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  1. #41
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    This thread is funny.

    The OE gear was delrin and blew up... The only way I'd bother 3d printing one out of anything plastic would be IF I was camping in the desert, the gear blew up, and I happened to have a 3d printer in my motorhome. As far as plastics go Delrin is nice stuff and it didn't cut it.

    A printed ABS one might get you home. It'd probably work just long enough for you to get lazy and then break once you were nice and hung over.

    What's the logic in substituting a Nylon gear for a delrin one which already failed? I mean really... I dont' really care if it comes out of a star trek replicator it's still not gonna cut it.

    Depending what it's running against I'd say I'd step up to at least bronze and have one cut. Or see if I could switch both this gear an the mating gear to something available off the shelf.

  2. #42
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    Quote Originally Posted by Zahnrad Kopf View Post
    I really have no interest in a debate of semantics with you. The Shaw Rule applies, still. I stand by my statement taken within its context. Let me know the last time you have put a SLA, SLS, FDM ( or any gear for that matter ) on a Vari-Roller, Gleason, or M&M inspection machine and what those results were. I have. So until you can actually give me numbers that equate to an actual, acceptable replacement for a gear in a consumer product that functions with accuracy and longevity from any of these methods I'll continue to stand by the knowledge and experience I have gained by doing so for myself and studying the subject at length with others in the field. I do have to admit to finding good humor in the fact that you seem to think that you can print an accurate Involute when you cannot even hold true roundness or size of a diameter.

    In fact...

    Here's an offer for any of the knuckleheads that just refuse to listen to reason, fact, and experience. Wanna waste your time and money as well as the OP's time and efort? Put your money where your mouth is.

    Make your gear. Send it to the OP. If it works as original and lasts, I will come back and declare your superiority and my own stupidity. If it does not work as original and with longevity, you will eat all costs related to it, as well as pay the OP for his time for removal of gear box, installation of yours, and removal again once it has failed, as well as purchase of an actual, suitable replacement. We will assign a typical average shop rate of $75 per hour to the tasks and put a cap on it at $1000.00 USD. And it ALL counts. Every minute of your time doing calculations and modeling and set up and printing and clean up. And as long as you're doing that, send me another one and I will put it on one of the above mentioned machines and film a video of its inspection for all to see so you know that I am not fudging the numbers. Longevity will be defined as a similar number of usage cycles equivalent to the number it took for the original to fail. So, if OP had it for 10 years, and used it 10 times a year, your gear must cycle 100 times to pass.

    Is that fair enough for you? Let's go. I'm willing to do it. Are you? I'll say it again - Put your money where your mouth is. Hobbyists need not apply.

    Until that time, every single word you write or speak regarding the subject is simply empty rhetoric.

    Let's see who's willing to piss away up to $1000.00 USD...
    Or just add you to the shortsighted ignore list, why would I pay anything for the OP to use a gear? Of course steel is going to be better but after the calculations are done, I could have the model done and printing before you set the machine up to make it and then pull a part off in a few hours that would get the job done for a much lower cost. Why do you think the teeth stripped? How did it work for so long and just fail? Think about that.

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    ???????? No, no... I think you might have missed something... I'll try to clarify, below.

    Quote Originally Posted by tjb1 View Post
    Or just add you to the shortsighted ignore list,
    Yes, you can. That is certainly your prerogative. Won't hurt my feelings one bit and might make you feel better.
    You can choose to stick your head in the sand about it, or we can both walk through this and actually have a test that settles it empirically.

    Quote Originally Posted by tjb1 View Post
    why would I pay anything for the OP to use a gear?

    You would not pay anything if it worked. If it worked, accurately and with longevity, you would be the one getting paid. In fact, I might even be willing to up the ante even further and foot the bill myself just to settle the issue. Of course, if I really believed the hype being dispensed, I'd just walk over and print one myself. But I digress... If the gear is satisfactory as has been discussed, you would be paid for the gear and I'll proclaim you are correct, I am incorrect and a sod for failing to see The Truth. Is that clear so far?


