Saturday, January 10, 2015

Unorthodox chisel grinding

In my possession are 4 typical Dutch mortise chisels. Two of them have allready been sharpened and used, but two were still waiting for some attention. I need a narrow one for the cabinet door, so this was a perfect moment. Problem is, the grinding angle they had was very obtuse, in the order of 40 to 45 degrees. They are the two right hand chisels in the picture. The two on the left are close to 30 degrees, which makes them perfectly allright. I drew a line on one of the misfits to show a 25 degree grinding angle.

As you can see, that is a lot of steel to remove. They are laminated chisels, but still quite hard, so filing wasn't an option. Even grinding would have taken a lot of time, and I don't want a hollow grind on them either. So I choose a rather unorthodox method, and a pretty radical one, the angle grinder!

Now, let me make one thing clear: Don't try this at home kids! It's a sure way to ruin a pair of fine chisels.

But being the reckless idiot that I am, I put them in a vise, got a very narrow cutoff blade and chopped a corner from the chisels. I made sure that I stayed away from the edge, put very little pressure on the grinder and took it slowly. Here the corner is still attached but one hit with a hammer was enough to seperate it from the rest.

Despite being very carefull I still decided to grind the edge back a few mm on the Cruessen bench grinder and proceeded to make a hollow grind. The hollow certainly not all the way to the edge, just enough to get a lot of metal out of the way. Then I grinded even more metal towards the heel of the bevel.

All this to remove as much metal as possible before I go to the next powertool, a belt sander. I don't have a professional one. Mine is a handheld model for wood, and I can't get metal cutting belts in this size. So I use a fresh 80 grit belt for sanding wooden and painted surfaces, clamp the sander upside down in the vise and start grinding the bevel.

It takes a while. I cool the chisel often in cold water and look carefully if it is keeping everything square, correcting as neccessary. I had another "puberty moment". This sander has been used for many jobs around the house, so it is rather filthy. And grinding steel produces sparks. One plus one is a smoking and very smelly sander! Time to dismantle it and clean out the mess.

But all this resulted in two 25 degree bevels, ready to be sharpened to usefull chisels on the wetstones. I will probably try a 30 degree secundairy bevel angle first to see how they hold up.

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