Grinding Jigs and Camber

[Jono M]

I have been building plane blade sharpening jigs.

Flat rest with magnets

537426

Fit magnets into holes - the small indentations, created with a hammer and punch, fix them in. I then glued on a mounting plate with tapped holes and fitted the rod blocks. A length of 12mm rod guides the assembly in front of the grinder wheel. The magnet clamping force is good and the blade will not move. Actually, it is more than enough and probably half the number of magnets would be fine.

537427537428537429

The 12mm rod is one meter long and I need to bend it to create a radius, that will in turn create a camber on the plane blade. A turnbuckle and wire pull/bend the rod.

537430537431

The cambered blade

537432

But the meter long 12mm rod and wire take up the whole length of the grinder and is not ideal.

Somewhere I saw this technique to make curves (cambers) using two points and hinged rulers. I plotted out the effects. You can change the curve by hinging the rulers more or moving the two guide pins.

537433537434

Then I tried to work out how to use this idea and turn it into a cambering jig - t slot aluminum- wood - rod - strut - angled blocks.....maybe I could but not today! ...then I just bent the 12mm rod to form the radius.

Bend the 12 mm rod with a clamp/s and check often you only need a very small radius. Make one for scrub planes and one for finer work. Of course, you need to keep one straight for flat blades.

537435537410

Showing the amount of bend for the large camber.

537411

Then....I "kinda" just stumbled on this idea.....

Place two fairly strong magnets on the bevel side of the plane blade. The second photo shows the magnets (hidden underneath) butted up against the board - push the blade up to the guide marks. This sets the bevel angle that I worked out earlier and aligns the magnets.

537412537413

Camber rod installed on grinder rest.

537414

Blade with magnets rests on rod and act as the guide for the blade. There is just enough magnet power to keep it stuck to the rod. Gently move the blade left and right as per normal to sharpen.

537415537416537417

You still have to check as you go and make small adjustments.

Square check.

537418

Camber check for both radiuses.

537423537425

Simple and cheap


I would also like to make a marking knife sharpening jig and maybe have the grinder motor movable back and forward to fine tune the bevel angle.

thanks

[D.W.]

Jono - these will help you reach your goal of getting sharp tools in the near term. i think in the longer term for both purposes you may wish do everything freehand for speed.

We typically maintain camber with honing and grind only to remove metal behind the honed edge (without removing the edge) to make it easier to maintain shape.

The confounding issue doing this is getting initial camber that's suitable for a given plane, of course.

But the thinking process is admirable, and thinking and experimenting in the shop is always good when results can be observed as in your case (not so much so when results are hypothetical and attainment of goals is also on a hypothetical basis!!).

[derekcohen]

Jono, I echo David's comments.

The only blades I use a machine to grind to a camber are those with marked camber, such as a jack plane (about 11-12 inches) and a scrub plane (3"). Even so, the bevels need to be honed by hand. All smoothers are cambered and honed by hand.

Years ago, Tormek released a holder for cambering. I recall trying it (per David Charlesworth's recommendation), and gave up on it immediately. Nothing like hand control for fine tolerances.

Regards from Perth

Derek (still in New Zealand)

[Jono M]

Hi David and Derek,

Thanks for your reply.

I have done some free hand grinding but need some practice. And do all my honing free hand.

What would be considered the best practice technique, for free hand grinding at the moment? I assume you rest the back of your fingers on the grinder rest, while holding the blade and concentrate.

And do you use the cambered blade to make square adjustments to the edge of a board? I am trying to do this effectively.

[D.W.]

Hi, Jono - I will say this in all seriousness - for me, it doesn't matter that much. Sometimes I grind with a tool rest set to an angle, and sometimes I leave the tool rest square. When the latter, I use my finger across the back of a plane iron almost as a jig to rid the grinder rest, but as mentioned previously, other than early parts of a tool's life (like in making in my case), I will keep the overall geometry with the hones and then use the grinder just to remove metal that is impeding working the edge easiest.