    Quote Originally Posted by tjb1 View Post
    Of course steel is going to be better but after the calculations are done,

    Wha...???? Who said anything about Steel? If I were to Hob one, I'd do it out of whatever the OP asked for. But if we're to have an actually meaningful comparison, then I would do it from a similar material so we would be comparing only the processes, and the results therefrom.

    Quote Originally Posted by tjb1 View Post
    I could have the model done and printing before you set the machine up to make it and then pull a part off in a few hours that would get the job done for a much lower cost.
    Using both processes on an almost daily basis, I find that almost laughable. I'd be done before your printer was. The calculations are the same for both of us. Math is Math. Ain't nothing gonna change there. ( you'll pardon my double negative for the sake of color ) In fact, I dare say that I'd be far ahead of you for simply not needing to make an accurate model! Just how long do you think it will take to Hob one? I can actually give you a very specific and real answer ( down to the minute ) since I have actually Hobbed some Delrin, Nylon, and GFN gears over the last 7 days. ( For the record, I have also SLA'd some in Acurra25 recently. ) As for the "lower cost"; while true, it's also a useless claim if the result is equally useless for the purpose.


    Quote Originally Posted by tjb1 View Post
    Why do you think the teeth stripped? How did it work for so long and just fail? Think about that.
    I have my own opinions regarding the "why", but frankly I really don't care as it regards this conversation. It's completely irrelevant to the actual discussion. OP asked if it would be a suitable replacement. People have weighed in with their opinions, knowledge, and experiences. A select few others propose that you can make an "accurate enough" replacement "strong enough" for the purpose. ( or something kind of, maybe, almost 80% or so... )

    So I propose they either put up or shut up.

    Maybe I need to be more clear... I'll try. I love what Additive Manufacturing does for me. I love what it does for my business. I use it all the time. Will ( as was proposed ) an FDM replacement work for the OP's situation? I do not believe so. Will FDM, SLS, SLA, etc... ad nauseum ... gears work for other applications? Absolutely! All day. Every day. So, I'm not against AM for gears, for the right reasons, and for the right applications.

    You and some others disagree. You say your recommended replacement will work just fine and OP will live happily ever after.

    I propose you ( or whomever ) put their money where their mouth is and actually get to backing up their assertions with real product and real numbers. Not "I think..." I am ready to do the same, and have even offered to do a video of an inspection of said gear so everyone else in the discussion can see whether the whimsical claims being proffered are worth the air expended for the purpose.

    Seems pretty straight forward and fair to me. What have I missed? Can I make any of this any more clear? That is a genuine, serious question.

    I'm willing to submit some effort to back up my opinion. What about you? avongil? Willing to put your money where your mouth is? Everyone's ready to bench race. It's a different story when people have to actually open their wallets and suffer consequences.

    Of course, I never bothered to ask the OP if he would even be willing to be subjected to the efforts, so this may all well be moot.

    Lastly, please do not take any of this so personally so as to feel hostility from me. I have none. I can assure you that this thread won't cross my mind after another 5 minutes. Or at least until I get notified of its update. I do, however, see an opportunity for some real world comparison.

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  5. #44
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    This is for a slide actuator in a motorhome.

    Lots of stresses there if not aligned properly and a printed gear may work perfect but it is not likely a good long term fix.

    Op needs to just get the replacement part but some manufacturers sell kits not parts so used are option.

    First action is to determine why part failed then take corrective action to allow it to last.

    Printed gear may be only reasonable short term replacement but better would be cut from proper material.

    That needs to be such to not destroy the mating gear and maybe incude a shear key like briggs stratten engines use.

    Op could look at irv2.com to see how others have solved this issue.

    If demand is there then one could creste a kit to market but the demand may not be there.

