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  1. #1
    hi all,

    Am pushing some ideas around on the back of a fag packet- doing some blue sky thinking whilst pushing my performance envelope- etc etc more generic management speak-!

    for my gear reduction for the 8 x 4 router- am looking at probably around a 3Nm stepper, running to a 16t timing pulley- to a timing belt- to a 60t pulley with a 20t pinion running on a rack- if that makes sense-!

    so questions are-

    1/ is a 3 (ish): 1 ratio the best- or is 2 better?
    2/ whats the best belt width?
    3/ hows best to keep tension/ the pinion on the rack
    3/ has anyone come up with a slick way of mounting all this stuff in a nice dust free casing?! am looking at obviously trying to support an 'axle'/ bearings for these and have seen some on other machines but can't find an off the shelf bolt in solution....
    4/ would you do the same thing on the 'Y' axis as well?

    so far have decided on the hiwin type linear guides/bearings so one each side on the 'x' with the above rack to drive, and for the 'y' probably 2 hiwins on the top and one on the back maybe? probably mounted on an ali extrusion say 80 x 120 again on rack & pinion?

    'z' i'm thinking of a ball screw linear table type thing- are these eay/ cheap to build or is it best to purchase an off the shelf type?- But will the 'z' want reduction?

    hope to be in a position to start me build in the next couple of weeks so if anyone knows of a cheap but good source for

    1/ the hiwin
    2/ the rack
    3/ the pulleys
    4/ steppers/ drives/ etc etc
    5/ decent maybe water cooled spindle with a vfd

    have been looking around at the usual places zapp etc etc but just on the off chance wondered if there was a guy in a shed somewhere selling them off cheap-!

    Gonna start me Cad drawings off and see how i get on...

    George

  2. #2
    it appears i have posted this in the wrong section..... embarrassed face mixed with sad face....... can an admin/ mod correct my hideous mistake and shove it in the router build log section... sorry!!

  3. #3
    Your wish is my command!

    Good luck with the build, look forward to seeing the drawings. Not done a belt system myself so cant comment sorry !

    .Me
    .Me

  4. #4
    Hi George,

    I've built a couple of smaller belt drive machines so have a little experience and they work very well.!! . . . . . That said thou let me try and talk you out of it.!!!

    It actually doesn't work out much cheaper than R&P or even cheap chinese ballscrews by the time you have bought the pulleys and good quality belt along with bearings,spindles etc. It's really doesn't lend it's self very well to large format machines due to the difficultys in keeping the belts correctly tensioned.

    My experence was that even 3:1 wasn't enough reduction to have a good resolution and keep the motors working in a nice rev range.!! . . . And this was with relatively small pinion so smaller Dia = less pitch or travel per rev. . . . IE: 25mm Dia pinion x Pi = 78.5mm travel(pitch) per rev / 3 for 3:1 reduction = 26.1mm per rev.
    So thats 25mm drive pulley with 75mm driven pulley.
    This is quite a high pitch, the machine will go like hell and well above 30mtr/min but the resolution will be lower.! . . Not so big an issue . . . BUT . . The bigger problem comes when you want to go really slow like 500mm/min this will mean the motors only turning 20 RPM and at this speed the motors complain and you can get cogging affect.

    If your only ever going to cut wood or plastics with a good quality spindle then an high pitch will be ok and will handle the high feeds ok.
    But if you want better resolution or have a desire to cut materials that require lower feeds then a pitch more like 10-15mm per rev would probably be a better all round target.!!
    This would however require 6:1 reduction and great big pulleys which are not cheap. Plus all the above figures revolves around using a small 25mm Dia pinion and what would more likely be the case given the size of machine and belt requirements is that the pinion would be larger which then means the driven pulley gets very large and expensive. (Unless you do multi stage reduction which gets complicated and more expensive.! smaller pulleys but more of them and extra belts)

    IMO the best option regards cost/performance/maintenance/ease of build for large format machines is R&P.! . . OR. . If you want to spend a bit more money and time then go for the ultimate and use ballscrews with a rotating ballnut like Jonathan's machine.
    My first choice would be Jonathans way every time because of the bennifits ballscrews give but if budget plays a part then I think you'll find that there's very little difference between R&P and belt drive done correctly.

    Regards Z Axis I'd build it my self using ballscrews and belts but no reduction 1:1, this is to help with resonance and also makes build and motor placement easier and that bit neater.!
    Best tip I'd give is don't skimp on the Z axis because it takes all the strain of cutting forces and no matter how good rest of machine if the Z axis flexs it means nothing.!!

    I can help regards linear rails I'll send you a PM.

    Hope this helps.!

  5. #5
    Hi Jazz-

    Not sure I explained myself very well-!!

    Was defiantly using a rack and pinion on both x and y but a ball screw on z- but wanted To do a reduction from the steppers to the pinion gear-

    Interested to hear of your sources-!


    G

  6. #6
    Quote Originally Posted by georgetheforge View Post
    Hi Jazz-

    Not sure I explained myself very well-!!

    Was defiantly using a rack and pinion on both x and y but a ball screw on z- but wanted To do a reduction from the steppers to the pinion gear-

    Interested to hear of your sources-!


    G
    Doh.!! . . Yes I did read it wrong ok I under stand now.

    Get drawing then give some more detail of motors,drives etc.

    Are you planning on using 2 slaved motors to drive long Axis or a single motor driving shaft with pinion on each side.?

  7. #7
    was going to have 2 motors working in opposite on the long axis

    here's a shot of the kind of reduction i was looking at-

    Click image for larger version. 

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    looks like he's just done a slide to manage the tension....

    G

  8. #8
    Looks to me like it's a fixed pinion with no on the fly adjustment while traveling, this is a bad idea to me because it doesn't account for any deviance over the racks length so will bind in places and wear quicker.
    Also if something like a decent size chip gets between rack and pinion it will potentially jam up or if traveling slow with high torque do damage as the pinion will try to continue on it's way eating it in the process, something will have to bend or move and chances are it will be the pinion shaft or belt will snap.??? . . .Either way something bust's.!!

    Yes even with on the fly adjustment way if something gets stuck between R&P it's going to jump teeth and lose position but no damge will be done to the machine.!!

    Another thing I don't like is the fact the belt or what ever he use's for reduction is on the inside in the firing line.!!. . . . not good Idea IMO.!

    Like those massive 35mm rails and flanged carriages thou, Shame he's attached it to what looks like a tall 15mm plate gantry side.!!! . . Would like to see the whole thing.

  9. #9
    having a wee look at this tonite-

    for the y axis... was thinking of using the 80 x 120 ali extrusion... with one 20mm hiwin rail mounted on the face

    a bit like this-? Attachment 5561Attachment 5562

    dunno if the 2 rails are over kill? for a router that'll mainly be doing sheet materials like ply and mdf with the odd bit of polycarb etc....

    the z'll be hiwin type again with ball screw-

  10. #10
    Quote Originally Posted by georgetheforge View Post

    a bit like this-? Attachment 5561Attachment 5562

    dunno if the 2 rails are over kill? for a router that'll mainly be doing sheet materials like ply and mdf with the odd bit of polycarb etc....
    These links don't work but if your thinking to use just one rail total then thats a bad idea even for MDF, PLY or plastics.

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