I’ve recently been attempting to turn some mild steel. I wasn’t getting good results.
I started out trying to use a HSS bit which was included in a set supplied with the lathe. I can’t say it was particularly sharp. I’d used it on a bunch of brass and aluminium and it had performed well.
The results with steel were, frankly, awful. Scored and lumpy (and this was supposed to be a bearing surface).
So I was inspired to try grinding my own.
I followed the Little Machine Shop guide to grinding tools that I’d found through google, http://littlemachineshop.com/instructions/grindingtoolbits.pdf
It is quite a simple guide to follow.
I don’t have a particularly good grinder. It is a cheapie B&Q special, upgraded with a wider pink wheel for sharpening my woodworking lathe tools and a newly fitted tool rest that I picked up cheaply at Cardiff Axminster’s opening day. Other grinders are far superior.
Anyhow, I set the rest to an eyeballed 10 degrees or so, angled the tool blank at an eyeballed 10 degrees-ish and ground the front face compound angle.
Then I put the bit parallel to the front surface of the wheel, overhanging the left hand side and ground the side relief to the 10 degree angle set on the table. This took some time and I dipped in a glass of water to keep it cool enough to hold comfortably.
The top relief was achieved by flipping the bit over to the right hand side of the wheel and angling it to an eyeballed 10 degrees-ish again. This grind took a while.
Then I touched the point surface on the wheel – you have to elevate it from the table as all the compound angles mean it’s quite high on the wheel.
So, all very approximate. I wasn’t expecting great things at all. I was expecting something that would cut, but probably no better than the blunt tool I’d used previously.
However, a quick check on some silver steel gave great results. So I pulled out my rough and horrible mild steel and gave that a spin. It cut like a dream producing lovely tightly curled long strings of springy swarf. The surface finish was vastly improved.
Either I have been really lucky and hit some magic angles, or maybe it’s just that any sharp tool gives a decent result. I’m sure I’ll find out sooner rather than later.
So that’s a happy bit of grinding 🙂