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    Quote Originally Posted by avongil View Post
    Those pictured gears work really well belive it or not.
    Gears for motion control under minuscule loads can be made of plastic. For example, they will handle paper feeders and the mechanisms of clocks. That does not mean such a thing is adequate for doing actual work, like cranking out the side of an RV. So when you say they "work," we in the gearmaking world understand your statement as a highly subjective opinion, not to say uninformed.

    No need to calc the addendum modification coefficient. I have just modified the profiles so they are undercut...Seems resonable considering the application. No need to examine every detail.
    I'm unable to compose a response to this. Every time I rerun it in my mind Diet Red Bull wants to come out my nose. AG, you think we're hostile, but that's not it at all. You probably remind Zahnrad of the guy who comes up and asks, "Hey, Boss--on this last tooth, d'ya want one thick one or two thin ones?"

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    My grandson got a clock kit for Christmas and the whole thing is cardboard gears and all.

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    Quote Originally Posted by Oldwrench View Post
    I'm unable to compose a response to this. Every time I rerun it in my mind Diet Red Bull wants to come out my nose. AG, you think we're hostile, but that's not it at all. You probably remind Zahnrad of the guy who comes up and asks, "Hey, Boss--on this last tooth, d'ya want one thick one or two thin ones?"
    OHMYFUCKINGGODS!!!! I just spit my drink EVERYWHERE. Holy crap that was HILARIOUS. Dammit man. Thanks. And yeah, you're not far off at all...

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    Meanwhile... back at the ranch...

    Hmm. In the span of just three days, we've made more Glass Filled Nylon AND SLA gears, as well as steel ones.
    And yet, in that same 3 days not one FDM person has stepped up to put their money where their mouth is. I'm so shocked.
    Attached Thumbnails Attached Thumbnails img_2785a.jpg   img_2786a.jpg  

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    We have several 3d printers at work and they are quite useful. Our ventures in plastic are mostly for mockups and fixtures. It has been mentioned several times as to why it failed and it may not be the gears fault. There is no doubt in my mind there material selection works under the proper conditions.
    We recently jumped into the metal 3d sintering arena along with its learning curve. I have attached a link to the metal gear we print or additive manufacturing I guess they call it. I also posted the link for what it sells for. They buy maybe 12 a year. If you have a model it could be included in a build. Most of the builds are in stainless at this time. There is a chunk of cost in getting the build wire edm'd off of the build plate. Plastic has the advantage there. The accuracy is OK and the finish is not a 63 or better but it is uniform. Even if it could be manufactured for under $40.00 it would just find the next weak plastic link and die when I had the slide out in the boonies. The folks that bought the timing belt pulley from us have oil running through their veins and are on a $ quest to find the next weakest link.


    https://www.youtube.com/watch?featur...&v=DXh1AbX5j20

    english racing, oil pump gear, under driven oil pump gear, underdriven oil pump gear,

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    One could probably assume that some sort of two-part mechanical actuator could be designed out of most low-precision processes to at least produce moulds for something strong enough if not the parts, it would just be a question of using the right structure.

    Given the esoteric geometry that is possible with 3D printing, presumably new rotary meshing shapes might be possible which take into account the strength and precision constraints? One might be able to come up with at least an estimate of how much cheese might be required (or string-reinforced wax).

    Certainly a conventional rotary gear for anything that connects a vehicle to anything that moves at speed with all sorts of fairly aggravated dynamic loads putting hundreds of tonnes momentary pressure on parts, one would not be advising any sorts of vanilla plastics for the bearing surfaces of such a gear system. Probably not even aluminium. I can't visualise the part in question but it sounds like big plastic cogs on things that do motorway speeds probably isn't ideal.

    If you are not too worried about weight, just get steel. Not worried about money, get Titanium. Both bearing surfaces / cogs / screws / wheels of conventional or esoteric form. Machined properly. Possibly replace axles & bearings also.

    Things that chew parts should really be given a proper overhaul, not just fed another part to destroy. Same part, same failure mode twice in a row, best look at the bigger picture and use better parts throughout.

