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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

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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

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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.

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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

  13. #13
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    Re: Spindle Regrinding Service for Benchtop Machines

    Quote Originally Posted by 109jb View Post
    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
    Hi, I thought about that too and if the top straight section is clearance you won't need to regrind it at all......however if the bottom taper section is running eccentric then regrinding that part will work to correct it.

    At a wild guess I would think that a die grinder on a small slide mounted against an angle plate and angled over at the taper angle would be a very doable DIY solution.....as Mac has said...….you only want to take off a few tenths at most and this won't affect the seating of the collet in the bore as it will only go back a few thou at most.

    I would hesitate to suggest.....but if the Devil drives then it could be done...….. that a mounted grind stone in a die grinder, clamped against an angle plate and suitably dressed then moved against the taper with the mill table X axis to remove a few tenths, could work as long as the stone was long enough to grind the whole length of the taper in one move.

    The stone would have to be mounted in the die grinder and dressed with a diamond initially to ensure it ran true.

    One big factor and that is the draw bar influence on the collet...…...due to the end of the collet being a clearance in the bore, if the draw bar pushes the end of the collet to one side as it tightens you WILL get cutter run out as the cutter will run eccentric and more so the longer the cutter is.

    BTW.....my opinion is...... the shortened collet of Dave D'C will not be supported as per a regular R8 collet, and as a cutter exerts considerable radial pressure when it is at a high feed rate the tilt over aspect would be a real problem......why then does an R8 collet have such a long length if it can work just as well as a cut down model?

  14. #14
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    Re: Spindle Regrinding Service for Benchtop Machines

    One big factor and that is the draw bar influence on the collet...…...due to the end of the collet being a clearance in the bore, if the draw bar pushes the end of the collet to one side as it tightens you WILL get cutter run out as the cutter will run eccentric and more so the longer the cutter is.

    BTW.....my opinion is...... the shortened collet of Dave D'C will not be supported as per a regular R8 collet, and as a cutter exerts considerable radial pressure when it is at a high feed rate the tilt over aspect would be a real problem......why then does an R8 collet have such a long length if it can work just as well as a cut down model?
    I suppose the drawbar could contribute, but I think for the drawbar to have that kind of effect would be extreme as a taper like the end of the R8 is enough to straighten whatever tool is in there on the taper.

    I don't doubt that the long R8 will provide a "stiffer" overall assembly, but I question whether this is necessary. Looking at Dave's videos, he is able to take some pretty hefty cuts with the shortened R8 tooling. Also, considering for example an R8 collet, that has flexible sides, I would think that all the rigidity in that system comes from the taper locking the bottom part of the R8 collet onto the tool. I just can't see the thin side walls of the R8 collet providing much to the rigidity when I can take an R8 collet and flex the side walls with my bare hands.

    One thing that comes to mind as far as why R8 collets are so long is so that long tools have a place to go in a typical R8 collet or tool, but not so in the short ones Dave Decaussin uses. For example a double end 3/4" end mill can be used in a 3/4" R8 collet, but there would not be enough depth in just the tapered part like Dave D. used. So the extra length could be for convenience for longer tooling rather than because it is more stout.

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    Re: Spindle Regrinding Service for Benchtop Machines

    I'm a very firm believer in "the proof is in the pudding" etc, and Dave D'C has proved that conclusively......pity these collets were not more freely available...….however if that was a fact, you'd have to have a mill spindle dedicated to use them.

    If they're commercially available I'd be in the market for a few as I have a small jig borer spindle I want to modify......…..it's 2 Morse at the moment but I'm redesigning it for R8, that'll be a tight squeeze in a 35mm spindle diam.

    In my case I want to use the jig borer as a manual mill so a longer draw bar would do the trick .....I already have a CNC mill

    There would be a lot of stiffness in that short R8 collet to allow the taper to clamp down but if an ER system can do it.....why not a short R8 too.....although the ER design has double ended slots and more of them.

    I suppose Dave D'C had his custom made......I liked his UMC10 mill, saw it on UTUBE many years back...…..steel tubing too, my favourite material.

