Hey BugBear... *LINK*

Re: Hey BugBear...

paul womack

>The text pretty much tells all; I marked a line and worked to it.

Pretty easy task, if you go slow and careful.

BugBear

Re: Hey BugBear...

Todd O. Cronkhite Maine Native, Presently Away

>Yeah, after I posted the question I read further into the text. that'll learn me not to ask questions until I've done more reading,but I was at work, and in a bit of a rush*. I will confess to being quite blown away by the nice arc you put on that blade that I asked the question on impulse.

I did at first think you did it with that Marples roller honing guide, but I guess you only used that to hone the edge after you had ground it.

At any rate, very nice re-confiquration job.

I'm not brilliant enough to do all those Maths, so what I'd do is find a circle of the desired radius and trace it.

T.O.

Hey Todd

Derek Cohen (in Perth, Australia)

>There are two ways to grind a curve onto a blade. The first is just do it freehand at a grinder. Since the surface is going to be chewed up (although it can be chewed up neatly!), the blade shape is less critical. So just get as close a curve as you can. The grind angle is best at 30 degrees.

The second method is the one I prefer since it produces a clean, smooth curve that gouges cleanly. Cut a piece of hardwood the same size as the blade. At the end of this piece, shape the curve you want to grind. Now, if you are using a Stanley or an old woodie blade, which has a groove down the centre, bolt the two together. If the blade you are using is solid (like the original Stanley scrub plane blade, or the LN or LV blades), then clamp it to the hardwood. What you are going to do is use the curve on the hardwood as a template for the blade. The curve runs up against the edge of the grinder rest, and the blade (bolted to the top) is extended until it contacts the grinder wheel (or belt sander) at approximately 30 degrees (preferred angle). You then turn the blade against the wheel using the curve of the hardwood template as a guide.

Regards from Perth

Derek

Re: Hey Todd

paul womack

>The second method is the one I prefer since it produces a clean, smooth curve that gouges cleanly.

Derek - I think your method works perfectly.

But I am convinced that you could get the SAME result from a simple "point" fence that allows pivoting (at the same position as the apex of your piece of hardwood).

argument:

Is is clearly possible to generate a full width "flat" facet on the blade at any angle, by simply keeping the blade in one position.

Further, the "flat" can be any distance (within reason) from the pivot; simply hold it on the abrasive for longer :-)

From these 2 facts (assuming you agree with the facts) I submit that generating a smooth curve on the blade is (actually) done by the operator, and that the curve on the piece of wood does not "Generate" the blade curve at all.

BugBear

Re: Hey Todd

Derek Cohen (in Perth, Australia)

>It is clearly possible to generate a full width "flat" facet on the blade at any angle, by simply keeping the blade in one position.

Hi BB

I used this jig to grind a 1 1/2" radius on a 2 3/8" blade for a #5 1/2 the other day, so the memory of what I did is still reasonably fresh in my memory ..... what was the question again ? :)

I am not sure that I can agree with your conclusion. My visualised reconstruction suggested that pivoting on one fixed point would not produce much of a radius. With this jig the blade starts off at one central point, mainly to initially remove corners. Gradually you will move to using the full camber of the jig. I suppose that you could say that the radius of a circle contains a multitude of single positions.

Regards from Perth

Derek

Re: Hey Todd

paul womack

>I am not sure that I can agree with your conclusion. My visualised reconstruction suggested that pivoting on one fixed point would not produce much of a radius. With this jig the blade starts off at one central point, mainly to initially remove corners. Gradually you will move to using the full camber of the jig.

That still sounds like the operator is providing the control, not the camber of the jig.

There seems to be very little difference (in practice) with the control provided by the cambered wood and a small pivot.

See the attached drawing - the blade is rotated at 15 degrees, and the difference in projection between the 2 pivots (one "proper" camber, one "point") is very small.

BugBear

Hey Paul

Derek Cohen (in Perth, Australia)

>There seems to be very little difference (in practice) with the control provided by the cambered wood and a small pivot.

