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Best gearbox style for torque?

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  • #16
    My mistake, 30lb-in = 4Nm which is the torque for a coax electrical connector (well way over actually). However I think that would be all you need for a 30int which takes drive from the flange slots not the taper. 40Nm sounds more like an SUV wheel nut setting.

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    • #17
      I owned a CNC mill with an electric impact wrench to tighten the NMTB 40 holders in the spindle. Because it hammers it did not need the spindle brake to take very high torque. It is also very fast because it spins about 1000 rpm until the torque increase engages the hammer. Our mill at work has an air wrench for the Cat 40 holders. It works well but is much noisier.

      Basicly the hammering torque mechanism air or electric is the right one for this job.

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      • #18
        The butterfly impacts will only provide about 30 lb/ft of torque at 90psi. I doubt you'll turn it into a "wheel-nut wrench" unless your working on a bicycle. I used mine all the time with car bodies and light engine work. I still have it and gave thought to building a power drawbar but I don't have a production shop. The five seconds it takes to tighten or loosen the drawbar is immaterial to my machine time. Besides, I just bought a new extended drawbar and the "kit" won't fit.

        I'd still be interested in what you come up with that will free-wheel when not engaged. But it sounds like it's getting complicated and expensive already.

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        • #19
          My first idea was to use a worm drive box - these can be mounted in a fixed position and have the torque transmitted via a sliding shaft that is keyed to the output of the box so no need to have the motor/drive hopping up/down onto the drawbar nut, just a small air cylinder to push/pull the output shaft and socket.

          The "youtube" do-all fix seems to be to throw on an air impact wrench, a couple of air cylinders to give downwards movement and some heavy springs to give return movement - this works but to me is "clunky" and more involved than my first idea above.

          The next idea given to me is to use a large stepper - Nema34 etc joined to planetary gearbox and again some air cylinders and springs for lateral movement. This is pretty cool but can be slow as the reduction is pretty high and steppers suck at speed. It is also so far the most expensive.

          The electric impact may actually be the one, thanks, providing they can be reversed electrically and not mechanically, i have no idea how they work internally but for £49 I could get one and find out. I have some cylinders that might work for up/down engagement and my drawbar has been fitted with a large Torx bolt head which is easier to engage than a hex nut I think.

          I still like the worm drive though as it is mechanically far simpler - no springs, only one cylinder, quiet etc but slower than the impact which can spin-up fast off-load.

          I also like the idea of the stepper drive as it means i could engage the drive, then index the spindle (my spindle is VFD drive so no home/park feature yet) and then lock/release it

          I just get baffled when someone says "you need 30ft/lb of torque on a BT30" then have to find a way of getting that etc
          If it does'nt fit, hit it.
          https://ddmetalproducts.co.uk
          http://www.davekearley.co.uk

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          • #20
            I expect that you probably know this already but just in case not: many of the commercial power drawbar actuators are in fact, based on just an air powered butterfly impact wrench. So while I have to agree that some of the DIY versions you see around the web are clunky, if you look closely at the commercial versions they as actually pretty compact and nicely designed. And not beyond what you could do in your shop if you were of a mind to.

            Just food fro thought. A big part of the fun is the mental exercise you get thinking a project like this through to do it your own way.

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            • #21
              I hate the idea of a PD on a home shop machine where time is not that critical - I like putting just the right torque on just the right endmill for the specific task at hand - I save my collets/spindle taper and drawbar threads for when I need them - chucking up a 3/4" endmill or my flycutter or my 5" chuck or whatever - the little 1/8" endmills barely get a cinch because their unit pressure is still off the charts with that...

              that being said if your incapable of tightening your drawbar properly due to health or physical reasons I would look into doing something with a simple cordless de-walt drill or the like - you would have to run a set of bevel gears to mount the unit sideways, you have gearing flexibility within this fact - the drill has immense flexibility with 3 speeds and torque ranges, and also has an adjuster ring to cam out for the smaller bits so your not godzilling your little endmills for no reason...

              just some food for thought...

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              • #22
                Yes, but, I did not add that this is the pre-cursor to an ATC project

                I have been doing it in steps - the mill was converted, next i added tool length comp to the knee so i keep full Z axis travel, next i dumped the R8 spindle and fitted a QC30 one with a drawbar for BT30 tooling, next i replaced all my R8 tooling with BT30 equivalents where needed.

