I definitely subscribe to the full contact approach between the holder and the rest. I can almost always get my clean facet on the knife before I lose contact, but if not then a quick downward adjustment of the height posts gets things ready again. If the knife edge ever falls off the edge of the stone the holder is misaligned. I never let the knife travel into space unsupported by the stone when it is moving.

I think I know where your non straightness issues are coming from. Remember that even though the wheel is spinning at a constant rpm, the outside edge of the wheel is traveling much faster than the interior near the cup, therefore cutting faster. Even though the same rpm, higher feet per minute at the edge versus the interior. This is where you have to use your skill and finesse to make sure the knife is spending the equal amount of time
on each area of the stone across the length of the knife. Use a good stiff ruler to examine your edge as you experiment with the feed across the rest. I like to get a clean facet and general straightness and then take rapid light passes back and forth to float out straightness. Before I do this I give the inside of the rest/holder a good dose of light oil (Zoom Spout is my favorite) so the carrier glides without friction. When you correct your straightness issues on your knives it may take several setting adjustments before you get to the sweeping back and forth method. I am guessing you are high in the middle and lacking on the edges. This is from advancing, stopping, and returning the carrier across those ends more than in the middle. I try to keep the stone as flat as possible but just by the fact that it cuts faster on the outside it is always trying to fall off. I always think of the knives I am sharpening as truing tool for the stones while they are being sharpened.

That machine is a multi-layered burrito of subtlety and nuance. I was just forced to figure it out but it gave me headaches for a long time. Feel free to continue this discussion at askwoodman@gmail.com with me.

Again sorry for the lateness of my reply.
Allan

The problem that I have is that I just can’t get the jointer or planer blade to sharpen straight. I’m probably overthinking this, but the problem to me is that the geometry doesn’t make sense! But, obviously, you are making it work, so perhaps you can offer some insight.

First, I’ve reviewed the PDF at HWW, and I understand that you want the stone to eventually develop a slight slope along the radius on the right side so that you are sharpening along the entire right side, hopefully.

However the dilemma, at least to me, is how the blade should be supported by the tool rest. There are two choices. First, you can allow a small gap between the tool holder and the tool rest, in which case the blade is “supporting” itself, as is the case when one uses the typical sharpening jig on a stone, with, for example, a chisel. When I tried this, I found that it was impossible to get a straight grind if the knife is not perfectly straight. This is apparently because at first, the stone literally only sharpens at the outside edge, and as the blade gets to the edge, it falls off, causing some curvature, which is is then accentuated as you continue. I suppose that if the stone wears enough, it might be better, but while the stone is pretty new, the blade is making contact at only a small area, which allows it’s contour to follow the stone, and, if anything, causes the non-straightness to be accentuated.

Or, you can have the entire tool holder supported by the tool rest, which is what it appears that you do in your video. However, I found that when I do this, the sharpening doesn’t work, since you very quickly grind off the lowest spot at each point on the blade, at which point the sharpening stops since the blade is no longer in contact with the stone, and is instead being supported by the tool rest.

I’m hoping that I’ve explained this well enough and that you can offer some insights into to solve the problem. There is no question that the machine gets the blades very sharp, but I’ve just never been able to get a straight edge on either the 8″ jointer or the 15″ planer blade, and it seems to me that it’s because the geometry is a problem…

But, you’ve obviously solved it, so I hope you can help.
Thanks.

http://www.highlandwoodworking.com/makita9820-2usersguide.aspx

Thank you, Bill

The 9820 is just what your school needs for self sufficiency. The machine is designed for sharpening up to 16″ knives without adjustment. But in your situation, where the choice is a little extra care shifting the blade in the carrier, or waiting with no blades. The choice is obvious. Once you get the feel of the machine, you will be shocked at how little material you actually have to remove to have perfectly sharp edges. Because of the isolated area of your school, I would probably invest in the course green wheel as well. You don’t use it often, but it makes such quick work of removing nicks from knives it will be seem like a small investment. The stone that comes with the machine is more for resetting a clean facet versus removing damaged edges. Plus the green wheel is just the ticket for reshaping axe and hatchet blades as well as quickly regrinding an edge on knives and machetes.

Soon I will have videos of my chisel and plane iron sharpening techniques. These will be very helpful to you and your students. I have developed a simple and foolproof low tech repeatable method for anyone to put a razor sharp durable edge on their woodworking tool. The technique is also very safe even for young, less coordinated student woodworkers. If you subscribe to askwoodman.tv you will be notified when new videos are posted. Please write with any other questions. And if you do buy this machine perhaps you can click through my Amazon store to do so? http://www.askwoodman.com/shop/