[QuinnSjoblom]

A blue test shows pretty clearly that there is good contact for about the bottom half of my bt30 taper and fading to no contact at all towards upper half. Checking with blue was done with a few holders and got consistent results. This is a cheap aliexpress bt30 cartridge so im not really surprised its not perfect. This is resulting in not perfectly consistent runout every time a tool is loaded. Im waiting for a quote to see how much it is to send it out for a grind, but i think i might be able to do this myself. In the attached pic is my old z axis and chinese 2.2kw spindle. I have clearance on my machine to mount this entire assembly at an angle on my machine to grind the taper of the bt30. Couple questions before i try this. First of all, will this 24k rpm chinese spindle be up to the task? Is that rpm (or slower) suitable? It has an er20 taper so whatever grinding tool i use, it needs to have max 1/2" shaft. If it it will work, What type of grinding tool specifically am i looking for? Im assuming silicon carbide and i know about what dimensions it needs to be, just dont know where to look or what to search for.

[QuinnSjoblom]

I guess pic didn't make it in. Heres my old z axis i wamt to fixture on machine to grind with

[Jim Dawson]

That should work fine. Just make sure the grinding wheel is rated for the spindle speed.

[QuinnSjoblom]

I was assuming if anything, faster than 24k would be better, no problem to go slower if thats where it needs to be. Keep in mind, this grinding wheel is only gonna be 1/2 to 5/8 on diameter to have clearance in the top of the taper.
Any recommendations on where to find the type of grinding tool i need? Ive been searching but just dont know what to look for. All i know is that it needs to be roughly 1/2 to 5/8 diameter, have about a 3 inch reach with tne whole shank being less than grinding diameter, and be able to chuck into a 1/2 inch collet. Any idea where to find something like this?

[Jim Dawson]

I would start here. https://www.nortonabrasives.com/en-us Good luck wading through the abrasive swamp. Maybe a call or email to your local distributor or to Norton sales engineers would be in order. There are so many options I don't even know where to start.

[QuinnSjoblom]

Ok thanks, ill check it out. Im not too worried about abrasive type. Probably more important if you want to grind many parts with decent tool life and a reliable process. I only need to take a few tenths off of one taper.

[QuinnSjoblom]

I sent off a couple emails looking for recommendations. Looks like a pretty basic aluminum oxide abrasive with 60 or so grit will do fine. I see that there are many mounted points that i could buy that have the correct size grinding portion, roughly 5/8 diameter by 1/2 long. largest shaft they come on is 1/4 diameter by 1 1/2 long. Im sure i could make a shaft that is 1/2 diameter and the needed 3 inch reach with a 1/4 hole bored in the end for mounting the mounted point, but i dont know if thats the best option. Im sure there could be a more solid setup than that, but i dont know how important that is. Doesnt necessarily need to be all that rigid and robust. I can take very light cuts and let it spark out, only stepping over a tenth at a time. I also dont know if i should be maximizing the diameter to the point of just being slightly smaller than the top of the taper, or if i should go smaller. 5/8 leaves pretty minimal room at the top, but it does clear. Im still trying to wrap my head around all the different possible alignment errors and how they effect the final shape. To me it seems that having the grind diameter very close to the diameter of the top of the taper will have a greater result of error if the axis of grinder feed is slighly tipped out of plane. I believe that results in a convex wall shape or bell mouth. Im trying to find more specifics on internal taper grinding but not having much luck. Couple videos out there but not much useful info in them. Not like searching how to machine parts which comes up with a million results and endless videos. Maybe im overthinking this, just seems like its something that needs to be done perfect and even a tenth or 2 error leads to less than perfect contact. I did hear back from the spindle grinding company and they didnt even give me a quote, they said it would cost more than what i paid for the spindle. Thats a bit disappointing to hear. I was hoping i would at least have a back up plan if i cant get the grinding done well enough myself.

Any other input, advice, video links, etc would be greatly appreciated.

[Jim Dawson]

Maybe a collet extension? https://www.amazon.com/CMT-796-001-0.../dp/B000P4NQCK

Setting that up is going to be is going to be tricky. You just need to get the grinder spindle lined up at the correct angle, but it's going to be a bit of trial & error to get it correct because you don't really have anything to dial in to.