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  1. #41
    that 4th axis looks posh, what bearings ??? stainless body??? what are you going to drive it with ??? what gearing ???

    for a moment there i thought you were using a hi-tec harmonic gearbox but im gessing the hi-tec box i can see has shoes int it lol

  2. #42
    Quote Originally Posted by blackburn mark View Post
    that 4th axis looks posh, what bearings ??? stainless body??? what are you going to drive it with ??? what gearing ???

    for a moment there i thought you were using a hi-tec harmonic gearbox but im gessing the hi-tec box i can see has shoes int it lol
    I mentioned it somewhere else on this forum...not sure which thread though.

    They're a pair of L 68149/L 68110 taper roller bearings. It's all mild steel - shows the dehumidifier is working as it's ages since I machined it. I'll use a stepper motor via timing belt to drive it since there's no way I could afford a servo. Also putting a disk brake using solenoids to hold it steady whilst milling. When I want to use it as a lathe I can put the big brushless motor on it. 6000rpm at several Kw would make a nice CNC lathe. I made it mainly to use with the milling machine, but I may well use it on the router.
    I've machined the shaft to fit an 80mm chuck, same as my C3 lathe, but I'll make an adapter to put a 5" chuck on it.

    Using 4th axis to make 4th axis (or should that be 5th?):
    Click image for larger version. 

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    Cross section, note disk break arrangement:
    Click image for larger version. 

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    Click image for larger version. 

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    Mounted on mill:
    Click image for larger version. 

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    Quote Originally Posted by chip View Post
    looking forward to seeing it running jonathan
    You're not the only one :)

    Quote Originally Posted by chip View Post
    get some videos up.
    Will do

  3. #43
    I mentioned it somewhere else on this forum...not sure which thread though.

    hahha!!! sorry jonathan, you did... on my build thread... it looks so much smaller on your router i thought youd built another one

    im still pondering the options for my fourth axis, im leaning towards a 50:1 harmonic with a stepper... it'll only be on light duties
    youve got me thinking now though.... it would be nice to be able to isolate the gearbox and run it up to lathe speeds

    think ill just sit back and see how you get on with yours :)

  4. #44
    Quote Originally Posted by blackburn mark View Post
    im still pondering the options for my fourth axis, im leaning towards a 50:1 harmonic with a stepper... it'll only be on light duties
    Could you use a timing belt inside the harmonic gearbox as the flexible gear thingy? Milling the inside out pulley would be fun. Probably do it in two semicircles...

    Quote Originally Posted by blackburn mark View Post
    youve got me thinking now though.... it would be nice to be able to isolate the gearbox and run it up to lathe speeds
    Yep, that's my plan ultimately - to be able to accurately switch between stepper and brushless motor drive.

    Made good progress on the router today. Milled and drilled aluminium box section and channel to mount X axis linear bearings. Also drilled and milled one side of gantry to fit that, and put slot in for timing belt to go through. Lots of smoke and blue swarf when drilling the steel. It's a 20mm wide slot so I chain drilled @ 16mm (biggest I have) to save time with the 20mm milling cutter. Will probably make more sense when I put photos tomorrow.

    Click image for larger version. 

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    I'm 14 holes and one slot away from finishing :) Plus a bit of assembly and wiring I suppose.

  5. #45
    Could you use a timing belt inside the harmonic gearbox as the flexible gear thingy? Milling the inside out pulley would be fun. Probably do it in two semicircles...
    haaha!!!! you read my mind this time :) iv already considered it, not really explored it deeply though, you would need a clever way to output the torque from your inside-out timing belt to your output shaft
    the beautful thing about using a belt for the strain wave gear is its so flexble you could use two simple bearings or rollers for your wave generator and use a slightly larger timing belt for the outer gear and pre-load it with your simple two bearing wave generator....
    im thinking it would take quite a bit of elegance to make it work... backlash might well be very small but with heavy cuts im thinking it will have quite a bit of give
    errrrr..... i dunno ??? youve got me thinking on the issue again.... if i try to fit any more in my head i think one of my eyes might pop out :)

    Edit: not sure why you would need to cut the internal in two halfs ?? i dont think you would need sharp corners at the root end of the pitch
    Last edited by blackburn mark; 16-12-2010 at 12:17 AM.

  6. #46
    Quote Originally Posted by blackburn mark View Post
    ...use a slightly larger timing belt for the outer gear and pre-load it with your simple two bearing wave generator...
    Surely a timing belt for the outer gear would have the wrong profile.

