Spindle Regrinding Service for Benchtop Machines
Hi folks,
I've got an RF-25 and I'm trying to find a spindle regrinding service to "dust" the R8 spindle taper to reduce runout. While this is an extremely common service for Bridgeport and similar machines, all the places I've reached out to don't want to touch my spindle without a >$500 charge. I do not have the means to do this myself unfortunately, and I'm willing to accept that there's not an economical way to get this done properly, but thought I'd ask in case anyone has any leads.
Thanks!
Cheers,
IHateMayonnaise
Re: Spindle Regrinding Service for Benchtop Machines
I can't see you having much luck without a heavy price tag attached to it.
To be honest the best option I found with my X2 machine is to use a direct collet when I need it a bit closer tolerance.
I can get anywhere between 0.004mm to 0.04mm throwing a cutter into a decent ER32 chuck and locking it up.
With a direct collet I can get anywhere from 0.004mm to 0.01mm.
Re: Spindle Regrinding Service for Benchtop Machines
Well, my BP clone spindle was about $900 including new bearings and regrind.
Re: Spindle Regrinding Service for Benchtop Machines
Quote:
Originally Posted by
dazp1976
I can't see you having much luck without a heavy price tag attached to it.
To be honest the best option I found with my X2 machine is to use a direct collet when I need it a bit closer tolerance.
I can get anywhere between 0.004mm to 0.04mm throwing a cutter into a decent ER32 chuck and locking it up.
With a direct collet I can get anywhere from 0.004mm to 0.01mm.
Its not that difficult to do it yourself you have to make up a slide and mount a small air grinder or electric grinder on it, your ER is 8 degree set this up with a sine bar to get the angle perfect, align to the center of the spindle rotate the spindle at the slowest speed you can and slide the grinder slide up and down, you must dress the grinding wheel true before you start grinding
Re: Spindle Regrinding Service for Benchtop Machines
CBN-tipped boring bar held in the vise. Run a mill-turn program to dust the taper only - don't open up the straight secton at the top. Doing it in place should result inthe lowest possible runout.
Sure it's not your bearings? Not thinking that that mill came with super-duper AC bearings...
Re: Spindle Regrinding Service for Benchtop Machines
It´s perfectly possible to self ghetto-grind the spindle taper using any of various methods.
Multiple anecdotes and examples from real professionals on the web attest to this.
Any grinding spindle with a mounted stone will work.
Dressing it with a diamond will help. Knocks off high spots.
Then just run the spindle in against the grinding wheel, spindle rpm maybe around 300 rpm.
It´s a 2-axis move.
A dremel, air die grinder, or bench grinder (low rpm, but still) should work.
Most of the error is likely bearing repeatable error - the bearing manufacturers guides all point this out.
Skf, timken etc. all indicate maybe - 0.01 mm error as-mounted but maybe 0.002 mm after grinding/lapping in their machine-tool guides online.
One should remove less than 0.02 mm, total, mostly much less.
Even a fixed grinding stone should work fine.
The rotating spindle will only hit on the high spots, with very low load, and a cnc tool can approach the inside surface with extremely small movements of 0.001 mm, 1 micron, or sometimes less.
And then keep repeating the grinding-cycle slow x-z movement.
Endless ghetto tricks can bias the mechanicals to take out most of the slop and bend.
A weight, pneumatic cylinder, rubber band etc., and a copper/brass/bronze/delrin/(ptfe ?) contact point can load the parts removing almost all slop.
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Re: Spindle Regrinding Service for Benchtop Machines
Here are the spec's for an R8 if you don't have them
Re: Spindle Regrinding Service for Benchtop Machines
Hi, it will be a bit of a bugger if the straight part of the spindle bore that locates the back end of the R8 collet is running out......once that has been ground to size it's there for good......you cannot regrind it a few tenths bigger to cure runout or the collet will end wobble and run out.
But you can touch up the front taper with a die grinder a few tenths and if you have access to a lathe or someone with one then you're home and dry.
With a lathe you would hold the one end in the chuck and run the spindle on its front bearing diam in a fixed steady and use a die grinder....whatever...... with the compound slide set over to the taper angle.
Without any access to any machinery at all or any ability to build a pseudo lathe.....that is, a set of linear rails and a pair of plumber block bearings for the headstock etc etc...…..anything you do to the spindle will probably ruin it for any further use despite the slight runout, so I would advise leaving it as is and pretend you didn't know it ran out...….or buy another spindle as a spare part.
Ian.
Re: Spindle Regrinding Service for Benchtop Machines
Quote:
Originally Posted by
handlewanker
Hi, it will be a bit of a bugger if the straight part of the spindle bore that locates the back end of the R8 collet is running out......once that has been ground to size it's there for good......you cannot regrind it a few tenths bigger to cure runout or the collet will end wobble and run out.
But you can touch up the front taper with a die grinder a few tenths and if you have access to a lathe or someone with one then you're home and dry.
With a lathe you would hold the one end in the chuck and run the spindle on its front bearing diam in a fixed steady and use a die grinder....whatever...... with the compound slide set over to the taper angle.
Without any access to any machinery at all or any ability to build a pseudo lathe.....that is, a set of linear rails and a pair of plumber block bearings for the headstock etc etc...…..anything you do to the spindle will probably ruin it for any further use despite the slight runout, so I would advise leaving it as is and pretend you didn't know it ran out...….or buy another spindle as a spare part.
Ian.
Correct. Better to have it done right, instead of something you learned from some guy on the internet who said it would work.
Re: Spindle Regrinding Service for Benchtop Machines
Quote:
Hi, it will be a bit of a bugger if the straight part of the spindle bore that locates the back end of the R8 collet is running out......once that has been ground to size it's there for good......you cannot regrind it a few tenths bigger to cure runout or the collet will end wobble and run out.
I'm not sure this is entirely true. On an R8, the straight portion of the collet/holder/whatever has a tolerance of 0.9490" - 0.9495" so right there is 5 tenths potential "slop" in that upper portion, and I am sure that the straight portion in the bore inside the spindle has a similar tolerance and undoubtedly a bit of designed in clearance. So there is not a "tight" fit there anyway and if needed, grinding another tenth or two out of that portion will have no detriment that I can see. The tapered portion of the tool would be able to "straighten" things out if re-ground. Indeed, a few years ago, Dave Decaussin of Fadal fame designed and made some very nice little CNC machining centers that used tool holders he called "Cat R8". These tool holders used only the tapered portion of the R8 and completely eliminated the upper straight portion of the typical R8 tool holder. Grinding that portion of the bore would pretty much just do the same thing and eliminate it from location the tools.
Look about 8:40 to see the Cat R8 tool holders.
https://youtu.be/b-y03hhCCME?t=519
Re: Spindle Regrinding Service for Benchtop Machines
Thinking about this a little it is possible to do this without too much extra stuff on a machine with a tilting head. You could tilt the head to the proper angle for the taper and then affix a die grinder to the table somehow and use the X and Z axes of the mill itself to re-grind the taper.
Unfortunately this won't work for a RF-25 like the OP has since its head doesn't tilt.
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