chain reduction drive - chain quality and lubrication/maintenance
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  1. #1
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    Default chain reduction drive - chain quality and lubrication/maintenance

    Hi all,

    I have a CNC router in my shop that has become somewhat neglected/orphaned since the original manufacturer was bought by a new company, and the new company is less than stellar about customer care, especially on legacy machines.

    The drives for all three axis are 440 oz in steppers with a chain reduction to the pinions that drive the machine. The reduction is 3.6:1. Chain is #25 1/4" pitch. I've noticed a fair bit of slop in the tolerances, and found that the chains were pretty slack from lack of maintenance, which allows excessive backlash. given how old the chains are, and in order to preserve the gears, I'm looking at buying new chain, but there are a whole lot of options out there, ranging from browning brand chain for $1/ft to morse brand and others for upwards of $25/foot. I see varying grades of the stuff, and am wondering when one starts to see diminishing returns on quality? Pre-stressed (to reduce stretch) seems like an important feature, are there any other things a person might want to consider when buying this kind of chain? All seem to have roughly the same working strength and tensile strength numbers, though some are rated as stronger than others.

    As to maintenance, how tight does one make the chain? I realize that too tight, and you just get excessive wear. the adjustment is to loosen the bolts holding the motor, and lift up on the motor, then re-tension. What kind of lubricant is best? These chains are covered and sort of protected, but they do get dusty both from the machine cutting, and other stuff that happens in the shop.

    I'm considering getting timing gears and timing belt to replace the gear and chain setup, and building a simple mechanism to allow spring tensioning of the pinion on the rack, too.

    img_7745.jpgimg_7751.jpg

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    I just realized that this isn't in the most ideal place, so Mods please move this to CNC machining forum if possible. Thanks!

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    You aren't going to get any kind of accuracy with chains. I'd change to tooth belts. Chains require some slack to work properly, which will kill your accuracy.

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    Timing belts really do not like dusty debris filled environments. They will stress and break when clogged. Chains will work just fine, but as you stated, chain quality with all the choices, is hugely problematic. Here's the best tip I can offer that comes from many years of experience. There is NOTHING better than modern motorcycle chain, especially the sealed type with O-rings. Buy it long, cut and rivet a fresh new link. Any decent motorcycle shop will have the tools. Make certain the sprockets are good or you will ruin the chain.

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    Motorcycle chain is much too big for this application. I’ll hopefully be able to re-design the drives at some point in the near future, but in the mean time I’m stuck with the chain system if I want the machine to keep working in the short term. Any tips on lube and how tight is too tight would of course still be appreciated. I ended up buying chain from McMaster Carr, made by HKK chain Corp. mostly because it is available today, and most of what they sell is high quality stuff. I also ordered some kind of Teflon chain lube from McMaster Carr, hopefully it does the job for now. I inherited the machine with the job a year and a half ago, and it didn’t come with any sort of service instructions, so I’ve been playing it by ear and doing the obvious, occasionally stumbling across problems like these loose and neglected chains when there is time to dig deeper into the machine.

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    I'm a fan of Diamond chain, at least the domestic made line. They also have an import line now to be competetive, I have no experience with that.
    When we've had lube related chain issues on race applications where the triflon style sprays weren't good enough, we lube the chain by cleaning it then submerging it in hot motor oil. You have to be careful not to spill it and set the place on fire, but warm up a pan of SAE 30 or thicker motor oil and drop the chain in until the bubbles stop, then let it cool off and take the chain out and wipe off the excess.

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    I would go with timing belts as well. Put covers over them if you are worried about debris.

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    Quote Originally Posted by EmanuelGoldstein View Post
    I would go with timing belts as well. Put covers over them if you are worried about debris.
    that is the plan, but I need to work with what i've got until I can machine retrofit parts...

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    I'm curious about the wear; has this machine got thousands of hours on it and the slop has got progressively worse? Or has it always been not great? There must be some tension adjustment on these drivetrains? I'd be surprised if the wear here made the backlash worse even after you brought the tension back up. Anyway, like others I'd try to get to toothed belts as fast as possible.

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    I have a customer that has Metlsaws and they are 50 hp motors with up to 32" saw blades on them. They are connected using a V tooth belt. It provides maximum grip under heavy applications so yes the belt method is best.

    Now the original way came with a timing type belt. That slips at times but the new V type cog works extremely well. Jus harder to find the right pulleys.

    Sent from my SM-G960U using Tapatalk

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    Quote Originally Posted by Bondo View Post
    I have a customer that has Metlsaws and they are 50 hp motors with up to 32" saw blades on them. They are connected using a V tooth belt. It provides maximum grip under heavy applications so yes the belt method is best.
    IIRC
    Enstrom helicopters use them to stay airborn....

