say it looks amazing like a hand rubbed finish, but it's considerably less work and I personally never liked a mirror or hand rubbed finish on a user knife.

Another thing you can do is to use Nathan's radius platen (water cooled) and line the blade up on the platen lengthwise and let the belt do the work.
But you need controlled speed for this.
I don't do this anymore so I have this available if anyone wants one.
 
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Several thoughts are as follows. As has been said, above 220 grit or so you aren't removing much metal. You are polishing, or refining the surface. Make sure your platen is flat. If you've been using it for a while and it has grooves or dips in it, resurface it flat. Also, your belt tension may need to be stronger. If you place a blade against a running belt on a platen, the pressure that pinches the belt between the blade and the platen can cause the belt to ripple a bit causing waves in your blade. Try to keep the blade cool as well. Too much pressure can cause heat that, coupled with dull belts, can cause kind of a smeared or rippled looking surface. Variable speed is great to have. I have found that in the higher grits and especially with the lighter weight belts that it helps a lot to use light pressure against the belt. Use fresh SHARP belts and light pressure. Let the abrasives do the work. Concentrate on nice smooth pulls. If you are getting clean bevels at 600 grit or so you can try following that with a cork belt as well.
 
HSC /// said:
I started with hand rubbing etc when I started making knives.
here's what I learned (from Murray Carter) and what I do now, it's very fast and productive and yields a very good working finish.


rough bevel grind as desired
belt remove scratches with 120 grit belt
flap sand 240
flap sand 320
buff polish with green compound.

This takes but a few minutes and I can do the last 3 steps in less than 60 seconds.
and if you ever need to refurbish a knife you can do it quickly and easily.
Click to expand...

HSC, a knife making teacher of mine here in Japan does this same thing. Out of curiosity, how big are the flap wheels you use (and how big are the one's in Murray Carter's shop)? I've wondered how small a flap wheel I could get away with, since the ones I saw over here are quite large and I would need a really big buffer for them.
 
another tip that might help - i use dykem marking fluid spray to make the blade blue between each grit. that way i can tell if i got the whole blade done. if you miss a spot @ 120 grit and dont notice it until 320 grit its really hard to get out.
 
Tenebr0s said:
HSC, a knife making teacher of mine here in Japan does this same thing. Out of curiosity, how big are the flap wheels you use (and how big are the one's in Murray Carter's shop)? I've wondered how small a flap wheel I could get away with, since the ones I saw over here are quite large and I would need a really big buffer for them.
Click to expand...

I use- UNMOUNTED 8" X 1" X 1" WHEEL on my Baldor 1800 RPM buffer/grinder machine.

here is a pic in Murray's shop

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4bbfceab378c1b0909a24bf75a10a6c4.jpg
 
With the flap disk, are you holding the blade vertical? How do you keep the plunge clean if you are?
 
kdogmcg said:
With the flap disk, are you holding the blade vertical? How do you keep the plunge clean if you are?
Click to expand...

i run the flap wheel and buffer in the opposite direction, away from me.
I know that's considered a big no-no here so I'm not going get into the why or how that works for me
I hold the blade horizontally on the top quadrant of the wheel with the blade edge away from me.
 
Regardless of the tools and belts you use, the main tip is - Remove all lower grit scratches and marks before go to the next grit. They will just get worse looking as the grits get finer.

I sand with 120, 220, sometimes 320, and 400, then use a Scotch Brite belt. Keep the blade moving all the time.


Caveat:
Flap wheels are great in the hands of professionals and trained people, but dangerous in the hands of inexperienced people.
 
woodster said:
another tip that might help - i use dykem marking fluid spray to make the blade blue between each grit. that way i can tell if i got the whole blade done. if you miss a spot @ 120 grit and dont notice it until 320 grit its really hard to get out.
Click to expand...

dykem :thumbup:

I use this on every knife I grind. You'd be surprised how much of the previous grit you can overlook, dykem helps it stand out.

Also, I think it helps speed things up if you can change the angle of the grind a little. This keeps grit from falling in a previous scratch making it deeper.
 
Great tips, thank you.

My platen should be flat, it's ceramic and relatively new. But belt tension I'm going to play with for sure. When I built this grinder that was a question and I kind of just guessed, but I did leave myself a way to adjust it.

I never thought of using flap wheels but I will give them a try. Cork belts, I have a felt belt but not a cork. Scotchbrite I have a love hate relationship with. If my belts were uncoated like the pads and discs I have at work, I think they'd be great, but the 2x72 belts I've purchased have this hard coating on them that just seems way too coarse for a satin finish, and really blows my lines away.

I got out of a habit of using dykem when I was a toolmaker. It was too thick for what we were doing, and primarily use sharpie marker, which doesn't hold up as well as dykem. Just habit. I think I've got a can laying around. Definitely will give that a try.


One problem I've had with my grinder, when I track the belt off the platen for a more radiused plunge, sometimes, depending on the belt, as soon as I get a bit of pressure on the blade, the belt will track itself back in the other direction until I relieve the pressure. I wonder if this is related to tension being too low, as it tracks quick well otherwise.
 
kdogmcg said:
With the flap disk, are you holding the blade vertical? How do you keep the plunge clean if you are?
Click to expand...

I don't worry about the plunge line. I think working on the plunge line is overrated :). I don't see what function it serves


Sent from my iPhone using Tapatalk
 
kuraki said:
. I wonder if this is related to tension being too low, as it tracks quick well otherwise.
Click to expand...

Yes that can be caused by low belt tension. I had this issue when I was using a grizzly grinder.

I would also agree with your first assessment that a variable speed grinder helps with belt finishes. There's less worry of ruining your temper.
 
If you really want to catch those scratches, you can't beat either full sunlight or LED above your grinder.
LED light fixtures will bump your work up to a whole new level, once you get over the shock of seeing all those leftover scratches that you have to get rid of!
(Thanks, Stacy, for the hot tip on LED and scratches.)
 
I have a couple of those silly 100 watt LED squares / 45mm lenses for a ridiculous "flashlight" I built...I should repurpose them to work lamps.
 
Stacy, are there special safety concerns with flap disks, or are they pretty much the same as for buffing wheels in general? I.e. they can rip a blade out of your hands and throw it before you even know what happened. I won't lie, when I've used them over here in my teacher's workshop, I had a healthy fear of them.
 
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