Grinding

[itsme]

Hi there,

I have set my Micro Mill up for grinding with a high speed rotary tool (approximately 30000 RPM) to grind internal shapes under CNC control, but I'm having trouble.

I am trying to grind cast iron with a grinding wheel that is 15.2mm in diameter. I have the wheel going at full speed, taking small 'cuts' (or whatever they're called) without any coolant. The problem is that the finish is less than perfect (much less!!!). It is leaving grooves behind and if you run your finger nail perpendicular to the direction of the 'cut' it feels rough.

I'm not sure if the wheel I'm using is classed as coarse or fine, but it doesn't seem very coarse. I also dressed the wheel on a diamond before use to make sure that it was parallel.

I'm using a feedrate of between 1 and 4 IPM, but there is little difference between the finishes. Does anyone have any suggestions as to what I can try to get a smooth, 'proper ground' finish? It almost needs to be like glass.

Thanks
Warren

[JFettig]

Do you have your head trammed up? stick an indicator in a chuck and test the right and left side, front and back to see if the head is true to the table. Depending on the mill, you may have to shim the column forward or back(its a micro mill right?)

Jon

[ViperTX]

Also, are you sure that the abrasive wheel is really round and running true? And you're not moving the quill of the Micro-Mill up & down?

[DieGuy]

30K rpm on a 15 mm wheel may be to fast. What size shank? does is shake at all, any vibration? You are using the "face" to do the grinding? Did you dress it in place? Cast iron is kind of not free cutting with a grinder. Pretty soft stuff. Are you seeing an deposition on the wheel surface?

[itsme]

Hi there,

I think it was purely just the wrong choice of wheel. I tried a finer wheel with a diameter of 19mm and 3mm thickness (the last wheel was 8mm tick) - also at full speed. There is no comparison between the first wheel and the second. The finish that I am now getting is satisfactory.

If the 'face' is the circumference of the wheel, then I am using it. I am also dressing the wheel in place. The workpiece is on one end of the table and the diamond is mounted in a vice on the other end (which means they're right next to each other on a micro mill...). There is no vibration and the wheel is running true - you'd be amazed at how 'wonky' these dremel type wheels are before you dress them.


Thanks for the suggestions.

Regards
Warren