Shopsmith Forums

I have wanted an inexpensive way to sharpen the jointer's blades using my new conical sanding disk. There is a simple little fixture in the Shopsmith library - a simple hunk of wood with a slot in it and which uses the fence as a support for alignment. I took that basic idea and (ego alert!) made a few improvements.
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Basically I took the block and slot concept and mounted the block on a matching piece of 3/4" plywood as a base. The base is mounted on a 'miter bar' (a piece of wood sized to fit in the miter bar slot). The block is adjustable (just a bit) with a pivot (1/4" dowel) and a 1/4-20 bolt which is threaded into the base. The jointer blade is retained in the slot with a 1/4-20 nylon bolt which treads into a tapped hole in the block. For a finish, I just sanded everything and used a couple coats of shellac.

Advantage #1: Using the miter bar slot means that sliding past the sanding disk is very controllable. Advantage #2: By moving the table up and down, you can get a very fine control of the horizontal movement of the jointer blade relative to the sanding disk (you get about 0.070 inches of horizontal movement for each inch of table movement up or down. And, finally, you can tweak the table tilt up or down to adjust the blade angle.

Yes. And I can see a longer block for sharpening planar blades.
Simple yet elegant!
Dan

bobgroh wrote:I have wanted an inexpensive way to sharpen the jointer's blades using my new conical sanding disk. There is a simple little fixture in the Shopsmith library - a simple hunk of wood with a slot in it and which uses the fence as a support for alignment. I took that basic idea and (ego alert!) made a few improvements.
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Basically I took the block and slot concept and mounted the block on a matching piece of 3/4" plywood as a base. The base is mounted on a 'miter bar' (a piece of wood sized to fit in the miter bar slot). The block is adjustable (just a bit) with a pivot (1/4" dowel) and a 1/4-20 bolt which is threaded into the base. The jointer blade is retained in the slot with a 1/4-20 nylon bolt which treads into a tapped hole in the block. For a finish, I just sanded everything and used a couple coats of shellac.

Advantage #1: Using the miter bar slot means that sliding past the sanding disk is very controllable. Advantage #2: By moving the table up and down, you can get a very fine control of the horizontal movement of the jointer blade relative to the sanding disk (you get about 0.070 inches of horizontal movement for each inch of table movement up or down. And, finally, you can tweak the table tilt up or down to adjust the blade angle.

Excellant idea. Much cheaper than using Shopsmith's solution. I have been sanding the knives at a 44 deg angle to prevent taking too much height off the knife (.688" minimum height) and make up for any honed knife that may have been rounded a little at the ends of the knife. I would recommend making the block longer to accept a planer knife. You should put a stop strip on each end to prevent the knife from being shot out of the holder when making contact with the sanding disk. You can do 3 joiner knives or a or a planer knife each time this way. I like to have all the joiner knives be the same height and weight. I would not use any kind of screw to try to hold the blade as it may distort the holder.

Many year ago, I used a similar wooden block where the block was sawed apart (horizontal) at the bottom of the knife groove and I used screws and wing nuts to clamp the two halfs together to hold the knife or knives. I used a small wooden spacer along the back of one of the split halfs so the knife was pinched between the two halfs when tighten the wing nuts. I switched to the Shopsmith sharpening setup a few years ago so this block disappeared. I love being able to recall a few things from my past.

Thank's for the comments to both of you. The comment about the longer block - definitely going to do that. In fact, I now have a Craftsman 6" jointer (a wonderful and very quiet beast) so I do need a longer block.

I will also incorporate some of Bill's idea's - a 'stop' block at each end and some type of 'pinch' mechanism to hold the blade in place. I am not worried about the block distorting (the screw push's DOWN on blade) but I do worry a bit about unequal pressure at each end of the blade. Not so sure a single point of pressure is a good thing (e.g. pivoting of the blade when it first encounters the sanding disk).

To further explain this last statement - the existing rig has one problem: a very slight deflection as the blade first encounters the sanding disk. Not much but it does put a 'bit' of a curve in both ends of the blade. Maybe only a thousandth of an inch but....just enough to be noticeable. Other than that - it puts a great finish on the blade. Anyways I want to try to stiffen the whole thing up, accomodate a 6" jointer blade and maybe handle a 12" planer blade.

bobgroh wrote: Advantage #2: By moving the table up and down, you can get a very fine control of the horizontal movement of the jointer blade relative to the sanding disk (you get about 0.070 inches of horizontal movement for each inch of table movement up or down. And, finally, you can tweak the table tilt up or down to adjust the blade angle.

