Precision Grinding a Hardened Shaft with an Improvised Toolpost Grinder

**Crusty** · Jul 13, 2020, 03:14 PM

I needed to resize a piece of hardened shaft for a fixture I'm making so I made a mount for my angle grinder to use it as a toolpost grinder on my lathe. I started with a good sized chunk of 6061 and hogged out the middle to fit my grinder then drilled it to bolt onto the top of my lathe toolpost. I've got a ¾" roughing end mill that's worth its weight in gold and the mill area looked like an aluminum blizzard had just hit when I finished. The mount is nice and rigid when mounted.

Since you can't reverse the grinder rotation the lathe needs to turn in the reverse direction so the surfaces meet in opposing directions. The lathe ways are shielded with some old jeans (wetted with water so they don't catch fire) and the grinding goes slow, never more than .020" off the diameter and feeding very slow, and you reach your target the same way you catch a unique rabbit - unique up on it ☺. The finished part doesn't have a $1000 ground finish because I used the wheel that came with my Hitachi grinder but it is dimensionally accurate and all it cost was the chunk of aluminum.

In action

Precision Grinding a Hardened Shaft with an Improvised Toolpost Grinder-grinder-mount.jpg

From the backside

Precision Grinding a Hardened Shaft with an Improvised Toolpost Grinder-grinder-mount-back.jpg

**celsoari** · Jul 13, 2020, 05:06 PM

Great work Crusty.
Cheers
Celso Ari

**Crusty** · Jul 13, 2020, 06:52 PM

The shaft turned out perfect and I've already used it to align a series of parts on axis.

A fine better quality wheel would no doubt leave a prettier surface but dimensional accuracy was all that I required. Perhaps with a good quality wheel you might be able to hold to half a thousandth, though that depends on the accuracy of your lathe.

Now that I've got a ½HP DC motor left over after my mill upgrade I think I'll use it to power an actual toolpost grinder with which I can do internal grinding with too.

**old_toolmaker** · Jul 13, 2020, 08:27 PM

Crusty,
A unique way to mount an angle grinder fo O.D. grinding.
By the way .020” is a deep cut in one pass with the piece protruding that far out of the chuck.

**Crusty** · Jul 13, 2020, 08:35 PM

It's between the chuck and the live center so a bit more stable and truth be told I never actually took more than a .010" cut off the diameter (.005" in on the dial).

I've been looking for a better grinding wheel for my angle grinder hopefully with a finer grit and I haven't found one so far. Any suggestions where to look?

**old_toolmaker** · Jul 14, 2020, 07:35 AM

Crusty,
I don’t own an angle grinder so I can’t comment on a grinding wheel recommendation. I believe the wheels normally used are resinoid bonded wheels which are resistant to breaking apart and usually don’t grind cool.

**Crusty** · Jul 14, 2020, 08:10 AM

I found a few at MSC that would likely do a nice job (some CBN even) but they're really expensive. It's tough to find a hard wheel that can take the high rpms in my price range. I'll keep looking.

The shaft did get hot so I had to let it cool several times before I hit my target diameter.

**Unkle Fuzzy** · Jul 14, 2020, 08:47 AM

McMaster-Carr has 60 and 80 grit wheels for 4 1/2" grinders for right about $6 USD ea.

MSC is insane.

**baja** · Jul 14, 2020, 09:46 AM

Originally Posted by Crusty

It's between the chuck and the live center so a bit more stable and truth be told I never actually took more than a .010" cut off the diameter (.005" in on the dial).

I've been looking for a better grinding wheel for my angle grinder hopefully with a finer grit and I haven't found one so far. Any suggestions where to look?

Try McMaster-Carr. They seem to have everything.

**Crusty** · Jul 14, 2020, 10:31 AM

Thanks all. I just ordered a couple of 80 grit wheels from McMaster and I'm waiting to find out if the shipping is double what the wheels cost. They look kinda flexible but we'll have to see when they get here.