Mortise Chisel Issue

[Bill Adamsen]

I needed the mortiser for something and decided the chisel in it (1/4") was fine. Then I looked closely and noticed burrs on the outer points of the chisel, but no burn or other indication of abuse. Being in a rush (lazy?) and only needing to cut about 50" of mortise I used it anyway, and it cut fine. But I'm going to pull it out and sharpen/hone the chisel. Anyone seen this? Does this happen from any hardwood or must I have hit something and not noticed it? I had been cutting a lot of Black walnut and White oak. It is a good quality Japanese chisel either Lee valley or Powermatic (they look identical).

[Dan Hahr]

If you think that's cutting fine, you will be very pleased to see how it cuts when you sharpen it properly. I would guess your bit is way too close to the chisel and is deflecting it into the corners.

Dan

[Bill Adamsen]

I think I used a dime to set the gap, and with no evidence of burn, I'd say bumping is unlikely. But the harder woods (the White oak) might provide enough resistance to deflect the bit via the stem. It is a pretty hefty older Yates #40 mortiser. I'm just hoping someone out there has actually experienced this and can provide insights.

[peter gagliardi]

There is no evidence of heat buildup, so either the heat treating of the chisel was very poor, or more likely those outer corners hit metal and bent.
The mushrooming in the crescent between points is most often seen when the drill bit is being pushed up into the chisel and rubbing, or rarely the drill bit not turning concentrically.
There aren't many reasons for what you're experiencing. Is the collet system on your mortiser set properly? On that style, you use the collet to bottom the back end of the bit against, and use the knurled collar to adjust the clearance between bit and chisel- in effect, the bit can never contact the chisel when set as such.
One problem with the Japanese sets is that the drill bit is rarely long enough to set this way.

[Lee Schierer]

From where I sit, it looks like the bit was dropped or pressed into on a hard surface. I would recommend sharpening that includes honing the outside to remove the swirl marks.

[Bill Adamsen]

Peter:

I looked at it again and it has to have been operator (me) error. I'm sure I inadvertently banged the chisel down onto metal at some point. It is just the "outside" two points so that too would point toward hitting metal with it. I can easily ressurect the chisel. The drill chuck is a CNC style and it holds very well. This chisel was a mid-job replacement and I never even honed it.

Peter, I didn't realize you have a K-25 (which is essentially the same thing as the M-40)! Would love to see a close up of the clamps on the hold down bar. I have never had a problem with the bit being too short, always too long, and I just cut them with a hack saw.

[peter gagliardi]

Bill, here u go.

image.jpg
image.jpg

These machines are apparently quite rare, but i would snatch up another in a heartbeat.
I believe the M designation was used on war or military machines.

[Bill Adamsen]

I have been looking for that original design for years. I cannot believe you've been holding out on me! I had designed my own hold down and had pretty much decided to go pneumatic. I had even created G-code from Sketchup to be able to create the dovetail (or use a file). But actually I'd love to see the original ... so one of these days I'm going to sidetrack to your shop to see the real thing. Yes, I've been told the M-40 was a military version of the K-25. My unit was supposedly at Boeing ... but who knows really.

[peter gagliardi]

I have yet to use those clamps. The backstop on mine has a full length horizontal lip that i just set at about 1/32" above the work, and the actual center workclamp does most of the holding, the lip is there just to stop it from picking up.
Maybe yours is different?

[David Spurr]

Nice morticer! I'm jealous.