flattening chisel backs part 2

[tablesawtom]

Since my last post received 6 pages which really surprised me I thought I would stir to pot. I put a 20 degree angle on my holding fixture and ground both sides of my my, now dove tail chisels, Back about 2 inches. Since the most acute dove tail angle I have ever heard of is 14 Degrees, I figured 20 would be enough. I didn't figure I would be doing any dovetail over 2 inches deep, and 2 inches back still lets me hold them in my honing guide.

I ground the primary angle at 15 degrees and honed the secondary at 30 degrees. This allows for a strong cutting angle but also allows for a little better penetration with out as much backward pressure.

[attachment=36481]

PS:  the backs are flat

Tom

[omark]

Tom, very nice.  Especially 20deg sides are great and unique -- why manufacturers put so sharp angles on sides of big chisels I will never understand.
Regards,
Miroslaw

[Derek Cohen]

For those of us without a surface grinder, there is an easy way to grind the lands. You need a belt sander. Use a coarser belt, say 80 - 120 grit. I used a 120 here.

Positioned vertically, with a table, and a platform angled (in this case) to match a 6:1 ratio ...



The aim is simply to run the side of the chisel along the belt. The angled platform will steer the bevel angle. (I chose 6:1 as I most tend to do 6:1 and 7:1 ratios for dovetailing).



This the case of this Japanese oire nomi (bench chisel), the sides are vertical (90 degrees) and the side bevels are wide. The result is to retain the same look, but now the sides are angled at 6:1. Perfect for dovetailing!



Sides blackened ...



Regards from Perth

Derek

[tablesawtom]

I owned a 80 inch belt sander for about 3 weeks before I resold it. Other wise never owned a belt sander .But it would work just fine. Derek you sanded the whole edge, but I still think one only needs to relieve the edge only as deep as the dive tails are that is why 2 inches. Some of the complaints I have read is getting cut because the edges are also sharp. Sharp edges also make holding it id a honing guide more difficult.
But all in all I think or hope we have given a few people ideas.

Tom

[Derek Cohen]

I owned a 80 inch belt sander for about 3 weeks before I resold it. Other wise never owned a belt sander .But it would work just fine. Derek you sanded the whole edge, but I still think one only needs to relieve the edge only as deep as the dive tails are that is why 2 inches. Some of the complaints I have read is getting cut because the edges are also sharp. Sharp edges also make holding it id a honing guide more difficult.
But all in all I think or hope we have given a few people ideas.

Tom

Tom, I did relieve the entire length of the blade. Remember, Japanese oire nomi have quite short blades. The chisels I did this to were a set I assembled of Kiyohisa oire nomi. These chisels can run $500 each! They are designed for chopping but, with vertical sides, are essentially firmer chisels. I wanted to use them for chopping dovetails as well. The aim of my method was to leave the chisels looking as though they had not been modified.

I first tried this on an older 36mm Kiyohisa I purchased on eBay. As it came ...



Sides ground to 6:1 ...




... and then blackened with ...




Result ...



As you can see, the side angle is not acute, but the lands are minimal, and therefore it will fit into the side of a dovetail socket.

Regards from Perth

Derek

[tablesawtom]

I chose Narex premium chisels because, as I die maker by trade, most of our die steel was hardened and then tempered back to 58-60 Rockwell C scale.  Chrome  adds a toughness to it. Had to buy individuals in metric sizes but it didn't matter because the bottom of dove tail are anything but standard. And I if I went to far when grinding the sides so what. Again I chose Narex for the 59 Rockwell and I have have less than $20 per chisel, prices went up since  I bought. I kind of liked the length too, Helps me eye ball vertical better.

I like to put it in a  honing guide a few stroked on the stone and I am back in business. But I have to say that their is a big difference in doing 3 of my chisels at less that $20 each and yours at $500 each.


Tom