Can M42 be used to manufacture exceptionally hard gears - Page 5
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  1. #81
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    Hi Carbide Bob:
    Obviously it does work very well in some scenarios, otherwise they wouldn't do it, and your example of carbide turning and milling inserts is an excellent example of one of those cases.

    However, I don't think the same conditions apply to these parts, and here's why I believe this to be true.
    First, this is never going to be a high volume part and if the OP is successful, he will reduce the volume of replacements even more so his success will kill his business in a way that does not apply to disposable tooling.
    Also, the investment in a mold will kill the project...I doubt he has or could ever generate enough volume to even justify the cost of the tool, never mind all the cost of making the process work.

    Second, unlike with a carbide insert, this production problem does not REQUIRE sintering as a first step...a bar of whatever steel in a Mill Turn with a subspindle will make these too and I believe at far lower part cost and for a far smaller capital investment.
    If it's possible to clear the stub shaft on the problem part, a clever guy should be able to mimic the motions of a spiral bevel gear generator and cut the teeth efficiently on a Mill Turn without even pulling the part from the subspindle.
    It's done routinely for large gears...no theoretical reason it couldn't work for small ones too.
    If the machine can be rigged with an induction heater I could even see heat treating the part while it's still on the bar, before the teeth are finished and then hard turning it all over; then finishing the teeth last.

    So lots of possibilities that avoids all of what it takes to make a sintered part; especially, if Dan from Oakland is to be believed that you cannot make a net shape spiral bevel gear with these performance requirements entirely with sintering anyway.
    To my mind the whole point of sintering is to get the hard-to-machine geometry some other way.
    Dan says you can't...you have to subject the teeth (and likely the bearing surfaces too) to a post sintering machining operation.
    Why make it hard for yourself and fight a fitzy little preform when you don't have to?

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by implmex View Post
    ....he will reduce the volume of replacements even more so his success will kill his business in a way that does not apply to disposable tooling.
    Actually this does apply to the disposal tooling market.
    If your new and improved runs five times longer what once was a good volume becomes small.
    I once put CBN into a auto production op and the tool engineer told me I should just lease the inserts as he would now only need 3-5 pcs a year vs the 50 a month he was buying in carbide.
    If you make it better and lasting longer they will buy less so that to be factored in when looking at what appears a gold mine in usage.
    The carbide insert world is way full of these stories.
    If a salesman that has the job but now has a better grade or geometry, do you slice your own throat?
    Will the customer appreciate if you do and reward you down the road? This not the same as it used to be.
    Bob

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    Cartoon of miter gears in motion:


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    we dont know what power has to be transmitted, but i assume the needed torque capacity is negligible. so two consequences:

    - maybe straight gears will produce less heat
    - maybe plastics should be looked at

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    Oh boy a lot of good information in some of the posts, I don't quite have the time to reply to all of the posts but I'd quickly add some bullet points here

    1. Changing the lube situation would be great if.... well it has to be actually proper food grade grease/oil as this is used in a horse's mouth and as I discovered on these units, there is basically no seal between the lovely delicate insides of these POS's and the diamond wheels, which obviously have small amounts of diamond dust coming off them and tooth detrisis. At this point we're redesigning the housing to use sealed ball bearings (I would have though the roller bearings used in the design would work great but I don't know what they where smoking, the thing has almost 1mm of movement side to side, it's not even close to fitting in the bore it's in. It's got a hardened steel 11mm bore but it's just all loose and not fit at all. I suspect maybe because the heads are made as cheap as possible and so they don't have to get an accurate bore in a threaded part (the bearing retaining cap thing is screwed on) so I might end up with the same problem bt switching to bearings if the tolerances on the head can't be done within budget these heads inside look almost case, some of it isn't machined, or maybe it was roughly EDM'd, not sure why you'd EDM something so simple though.

