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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > Spindle Regrinding Service for Benchtop Machines
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  1. #1
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    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

  2. #2
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    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.

  3. #3

    Re: Spindle Regrinding Service for Benchtop Machines

    Well, my BP clone spindle was about $900 including new bearings and regrind.
    Jim Dawson
    Sandy, Oregon, USA

  4. #4

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    Re: Spindle Regrinding Service for Benchtop Machines

    Quote Originally Posted by dazp1976 View Post
    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
    Mactec54

  5. #5
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    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...

  6. #6
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    Quote Originally Posted by spumco View Post
    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...
    I have two tapered roller bearings (30205 and 30206). I purchased new FAG bearings, and to say that I installed them carefully is an understatement. All 4 bearing surfaces were pressed on by using bearing adapters and screwing on carefully using threaded rods, along with heat and/or cooling to ease insertion. I also purchased two P5 bearings for the tapered spindle sleeve, and installed them in the same manner. The preload was set initially to reduce play (close the gap) by measuring run-out on the R8 taper with the quill clamped to v-blocks on a surface plate. I packed the bearings with Nubar isoflex-15, and I'll begin the burn-in procedure today by tracking the quill temp using a thermal camera.

    I bought a brand new collet set from Hardinge, and the spindle that I'm using is new from Grizzly (old one was loose in the tapered spindle sleeve). I noticed that when I installed one of the Hardinge collets with the drawbar that there is uniform contact around the entire circumference of the back (non tapered) of the collet, but I could hardly see any contact marks on the tapered section (this was verified using layout fluid). When installing a bit, the collet does appear to close, at least enough for me to not be able to rotate the bit by hand. I'm not yet at a point where I can test the holding power on a work piece, as obviously that is the true test.

    The run-out on the taper (as measured on my surface plate) was a few 10ths, and when I installed a new Hardinge collet with an oversized gage pin I was reading a couple thou at the base of the pin. I did this with several pins and collets, had very consistent results.

    I'm curious to see what it looks like after burn in, as I may have to adjust the preload. I'm not expecting much if a change, however, and if I can't find a place to regrind my spindle for less than $200 or so, then I'll be call it a day and just live with the run-out that I have.... I can't imagine doing anything more carefully than I have already, and I'm not prepared to waste a lot more time trying to make a benchtop machine a precision apparatus when it's clearly not in the cards.

    Cheers,
    IHateMayonnaise

  7. #7
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    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.

  8. #8

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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
    Attached Thumbnails Attached Thumbnails R8 Spec's.PNG  
    Mactec54

  9. #9
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    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.

  10. #10
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    Re: Spindle Regrinding Service for Benchtop Machines

    Quote Originally Posted by handlewanker View Post
    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.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router

  11. #11
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    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.
    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

  12. #12
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    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.

    Attachment 421042

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