I think a rest for most people will work best - as in one set for the wheel, and then fingers close to the iron bevel for feel, and you can use the opposite hand fingers to create a fence lower on the iron so that it can't lift a little above the rest and waste your time.

yes on the plane irons - I do not generally keep any that are "perfectly straight" across outside of fillister and rebate planes, and perhaps a shooting board plane - but even there it won't matter as much as just setting the plane properly.

But all of the edges that I use to match or strike edges have a small amount of camber. It is on a jointer, perhaps only a few thousandths of an inch, and on a try plane, a little more. By I have had great invisible edge joints off of the try plane without having to go finer. The camber is maintained in honing just by deciding where the pressure will be.

For example, if you are using a jointer and it seems like the shaving is a little narrower than preferred, you make mental note and then work the center of the iron more than the outsides when honing the next time. if it's the opposite, then some emphasis honing the outer areas of the iron a little more next session. Nothing ever really gets away from the ideal set very far, so not much capability is needed then in considering how to get from something out of whack to something good. The same is true for skewed irons like a moving filister - they are honed freehand and if it seems like the angle is getting away from what the sole and bed of the plane want, then the area that's getting a little high, you just hone a larger burr on that side when you hone once or twice and all is well again. And then freehand grind without removing the edge, just the same. there is no great need for any fixturing with a skew then because it only needs a rest like the rest of the tools. The grind will not be used to set an angle, so needing something to set the grind precisely goes away and isn't needed.

[Jono M]

David,

Thanks for explaining how to look at what the shaving / plane is doing and then fine tune the blade with honing to make corrections.

I will make it a part of my sharpening.

[D.W.]

I think you'll still find your problem solving skills and setting things up useful from a toolmaking and getting tools in shape side of things, though.

Toolmaking is fun.

What we talk about a lot is what shape we have to get tools in. it's really about results even though I did more method describing here than usual. But what isn't discussed often is when you have a tool performing really well, how do you keep it performing well like that. Which is more what I described. There is much work getting a tool there but not that much in keeping it there.

[Jono M]

I had to drive 3 hours to Wodonga the other day.

Do I concentrate on the truck ahead of me, the Kangaroo bounding up alongside or if I am over 110 km/h........no I start thinking about grinder rests:)

The idea is to have two parallel 12 mm rod rests, fix them to a disk and make them rotate, with one rod fixed at the center of the disk. Rotating the disk will make the outer rod raise or lower. The tool is placed on both rods and the movement will allow for different bevel angles to be ground.

The idea is now in prototype phase and the build is below.

I cut out a disk with a circle cutter on the drill press and round over the edges with router and round over bit

538514538515

Make the disk hole 11.5mm and hammer the rod in for a friction fit and I cut it to size with a small grinder

538516538517

A second hole is drilled in the disk (for the second rod) and a spacer is made to keep the rods parallel. Note that the other holes in the disk are not intended.

It is then mounted on the table. The hand wheel did not give a smooth rotation, so I added a lever for finer control but decided on using a screw adjustment.

Using metal strut I made space for a strut nut and hammered it in and screwed the assembly to the disk (the strut is slotted and allows for some movement). On the table is fixed an eye bolt and then the threaded rod is added and fixed with nyloc nuts so that it can rotate. The turn nob is a worn-out hole saw. The whole screw adjuster does not have to move much to do the work and I did not see any racking/deflection going on

538505538506538507538509

Showing the movement of the disk and rods

538510538511

The ground chisel and finished

538513538512

I have a grinding rest as shown below and essentially it is what I have made above but without screw adjustment.

Some advantages the rod rest has.

The rod rest allows you to sharpen short chisels (the handle will bottom out on the edge eventually)
The rods a smooth the tool glides over them
Fingers can "gauge" along the smooth rods when sharpening
There are no brackets below the sharpening area
It's better than my magnet idea above
The two rod mounting brackets (fixed to the slot) are independent, and you can easily adjust the rod parallel to the face of the grinding wheel
https://www.carbatec.com.au/Images/ProductImages/Medium/CT-CGJ-01-Blue-Etched.jpg

Adding a CBN wheel and digital angle cube would add angle repeatability for all the different tools....

Or make the rods independent and one adjustable.......time for another drive

Jono