    2. I tested one of the gears with a cheap file and it didn't skate across like I'd expect but did cut in slighly (that's the badly mangled gear, I use mangled because this isn't abraded it's been mushed out of the way, there is even a bur from where it deformed) so these gear are just rubbish, the shaft it's on is nicelt ground and decent and another one of the heads I have has a really nicely ground gear but it's clear the same thing is happening, it also isn't even close to 60 HRC, I'd guess low 50's. From the sloppy bearing fits and other corners cut I think the gear mesh was the design compromise that they decided to go with. At $250 a unit it seems ridiculous that it'd only last a few months of moderate use. I did ask him about how they're used and he takes better care of his than some of the other dentists, so these tools are being treated like how an angle grinder would be treated by a welder having a bad day. So to sumarise I don't think these gears are through hardened, maybe they kept cracking but they don't seem very hard on the surface either. These are two pieces too, the gear part is interferance fit onto the nicely ground and actually decently hard shaft (even my nicer files didn't cut it but I don't have any of the fancy hardness files or a proper hardness tester)

    3. It's only the gear with the fancy geometry that seems to be taking a beating, the other gear is located by.... this hurts to say, two roller bearings, nicaly sized, but still more slop in the fit than I'd like for such small gears, and... a hardened steel bushing riding on the backside of the gear and running against the casing of one of the roller bearings.... Oh boy, This I think needs a thrust washer as it's retained by a screw type retainer that also likely pushed the bearings together, so, looks like I need to find a 10mm ID, 13.5mm OD 2mm thick thrust or have one made, which isn't that absurd but not too cheap, however two washers with a 1mm round track machined into it that takes 1mm balls probably isn't that hard, would be better than a bushing on a roller bearing case.

    4. In the drawings (and I assumed wrongly they'd be like in the drawings) the gears are straight toothed but in actually they're ever so slightly spiraled, not much but a little bit, visible in the photos. So that suggestion seems moot if they're already slightly spiraled.

    The person I'm working with has taken to replacing the crappy roller bearing units with bronze bushings, and apparently they work a lot better which lead me down the rabbit hold of how crap the current system was is a bronze bushing did a better job. The one pictured is heavily worn but has about the same amount of play as the roller bearing had, and doesn't rust unlike the roller bearing (which to fit it into the space had to have it's roller cage removed, hense the hardened bushing) , this is why I tried to anneal and drill the bushing out to 12mm to fit some bearings I happened to have to work, but unfortunatly the equipment I immedient had to hand wasn't really good enough (a 12 speed drill press and a map gas torch) so it cut the hold sort of, but it wasn't close to straight and correctly to size, but it served the purpose (see video) perfectly to demonstrate how much less play there is when the ball bearings are used. Given these ones are sealed I think for now until a better option is found ball bearings is what the redesign will use.

    Further info worth adding. I checked with the dentist (at this point basically might as well call him my client) and he confirmed that he rarely has to run the tools up to 25k RPM, that;s only for short periods because he noticed the heads fail remarkably quickly at that speed, usually it's around 8K-10K, so closer to what the gears can reasonably be expected to say, but they can and do see occasional use at 25K RPM. I'm not sure the exact torque figure but since a brushed DC motor powered Makita die grinder is the power source I'm going to assume it's not super high but pretty high. Since these immages are sorta large and there is aslo a video I'm sticking them onto a google drive folder so you can view them in the original high definition. You can cleary see how one of the gears is mangled and the other is in better condistion but has some surface corrosion on it, clearly the grease didn't spend too long on it as someone guessed correctly itseems, but you can also see the grind on the gears aren't awful either, as I think I mentioned before the slightly corroded, not as badly worn gear seemed to be a good bit harder than the other one. Saved Pictures - Google Drive

    If anyone more skilled in seeing failure modes think I made a moron of myself with my hypotitis please feel free to let me know, as for the redesign I'm hoping the potentially tighter tolerances from getting them made closer to home with an actual person we can talk to in the future means there will be better quality drill heads before deciding if a more suitable steel is needed for the gears.
    Last edited by Joshua Nicoll; 04-21-2021 at 12:17 PM.

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    I see the pressure angle is a standard 20°
    On a working gear you have a rolling component and a rubbing component there were the teeth meet oneanother
    On most handtools and other mass produced gears like on cars the pressure angle is optimized to get the rolling component as big as possible and the rubbing as small as possible
    At least so it was explained to me by a gear manufactoring engineer But he was on the other side of the spectrum with up to 16mtr gears
    Worth looking into IMHO

    Peter
    Last edited by Peter from Holland; 04-21-2021 at 09:07 AM.

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    no idea how to view the folder.

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    Hi dian:
    To access the folder, copy this part of the link to the address bar. (See thumbnail below)
    That will get you to the Google drive.

    Hi Joshua:
    These gears and their mounting look terrible, absolutely awful and the video at the end is worth looking at just for its entertainment value, never mind it's instructive value.
    Just about anything that is done to improve that abysmal situation will be miles better.

