Finer Points of Sharpening (excuse the pun)

[iron bark]

:? I am going to try and sharpen 12.5" thicknesser blades on my 8" grinder with a white wheel following a bad experience with professional grinding. I will make a jig up but the following questions arise: ( :( I apologise to those who think these are dumb questions)

:~ If I do it on the outer edge or tangential to the circumference of the blade -- do I get what I see referred to as a hollow grind?? If so does that preclude me using the Carba-tec planer blade hone??

If I do it on the side of the wheel, (like a surface grinder) will it work and give a flat grind or will it just stuff the blade and the wheel?

What is the optimum (from experience) angle for grinding blades?

Is a hollow grind angle measured across the average bevel or is there some dark side secret to achieving a hollow grind angle?

Last question, is a hollow or flat grind better on thicknesser blades, and should the angle for each type of grind be different???

Cheers,

Ned

[soundman]

Best of luck chum.

I'd recomend finding a better sharpening service.

cheers

[outback]

:? I am going to try and sharpen 12.5" thicknesser blades on my 8" grinder with a white wheel following a bad experience with professional grinding. I will make a jig up but the following questions arise: ( :( I apologise to those who think these are dumb questions)

:~ If I do it on the outer edge or tangential to the circumference of the blade -- do I get what I see referred to as a hollow grind?? Yes If so does that preclude me using the Carba-tec planer blade hone?? No

If I do it on the side of the wheel, (like a surface grinder) will it work and give a flat grind or will it just stuff the blade and the wheel? I can't work out how you can sharpen a 12.5 " blade on the side of a grinder wheel

What is the optimum (from experience) angle for grinding blades? the angle which you have now is probably correct

Is a hollow grind angle measured across the average bevel or is there some dark side secret to achieving a hollow grind angle? across

Last question, is a hollow or flat grind better on thicknesser blades, and should the angle for each type of grind be different??? hollow grinding introduces it's own micro bevel, sorta. This makes the edge a little more prone to damage than a flat grind. Having said that, there are those here which use a Tormek for sharpening jointer/thicknesser blades, this will give a hollow grind, and I can't see any trouble. This is what I'll be doing when the time comes.

Cheers,

Ned

[iron bark]

Quote:"I can't work out how you can sharpen a 12.5 " blade on the side of a grinder wheel"

Thanks for the answers outback - I was thinking of a jig that would let the blade slide across the side of the wheel like a vertical version of a surface grinder - for this application the wheel would not have any sort of guard on it - may or may not work - still tossing ideas around
Thanks again for your response

Cheers,

Ned

[silentC]

I got an electric motor out of an old washing machine, mounted it upright and fixed a grinding wheel on the shaft. I made a jig out of ply just to try it out and it seems to work OK. When I get time, I'll make something more permanent. I've only used it to sharpen 6" jointer knives though.

[son_of_bluegras]

For the typical thickness of planer blades there is negliegable difference between hollow and flat grind unless you go with way too shallow an angle.
I think the typical speed for 8" grinders are way to fast to mess with the side of the stone. Personall opinion and if you want to try don't let me stop you but realize the potential hazard change.
If you have a new set measure the angle on those. If not does the manuel say? Depending on the wood being run through an angle from 20 for soft, easy to work woods to 40 for wood that is harder on blades. The shallower the angle the faster the edge dulls. Slower feed speeds with shallow angles leave a better surface.
One other point, take your time and work careful. If you aren't experienced using a grinder practice first. Be carefull not to burn the temper out of the steel- a very real posibility on grinders. If the temper is changed the blade is ruined. If the blades are plain carbon ANY color change on the blade should be considered as changing the temper. (Do you know the steel alloy?)
You may want to post a picture of the jig you build for feedback from those who have tried this before.

ron

[outback]

The sides of wheels are carily not flat. I dunno about this one.

I like Silent's idea. Sounds all pretty basic and simple.

[Carpenter Eiji]

Get a Tormek.:)

[iron bark]

Carpenter, I might just do that down the track, but meantime I like a challenge

Outback - yeah, I think in the interest of keeping the thing cool, my first prototype jig will work on the normal wheel edge

S O Bluegrass - the blades are HSS 18% - I have messed with a bit of it with the white wheel, and by just touching the wheel and removing a gnat's dick at a time, it doesn't seem to get hot enough to blue the metal

Silent - have you noticed any blueing with your method??

I started building my jig today - will be a bit "heath Robinson" and over-engineered to buggery, but I don't want anything to move once I start, apart from some sort of vernier control to move the blade and its holder/clamp a micro-fart closer to the wheel each pass.

Question - What is the general concensus on whether the wheel rotates from thick to thin on the bevel as opposed to thin from thick ie for example I want to work bevel down, so that will decide whether I mount the jig in front of or behind the wheel - no guard on the wheel for this setup - only talking about grinding here, honing & polishing will be convential

[silentC]

have you noticed any blueing with your method??
No because the wheel spins a lot slower than on a bench grinder. I do all my chisels and plane blades on it as well. It takes a bit longer to remove a lot of steel, so I sometimes use the bench grinder first to get a straight edge, then go to the horizontal one to grind the bevel.