Tuesday, August 02, 2005

Part 3, grinding the blade

I covered equipment and such on grinding here and buffing here. I will repeat a warning: you CAN get hurt doing this. If you slip and stick a finger or knuckle into a grinding wheel or belt, you will lose skin at the least; if you've got a lot of pressure on, it can cut deep enough to do real damage. The edge of a grinding belt can cut like a knife(no pun intended) if you slip into it. Sometimes a belt or wheel, along with the tearing, can generate enough friction to give you a combined tear and burn. A buffing wheel can grab a piece out of your hand and throw it. And they all throw off a lot of material; metal bits, abrasive bits, lint, and in the case of buffing the glue or grease used to hold the abrasive. So do please be careful.

On to the actual work. If you are in any doubt as to keeping the shape of the blade in your mind as you grind the profile, get a Sharpie or something like it and draw it in. Once you start, at this stage it really doesn't matter how hot it gets, other than if it's too hot you can't hold on. I keep a bucket of water with a few drops of dish soap added in to cool the piece off(the soap breaks the surface tension and helps bits washed off to sink instead of floating). Grind the blade to just a touch outside the final line you want over the entire profile, from point to end of tang.

If you're doing a narrow tang and have trouble getting the tang/ricasso junction even, clamp it in a vise and use a file. What I'll often do here is clamp the blade in the vise point down, with the part that needs to be cut away even with the jaws, clamp it tight, and file it down. If your vise has really coarse jaws, you might want to use a piece of leather to pad them. What I've seen some bladesmiths do is get two pieces of spring steel long as the vise jaws, weld or bolt them together at one end with a spacer in between, grind one side dead even, round the corners a bit, then harden them; you clamp the blade in this, and can only file down to the hardened steel; if you temper it only enough to not be brittle, the file won't want to cut them.

In the next step you are actually grinding the angles in. Some prefer to flatten and true the ricasso and tang first- sometimes with a slight thinning toward the end of the tang- and then move onto the edge bevels, some rough the bevels and then the ricasso-tang; you'll have to try different ways over time and see which works best. I generally use the first method.
What makes this tricky- flats and bevels both- is you have to hold onto the piece as it's angled across the belt without burning yourself as it gets hot and without it slipping and running your hand into the belt. Three main points: first, a sharp belt cuts faster and runs cooler than a dull one; second, use a push-stick or something to help hold the blade; and third, take your time. Hurrying here either gets the piece ruined, or gets you hurt, or both. Light pressure only and let the belt do the cutting. There are belt lubricants made for this, they keep the belt running a bit cooler and keep it from getting clogged as badly by metal dust; they also make what amounts to a big eraser for cleaning belts, I recommend both. If you're flat-grinding, you can hold the piece flat on the platen- the surface supporting the belt- , if you're hollow-grinding you'll have to use the surface of the wheel the belt runs over. Note: you can hollow-grind with a grinding wheel; you have to keep the surface trued up to get a smooth cut, and you'll have to start out with fairly coarse buffing compound to clean it up.

Work one side a bit, then turn it over and work the other side. Keep an eye on the edge to make sure you keep it centered. Remember to leave the blade thicker than you want the finished piece to be. The part of this that can be a pain is when you get back to where the bevels meet the ricasso; getting the angles even and matching on both sides takes time and care. First time you try it you may wind up saying things that make the dogs hide, but keep at it and you'll get the method. Here's another place where some people leave the power equipment and go to the vise and files. Some have made jigs that hold the blade and allow them to cut the junction cleanly and precisely every time; if you wind up doing this stuff a lot, it'd be worth it to put something together.

I usually start with a 80-grit belt if there's much to cut down, a 120-grit if less. And the nice thing about a belt grinder is you can cut it clean with the coarse belt, then switch to a finer belt to clean away those marks, and so on. At this stage I wouldn't take it any finer than a 240-grit belt. If you're doing your own heat-treating with the forge, you'll have to regrind to clean up the surface( you DID leave it a bit oversize, DIDN'T YOU?); if you send it to a pro, or have/have access to an electric furnace for that part, you can go to a finer finish if you choose.

Assuming you want a flat finish, no signs of hammering left, grind deeply enough with the first belt to get rid of the marks and no further. When you switch to the next finer belt, try to work the piece at an angle to the previous grind, it makes it easier to see if you've got all the prior marks cleaned up. And so on, until you're done.

When you think it's done, cool it off so you can examine it closely without burning yourself or having heat waves blurring any spots. Make sure the whole thing is straight; that the edge is centered and not wavy; that the changes between blade parts are smooth and even. You can regrind to correct these after heat-treating, but it both takes longer and you have the risk of messing up the temper if you overheat it. So get it right now.

Everything is even? All is to your liking? Next step is hardening and tempering.

Forging, part 1
Forging, part 2

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