    I'd focus as you've done...solve that godawful mounting problem first.
    If you do that, the original gears will probably last for a million miles, even if they're not great gears.
    No need to go crazy...almost anything would be an improvement.

    A small point about the gears...are they spiral bevels or skew bevels...they're so fucked up it's hard to tell.
    Not that it matters a whole lot...this is so bad the engineering on the gears is the least of the problem.

    Cheers

    Marcus
    www.implant-mechanix.com
    www.vancouverwireedm.com
    Attached Thumbnails Attached Thumbnails gear-url.jpg  

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    Quote Originally Posted by implmex View Post
    Hi dian:
    To access the folder, copy this part of the link to the address bar. (See thumbnail below)
    That will get you to the Google drive.

    Hi Joshua:
    These gears and their mounting look terrible, absolutely awful and the video at the end is worth looking at just for its entertainment value, never mind it's instructive value.
    Just about anything that is done to improve that abysmal situation will be miles better.

    I'd focus as you've done...solve that godawful mounting problem first.
    If you do that, the original gears will probably last for a million miles, even if they're not great gears.
    No need to go crazy...almost anything would be an improvement.

    A small point about the gears...are they spiral bevels or skew bevels...they're so fucked up it's hard to tell.
    Not that it matters a whole lot...this is so bad the engineering on the gears is the least of the problem.

    Cheers

    Marcus
    www.implant-mechanix.com
    www.vancouverwireedm.com
    Yes, I expected it from the bushing as my client only has a drill, he doesn't have a lathe or reamers, but I've told him I can make some better bushings for the older heads too, since they seem to last longer with a bushing, which you'd think the bearing is better because bearings do better at high RPM but I guess the loads on these gears because the diamond grinding pads also mounts directly to that... I'll just call it the pinion even though it's not really a pinion gear... and transfers all the load of drilling and the counter forces to those bearings, the fact the roller bearing they used was actually slightly *worse* and how much better the bearings hold it in place this is probably a leading cause of their death, oh and that diamond dust I'm sure is produced getting everywhere and into the heads.... Fun fact the grease that was in the head, when disolved into ethylbenzene and left to evaporate... had a lot, and I mean a lot of particulate in it, some of which was magnetic but it also was a pretty shitty but usage lapping paste so the diamond dust is getting into the gears and bearings definitely. Sorry about the link too, I fixed it so it works now. I also beleive they are spiral gears as the tooth profile is slightly curved and not just at an angle. These gears are tiny though, no joke about the size of my thumbnail and I only have medium sized hands (UK size 7 1/2) so absolutely tiny.

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    Quote Originally Posted by dian View Post
    no idea how to view the folder.
    Sorry Dian, I fixed the link now so it'll open into google drive.

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    Quote Originally Posted by Peter from Holland View Post
    I see the pressure angle is a standard 20°
    On a working gear you have a rolling component and a rubbing component there were the teeth meet oneanother
    On most handtools and other mass produced gears like on cars the pressure angle is optimized to get the rolling component as big as possible and the rubbing as small as possible
    At least so it was explained to me by a gear manufactoring engineer But he was on the other side of the spectrum with up to 16mtr gears
    Worth looking into IMHO

    Peter
    Yes these seem to be just normal proportioned but tiny gears, I doubt any real engineering when into them as from what I can see none of the companies involved are speciality engineering firms, they're all just normal small scale customer production outfits. I am not a gear specialist either but I understand that and that I have no real idea how to make these better other than fixing the god awful mounting and looking at ways to keep dirt and diamond dust out and keep the gears in proper mesh even when someone is pushing a diamond gridning pad into a tooth and the gears are likely walking all over the place, these are just awful.

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    What type of roller bearings? Not needle roller bearings, I hope? Even deep grove ball bearings are okay but not great here.

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    Quote Originally Posted by Strostkovy View Post
    What type of roller bearings? Not needle roller bearings, I hope? Even deep grove ball bearings are okay but not great here.
    Yes needle roller bearings for the most part, and not well fitting ones either, however there is no hope of a deep grove ball bearing, right now I'm working with 8mm ID 12mm OD bearings and that is about as big as has any hope of fitting, I hope to find dual race ones soon but for now two stacked up will have to do.

