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Nagoya tool and cutter grinder for necking down cutters


Jun 23, 2017
Marcus asked what I used to neck down my cutters with. I use a Nagoya grinder that I got from a friend a few years ago. I'm currently in the process of designing a drive to rotate the cutter during grinder. I previously used a battery powered drill but it rotated too quickly. I'll update the thread as soon as I finish the drive mechanism etc. Not as nice as Marcus's but then again it was free.

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Haha. Thanks for giving me a case of 20-year-ago regret with one post. I could right-now use a tool for necking endmills and used to have a valve grinding machine that I gave away because I figured I'd never have a use for it. Seeing what you're about to do, that valve grinder came flashing back in an instant.
Here's a cutter I necked down to 25mm length. 1.5mm diameter ballnose. Before anyone says anything about the finish. It was done on a D bit grinder and is the reason I cobbled together the other one. That cutter did enough valves to earn me way over $250k from the customer. From memory I ran it at 9000 RPM which was maximum speed for the Deckel 50T. Material was Delrin.
Good morning ???
Thanks for that...I didn't see your post until this morning...it's a good solution to a common problem.
I used a Deckel SO D bit grinder like you did for many years, and it was always a PITA in three respects.
1) I sometimes needed to just get another 0.020" of length out of the cutter, and the wheel was always way too wide unless I tilted the work so I could reach in with just the corner of the wheel.
2) When I had a very long cutter to neck down the side pressure would sometimes break the cutter while I was grinding it
3) I couldn't make things like Tee slot cutter blanks.

So I went to a motorized spin fixture on my surface grinder.
But it was always a PITA to set up, and even though I made it pretty simple, I would still mentally resist it every time I had a cutter to neck.
Then I got old and it became hard to see tiny cutters and awkward to bend over with a magnifier in order to see what I was doing.

So, like you I was looking for a better solution and I came up with using a Sherline mill as my base because they're cheap and I didn't have to build very much to make it work.
Also, I could hang a cheap stereo zoom microscope over it and sit down to work on it.

If I had your starting point, I'd have done something very similar to what you've done.
The only thing I'd do different is to spin the wheelhead axis 90 degrees and use a cylindrical wheel instead of a cup wheel.
I prefer a narrow cylindrical wheel because I can dress the leading edge of it back to 30 degrees and leave only a narrow land of about 0.040" that remains cylindrical.
That's still wide enough to stand up well but narrow enough to allow you to neck a cutter only a little bit if you want to.
The 30 degree conical area is what I use to put a lead-in angle onto the zone just above the neck, so coolant can get in there easily and I can see what the cutter is doing if I need to.
30 degrees has turned out to be just about right for me, and with that angle dressed on the wheel, I don't need to spin the workhead to make the angle...I can just fake it with successive plunges each going just deep enough to kiss the last angled face until I've made it from the neck all the way out to the OD of the shank.
It's super fast...a bit rough compared to angling the workhead but for a lead in bevel...who cares!

So thanks again for showing it off...I always learn something cool from posts like these.


Buck no where to mount a guard on this machine. I am also super careful where I stand on grinders and always wear eye protection.

Marcus the angle is so steep because I needed all the length I could get on the shank. I also plunge on the small cutters. I have a similar length in 1mm somewhere that I busted one trying to grind in light passes. I am looking for a new straight wheel unfortunately Australia has very limited access to the requirements of manufacturing so I need to get it from China. The toolmaker in me likes your elegant solution a lot more than mine. I will change to a belt drive as the gears definitely cause some vibration