First expirements in hollow grinding of saw blades

After a tumultuous, laborious and exhausting year to this point I've finally found some time to service an overdue obligation.

Most who frequent this subforum will be well familiar with taper ground saw blades. These blades have an essentially straight taper from tooth line to spine. That is, the toothline is widest and the taper is greatest at the spine/back of the blade. Like so:

Attachment 441235



The problem with the use of taper ground blades in backsaws is that the thickness of the blade at the back becomes very thin, sometimes 0.010" or less, which creates difficulties in mounting a folded saw back, particularly with blades thinner than 0.025". The forces applied in mounting and tensioning a folded back will often tear or otherwise irreversibly distort the thin edge of the saw plate.

It occurred to me that I could in principle create a hollow ground blade that would have a relatively thicker spine and toothline with relieved sides between, something like this:

Attachment 441230

Thus, I set out to see if I could do it. I quickly realized that I needed a new grinding machine so I built one (more later :sssh:).

Yesterday and today I finally got some time to set up and use the thing. I ended up making these.

Attachment 441231


I found that I can make a hollow ground profile blade but it is a bit tricky to get it right.

Attachment 441232


If you look closely you'll see that there is a deflection from the back to the toothline.

Attachment 441234Attachment 441233

The above photo's are the 0.042" thick blade. Since these photo's were taken I've found that I can correct the cupping by judicious grinding. Three of the six blade assemblies I made will require some correction, though this one is the most distorted.

I plan to keep updating this post as long as I can, now done. I think I beat the 24 hr. editing cutoff by just a few minutes. :U.

Here's the 0.042" blade with the back to toothline deflection fixed.

Attachment 441304Attachment 441303


The deviation from flat is the hollow.

This is the convex side of the blade after grinding.

Attachment 441305


If you look closely you can see the pattern of grinding that I did to correct the strong transverse and slight longitudinal bows.

Interesting concept. Will be very interested to see your post on the grinding set up, my first thought was a pendulum set up, but what would I know (you could fit my knowledge of this on the point of a needle)

Take this for what it is worth, probably nothing. I would think what you are trying to do is something like what happens when a metal panel is put through a wheeling machine, the panel gets made thinner under the wheel and this forces the panel to change shape. Maybe not quite the same but the principle could apply and Matt (Simplicity) might add more if it is worth more consideration.

Welcome back Rob

I saw this thread only because I realised you had been really quiet of late and I wondered when you had last posted. When I finally found you it was indeed only a couple of hours before!

A ground breaking concept and probably most difficult to apply to an existing saw plate. I imagine it would be easiest to form when the plate is first rolled by means of very slightly convex rollers. However, that is unlikely to happen. One issue I see is that the grinding process would ideally take place in a longitudinal fashion, but I am guessing that you are grinding from the back to the tooth line.

A secondary issue, in what must be an extremely difficult process, is that the first grind on one side, while in itself being no mean undertaking, is nothing compared to the problem of grinding the reverse side.

Regards
Paul

Rob,
Welcome back we missed your antics.

I’m going to ponder this one for a bit,but I say one thing you are a very brave man.

Cheers Matt.

Quote:

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Originally Posted by Chris Parks

Take this for what it is worth, probably nothing. I would think what you are trying to do is something like what happens when a metal panel is put through a wheeling machine, the panel gets made thinner under the wheel and this forces the panel to change shape. Maybe not quite the same but the principle could apply and Matt (Simplicity) might add more if it is worth more consideration.

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My thoughts exactly. Over time my understanding of the concept of tensioning as it applies to hammered handsaw blades has evolved. Originally I subscribed to the idea that hammering induces tension in handsaw blades and would make them stiffer. After taking a series of droop measurements and seeing no real difference I've come to believe that the hammering (or grinding) adjusts or alters the balance of the strains or forces within the metal rather than creating strain where none existed before.

Speaking to the concept of tensioning as applied to saw blades generally I think that there at least five ways the word is or was used.

1) Tensioning applied to handsaw blades as mentioned above as an adjustment of the internal forces within the corpus of the blade by hammering or grinding. (https://www.woodworkforums.com/f278/b...nd-saws-201386)

2) Tensioning as applied to backed handsaw blades where the concept relates to the grip of the folded back on the spine of the blade. This is done by adjusting the relative positions of the blade and back. (https://www.woodworkforums.com/f278/t...w-plate-189765)

3) Tensioning as applied to bandsaw blades in the sense of longitudinal tension applied by adjusting the positions of the drive and idler wheels.

4) Tensioning of bandsaw blades by hammering (or rolling as BobL did, can't find his thread at the moment) to adjust the blade dynamics.

5) Tensioning of circular saw blades to alter the performance of the blade in such a way that the centripetal acceleration, friction and cutting backforce are compensated such that the blade cuts straight, without binding or oscillation. This is also done by hammering. I suspect that the small cut features of modern saw blades have a similar objective.

Quote:

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Originally Posted by rwbuild

... my first thought was a pendulum set up ...

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The pendulum setup was a very very early approach which I've reproduced here for posterity. I abandoned this design as I found that when the tree from which the grinder was suspended swayed in the wind the profile produced was somewhat less than perfect.:doh:

Attachment 441306

:)) ....good one..