    I can't really think why I wanted to go to R8......seemed like a good idea at the time...….. when the spindle end could just be made to use ER40 directly in it...…..2mm to 35mm.....hmmmmmm, why not.
    Ian.

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    Re: Spindle Regrinding Service for Benchtop Machines

    HW, I have a UMC10. I cant say I am overly impressed with the toolholders themselves. That short modded R8 might be its issues.
    A lazy man does it twice.

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    Re: Spindle Regrinding Service for Benchtop Machines

    Hi, I don't think you can go back from the short R8's unless you change the whole head as the bearing configuration wouldn't allow a bigger diam. spindle to be fitted...….it's probably right from the beginning with a new tool holding design that decides the size of the bearings.

    R8, being approx. an inch in diam. or thereabouts at the top end, would mean a spindle of at least 40mm diam. and bearings for that size in A/C are pricey as well as not good for high rpm etc.

    In a spindle design from the outset, if you went for ISO 30 and dropped it's position down a bit you could get it into a spindle of approx. 35mm diam. as the dumpy end of the '30 would allow A/C bearings with a 35 mm bore.

    That being said, I think the designer of the R8 knew what it needed to make the collet stable and run true etc.

    It's strange, but looking at the video by David D'C, he appears to mill quite happily on the UMC 10 with a large depth of cut in aluminium without any apparent tool wobble etc...…...maybe his draw bar pressure is big enough to hold the collet firmly.

    Perhaps milling in steel etc would be a different matter.

    The draw bar end, in that case, would be an asset as it would ensure the collet didn't tilt in it's seating.

    At a guess I would think that when it was stationary, a tool in the short R8 would dial up running true, but under a cutting side load you could get some "tilt over" deflection that would not be apparent when the draw bar was pulling up with force once the spindle was stationary again......the long R8 collet would not do this.....ever.
    Ian.

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    Re: Spindle Regrinding Service for Benchtop Machines

    The short R8 is an interesting idea in theory but it in reality it comes up short.
    For a machine made to use a standard R8, retrofitting a short R8 doesn't offer many advantages.
    In a machine designed from scratch, there are now many alternatives that are , on the whole, preferable to the short R8.

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    Re: Spindle Regrinding Service for Benchtop Machines

    Quote Originally Posted by cncuser1 View Post
    The short R8 is an interesting idea in theory but it in reality it comes up short.
    For a machine made to use a standard R8, retrofitting a short R8 doesn't offer many advantages.
    In a machine designed from scratch, there are now many alternatives that are , on the whole, preferable to the short R8.
    We seem to have digressed a bit. I was the one that originally mentioned the short R8 used by Dave Decaussin, but it wasn't to recommend to anyone to go to that system, but rather to point out that most of the work in an R8 setup is done by that lower tapered portion and that the upper portion could have, and undoubtedly does have, some clearance to the top portion of standard R8 tool holders. This was to refute a claim that the upper cylindrical portion inside the spindle could not be re-ground. I believe it can within reason of course. This was the only reason I brought up the short R8 to show that the taper portion alone could do the job.

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    Re: Spindle Regrinding Service for Benchtop Machines

    Quote Originally Posted by cncuser1 View Post
    The short R8 is an interesting idea in theory but it in reality it comes up short.
    For a machine made to use a standard R8, retrofitting a short R8 doesn't offer many advantages.
    In a machine designed from scratch, there are now many alternatives that are , on the whole, preferable to the short R8.
    Thought I would also mention that if you watch Dave D's videos he discusses why he chose the short R8, and it was not because it was superior to anything else, but he was able to use a standard unmodified R8 spindle with a pull-stud tooling system. He mentioned that he did this because he felt it would present a way for hobbyists to do the same easily. So, it wasn't a system for a machine "designed from scratch", but for existing machines.that already had R8 spindles. Indeed his first machines he did this to were off the Shelf Grizzly machines. He even did a nice G0704 conversion complete with auto tool changer, and the short R8. Would some other tooling system have worked better? Probably, but it would require a spindle change that the short R8 design didn't.

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