Rob Cosman's dovetail chisel

Re: Rob Cosman's dovetail chisel

A. J. Byrd

>Derek,

Very impressive work! Seeing your chisel modifications and those recently posted by Bob Smalser makes me want to take some of my old "scrub-o'-the lot" chisels and put them to good use. But some very important questions:

1. How do grind away all of that very hard high quality cast steel without overheating it and losing the temper? (I've rehabbed a couple of old Swan firmers and it took forever to just grind past a couple of pits that were right next to the cutting edge)

2.If you do retemper the edge whats the best way to go about it?

I would really appreciate any info you have on these subjects because I have about 8 old chisels that were abused by previous owners sitting out in the shop just begging {and if youv'e ever heard a chisel beg you know tis' a pitiful sound :-) } to be put back to useful work.

Thanks,

A.J.

Re: Rob Cosman's dovetail chisel

Derek Cohen (in Perth, Australia)

>AJ

This really wasn't as difficult as it appears.

This particular chisel has been on my To-Do list for several months (ever since I saw Rob's video). His argument for this design over skew chisels made sense. Around this time he described (on this forum) how he had ground his chisel (a 3/4" in his case) on the side of his grinder's wheel. I wasn't too thrilled at that prospect, so I procrastinated. Yesterday it came to me that I could also use my 4" angle grinder. This turned out to be so easy to grind this way. And as long as you stay away from the bevel area until the end, the metal does not heat up much. At no time did it change colour. To be safe, I dipped it in water when it began to warm.

Regards from Perth

Derek

Re: Rob Cosman's dovetail chisel

Rick Hoppe (Los Angeles)

>A.J., I've made one of those dovetail chisels too. Whenever I need to hog off large amounts of steel, I use my Dremel Moto Tool with a cutoff wheel. The wheel is an abrasive disc that is about 1/32" thin. The wheel is not meant to grind, but to cut, and it cuts tool steel very quickly because of the narrowness of the kerf. So, I just cut along a layout line and touched it up on the grinder.

It shouldn't be taking you so long to grind past some pits. You may be using a wheel with too fine of a grit. For heavy grinding, I use the 36 grit gray wheel that came with my grinder. Also, the coarser the grit, the cooler the grind.

You also may be too cautious in your concern about bluing the steel. It�s harder to blue the thicker steel in the body of the chisel than it is to blue the fine cutting edge of the tool. With the above grinding wheel, I could grind for about 20 seconds then dip it in a cup of water (with ice added) for about 3 seconds then go back to grinding.

Good luck and happy grinding! - Rick

Re: Other dovetail chisels?

William Duffield, on the Cohansey

>Great save!

For those who may not want to grind their own, there are alternatives. For example, Ashley Iles makes a fishtail gouge that looks like it has the necessary geometry.

54 X 2 Fishtail Corner Chisel

Pfeil also makes a series of #1 fishtail gouges, but I don't know whether their flair is sufficient for your preferred dovetail angle.

Thanks for the info.....

A. J. Byrd

>...youv'e both hit on things I've been doing wrong.

Looking back I realize that I have been doing all my grinding on a 120 white wheel(I keep a felt wheel mounted on the other arbor the bench grinder is used mostly for HSS turning tools)and I had never considerd using my angle grinder or dremel tool on my high carbon chisels. Appreciate your input.

Derek, one more question, what grit wheel do you use on your angle grinder?

Thanks,

A.J.

Re: Rob Cosman's dovetail chisel

Alan Bierbaum

>I guess that I am just somewhat on the dense side. I don't understand where you would need a chisel of this shape or how you would use it.

Re: Rob Cosman's dovetail chisel

Jack Guzman from Maine

>Rob Cosman uses it to clean up the corners of half blind dovetail sockets(is my terminology correct?).---Jack

Not to be contrary...

Paul in NJ

>but I find a skew works better for me paring out the waste in the acute corner of a blind dovetail socket. I re-ground one of my flea market chisels to a fishtail shape and it didn't work that well for me. I admit I haven't seen Rob's video so I might be missing something. When you use the fishtail shaped chisel you have to push a little sideways as well as forward, with the skew the 'push' is more direct. I don't even bother with a left and right skew anymore, I just flip it over. The 25 degree bevel on my skew is long enough to register to the work. I hope your chisel works out for you, this wouldn't be the first time I missed something.

Paul Dzioba

Re: Not to be contrary...

Derek Cohen (in Perth, Australia)

>Paul

The point made by Rob is that it is easier to pare forwards (with your weight behind you) than on the diagonal. I find that this is so in practice. Having said that I still have use for my skew chisels. For example. they are great for cleaning out in the corners of the tails (although a sharp knife could do this as well).

Regards from Perth

Derek

Re: Thanks for the info.....

Derek Cohen (in Perth, Australia)

>AJ

I have no idea what type of grit is involved in a angle grinder's cut-off wheel. I don't think that there is a rating for that. My high-speed bench grinder uses a 60 grit white wheel.

Regards from Perth

Derek