                The next step is the drawbar - an ATC will go nowhere without one of these, following that will be spindle indexing then the ATC
                If it does'nt fit, hit it.
                https://ddmetalproducts.co.uk
                http://www.davekearley.co.uk

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                • #23
                  Originally posted by A.K. Boomer View Post
                  I hate the idea of a PD on a home shop machine where time is not that critical - I like putting just the right torque on just the right endmill for the specific task at hand - I save my collets/spindle taper and drawbar threads for when I need them - chucking up a 3/4" endmill or my flycutter or my 5" chuck or whatever - the little 1/8" endmills barely get a cinch because their unit pressure is still off the charts with that...

                  that being said if your incapable of tightening your drawbar properly due to health or physical reasons I would look into doing something with a simple cordless de-walt drill or the like - you would have to run a set of bevel gears to mount the unit sideways, you have gearing flexibility within this fact - the drill has immense flexibility with 3 speeds and torque ranges, and also has an adjuster ring to cam out for the smaller bits so your not godzilling your little endmills for no reason...

                  just some food for thought...
                  Eat this then and use a pneumatic or electric impact driver. The final torque from an impact type driver is adjustable... by time. Couple of "clicks" for an edge finder, 3-4 for a small EM, 2-3 seconds for a larger EM. I do this all the time.

                  Pneumatic also has the advantage of auto-oiling (install one).
                  Last edited by lakeside53; 03-11-2018, 12:13 PM.

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                  • #24
                    It's all good but by the time you click in your setting and then go to proceed iv already got my tool changed and clamped down with the proper amount of force that "I felt" lol yeah - im that good

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                    • #25
                      Nooooooo.... the "setting is your ear; Press button, count impacts/time... [it's even in the kurt manual].

                      Mine tools are changed before you even get up on the step stool to reach the top of the draw-bar.

                      I'd say a good amount of my changes per day are for for edge-finder or probes. Easy to damage the typical hollow tube EF if your don't take some care with a power draw bar.

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                      • #26
                        Fair enough you got me there, except for the Zen part

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                        • #27
                          Gearbox type I would go with a planetary,IIRC they are much more efficent as the ratio increases than a worm gearbox.
                          I just need one more tool,just one!

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                          • #28
                            Planetary system is a beautiful thing, loads are all self centering and yes very efficient, it's the reason why a modern automatic transmission with torque converter lock-out can out-due a modern manual MPG's that's using the same thin fluid...

                            I do not like worm drive, LOTS of friction there they basically operate on "scuffing" action. although there are roller worm drives that eliminate that, very pricey

                            there's also duel planetary that rival the gearing ratio's of many worm drives but now your talking complexities and money also ...

                            Edit; im wondering if anyone knows of a 3 speed manual transmission that has ever been in production for automobiles or even trucks that used the planetary system --- for along time i thought "why not" but now im thinking it might be hard to add synchromesh to units like this...
                            Last edited by A.K. Boomer; 03-11-2018, 01:32 PM.

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                            • #29
                              Syncromesh comes from cone clutches just ahead of the drive dogs.
                              It has nothing to do with the gears.
                              -D
                              DZER

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                              • #30
                                Originally posted by Doozer View Post
                                Syncromesh comes from cone clutches just ahead of the drive dogs.
                                It has nothing to do with the gears.
                                -D
                                Correct - not talking about the gears at all - talking about fitting that into the ends of the planetary cage and all it's mass to have to stop or accelerate before engagement - keep this in mind - while that's all going on your having to do the opposite to the other either sun or ring - there's multiple combinations of what you have to start and stop - it's a hat trick to say the least...

                                all gears on a modern manual transmission (non-crash-box) are in full engagement at all times (except reverse) they are just freewheeling as their engagement dogs (off to the sides) are not engaged (neutral) only one engagement dog can be engaged at a time {1/2/3/4/5)

                                in the case of the planetary system actually TWO engagement dogs would have to be engaged at the same time to create a power transfer --- get it ?
                                Last edited by A.K. Boomer; 03-11-2018, 02:32 PM.

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