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    Hi again Joshua:
    If these diamond discs are anything like I used to use when I was a dentist, they're likely single layer nickel plated onto a steel shank and will not come off unless they're really abused on something like a piece of hard metal or a piece of carbide.
    What you're likely seeing in the dirty grease, is debris from the wear of the gear against the housing.

    So I wouldn't personally sweat what comes into the gearset from outside...yeah it's not ideal but it's not going to kill the gears even remotely like the misalignment from the sloppy, torn up housing will.
    Most slow speed dental handpieces have unsealed gearsets and do OK if they're kept lubed...they die very quickly if they're not.
    They're typically not too bad when you take them apart unless they've been run dry, so my belief is they don't get too much junk coming in from outside, even with no seals and what junk does come in doesn't do too much harm.

    Just fix the mounting and don't obsess over it otherwise...it'll be so much better than it is now, everyone will love you.
    If it's still not as good as the customer would like it, you can always try to make a labyrinth seal like a grinder spindle uses.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by dian View Post
    what kind of power are we talking? these guys have done it for 100w. (somehow i think it used to be 200w).

    PROXXON - LHW
    Not sure that this can be considered to have "done it". About 20% or more of ratings on various sites state that the unit is wimpy, burns out quickly under moderate use, etc. That said, it is a good design example as you can see that they use two key design elements: The final (short) spindle (the one with the burr or wheel mounted) seems to have bearings on both sides, like the OPs does I think. Also, the driving shaft that drives the final spindle is long, likely with bearings on both ends. If the housing is rigid enough, this should give adequate support to the shafts so that bear wear is minimized.

    BTW, the Makita angle grinder has spiral bevel gears driving the grinding wheel.

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    Plain bearings have a lower surface speed as the balls in a bearing Much lower Deep grove ball bearings that size are in ratio pretty big
    So a plain bearing with even a smaller shaft might do pretty well
    Carbon filled bronze perhaps ??


    Peter

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    My first Dentist had a belt-driven drill:



    What about a belt drive for the horses that looks somewhat like this:

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    Quote Originally Posted by David_M View Post
    My first Dentist had a belt-driven drill:



    What about a belt drive for the horses that looks somewhat like this:
    Far too large, as it stands some of the dentists want an even smaller version than this one, which might be possible if we firmly tell them don't go above a certain speed, possibly, I'll be looking into it, the head diameter is only 18mm, with the diamond pads not being that much larger, some of them are quite small, mostly for getting to the teeth are the very back. Given the service life and how these tools are used I don't think a belt drive would work, the die grinder is worn like a satchel around the back and connected via a flexible drive shaft to the handle of the drill and then into a rigid shaft all the way to the head, where is it turned 90°.

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    Quote Originally Posted by implmex View Post
    Hi again Joshua:
    If these diamond discs are anything like I used to use when I was a dentist, they're likely single layer nickel plated onto a steel shank and will not come off unless they're really abused on something like a piece of hard metal or a piece of carbide.
    What you're likely seeing in the dirty grease, is debris from the wear of the gear against the housing.

    So I wouldn't personally sweat what comes into the gearset from outside...yeah it's not ideal but it's not going to kill the gears even remotely like the misalignment from the sloppy, torn up housing will.
    Most slow speed dental handpieces have unsealed gearsets and do OK if they're kept lubed...they die very quickly if they're not.
    They're typically not too bad when you take them apart unless they've been run dry, so my belief is they don't get too much junk coming in from outside, even with no seals and what junk does come in doesn't do too much harm.

    Just fix the mounting and don't obsess over it otherwise...it'll be so much better than it is now, everyone will love you.
    If it's still not as good as the customer would like it, you can always try to make a labyrinth seal like a grinder spindle uses.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Yes they're nickel sintered or plated or bonded, not sure how that works, but from looking at used pads and the grease some of it is defintiely getting in, mind you it's sub micron, I could barely see it with a microscrope but it was hard enough to lightly scratch a tungsten carbide insert so there is defintiely a tiny amount of the diamond getting in, however this is after probably 40 horses where worked on by the tool in particular I looked at, it's possible if the service like gets extended it will become even more of an issue. The pads when inspected after use didn't show much signs of wear but some had definitely become dislodged. I'm not sure if that's just cheap pads or if there was something in the tooth, I'm not a dentist myself so I can't say what you might find in there.

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    What about a real NSK right-angle head?

    This is a video showing one attached to a Lyndex-Nikken tool:

    Lyndex-Nikken - Modular Angle Head Demo With NSK Adaptor - YouTube


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