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Old 09-03-2011, 08:02 AM
algale algale is online now
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Default Jointer knife jig sharpening angles

I plan on making the jointer sharpening jig shown here. http://www.woodshoptips.com/tips/052404/index.htm

I will use this jig in conjunction with my newly acquired conical disc sander to sharpen the knives on a Grizzly jointer that I am restoring. The knives on the Grizzly seems to be sharpened to 45 degrees. This got me to thinking about the angle to cut the slot in the jig for the blade. Should it really be at 45 degrees as shown on the Shopsmith jig? Given the way the conical disc sander works, won't I be tilting the table about 3-4 degrees anyway? Would it be better to build this 3-4 degree tilt into the jig by cutting the blade slot at, say, 48-49 degrees and then just leaving the table at 0 degrees? That got me thinking about the jointer/planer sharpening jig that Shopsmith sells, as shown here. http://www.woodshoptips.com/tips/052404/index.htm

Does that jig require the table to be tilted or is the tilt angle already built into the jig?

Last edited by algale : 09-03-2011 at 08:15 AM.
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Old 09-03-2011, 09:27 AM
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IMHO tis easier to just cut the slot to 45 and make any small grind angle changes with the table.
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Old 09-05-2011, 06:49 AM
michaeltoc michaeltoc is offline
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Yes - you need to cut the slot at 49 degrees to compensate for the 4 deg tilt of the conical disc.
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Old 09-05-2011, 07:02 AM
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Quote:
Originally Posted by michaeltoc
Yes - you need to cut the slot at 49 degrees to compensate for the 4 deg tilt of the conical disc.

I think the first task should be to either do or check the complete alignment of the main table. Then install the conical disk and check for the relative angle of the disk face to the table. I suspect that you are going to find that the difference is neither 3 nor 4 which means that it will become necessary to tweak the table no matter what.
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Old 09-05-2011, 07:32 AM
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Quote:
Originally Posted by dusty
I suspect that you are going to find that the difference is neither 3 nor 4 which means that it will become necessary to tweak the table no matter what.

I think you may be right. Does anybody who actuallys own the jig Shopsmith sells for sharpening jointer/planer knives know whether the Shopsmith jig require the table to be tilted to the angle of the conical disc first? If so, I believe Dusty is correct. It would mean Shopsmith believed that the angle on the conical disc was simply too variable to build the angle into the jig.
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Old 09-05-2011, 09:05 AM
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Quote:
Originally Posted by algale
I think you may be right. Does anybody who actuallys own the jig Shopsmith sells for sharpening jointer/planer knives know whether the Shopsmith jig require the table to be tilted to the angle of the conical disc first? If so, I believe Dusty is correct. It would mean Shopsmith believed that the angle on the conical disc was simply too variable to build the angle into the jig.

If memory serves correct, the jig-manual says to leave the table at normal horizontal position while using the conical sanding disk. However, I do recall a Sawdust Session in which Nick noted that these jointer/planer knives have a nominal factory angle (45 degrees?), but some of his craftsmen friends have deliberately gone to a different angle such as 37 degrees. I suspect there's a decent tolerance for variation, and any one angle is a compromise over different wood species.
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Old 09-05-2011, 09:28 AM
pennview pennview is offline
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Here's another option for sharpening or honing planer and jointer knives -- http://www.woodcraft.com/Product/208...px#Information -- It's rather slick in it's simplicity.

There's a video on the Woodcraft web page showing how this jig is used to sharpen the blades of jointers and planers. It's worth watching as it might give you some ideas on how to adapt this technique to a simple home-made jig that will do the same thing. No need for a conical disk and all that, just a some sandpaper and float glass. It seems to me you could make your own jig in a couple of minutes and use MDF instead of glass. In any event, it's worth the look I think.
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Old 09-05-2011, 09:35 AM
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Suggestion(s) [and relevant details]:

There is nothing magic about a 45 degree angle other than its ease of grinding or cutting. Machinery typically have stops for that angle.

Jointer/planer knives usually perform better at a slightly steeper(more pointy) angle.

That angle will vary depending upon the species being cut.

The conical disc is not 4 degrees as stated by SS, but nearer to 3 degrees and is likely to vary from disk to disk.

With a jig angle of 45 degrees and a conical disc angle of 3 degrees, a table setting of 0 degrees results in a grind angle of 42 degrees on the knife(+- disc angle variation).

IMHO that is a good compromise angle for varying wood species.

If one typically planes different species the grind angle can be adjusted from that nominal 42 degree angle by table adjustment.

If you do desire a 45 degree grind, a 45 degree jig will produce that grind angle if the table is squared to the disc.

Adjusting the table gives you control of the grind angle. Tricky part is understanding(knowing) the starting point(jig angle and disc angle).
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Old 09-05-2011, 11:22 AM
algale algale is online now
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Quote:
Originally Posted by nuhobby
If memory serves correct, the jig-manual says to leave the table at normal horizontal position while using the conical sanding disk.
If that's the case, it looks like Shopsmith must build into it's jig the extra angle to compensate for the 3-4 degree angle of the conical disc. One advantage of doing this i can see is that by leaving the table flat there will be no tendency of the jig to slide down the tilted table, away from the fence and toward the disc. In my limited testing of my conical disc with some wood scraps, I have noted this tendency of the work slipping down on the outfeed side of the disc if I am not careful. Incidentally, as those of you who own it already know, the conical disc works as advertised and gives excellent results.
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Old 09-05-2011, 11:36 AM
algale algale is online now
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Quote:
Originally Posted by pennview
Here's another option for sharpening or honing planer and jointer knives -- http://www.woodcraft.com/Product/208...px#Information -- It's rather slick in it's simplicity.

There's a video on the Woodcraft web page showing how this jig is used to sharpen the blades of jointers and planers. It's worth watching as it might give you some ideas on how to adapt this technique to a simple home-made jig that will do the same thing. No need for a conical disk and all that, just a some sandpaper and float glass. It seems to me you could make your own jig in a couple of minutes and use MDF instead of glass. In any event, it's worth the look I think.
Thanks for the link. I've seen some homemade examples of this. One problem I see with this jig is that you have to do two knives at once, which means that it will be very hard to remove the same amount of material from all three blades because after you do two, you pull out one and put in the third blade and then hone those two evenly, even though one has already been honed. This could lead to the blades being of different weights and cause vibration of the cutter head.
With the Shopsmith jig or a homemade version, as long as one bottoms out the blade and keeps the same fence and quill settings, you could theoretically hone all three blades the exact same amount, meaning the blades would stay balanced and you would reduce cutterhead vibration.
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