Soft Spot in Chisel

[Chris Griggs]

Okay, first a little back story. A while a back I bought a used set of AI butt chisels that came to me in pretty rough shape (see thread with angry rant here: http://www.sawmillcreek.org/showthread.php?161001-Dubbed-Chisels-I-am-so-very-frustrated&highlight=)

Since getting them I fixed most of the issues which mainly involved lapping the backs like crazy and grinding past the areas that were back beveled/dubbed. Additionally, The older AI chisels didn't have side walls ground as narrow as they do now, so I also ground down the side bevels to make these more ideal for chopping dovetails.

However, this past week I noticed that the about 1/16-1/8 of the edge/corner of the 3/8 chisel started crumpling immediately after sharpening/honing. That is to say, the left corner would crumple while doing a test of sharpness paring pine end grain.

The edge is hollow ground to about 30 degrees, and then honed on Ark stones followed by a strop. It is not burned... really it isn't, I've checked it several times. I even went back and reground the edge a couple of times and turned down the speed all the way down on my 6" grinder just to be sure there would be no burning that I wasn't seeing.

So anyone have any idea why my chisel has a soft spot. Is it possible that I drew some temper while grinding, without seeing any burning? Is it possible that it was improperly treated when it was made and that there is a soft spot that I will eventually grind past?

So do ya'll think?

[Johnny Kleso]

Heat Treating even for pros is not a sure thing..
Since you have altered the chisels your kind of on your own now..

[george wilson]

If you did not burn the metal blue when grinding the bevels(assuming the metal surface was bright enough to see the colors of burning),it is unlikely you messed up the chisel. Suggest you grind away about half the bevel,and re bevel. Then,check and see if the corner still crumbles off. You could also test the bad area with a SHARP,smooth cut Nicholson file made in USA. If the chisel files easily,you have a soft spot. Unless you undertake to re harden and temper the chisel,the only recourse is to shorten the chisel until the soft area is gotten past. Can you just file the bevel on the side of the chisel a little,to see if it is soft enough to file easily? That would be the best thing to do before you grind your chisel shorter. If the bevel shows it is too soft,the chisel needs to e re hardened and tempered.

[Chris Griggs]

Thanks George. I figured you have some helpful input.

I'm pretty sure I didn't draw out any temper when I ground the chisels down, but it is possible. There definitely isn't any visible sign of heat damage. Is it possible to blue the metal when grinding without having an actual burnt spot be left behind? The chisels definitely heated up when I reground them but I think I was careful and kept my hand near the area being ground at all times. They got borderline too hot to touch when I ground them but I quenched them frequently and once again didn't see any yellowing or bluing. I reground a whole set of 6 chisels and the 3/8" is the only one with this issue.

Anyway took your suggestion and filed a bit on the side with the file I use for jointing saws. It's not new sharp but cuts. It was hard to see if it was cutting more in one area than another, but it did feel like it might have been biting in a little more in the area closest to the tip, near where the crumpling is happening (not certain though). I will probably just grind some more off and see if I can get past the soft area.

[george wilson]

No,if you burnt the steel,you would see colors IF the steel was not rusty,black,etc.. If you can file the steel with any ease,I am afraid that chisel is just too soft. Usually,back when I had simpler means,I heated from the tang end,and let the colors creep towards the cutting edge. I don't know how others may do it. If they are using a reliable,temperature controlled furnace(which they SHOULD be using,I have 1 myself),they could just put the whole batch of chisels in there and let them soak at the pre determined tempering temp..

If your chisel is too easy to file on up the bevel,grinding it back will not fix the problem,and will just waste metal.

I have noticed a fair amount of variation in my antique chisels,even of the same make. Todays should be better,if modern heat treating equipment and good steels are used,because the human error factor is lessened. Some of my antique Addis carving tools can range from softer than I would like,to so HARD that they won't take a decent edge. I have a whole set of pre war Addis's like that. I had to lay them on my guitar side bending iron and heat them up to temper them to where they should have been in the first place. This was when I was in the Musical Instrument Maker's Shop. Several times,I'd soften too brittle jeweler's saw blades the same way. They were fine after the re tempering. You,however,have the opposite problem,which is a more serious fix.