Tool Grinding Experiment

Being motivated by Mikey's great instruction on tool grinding, I dove in today and seems I was reasonably successful.

Success (I think?) grinding a turning (square) tool. I'm sure it would be easier with the models on hand, but wanted to try it just based on Mike's pictures and descriptions. I think I'm close (it seemed to work very well in brass, just ok on 303 stainless)

I installed the platen on my 1x42 belt grinder. It's just steel, but seems flat.


Set the table to 15°


Laid out the geometry on the blank. I reused a MoMax blank, so it looks a little funky, but I think I got the tip geometry correct.



After grinding the shape, I honed the cutting surfaces on 80um diamond film and finished with a 6000 grit water stone. Here are the results on brass:


Short curls. Still a lot of glitter--think I need to take deeper cuts?

 

Generally with brass tools, you do not use side rake, the tool would be flat on the top, and yes, the chips should be curls; more feed.

 

Brass tool should be flat on top, so no chip breaker?

What’s the preferred cutter style for 303SS?

 

Probably best would be a semi circular ground in chip breaker / curler, but side rake would work, but may result in stringy chips, or possibly a step chip breaker on the side rake angle would work; I have machined hundreds of pounds of 303 chips, mostly with carbide TPG tools with a adjustable chip breaker adjusted about 1/16 - 3/32" behind the cutting edge; feed is adjusted until the chips curl or with more feed will break into short curls or C shaped chips.

 

John,
That explains a lot. I was getting very stringy chips on my stainless test piece. I also got feedback from Mike that my back rake was off. Learning lots (even broke out Machinery's Handbook this morning!)

Is this the type of tool you're talking about with an adjustable chip breaker?



I'll noodle on it this week and hit it again in the evening or next weekend.

Thanks,
Evan

 

What kind of brass is it??? Not every family of brass will leave a stringy chip. And if you are looking for a nice finish? Sometimes the machine has too much noise and that noise gets telegraphed into the tool cut leaving a poor finish…Dave

 

Sorry my post was confusing. The brass (MB--mystery brass) came off in little curls--the chip breaker seemed to do its job, and the finish was decent.

The strings I was having trouble with were on 303SS. I'm guessing this has to do with the negative rake that Mike pointed out on my tool, which I'm guessing would work ok on brass but not on SS.

I'm pretty sure the chatter had more to do with my set up than the machine itself. The 11" 303 rod was too large to slide into the headstock, so I chucked it in my 3-jaw and used a live center to stabilize things. The chatter was very low close to the chuck, but there was a nasty resonance out toward the live center. In hindsight I probably should have used a dog and turned between centers, but I just wanted to rough it to size and cut into rough lengths. I succeeded on the rough part!

 

Evan, I recommend that you not use your precision vernier bevel gauge on the belt to check the angle. It won't be precision for long. Anyway, the angles do not need to be held within anywhere near the accuracy of that gauge. Something much simpler would work fine, and would be quicker and easier to use as well.

 

Bob,
That’s a good tip. The belt was stationary, and I vacuumed and cleaned the table, but you’re right. I’ve got a Veritas angle gauge that would be safer.
Evan

 

I use one like this for the grinder, seems to do the job.