    If you think about an industrial lathe, and then put a car wheel in the chuck, and then multiply that by about 10, that's a car. 150kW or so minimum, and run the thing un-tethered, the whole machine running about at a good 35m/s with a can of flammable fuel strapped to it... and have you seen the people operating these things?

    Heavy machinery requires warning stickers, a lot of motor vehicles should come similarly equipped. It's terrifying if you think of the power and weight of the things in kW and m/s. The ratings would be fairly terrifying if found on machine tooling.

    A contemporary sportscar chucks out about 500kW. I don't know who uses 500kW milling machines, and at least those presumably don't run about at 70mph piloted by... beer in hand...

    One would almost definitely recommend at least using steel, or if you must plastic some sort of high-carbon-fiber content moulded thing. Possibly get away with aluminium. If stainless steel, or brass, then you could probably make it all a bit smaller, and it'd plausibly be strong enough. Maths might be involved.

    If one were doing the rapid prototype print-out of the part in whatever abstract shape, one could machine a plastic positive to precision and surface quality, then take a sand cast from it and render that in steel, brass or aluminium, then precision machine that.

    I have met many plastic cogs on metal shafts. Toothed belts are better in most respects.

    Plastic cogs of most sorts do not like heavy loading, neither briefly nor extendedly. This applies to anything from bicycle drivetrains to RC servos. They are quite intolerant to "chew", where overloading compressive forces applied by mismatched very hard materials vs relatively soft materials, pinching or cutting, the plastic can be eaten either at the axle or by the teeth by a much harder material, putting the plastic into plastic deformation.

    Grew to analytically hate the plastic cog at 16, operating a film processor like a large mangle in a box with nylon cogs, must have fed that thing 1000s of cogs. Every time a bit of film jammed in it, it'd shred at least a few teeth right off each cog, minimum. Metal cog + plastic cog + torque = plastic cog cutter. It was hatefully designed, moderately functional otherwise and installed between two rooms, and so we just had to climb all over it and feed it plastic parts constantly, but they were like mechanical fuses, making a warning squeak before going into destructive fallover.

    Oddly shaped compromised and inconsistent plastic 3D voxel-cog with noise jitter and droop but of otherwise conventional format? Doesn't sound favourable.

    Probably better off with the proper factory-made nylon ones from the packet in the film processor case. However, they weren't great either. Started off the right shape but it wasn't long before they declined into rough bits of chewed plastic.

    For a load-bearing surface on a piece of automotive transport equipment rated at X00kW and travelling unrestrained with considerable speed and kinetic energy... hit a badly maintained bit of tarmac and it'll likely chop plastic bushings up like a person chewing wine gums, let alone deform the mating surfaces of cogs, even if they're fairly large.

    Delrin is Acetal resin, can be additively formed in various ways, if modelled accordingly etc, printed and subsequently processed & machined a feasible part might be in operation roughly as good as a conventionally machined or moulded plastic part, but when comparing with any one of 1000 proprietary acetal resin blends of various waxy squishiness, and might fare better than urethane skateboard wheels, or might not. If you use skateboard wheels you'll probably have enough grip to do various sorts of gearbox effects with cylinders under load, so as not to need any teeth.

    Hard to say without seeing the whole part in context, but there's plastic gears and metal gears, and load bearing automotive uses generally aren't to be found employing plastic gears. Carbon fiber driveshaft yes, but plastic diff is very unlikely.

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    Bishop...

    You just had to go and pick the scab off this year old thread didn't you...

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    Preaching to the dead . . .

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    I made at least 8 different sizes of gears on my FDM/FFF machine with a good light press fit onto the shafts, which meshed wonderfully with their factory counterparts, and have been running under severe abuse over the last several months.







    But they're LEGO gears for some Lego machines my 9 year old makes. So maybe that's perspective :P

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    Quote Originally Posted by IronReb View Post
    Bishop...