    Quote Originally Posted by blackburn mark View Post
    Edit: not sure why you would need to cut the internal in two halfs ?? i dont think you would need sharp corners at the root end of the pitch
    Maybe we are talking on cross purposes. I suppose it depends on the timing belt you choose. If it's one with round teeth then you could CNC mill it easily without a 4th axis. If it's say XL then you'll want to mill it with a 4th axis, but clearly the chuck will collide with the other side of the pulley when it's milling the teeth, unless you did it in two halves...or more realistically thirds.


    Finished all machining for router this morning! *Just* needs assembling - waiting on my dad to put some bigger legs under it since the previous arrangement was designed for a 10kg gantry, not >50kg!

    Been thinking about how I can clamp stuff to the bed to machine it. It would be nice to have T slots like on my milling machine since then I could use the same clamps and easily put the vice/rotary table etc on it. I do have some HSS T slot cutters however I think cutting MDF will destroy them.
    My plan is to buy two sheets of 18mm MDF. Glue/screw one down to the bed, get the router to cut the wider part of the T in that and level it, then put another sheet of MDF on top of that and cut the top of the T slot. That way I can use standard router bits...My only worry is if MDF is going to be strong enough?

    Just been making collets for the cheap router I'm using. I'll post a video here soon...

  7. #47
    giving the MDF a few coats of thin epoxy should provide some strength ... thin enough to soak in at first but not too much otherwise the MDF will swell an alternative could be the single T slot strips from Axminster or Rutlands etc. secure them to the lower panel and infill the spaces with the upper panel ...
    Tim G-C

    I disapprove of what you say, but I will defend to the death your right to say it.

    (attrib. Voltaire but written by Evelyn Beatrice Hall "The Friends of Voltaire" 1906)

  8. #48
    Quote Originally Posted by Jonathan View Post
    Been thinking about how I can clamp stuff to the bed to machine it. It would be nice to have T slots like on my milling machine since then I could use the same clamps and easily put the vice/rotary table etc on it. I do have some HSS T slot cutters however I think cutting MDF will destroy them.
    My plan is to buy two sheets of 18mm MDF. Glue/screw one down to the bed, get the router to cut the wider part of the T in that and level it, then put another sheet of MDF on top of that and cut the top of the T slot. That way I can use standard router bits...My only worry is if MDF is going to be strong enough?
    Sorry but you are gonna be wasting your time using MDF and an accident in the making for sure.

    Quote Originally Posted by Wobblybootie View Post
    giving the MDF a few coats of thin epoxy should provide some strength ... thin enough to soak in at first but not too much otherwise the MDF will swell an alternative could be the single T slot strips from Axminster or Rutlands etc. secure them to the lower panel and infill the spaces with the upper panel ...
    More bad advice The only thing MDF should be used for is a spoil board

    Phil

  9. #49
    Surely a timing belt for the outer gear would have the wrong profile.
    i compleatly missed that,,, i think your right

    iv got another one for you to ponder... there is probably somthing obvious iv missed but if you use a double sided timing belt you might be able to exit the belt through the outer gear wall (using small rollers maybe) to drive an output pulley, that
    might solve the main stumbling block to the idea and give you a sturdy output (if it could be made to work)

    Click image for larger version. 

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    it would make an interesting project but i think im going to admit defeat and try to get a second hand hi-tec drive :)

  10. #50
    Quote Originally Posted by M250cnc View Post
    Sorry but you are gonna be wasting your time using MDF and an accident in the making for sure.
    Can you think of anything better to use that's not too expensive? Maybe plywood, but I guess that's not much better. Vacuum table isn't much good for metals. Bear in mind it needs to be about 800x1900mm ... so clearly I can't afford a nice piece of tooling plate that size!

    I'm not sure about the epoxy idea either, wouldn't it just crack/crush?

    Making collets for router:

    http://www.youtube.com/watch?v=m98fPg-_vUU


    Not quite sure with what you mean by exiting the belt through the outer wall, diagram?
    I agree buying one is probably the safest option! If you're after a really big reduction then perhaps several timing belts and pulleys could work. If each one gives 1:4 (feasible I think) then you only need 2 belts to get close to 50:1. Timing belts don't have backlash, but I'm not sure about stretching. Why do you want such a high ratio anyway? My rotary table is 1:90 and it takes forever to rotate, even with the 70v stepper drivers.
    Last edited by Jonathan; 17-12-2010 at 01:11 PM.

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