BB

Nice graphics!

There was something troubling me about my previous reply. What I meant to say was that the camber of the jig provides a way to grind to a specific radius, and to set this up quickly. This jig is not simply about grinding a camber, but grinding a camber of a specific radius.

From memory, the Stanley #40 has a radius of 1 1/2". This is expected to cut a narrower groove than a scrub with a 2" radius. In practice, the difference is not great, as my drawing will illustrate (one thought here - this may account for your own results). Still, a narrower cutting edge should with less effort, which is the whole purpose of this exercise.

I am not sure how accurate these dimensions are as I drew this about a year ago.

Regards from Perth

Derek

Re: Hey Paul

paul womack

>There was something troubling me about my previous reply. What I meant to say was that the camber of the jig provides a way to grind to a specific radius, and to set this up quickly. This jig is not simply about grinding a camber, but grinding a camber of a specific radius.

But that is EXACTLY where I disagree with you.

The intention of my diagram is to prove/show that even an extreme change in radius of the pivot makes very little change to the projection (and hence grinding) of the blade.

Or, put another way, the radius of the wooden block has little or no effect on the radius on the blade.

BugBear

Re: Hey Paul

Derek Cohen (in Perth, Australia)

>BB

We are splitting hairs here. I agree that there is little effective difference in the cambers of blades ground with different radii. That was the point of my illustration. But there is a difference and, small as it is, it demonstrates that the jig is transfering the shape to the blade.

Here is a picture of a set of jigs I have made and use. The blades so ground all have a slightly different radius.

The reason I have taken an interest here is because I use a variety of scrub planes. These range from the narrow Stanley #40 (1 1/4" wide blade) to the LV (1 1/2" blade) to a Stanley #5 1/2 (2 3/8" wide blade). I want to determine whether a reducing the radius of the blade to 1 1/2" for the #5 1/2 will make a noticeable difference in use. The answer is probably going to be that it will not since all the various radii are not significantly different when they project 1/16". But the profiles of the blades are different and do reproduce the jigs from which they were made.

I think we agree with the observation but not with the conclusion.

Regards from Perth

Derek

Hey Paul & Derek

Todd O. Cronkhite Maine Native, Presently Away

>Thanks for the add'l info and follow on. Come to think of it, I had seen this before but had forgotten. I might even have it book marked. :~O It's he!! growing old isn't it.

T.O.

Much ado about nothing?

wilbur

>This may all be a moot point since in the vast majority of cases, after using the scrub plane you'll be going over the planed surface with a smoothing plane anyway. So it probably doesn't matter much what the exact profile of the scrub plane blade is.

I would think a camber template, if needed, would be much more useful for the final step in the planing process. (I've been freehanding this step.)

Ummmm...A question?

John in New Mexico

>If a 2" radius is desired, for example, why not just put your c-clamp 2" from the cutting edge, centered on the blade, and use it as a pivot against the tool rest. Too easy. Or am I missing something here?

John

Re: Hey Paul

paul womack

>But the profiles of the blades are different and do reproduce the jigs from which they were made.

I don't think so, and you've offerred no evidence, other than successfully cambered blades.

Agreed facts so far:

* the template does not constrain a flat from being created (over grinding at any point on the circumference)

* the actual projection difference (which is the only possible control mechanism the template could apply) between a "template curve" an a simple pivot is negligible (see graphic)

* you are successfully creating cambered blades with a template

* I am successfully creating cambered blades without a template

Putting all this together I claim that your blade cambers are created by your care and skill, and could as easily be made by a single "pointed" hardwood piece.

BugBear

Re: Ummmm...A question?

paul womack

>If a 2" radius is desired, for example, why not just put your c-clamp 2" from the cutting edge, centered on the blade, and use it as a pivot against the tool rest. Too easy. Or am I missing something here?

Yeah - that only works if the blade is at ninety degrees to the abrasive.

BugBear

Aha... I knew there had to be something

John in New Mexico

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