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  1. #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?

  2. #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.

  3. #15
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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.

  4. #16
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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.

  5. #17
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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.

  6. #18
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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.

  7. #19
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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.

  8. #20
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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.

  9. #21
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    Re: Spindle Regrinding Service for Benchtop Machines

    109jb, As a retrofit for a hobbyist, I agree, the short R8 is a good improvement over standard R8 as an entry into quick, repeatable tool changes.

    How would you compare the short R8 to something like the TTS? Pretty close I'd say? 6 of one, half a dozen of another? My personal preference would be to go with a TTS ( or clone) rather than the short R8 so I don't have to deal with a pull stud system that might be lightly supported ( commercially) and or pricey.

  10. #22
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    Re: Spindle Regrinding Service for Benchtop Machines

    You can always regrind teh R8 spindle to the BT30/Cat30 taper and use a pull stud set. There IS room to make it happen. It HAS been done.

    Just a thought , (;-) TP

  11. #23
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    Re: Spindle Regrinding Service for Benchtop Machines

    Vmax, do you have an example to show?

  12. #24
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    Re: Spindle Regrinding Service for Benchtop Machines

    Quote Originally Posted by cncuser1 View Post
    109jb, As a retrofit for a hobbyist, I agree, the short R8 is a good improvement over standard R8 as an entry into quick, repeatable tool changes.

    How would you compare the short R8 to something like the TTS? Pretty close I'd say? 6 of one, half a dozen of another? My personal preference would be to go with a TTS ( or clone) rather than the short R8 so I don't have to deal with a pull stud system that might be lightly supported ( commercially) and or pricey.
    I'm not a huge fan of TTS as I've never been a fan of R8 collets in general and the heart of the TTS is a 3/4 R8 collet. I prefer solid R8 tooling. If things work right, the 3/4 shank too won't pull out, but it is a concern I have. With a solid R8 tool or even a short R8 with a pull stud the concern about slippage is reduced.

    Having said that, I did buy some 3/4" shank ER collet holders to use as TTS-ish tools. I don't currently have a belleville spring type drawbar, and just loosen and tighten the drawbar to change the tools. I still find myself using solid R8 tooling more than the ER holders with the R8 collet. I find the tool length repeatability just fine using R8. Maybe if I bought more 3/4 shank tools I'd use the TTS style system more, but the benefit isn't there without an auto drawbar. Way back when I used a Bridgeport with a pneumatic impact drawbar and that seemed plenty fast enough for me and is an option for my RF-45 size machine I am sloooowly converting. That's off on the horizon but I have considered a few options for that machine, which include just leaving the standard drawbar and wrench option, the pneumatic impact drawbar, TTS with a pneumatic or manual release and the short R8 with pull stud and pneumatic or manual release.

    As I see it the benefits are:

    1. Standard drawbar w/wrench - Versitile but slow. Can use standard R8 and TTS type stuff.
    2. Pneumatic impact drawbar - Versitile and faster. Can use standard R8 and TTS type stuff. No feel for tightening torque
    3. TTS - If used with a belleville system is fast, but I would consider it horsepower limited. Lots of posts about slippage and tool pull out which raises concern
    4. Short R8 - Fast, but now your stuck with it and except for buying from Dave D, would have to make your own tool holders.

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