DIY high speed spindle

[jacampb2]

I am running this project by you guys to see what kind of ideas turn up, as well as to get an idea as to how feasible this is...

I have tried many things for a high speed spindle on my b'port SII CNC. The last generation was a bracket and high speed mini air die grinder that was proposed by someone on this board. It served well for milling and drilling PCB's, but anything past light duty engraving and it just didn't have enough power. Add to that, that it has started to destroy itself from the vibrations (it was a cheap HF grinder, was not expecting great things, but it is really out of balance to run at 50K rpms...), and I need a new design.

I am currently fitting an old rotozip spiral saw in it's place. This is not my long term solution either, but just a stop gap for the moment. I rebuilt the rotozip with new abec 7 bearings. I am not going to clamp the rotozip, but machine one side of it's body flat, and drill through 4 of the case bolts and bolt it to a backing plate. The rotozip should have decent runout w/ the new bearings, but spindle float will be a problem. There is no way to preload the bearings that I can see. Add to that, that the plastic case is "plastic" enough to give under cutting conditions, I hold no illusion that it will be a high tolerance tool.

Anyhow, I am working on an idea based on a picture and a thread over on cnczone. Evidently there was a article in Home Shop Machinist a while back about making a high speed spindle cartridge that is powered via a dremel. I am thinking about doing something similar, but driving it with the rotozip in the next generation. Here is a picture from the article.



Anyhow, I need this to fit a QC30 taper. I am thinking of machining the cartridge for QC30, then fitting a small spindle in the cart. As for a spindle, I don't know what material I need? Is mild steel acceptable, or does it need to be SS like a lot of the folks on cnczone do? I am thinking a pair of ceramic 608zz deep groove bearings w/ some ability to preload. Possibly a spacer between the set and a simple nut on top? I know ball bearings are not optimal, but I have them. Would I be better off to try to find one tapered roller for the lower bearing?

The last question/issue is I would like to use the common "rotary saw" collets like the rotozip uses. They have enough sizes to allow for most small tooling, and it will be satisfactory for me. Do any of you know the specs on the collets, angle, spindle nose thread, and bore?

Tell me if I am on the right track, or what I should consider doing differently. Please don't start a huge bearing discussion, because I don't understand all the technical aspects of it. This will only be for occasional use, and I can't see me needing to run the spindle for more than a few hours at a time.

Thanks,
Jason