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  1. #1
    Join Date
    Sep 2005
    Posts
    167

    new linear motion driving idea

    i am building a new router, it will be mainly for foam cutting.
    i was thinking what can i drive it with ?

    2 screws in each side ? expensive and complicated setup
    2 belt and pully system ? well maybe

    i thoght also about chains but i was worred about wear, tensors and so on.
    now i have this idea, i dont know if it was done before or not, anyway


    how about placing 2 chains (maybe welding them on the machine body side and not making them hang around as usual) side by side with one of them ahead of the other a little bit so that the teath of the sprockets are always in a good contact with the chains

    then placing 2 sprockets on the motor shaft and making them roll on the chains as if it was rack and pinon


    and repeat that on each side of the router ?
    Attached Thumbnails Attached Thumbnails Graphic1.jpg  

  2. #2
    Join Date
    May 2005
    Posts
    1810
    I am not sure I understand the need for two chains, nor do I understand the need to stagger the chains, but your idea will work.

    I have used a single, tensioned chain as a gear rack on an industrial machine in the past.

    Scott
    Consistency is a good thing....unless you're consistently an idiot.

  3. #3
    Join Date
    Sep 2005
    Posts
    167
    hello mxtras
    thanks for your reply.
    the reason is to minimize the backlash thats all.
    maybe i am mistaken on the concept as i thought that the teach will always be in good contact that way.
    so how was ur machine performance when u used that idea ?
    you used it as a gear rack or you meant a sprocket rack ?
    any backlash ?
    what was the efficency of motion transfer compared to other systems ?
    and what size chain have u used ?
    sorry for so many questios , but i am build a table which is about 3meter long x 2 meters wide
    one last thing on a table that long can i place the rach on 1 side only ?
    thanks

  4. #4
    Join Date
    Jan 2006
    Posts
    738

    Chain drive

    Your idea should work as stated. Judging by the size you are talking about I would probably put a chain on each side. If allowed you could put a shaft across the width connecting the two sprokets. If you have your linear track and truck system set up, there might be an alternative to welding the chain down. In some machines I have worked on a system of 2 idler sprokets and one drive sproket was used. The chain was pulled tight with a piece of thredded shaft attched to the end and layed on a support if horizontal. Think left to right here.... chain about 1/3 way around idler in CCW dir, then 2/3 around drive sproket in CW dir, then 1/3 around second idler in CCW dir, and back along original path. Chain makes an "omega symbol" path.

    Check out the drive system for a copy machine mirror/lamp carriage. Many are a piece of wire cable (small) wrapped around a drive spool. Very smooth operation, no backlash, and can be very accurate. Could be scaled up to any size. Just a thought.

    Steve

  5. #5
    Join Date
    Nov 2006
    Posts
    262
    If you could get chain wide enough or sprockets narrow enough you could mount two sprockets tight together and have a provision to adjust them to remove backlash, might be easier than 2 chains ??

    Bill

  6. #6
    Join Date
    May 2004
    Posts
    314
    why not use larger size toothed belt instead of chain, its lighter, thinner and quieter and needs no lubrication. you can use the same method as the chain basically. Ive been told by people that have used it, that after an initial stretch, there is no noticable stretch. You could also glue it down to a rail upside down as you were planning to weld your chain. just a thought
    Lemon Curry??

  7. #7
    Join Date
    Sep 2005
    Posts
    167
    i thought about the belt beeing used instead of the chain
    but i dont think there are belts that have teeth that long ?
    i mean the gears can jump the teath of the belt if there are a strong resistance for any reason, or maybe i am wrong

    however since my printers are my main job, i see all new printers and even some plotters that uses wires instead of belts.

    just a normal steel wire with no threading.

    did anyone tried this before ?

  8. #8
    Join Date
    May 2004
    Posts
    314
    I would worry more about the cable system slipping on a larger scale machine than i would the belt. and if you were to use the belt in the format the other poster mentioned about two idlers and a powered pully, for the belt to skip you would have to skip a good many teeth. also concider the fact that the belts teeth maybe as close as maybe 5 per inch on a larger size belt. even with the smallest chain that ive seen you still only have 2 or 3 at the most.
    i know it sounds like i work for the belt company Ive just seen how nice they are on motorcycles, and some machines we have converted from chain drive to belt in cases where its practical.
    Lemon Curry??

