Recently updated on March 7th, 2023 at 01:58 pm
Frank Mari (Maritool.com) did.
A spindle rebuild involves fitting new bearings. Most folks will suggest that if you want to minimize runout, you will have to regrind the spindle taper while it is spinning in the bearings. This is standard procedure when manufacturing new machine tools and getting a quality rebuild. But, it’s something the average shade tree machinist probably doesn’t think about too much. At least until now. I saw this thread on PM about how Frank Mari reground the taper on a VMC as it sat on the machine and love it.
Here’s the story. Seems a customer of Frank’s had been ignoring pull stud replacement. Eventually a Bad Thing happened to a tool holder and his machine’s taper:
Whoa! Seriously chewed up with a fair amount of horsepower…
No love at all in the spindle taper. Take care of your pull studs, people! Check the drawbar tension while you’re at it too.
So, the good doctor prescribes a boring bar with a diamond insert (PCD). This is a hard turning application, meaning that the bore is hardened. The bar and insert are only used for spindle taper work, so they’re pristine…
Sparks like this are normal in hard turning…
Wow–serious improvement!
A few notes:
– Mari “tweaked in” the spindle by bluing a spindle test bar and tweaking his program.
– When the program was fully tweaked in, he ran the bar to identical start/stop points 4 times.
– Accuracy afterward measured to 25 millionths at the top. .00015 at 8 inches down using the test bar. Total elapsed time for the work: 1 hour.
Sending your spindle out to be reground at a spindle shop would probably produce better results, but this is a lot cheaper and faster. Something to consider if your machine is older and not worth the more expensive treatment.
I was so pleased to find this article while researching spindle runout that I immediately bought a set of ER32 collets from Maritool, Frank’s company. Of course it helps that they have some of the best prices in town too!
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I have a video on youtube of doing the of my tormach spindle, it’s a fun show to watch! Like 4th of july.
Resurrecting an old thread. does anyone have a link to Brad’s video on doing the Tormach spindle on-machine? Or has anyone here done it?
Oof. I’m conflicted on this. Tormach will sell you a brand new spindle cartridge pretty cheaply. I sure would be tempted to go that route for that machine!
Used an air grinder with a diamond wheel on mine. Didnt have all that damage though.
A similar approach can also be utilized with improving the run-out on your lathe chucks although you need another adapter to reflect the more accurate position of the jaws when under tension. Mounting them “in-line” with the spindle gives the best viewing options. A long shank grinding wheel, some good light and some bluing will tell the story! Same thing done in the lathe probably brings in other influences that are more productive but for the chucks to be mounted on the cnc table, this has been helpful.
Someone must have wished they had some ear protection with the amount of damage shown… WOW!
I would have never considered doing this until this article and like Ken I would use the grinder method but wow, what a way to save some major cost.
Thank You.
How do you determine when to replace pull studs?
when you can actually see any deformation or, “fresh Metal” on the grappling stud…..if you can see any, ‘ugly spots’, it’s best to check the drawbar thru the spindle to see if it also has any deformation or gall marks….replaced many a drawbar and pullstuds in our machines….usually because SOMEONE (I won’t refer to them by name online), refused or forgot to blow any chips and dirt/dross from the mating surfaces….makes me CRAZY…grrr…
You’re absolutely correct….many don’t realize that the few thousandths of mat’l one grinds off, can have a deleterious effect on properly snugging up the taper to pitch…..one also has to mate the FACE (sans drive dogs) to the proper pitch in relation to the tapered bore…