Advice appreciated on sharpening Chipper blades

[mike mercury]

Here in the UK we call the small electric-powered machines 'shredders', which have 2 spinning blades to chop up garden waste. Although I've had one for some 15 years, the biggest bugbear is sharpening the blades. I've never had a grindstone, so hand sharpening is a lengthy chore. Without any kind of jig, keeping the right angle (although not that critical) is nigh on impossible to achieve.

The blades are 60cms/2½" long, and 25cms/1" wide. See here for an illustration:

http://i35.photobucket.com/albums/d152/ISO1/blades-1.jpg

I'm contemplating buying a wetstone grinder (which will come in handy for other jobs) and have read good comments on the Scheppach Tiger on this site.

But I'm uncertain which jig will suit my blades. The additional Planer blade attachment costs more than the machine itself, but is there a similar, but smaller, jig that would do the same job?

[harry strasil]

Here is a small easily made jig I use to sharpen my jointer knives using my drill press.

http://img.photobucket.com/albums/v81/irnsrgn/wood/knifejig001.jpg

I have a wedge cut from a scrap of 2 by material that has a scrap of plywood fastened to the bottom and another fastened to the back side to keep the jig sliding up it from going off the back side of the wedge from the force of the grinding wheel. I mount the grinding wheel mandrel in the drill chuck, adjust the speed for a medium speed, mount the blade in the jig and then move the table up to where the grinding wheel almost touches the blade.
I move the wedge to where it just touches the grinding wheel and clamp the wedges plywood base to the table and then move the blade slowly up the wedge several times.

With 3 knives to sharpen, I mark where the end of the blade is in the jig and do each blade the same before moving the wedge just a wee bit to take a bit more off if needed. This is so I don't get the blades out of balance by removing more from one than the other two.

This also gives a bit of hollow grind to the cutting edge and then I stone them just a wee bit to remove the burr from the back and hone the front surface.

http://img.photobucket.com/albums/v81/irnsrgn/wood/knifejig002.jpg

hope this helps.

[Jim Koepke]

Mike,

Welcome to the Creek.

My tendency would be to make a holder myself for the blades so that they could be sharpened manually. It could end up looking strange, but it wouldn't matter if it made the job quicker and easier.

Maybe use the mounting holes to register the blades in the holder and use some clamping design to hold them. Then there would have to be a way to make the angle adjustments.

jim

[harry strasil]

I got to looking at the knife I used for the above pictures. I got the set from a friend who got them in a box of junk at an auction, and they were in sad shape, nicked and upon closer inspection, they had been ground tapered by the last person or place that sharpened them. So I decided to go ahead and sharpen them up. And while I was at it I took a picture of the setup in progress. Sliding them along the taper in the jig makes for a very small area in contact with the stone, so heat build up is at a minimum and changing blades after each pass lets what heat there is, dissapate.

http://img.photobucket.com/albums/v81/irnsrgn/wood/knifejig.jpg

Its really an easy jig to make and set up.

[mike mercury]

Sory for the delayed reply - am currently having some 'Waterworks' problems. The details are definately not for this forum!

Hi Jim. Your suggestion of a hand jig is one that I've long thought about, but never gotten round to. Years ago a workshop in a local Hospital where I worked had a floor-standing Linisher which could sharpen my blades in seconds. I tried to duplicate the method by clamping a hand-held belt sander to a bench (belt side up). Although the belts were labelled as being suitable for metal, in practice it took as long as using a hand file!

More recently, in answer tto customer feedback that the blades wore down too quickly, the company's blades are now harder (laser sharpened) making sharpening even more difficult. The current price for a set of two is $30 in your currency, and you take the 'edge' off them in a single shredding session.

Hi harry strasil. By your clear photos I can see how your jig performs. Unfortunately I don't have a Drill press, but I like the idea.