    You just had to go and pick the scab off this year old thread didn't you...
    Just coughing up a hairball there

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    http://i.imgur.com/QajzzFS.jpg
    http://i.imgur.com/PZQYabU.jpg


    I figured a replacement for my broken back gear would be a good conversation piece. The inside diameter is 1.125" and a sintered bronze bushing is inserted on both sides. the gear was printed with 15% infill, three perimeters, from PLA.

    I have loaded my half inch wide, 20 degree pressure angle 18 DP change gears to ~200 pounds loading (at which point three teeth are in contact for two 72 tooth gears) and they hold up to that without breaking.

    16 DP 14.5 degree pressure angle cast iron back gears at .625" width might have a safe tooth load of just 100 pounds for 30,000 psi tensile cast iron if that number is correct.. its about half as much as it needs to be, as these southbend lathes shipped with a 1/3rd hp motor, at 40 rpm that is 40 foot pounds of torque at which point about 200 pounds of force is exerted on the spindle drive gear.

    The two 32T 20dp idler gears are press fit on 608z bearings btw.

    On the to do list is a bearing replacement for the next gear in line.

    I have two gears printed at 100% infill, solid. 62T and 24T. I had intended to mechanically fasten them together to make the back gear assembly (because printing the entire thing solid would take 17 hours), but instead I'm intending to simply load them to failure at zero rpm. the back gear in the lathe now took 7 hours to print.

    I think the gear will sheer off the shaft, rather than break the teeth. so i would rather just rig up a mechanical brake and load the spindle to 20 foot pounds and leave it running for a long time and see how the gears wear.


    Does anyone here have a rotating stress fatigue measuring machine? at the moment there is very little data concerning the fatigue resistance of three d printed plastics.


    Btw, the belt in the photo is a 1 inch wide strip of a bicycle inner tube, cemented together. a single strip of duct tape makes (i think) two and a half loops around the belt. it works very well.

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    you guys do know that Inventor (and probably Solidworks) have design accelerators for things like gears right? took me about 10 minutes to draw up a roller sprocket for a production item here, works perfectly. I cut em on a hankwang laser and they drop onto a splined machined shaft.

    couple that design accelerator with say, a Markforged fiber reinforced nylon print, and you have some easy gears that should replace other conventionally made plastic gears no problem. No need to own a printer either, you could just pay someone else to run them off for you. Won't be long until we get one of these printers.. machining is so busy and printing is a great alternative (along with laser/router cut weldements etc)

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    Quote Originally Posted by apoc_101 View Post
    you guys do know that Inventor (and probably Solidworks) have design accelerators for things like gears right?
    I cannot speak to Inventor, but the people that do know about the ones in SW have also come to know that they are also inaccurate and inadequate for many real world applications. The powers that be having taken liberties with the forms and minutia. Work fine for applications that do not have much real world importance or demand, but fall grievously short when they do. YMMV.

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    Ahh, sorry to hear that. I know for certain that Inventor does not cheat and can definitely be counted on for it's engineering features across the professional package. added bonus, HSM (integrated CAM) is fantastic (there's free versions and paid versions if you use 3D and 5 axis processes)

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    Quote Originally Posted by apoc_101 View Post
    Ahh, sorry to hear that. I know for certain that Inventor does not cheat and can definitely be counted on for it's engineering features across the professional package. added bonus, HSM (integrated CAM) is fantastic (there's free versions and paid versions if you use 3D and 5 axis processes)
    I ( and doubtless many others ) would be interested in hearing to what level of accuracy the Involute is created and what manner of geometry it is comprised of. As well, what specific gear related considerations are user input and able to be controlled. Too, how do you know this "for certain"? Are you involved in it? Seen the back end? Just curious and interested.

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    gears.jpg
    (see attachment for the screens)

    the geometry and mechanical calculations are sound, and the actual geometry output has all the required features. The results can be checked against the Gearing section of the Handbook and in the past when I've verified all the features, everything checks out

    And of course if you really want to, you can input all the loads and mechanical figures, and test out the interface with FEA simulation. We don't usually simulate things, unless a customer specifically requires it to be done.


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