Help with some specifications

Hey guys, I've got a Japanese blacksmith who's interested in making me a 1/4 hollow ground razor (instead of the Kamisori) but he's never done it before and I want to give him some specs to guide him.

I'm working in MM here, so bear with me Americans.

I'd like a 25mm blade (roughly 8/8), so I think that would mean the distance form the point of contact on the spine to the edge should be about 23mm. Does that sound right?

This makes me think the width of the spine should be 6-7mm, which should give a blade angle of 16-17 degrees (I'm not being too precise because he's not that precise himself).

In addition, he's wondering about using the traditional Japanese method of welding a steel blade onto a wrought iron spine. This is how Kamisori are made, but I fear that over time, the different honing effects would lead to problems with spine width. Is that a valid fear? Or should I just let him do it the way he's accustomed?

Any advice or thoughts would be appreciated.

Thanks guys!

How does the different steel effect the hollow side of the kamisori?
Over time... How many generations are you suggesting?

There are both framebacks and partially hardened blades so i dont think that would be a problem

I would think with a rounded spine 21-23 for a total with of 25 should do nicely

Dont remember the formula for width-size 1/4???

I think your math and figuring are correct. I would not get too hung up on getting an exact angle. somewhere around 16 will be fine.

I think a welded blade would be cool. There are some very old frame backs that have a brass back that have lasted this long. I do not think an iron spine not be an issue.

It sounds like a fun project.

Charlie

Thanks guys, good to know I'm in track, at least.

Janivar, my concern was with the 1/4 hollow thing--I hate the look of huge old hone-wear on a heavy razor, which might be amplified by the softer iron.

Charlie, yeah, the weld might be cool looking. I know a guy who does awesome polishing, too, so I might get the hamon to come out on it.

Cool, guess I'll get back to him.

That sounds like a very nice razor. I would like to see pics when it is done. If you are worried about hone wear why not just use tape? Provided it never gets chipped needing a lot of steel removed I doubt you will remove enough steel from the blade to significantly change the angle.

Jim,
you might find this info on geometry from Robert Williams' site useful
Razor Edge Geometry Introduction | Robert Williams Custom Straight Razors

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Originally Posted by mainaman

Jim,
you might find this info on geometry from Robert Williams' site useful
Razor Edge Geometry Introduction | Robert Williams Custom Straight Razors

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Is it correct to interpret this as the spine width and the width of the blade is measured at the points of the spine and the cutting edge that will contact the hone? I know on the WIP below using these points would make this a 7/8 with a 4:1 ratio, whereas using the back edge of the spine it would be 9/8 with a 6:1 ratio.

Attachment 135840

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Originally Posted by dcraven

Is it correct to interpret this as the spine width and the width of the blade is measured at the points of the spine and the cutting edge that will contact the hone?

Attachment 135840

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Yep, the two contact areas are where the angle of the blade measuring is done. As for the width I have seen people do it both ways, total width or the width between the contact areas.

Charlie