SE-76 Squareness revisited

[Jan]

The lessons I have learned from the few examples shown here can be summarized as follows:

A)  When after truing, the grindstone is not square, but conical, we will not get square grind for a toll squarely mounted in the SE-76 jig. The cause of grindstone conicity may be a bent bar of the US.
We can significantly reduce the non squarness of the bevel by aligning the longitudinal tool axis parallel with the side of the grindstone. (We have to use the same sleeves and the same US, which were used for truing the grindstone.)


B)  When after truing, the grindstone is square, and we are not getting square grind we can deduce that the tool may be twisted or its mounting in the SE-76 jig is twisted.
To compensate for the effect of the twisted blade we have to skew its mount in the SE-76 jig. Using trial and error method we have to find whether clockwise or anti-clockwise rotation of the tool in the jig will compensate the twist. (For more detailed description see Robin's topic.)

Under compensation I understand getting the skew of the grind less than 0.5 degrees. Ideal squareness 90.000... degrees cannot be achieved, when angular misalignments are in play.

Jan

[Ken S]

Jan,

I agree with the idea of striving for accurate work, however, I would verify that the tool being ground is straight, parallel, etc. first.

I think it is wise to keep a "known good" chisel in reserve as a system check. If the known good tool can be accurately sharpened, the Tormek is working properly. If not, the Tormek warrents some careful examination.

This idea is a carry over from my photo darkroom days. I would keep a known good negative handy for printing sessions that did not go well. Using the known good negative when needed cut down my trouble shooting time.

Ken

[Jan]

Ken, I have only summarised my recent findings based on 3D CAD modelling. I have had no ambition to provide a checklist to verify that Tormek or the tool is OK for sharpening.

Jan

[Ken S]

Jan,

I did not mean to imply that I wanted the Tormek to be OK. Checking the tool first, and/or having a known good tool to test just seems the most efficient way to begin trouble shooting. Let the trouble be where it is. I just want to locate and correct the problem.

Ken

ps Be sure to follow the topic in scissors. Your suggestion to use something thinner in the knife jig works very well with the scissors jig. Good thought!

[Herman Trivilino]

Why didn't I think of this before? I trued my grindstone today and then measured the diameter on both sides. Outer side diameter: 208 mm. Inner side diameter: 208 mm. I estimate an error of less than 0.5 mm using a steel rule, years of experience, and 60-year-old eyes.

I should have also checked to see if the sides are square to the edges.

[Ken S]

Herman,

We might be better served by relying on our sixty year old fingers than our eyes. A traditional machinist could measure to within about a thousandth of an inch feeling with calipers. The actual millimeter or inch reading seems less important to than how the two sides compare.

Ken

[Herman Trivilino]

If only I had calipers that open that far. I was wishing I had them when I did it.