  9. #9
    Join Date
    Feb 2006
    Posts
    1260

    drive picture

    maybe a picture/sketch worth more than words. Many people on here using either of the designs pictured below to drive plasma, Ox Fuel, Router tables & find both notched belt & sprocket chain in these type(s) of drives.

    I think by wrapping the chain or belt around a pulley as opposed to using it rack & pinion style would best eliminate backlash.

    I do think what you are suggesting will work if:
    (1) Your chain is of high quality & spec.
    (2) You get the chains spaced on EXACT centers.
    (3) You get your sprockets timed EXACTLY around the drive shaft.
    (4) Your Sprockets are of Machined Quality as opposed to stamped or cast.

    Just my opinion.
    Attached Thumbnails Attached Thumbnails drive system.jpg  
    If it works.....Don't fix it!

  10. #10
    Join Date
    May 2004
    Posts
    314
    keep in mind that both of the styles have pros and cons. on one hand, while the top style cuts the length of the belt or chain almost in half, the moving aspect of the axis now bears the weight of the motor and mounting hardware ect. the lower style lowers the driven weight a bit due to the remote motor location, the accumulated play in the belt or chain would be greater.
    Lemon Curry??

  11. #11
    Join Date
    Sep 2005
    Posts
    167
    i just rememberd a quote

    its true that a picture worth a thousand words
    but do u know how megabyte it can take

  12. #12
    Join Date
    Jan 2006
    Posts
    738
    Quote Originally Posted by erase42 View Post
    I would worry more about the cable system slipping on a larger scale machine than i would the belt.
    Should have clarified, the cable is bound to the spool through a slots to pins. A lot like a spool on a giant 200 ton overhead crane I once worked on only the copy machine has a return path counter wound on the spool through the other slot.

  13. #13
    Join Date
    Nov 2006
    Posts
    5
    Two words: Magnetic drive.

  14. #14
    Join Date
    May 2004
    Posts
    314
    yeah two words back at ya. hobbiest budget
    Lemon Curry??

  15. #15
    Join Date
    Nov 2006
    Posts
    5
    True. But it would be great to come up with a DIY for foam and plasma.

  16. #16
    Join Date
    May 2004
    Posts
    314
    are you talking about linear motors? where a rail becomes the moving part of the motor? if so, how would you get feedback? a rotory encoder driven by toothed belt?
    Lemon Curry??

  17. #17
    Why not just use rack & pinion? It's not that expensive, it lasts long, gives good resolution and is pretty much maintenece free...

    -B

  18. #18
    Join Date
    Aug 2003
    Posts
    494
    Hi all,
    Getting back to cheap drive products........
    Look up SDP/SI stock drive products as they have unjoined lengths of toothed belting that sell by the foot and an online catalogue, or McMaster Carr also have a heap of stuff in their catalogue but they don't send overseas anymore due to too much paperwork for customs.
    I just purchased 12 feet of 3/8 wide by 0.200 in tooth spacing for $75 with 2 plastic gears to suit. Total with $24 shipping was just over $100.
    If you're not worried about noise and can get cheap chain then go that path as it will last a damn long time..... with lube (just look at what a motorbike subjects them to) but if it's quiet motion and smoothness and don't mind spending a bit of extra cash then I would recommend the toothed belt. Cars don't need to change theirs on the timing gears for 100,000 miles (as a precaution) and they pull 7,000 revs occasionally. Just get a belt that is suitable.
    If it's for a wire foam cutter with a small load then it wouldn't have to be more than 1/4" width.
    As with the 2 sketches above from Millman52, I would go for the top 1 and wrap the chain around the sprocket and tension at 1 end of the chain. If you had a chain either side then you can tension from both ends of the chain on 1 side which would allow you to match up the alignment with the other side and also have the chain supported over it's length by lying on a flat piece of steel so as not to sag and put more load on the supports than necessary.
    Both methods will work but for a foam cutter, I would go down the toothed belt path......just my opinion.
    I hope it helps somewhat.
    I am not completely useless.......I can always serve as a BAD example.

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