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    Honestly yes thoes chains are worn, but best bet is to just tension them up a little slack is best than too tight. Then oil generously, as much to wash of the crap as to lubricate.

    Putting new chain on sprockets that worn is likely to cause you more issues not less. They very much bed into one anouther as the chain wears and stretches, new unstretched chain won't sit right on worn sprockets and if you think you have accuracy issues now it will be far worse with new chain!

    Lube it, adjust it then start working on replacements asap! As chains stretch and wear the wear kinda accelerates, you need to be working on replacements not messing with what you have there based on the pic.

    If chain and sprockets worked fine, it may not be wrong to just do the same once more, stock sprockets are readily available and just need basic lathe work to fit.

    What chain is largely immaterial, under low loads like you have here maintenance - lubrication is far more important than just chain quality!

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    from another machine that I had with chain drive, and a non replaceable large sprocket, as long as you replace the chain after two tensionings, the manufacturer said the sprocket would hold up. the worst for a sprocket seems to be having tight overly stretched chain on it. fortunately the sprockets looked to be in very good shape still. New chain and tensioning has helped, though I need to go back in and double check that it's not too tight.

    After replacing with new chain yesterday, I made a number of test cuts today and tolerances were much better. I'm actually getting round holes, and cutting a slot is close enough that things slide together without too much slop or pinching in multiple spots on the table. the big problem now is that the pinions are getting worn, and there is no proper adjustment to snug them against the racks. The racks may be getting worn too, but are hardened steel with a softer pinion, and didn't look like they had obvious marks on them from wear the way the pinions do. I've got some ideas about how to make a spring loaded system to tension pinion to racks, but I need to look into whether the linear bearings/rails are still good enough, and do an assessment as to whether it's cost effective to rehab this machine further, or whether I put in for a new one and make do until it gets replaced.

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    Quote Originally Posted by rcoope View Post
    I'm curious about the wear; has this machine got thousands of hours on it and the slop has got progressively worse? Or has it always been not great? There must be some tension adjustment on these drivetrains? I'd be surprised if the wear here made the backlash worse even after you brought the tension back up. Anyway, like others I'd try to get to toothed belts as fast as possible.
    I have no idea if it was great when new. I've been working in this shop for a year and a half, and it seems to have slowly gotten worse. It's got many hours, but I don't have any idea how many. There's a tension adjustment to the chains. you can loosen four bolts and lift the motor and snug everything back up. there is no tension/pressure adjustment for the pinions against the rack, at least not as far as I can tell. worn pinion and possibly worn rack seems to the the next thing to tackle, though I also need to more closely and thoroughly inspect the linear bearings, to make sure they're not causing problems either.

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    Quote Originally Posted by adama View Post
    If chain and sprockets worked fine, it may not be wrong to just do the same once more, stock sprockets are readily available and just need basic lathe work to fit.
    For this kind of job, chains never really "work fine." If you think about it, sprockets are not a circle. They are a polygon. Take where the pins go, draw straight lines between them, and that's what a sprocket is. Now turn it. Smooth even motion ? No.

    Belts are a lot better.

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    Quote Originally Posted by EmanuelGoldstein View Post
    For this kind of job, chains never really "work fine." If you think about it, sprockets are not a circle. They are a polygon. Take where the pins go, draw straight lines between them, and that's what a sprocket is. Now turn it. Smooth even motion ? No.

    Belts are a lot better.
    my man, I get it. but I can't put belts on right now... trying to work with what I've got, and plan improvements to be installed in the future. My machine is cutting worlds better than it was, now that there is less play in the drive train.

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    Your pinions are probably a off the shelf item, just need machining to fit the shaft, check out some of the gear suppliers, Power Transmission, Material Handling & Hand Tool Manufacturer Has been recommended on here before. Gears are pretty dang cheap, certainly far less than the costs of moving to a new machine if this one is then good enough for your needs.

    "Work fine" is in relation to the OP's needs, not theoretical machine design!

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    Quote Originally Posted by Mud View Post
    I'm a fan of Diamond chain,
    A friend works for a company with a 4 square tester set up to test roller chain. Every so often a salesman will convince a new purchasing agent they have a roller chain as good as Diamond. So a chain sample goes to engineering to test on the 4 square. Nothing else has reached the lifespan required to be used as OEM chain. The chain on the other end of the machine is Diamond chain. It has been on the machine at least 25 years and has worn out every sample ran.

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