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darryl
12-20-2008, 05:44 PM
I've been meaning to ask for some time now- I built my tp grinder to use the Unimat grinding wheels, and have made a couple adapters to allow the use of typical 3 inch cutoff discs as well. Most of the time I'm using the cutoff discs because they're more convenient to do a wider range of grinding operations.

I recently made up a jig of sorts so I can grind slot-car axles to my own specs. I taper the ends and mount wheels with tapered bores, plus there's two ball bearing seat areas ground on the axles- at any rate the wear on the cutoff discs is playing havoc with my settings. I'd like to be able to grind one end, turn the axle around and grind the other end, without having to compensate for disc wear. I'd like to have these discs in cbn- so far I'm not finding them. I'd also like to have a couple choices of grit size. Am I hooped?


A description of the grinding jig- I built a rest for the lathe so I can grip an axle in the chuck then support the outboard end in the jig. I grind a 45 on both ends of the axle, with the supported end very close to where I'm grinding. In other words, the axle goes through the support hole with only about 1/8 inch sticking out. This way the 45 is ground about as concentric as it can get, and then the axle gets mounted in the jig which holds it by the tapered ends.

This is basically holding the work between centers, only in reverse. The axle supplies the centers, while the jig supplies the indents for the axle to center within. The entire length of the axle is available to be ground on, and the jig has an angle adjustment so I can grind the shallow tapered ends that the wheels will fit onto. I lube the centers, then spin the axle with my fingers as the grinding disc takes off the material. Works nicely. I only need two hands to do this- one spins the axle, the other moves the carriage with the tp grinder on it. No taper attachment is needed for the lathe itself.


The axles are being made from music wire (drill rod, silver steel) Grind one end to a slight taper, reverse the axle in the jig, grind the other end- set the jig parallel then grind the bearing seat areas. The lathe spindle is not used in this process, only when the ends of the axle are first being coned. One axle has the slight taper ground on one end only, and this subsequently is made into a D bit, so it becomes a reamer to do the tapered hole in the wheels.

This is my solution to having the wheels removable, but always able to remount perfectly concentric to the axle. A further step will be to press-fit a hub on each side, then tiny bolts can thread into this hub to pull the wheels tight onto the tapers.

In case anyone is still reading this, the main reason for going through all this is to give a means to grind the tires true without losing the ability to have them turning perfectly concentrically once mounted on the car again. The tires have to be glued to the wheels so they don't spin, and many of us would like the option of having more than one set of tire/wheel combos trued and ready to go- but it's important that they run true anytime they are mounted.

I'll have several sets of tire/wheels ready to true, then turn the correct taper on a stub, then mount and true all the sets without disturbing the stub in the spindle. Anytime I go to true up more, I'll have to re-true the stub taper before going on.

But- back to the question- can I get cbn discs or thin grinding wheels in a 3 inch diameter?

Evan
12-20-2008, 06:36 PM
PM me for information about CBN wheels Darryl. My wife can get whatever you need, custom made if necessary. There is no extra charge for custom wheels.