Hitchcocks Forum

off the marque I'm afraid but I thought I'd ask anyway. I need to machine the disks on the V50 Monza and I have them set up on a big lathe at a friends place. I'm looking for info on the best grinding material for the spindle grinder. I recently heard that diamonds are a no go due to "chemical" issues. I presume that as diamonds are carbon there is some form of steel making that happens when you grind iron with them. Anyway keen to hear if any of you are in possession of this sort of alchemical knowledge.

Grinding discs on a lathe? I am puzzled. If by discs you mean brake discs, a tungsten carbide tipped turning tool is sufficient.

I can't help you with what kind of grinding wheel; there's probably lots of info online.

However, I would make the point that grinding a cast disc to restore its surface is the way to do it, NOT turning. Again, there's lots of info online as to the reasons why.

You need a skilled machinist. There are many factors such as tool angle, lathe speed, tool shape, feed speed, and correct cutting fluid. With a large diameter you have to vary the chuck speed from inside to outside. If these are indeed brake discs then there is a minimum thickness needed to dissipate heat, not to mention strength. Brake discs are 'consumable' parts, the pads grind them away, usual method is to simply replace them.

Another Allan, I have refaced loads of cast iron brake discs in the past as part of my past employment. I am seriously puzzled by your comments.

It is stainless steel brake disc that are problematic to skim on a lathe due to the hardness and abrasive nature of stainless plus the interrupted cuts due to the number of holes, slots in the discs.

If it's stainless and a toolpost grinder is available I would try that. If the disk is unusable you can't make it worse. Any decent stone would do the job BUT don't use one that has been used on non-stainless. Either use a new one or dress the stone to remove any trace of the non-stainless. If you don't, you run the risk of contaminating the stainless and you may get rust problems.
Grinding or cutting, I assume your friend knows how to set the disk up in the lathe? You want to be in a 4 jaw chuck and the part must be dialled in accurately.
The proper way to do it would be on a surface grinder with a rotary table. Like this.

Personally, anyone using a grinder near or on a lathe should be taken outside and shot.

Brake discs are consumables so I am wondering why the need to grind/ cut a knackered old disc ?

No problem Papa if you take the appropriate precautions. I agree, it's not ideal, but sometimes you have to use what you have. It's also a good excuse to clean the lathe properly afterwards. If this earns me a bullet I should have been dispatched many years ago