Grinding wheel rounded corners

[Wannabewoodworker]

I have had a T7 for about a year now and frankly I am kind of frustrated and disappointed with it. I am hopeful that it is just me and not the machine. When I use the T7 to sharpen anything it seems like the wheel does not stay flat across it's surface for any length of time. I use the truing tool to get it flat across the face and then with in several swipes with a knife or jointer blade the corners are rounded off. This as you can imagine doesn't bode well for getting nice edges on anything. So what the heck am I doing wrong? I have watched the videos so many times I can almost recite them by memory. It would seem to me that the wheel should stay relatively flat across it's face for longer than a few 5-10 swipes across it. Also is it normal for the wheel to load up with material while sharpening? What I mean is there seems to be a significant amount of metal that gets imbedded into the middle part of the wheel mostly and I have to use the stone grader to attempt to remove that material so that I have clean stone facing the tool i am sharpening. My last question is about the OEm stone, is it capable of sharpening jointer knives adequately in a reasonable amount of time or should I be looking at getting the black stone to do the jointer knives? It seemed to take a very long time to sharpen 4" jointer knives on the T7 and when I was done I ended up with somewhat sharp knives but they were not square/flat across their length. If I put them on a flat cast iron table I could see light underneath the knives which is not good for getting a nice flat cut across a piece of stock obviously. I really want to be able to use this machine i paid a lot of money for but it is really causing me to feel beaten and broken. I have really screwed up some of our kitchen knives sharpening them as I kept sharpening them probably too long and ended up causing the blade to not be flat any longer or completely changing the blade profile altogether due to excessive grinding. I need help here please.

[Jeff Farris]

1) Yes, it is normal for the SG-250 stone to become loaded with dross (metal cut from the tool). The stone grader is the correct approach to clean it, and may be necessary every few minutes of grinding, depending on the type of steel being ground.

2) The SG-250 is capable of grinding even badly damaged planer blades, but it can be time consuming. The SB-250 is specifically formulated to cut HSS blades, such as that found in planer blades. It is significantly faster than the SG-250, however, before you face even further frustration, I will add that low speed water cooled grinding takes more time than dry grinding, but delivers a better, longer lasting edge while removing less steel from your valuable blades.

3) If you did not achieve a straight grind on your planer blades, you either didn't set the limit of the cut correctly, or you stopped grinding before the jig reached the cut limit. Take another look at the handbook directions on setting the limit of the cut.

4) Rounding over the corners with the planer blade attachment sounds like you are not adjusting the travel limits so that your 4" blade does not travel beyond the edge of the stone. You don't necessarily have to use the travel limits, but if you don't set them, then be sure you don't run the blade completely off the edge of the grindstone.

5) The problem you have on the knives is exactly the opposite of what you're facing on the jointer blades, that is, you have a very soft steel, that is ideally suited to the SG-250, and it has a very thin profile, so it cuts, FAST. I carefully dress the grindstone to the fine cutting surface with the smooth side of the stone grader before I sharpen knives...even knives that need a lot of work.

[Wannabewoodworker]

Thanks Jeff,
                  I don't have the planer blade jig so I used the scissor jig instead feeling that it was similar in use and I only need to get the bevel angle set then it is just a matter have moving the jointer knives across the stone. They are only 4" knives so getting a very expensive jig that holds very long knives wasn't something I wanted to do. Is that the biggest problem that I used the wrong jig or is it possible to use the scissor jig in my hand tool kit to do my small jointer knives?

How many swipes across the stone is usually needed to get a fillet knife sharp? I understand there are varibles but in general with a knife that is relatively good condition how many times should I be moving each edge over the stone before it is ready for honing?

[Jeff Farris]

Achieving a perfectly straight cut on a planer blade with the scissor jig would a painstaking task that would require constant observation and adjustment. The jig is designed to follow the contour of a curved scissor blade. Nothing about the design encourages it to move in a straight line. To make it work, you would have to grind where the blade is high and not grind where it is low. I'm sorry, but in this case you either need to purchase the right jig for the job, or lower your expectations...or practice a lot.

A knife that is in reasonable shape and needs just a touch up could be done in 4 or 5 passes per side, with the stone graded to the fine cut. That said, number of passes is not the way gauge your work. Grind one side until you can feel a burr, then flip the knife and repeat. When the burr is present on the second side, move to the honing wheel.

[Herman Trivilino]

The only thing I would to Jeff's last paragraph is that if you don't feel the burr, and you've ground long enough that you're getting frustrated, examine the edge you are grinding under a magnifier.  (I keep one mounted next to my machine, and it has a light on it, too.)

You might be grinding at too shallow of an angle.