I use my conical disk for all kinds of projects. It had not thought about adjusting the table hight Thanks for the tip.

bobgroh wrote:To further explain this last statement - the existing rig has one problem: a very slight deflection as the blade first encounters the sanding disk. Not much but it does put a 'bit' of a curve in both ends of the blade. Maybe only a thousandth of an inch but....just enough to be noticeable. Other than that - it puts a great finish on the blade. Anyways I want to try to stiffen the whole thing up, accomodate a 6" jointer blade and maybe handle a 12" planer blade.

This slight "bit" of a curve also happen when using the Shopsmith Planer/Joiner Knife Sharpener. It is not because of your rig/jig. The conical sanding disk and and sandpaper actually flexes a little (.001"-.003") when the knife starts contacting the sandpaper. Most people will never notice this slight offset and seriously doubt if it makes any difference when joining or planing wood with knives that has this slight end difference. A a thousandth or two of an inch when working with wood!!! Same thing happens at the end of the knife edge as the disk and sandpaper unflexes.

For us perfectists, I minimize this deflection by making at least 3 or 4 slow passes without any adjustment at the end. For each of these passes, the disk and sandpaper will flex a little less as you are removing a little less metal and sandpaper on each pass. The final one of these passes should generate very little sparking from the sharpening.

I have been using the method shown in my jointer owners manual from 1979. Item no. 505681 Article no. 84-3449. Page 9 - fig. 32 shows the method you have been discussing. Figure 33 shows another method using the same design of blade holder. I have been using the second method with a little modification. I have a Craftsman 100 grit 4" diameter grinding stone that is 1" wide. I mount this on the quill and adjust the table and miter gauge to position the blade for grinding. With the quill extended and locked I then slowly move the blade across the grinding wheel. Change blades and grind the second one. Change blades and grind the third. If necessary, place a 0.002" spacer behind the blade holder and repeat the process.
Two things I really like; 1, the blades are hollow ground. 2, the blades is not thrown out of the holder.

billmayo wrote:This slight "bit" of a curve also happen when using the Shopsmith Planer/Joiner Knife Sharpener. It is not because of your rig/jig. The conical sanding disk and and sandpaper actually flexes a little (.001"-.003") when the knife starts contacting the sandpaper. Most people will never notice this slight offset and seriously doubt if it makes any difference when joining or planing wood with knives that has this slight end difference. A a thousandth or two of an inch when working with wood!!! Same thing happens at the end of the knife edge as the disk and sandpaper unflexes.

For us perfectists, I minimize this deflection by making at least 3 or 4 slow passes without any adjustment at the end. For each of these passes, the disk and sandpaper will flex a little less as you are removing a little less metal and sandpaper on each pass. The final one of these passes should generate very little sparking from the sharpening.

After further thinking about it, it may be the table legs and carriage that allows some of the flexing that I have seen but it does occur. I believe it is nothing to worry about.

Thanks, Bill, for the words of wisdom regarding the bit of a 'rolloff' that I see on my blades. Makes me feel a bit better about it. I am going to reconstruct my fixture in any event - just to tweak it a bit. Need to accommodate the longer blades on my 'new' jointer (the Craftsman - bought from an estate sale a couple of months ago) and incorporate a few other ideas of mine and others (including, of course, your suggestions.

bobgroh wrote:I have wanted an inexpensive way to sharpen the jointer's blades using my new conical sanding disk. There is a simple little fixture in the Shopsmith library - a simple hunk of wood with a slot in it and which uses the fence as a support for alignment. I took that basic idea and (ego alert!) made a few improvements.
[ATTACH]22272[/ATTACH]

[ATTACH]22273[/ATTACH]

[ATTACH]22274[/ATTACH]

Basically I took the block and slot concept and mounted the block on a matching piece of 3/4" plywood as a base. The base is mounted on a 'miter bar' (a piece of wood sized to fit in the miter bar slot). The block is adjustable (just a bit) with a pivot (1/4" dowel) and a 1/4-20 bolt which is threaded into the base. The jointer blade is retained in the slot with a 1/4-20 nylon bolt which treads into a tapped hole in the block. For a finish, I just sanded everything and used a couple coats of shellac.

Advantage #1: Using the miter bar slot means that sliding past the sanding disk is very controllable. Advantage #2: By moving the table up and down, you can get a very fine control of the horizontal movement of the jointer blade relative to the sanding disk (you get about 0.070 inches of horizontal movement for each inch of table movement up or down. And, finally, you can tweak the table tilt up or down to adjust the blade angle.

I'm not sure if I understand the adjustment. It looks as if the bolt and dowel pins the block in place, and with the miter slot being used seems like it won't allow any horizontal movement towards the sanding disk