Trouble hollow grinding

[Marc Kerschner]

I am having difficulty grinding a square edge and I am hoping to get some assistance. I have an inexpensive Porter Cable adjustable speed 6 inch grinder with a Norton white wheel. I removed the factory tool rest and installed a Veritas tool rest. I tried grinding free hand and noticed that, even on narrow chisels, the bevel was skewed significantly after grinding (I can see a lot of light when I hold a square up to the edge and I can tell just by looking at it that something is terribly wrong).

I then made a few adjustments hoping that things would improve. I crowned the Norton wheel and clamped the chisel to a straight scrap piece of wood. I also double checked the tool rest to make sure that the front and back of the rest are parallel to the cutting surface of the wheel and perpendicular to the sides of the wheel. When grinding, I made sure that the scrap of wood stayed in contact with the front edge of the tool rest as I moved the chisel back and forth. The skew of the bevel after using this method was almost identical to the skew I got when I did it freehand.

The wheel wobbles from side to side significantly. The cheap stamped washers that clamp against the wheel seem to be the culprit since they aren't machined and don't look all that flat when I lay them on top of a cast iron table. I ran then across some sandpaper to see if that would help but the shoulder on the shaft that the stamped washers press up against are tiny - not much surface to register on. I've tried different locations for the washers relative to the wheel, as many people suggest, and although the wobble is decreased, it is still pretty pronounced.

Is it the grinder or is it me?

Thanks in advance for your help.

[Jim Koepke]

Is it the grinder or is it me?

I am not expert on grinders, but if my wheel didn't run true I wouldn't accept it. If the salesperson or company rep told me they were all that way, I would say, "then they are all wrong and you can start fixing it with this one."

Not long ago someone else had a wobbly grinder. (no not from that workers organization) They documented how they took care of it here on SMC. It is likely worth your time to search for it.

jtk

[Daniel Rode]

I'm not sure I understand how the wobbling wheel would cause the grid to be skewed.

[David Weaver]

Two separate issues (wobbly wheel, etc). Using a grinder is a matter of touch. My baldor grinder rests aren't even dead square, they are close but not perfect, nor were the ones I had on a grinder before.

You grind to establish the bevel geometry, and then you hone to square. If you are very far off to start, square your chisel on a stone by scribing a line on it and grinding to that (you can do this on a grinder) and then grind the hollow off - this is a light and little time involved issue on very narrow chisels.

Once you've got the chisel fairly square, you maintain squareness by honing and you remove most but not all of the hollow when you grind.

Stick with it, it won't take long.

For years, I used a ryobi grinder that I got on sale for $29. It wobbled like crazy and had to be clamped down, even with good wheels. I could still be using it fine if I wouldn't have indulged myself with a baldor grinder.

(if it makes you feel better, baldor sent me cheap stamped flanges with my grinder - which is the 6" grinder with cast rests and guards. I was offended at first, but in reality, it makes no difference in actual use - you're not using the side of the wheel - the rest will true itself to the dresser and your tools).

[Jessica Pierce-LaRose]

Dave's got it - if I have to do a lot of grinding, I scribe a line square on the back, and grind back to this line, grinding a square (blunt, 90 degree-ish) bevel. Then the actual hollow grind is just approaching this blunt line. Frequent, quick checks (more frequently as I go along) tell me if I'm removing material evenly or not - where the flat gets ground away to hollow, "thicker" sections need to be addressed more.

The veritas tool rest is actually really helpful if you've got it mounted square to the wheel - you can visually check against the lines on the rest to make sure the iron is staying parallel. I generally wrap a finger against the back of what I'm grinding and sort of use that as a fence against the back of my grinding rest.

If you have access to it, Joel Moskowitz's article in Fine Woodworking a few years back about grinding is a great primer for this sort of stuff.

Once an iron's in good shape, just touching up the hollow to keep honing quick is usually pretty easy, especially since I don't always work all the way to the edge. A quick inspect points out places the hollow isn't as even as others and gives me pause to go back and hit that spot a little more.

While most of my grinding comes out pretty darn square, I don't often worry overly much about it - with chisels, a little out of square isn't the end of the world, with rougher planes, the lateral adjust can keep things in pretty good shape. With planes that are to be finer set, as long as it's pretty close, I can usually adjust any out-of-square with the first sharpening pass on the stones, and then it tends to follow that path pretty well with subsequent sharpenings.

I don't think there's really any magic bullet, just practice. It's a hand and eye thing that I stumbled with the first couple of times, and then got pretty well after that. The only trick is for things where the edge is narrower than the grinding wheel, it helps to make sure the stone is profiled relatively perpendicular to it's axis, so a good dressing helps.

[Marc Kerschner]

Sounds like I need to continue practicing. I was surprised that the bevel was still skewed when I clamped the board to the blade to act as a guide-I expected that to eliminate some of the operator error.

[Tom McMahon]

Joel Moskowitz's article on grinding from Fine Woodworking is available at his blog or from
Google. I believe it is one of the best things ever written on grinding.

[Chris Fournier]

Honestly guys seem to loose their minds when it comes to grinding on a bench grinder. This is simple. Set up your tool rest/ guide and then true your wheel off of this set up. Now sharpen your tools following the guide, they should be square. If they are not the problem is the sharpener/operater! A bit of practice will have you on your way, the fact that you see the problem is half the solution.

[Daniel Rode]

I just got the Lee Valley tool rest. It's expensive considering it's just a tool rest, but it makes grinding so much easier. Tonight I took an old beater 1/2" Sears chisel, and after flattening the back, put a 20 degree bevel on it. I squared it up by eye as I ground. After 20 seconds on my finest honing stone, it cut pine end grain cleanly. I am by no means experienced at this. I just bought the grinder a couple weeks ago.

I'd suggest picking up the $7 chisel set at harbor freight or something from a garage sale and practice a little. It's pretty easy to do a square bevel.

Making skew chisels was not as easy. I just couldn't hold them to a consistent skew, so I used a jig for that. With practice, maybe I could do it, but I had the jig, so I used it.

[Marc Kerschner]

That is a good idea Daniel. I could grind and regrind some cheap chisels to improve my skills. The grinder is now also making a horrific screeching noise (bearing?) so it looks like I may be in the market for a new one. For now, I will just wear hearing protection.