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  1. #1
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    Default Printing a gear?

    I'm in need of a plastic helical gear for a motor home slide out.. had a fellow on here offer to machine one for me and it looks like I may get him to do it.. on another forum someone suggested getting one printed.. would a printed gear be strong enough to hold up? I know nothing about this.. the gear is 2.300 in dia. .480 thick and 88 teeth.. thanks!

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    It depends a bit upon the rapid prototyping process and the material used. Inquire about the tensile strength, wear properties etc. compared to the original material. You'll also need an accurate model of the gear to start, possibly an additional cost.

    What material is the one that failed? Even if plastic, there's an order of magnitude difference of strengths between different common plastics.

    If it's the typical low end 3D printer that uses thermoplastic spools, I'd suggest you also take and print a picture of your motor home in the slid-out position. After a while that may be the only way you'll see it there.

    If you have someone willing to machine it (or just buy a new or salvaged replacement), that's likely the way to go. Suppliers like Boston Gear also make stock helical gears that might fit. Also wouldn't surprise if there was a market for more than one of these, if making one new. In any case, the existing failure suggests you don't want to give up anything in terms of material properties.

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    A picture of it is here in this thread Need a gear made..
    the teeth have 14.5 degree angle on them.. I have searched stock gears all over the net and keep coming up with nothing.. this one is delrin.. boston has 45 degree on their helical gears.. thanks!

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    Quote Originally Posted by pressfit1 View Post
    A picture of it is here in this thread Need a gear made..
    the teeth have 14.5 degree angle on them.. I have searched stock gears all over the net and keep coming up with nothing.. this one is delrin.. boston has 45 degree on their helical gears.. thanks!
    I suppose another option might be to replace both the broken gear and the worm with standard parts; depending upon what all goes along with the worm?

    When you say 14.5 degrees, I'm assuming you actually mean the helix angle and not the pressure angle.

    On edit: you say the gear is Delrin. Pretty tough stuff and sometimes filled with PTFE to reduce friction. If your gear system wasn't packed with grease etc. this may be a factor in deciding what to replace it with.

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    If you know the specs, and have the machines, making the replacement is kind of trivial.
    I stayed out of it before as it appeared that Dan was helping you. If he's who you are referring to, let him do it. His work is top notch.

    I am intimately familiar with SLA and SLS, as well as using both ( and others ) for gears. Don't waste your time. You will not be satisfied with the result.

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    FDM print in nylon on a Fortus 400 or 900 printer would be the only way to go if you end up printing it. ABS will degrade over time and fail.
    I printed small gears for projects and they work great. Something like that is doable if your loads are not approaching the limits of nylon in the original. The only issue with FDS is that there will be less strength in the Z direction of print. Should be ok with this gear.

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    IMO The pitch of the teeth are too small for FDM.

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    I think it will print ok, but the tips will be rounded. This partial gear I printed would have had 48 teeth If I remember correctly and its about 1.25" in diameter.
    https://lh4.googleusercontent.com/-F...221_200402.jpg

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    Quote Originally Posted by avongil View Post
    FDM print in nylon on a Fortus 400 or 900 printer would be the only way to go if you end up printing it. ABS will degrade over time and fail.
    I printed small gears for projects and they work great. Something like that is doable if your loads are not approaching the limits of nylon in the original. The only issue with FDS is that there will be less strength in the Z direction of print. Should be ok with this gear.
    Both the resolution and surface finish will flat out _suck_ if he went this way.

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    The top and bottom surfaces will be rough. Surfaces that count will be smooth radially, with .005" layers. Acceptable for a gear. Don't have any pics of the teeth, but they work great.

    AG

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    Quote Originally Posted by avongil View Post
    The top and bottom surfaces will be rough. Surfaces that count will be smooth radially, with .005" layers. Acceptable for a gear. Don't have any pics of the teeth, but they work great. AG
    As proof of concepts, yes. As anything else but a curiosity, no. I'll point out that .005" of _anything_ on a gear is unacceptable for a replacement of an actual working gear. For the money that such a part would cost I would rather buy the appropriate Involute Mill and mill them. It would be more acceptably accurate. In your BEST case scenario, let us assume an actual perfect Involute, with the result being as you say above, even though there is no way in hell that a FDM printer will create an actual perfect Involute, as neither the machines nor the materials are capable of that kind of accuracy. This will mean a gear that will have high spots and low spots on its teeth, varying by .005". Given the size range of the gears being discussed as applicable to be printed, this represents all of the typical backlash. So, if working to a fixed center distance once has just completely blown the backlash spec at best and caused a bind, at worst. I am willing to be wrong on this, but years of running and maintaining 3D printers and running an actual gear producing shop tell me otherwise. Let me know when you start finding FDM gears in mass produced consumer goods requiring good function and durability.

    EDIT -

    I'm wondering how you can say it's accurate when you earlier state -

    Quote Originally Posted by avongil View Post
    I think it will print ok, but the tips will be rounded.
    /EDIT


    2nd Edit -

    Never mind. I just realized that you're a reseller and salesman for FDM printing services.

    /EDIT

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    Machining said gear a little tricky on a conventional mill, lathe or grinder. Machining across at the angle will cut most deep at center and less at both ends perhaps .005 or more. One way would be to indicate across in part feed path to find the loss at the ends. Cut center portion first on the correct index, then swing set-up to cut right then left arc at the amount perhaps to a wire size for each facet. Yes the gear will be cut in three facets and not be a perfect match. Might be a tad tight at facets peaks at first until wear in occurs. Might have to jo-block from shaft or still in place other gear to get proper pitch diameter and check with wires to get the machined gear the right size. .005 tight would not be good IMHO

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    Quote Originally Posted by michiganbuck View Post
    Machining said gear a little tricky on a conventional mill, lathe or grinder. Machining across at the angle will cut most deep at center and less at both ends perhaps .005 or more. One way would be to indicate across in part feed path to find the loss at the ends. Cut center portion first on the correct index, then swing set-up to cut right then left arc at the amount. Yes the gear will be cut in three facets and not be a perfect match. Might be a tad tight at facets peaks at first until wear in occurs. Might have to jo-block from shaft or still in place other gear to get proper pitch diameter and check with wires to get the machined gear the right size.
    Buck, that's my point - Even one milled would still be more accurate than the FDM one the salesman is proposing. To be sure, a hobbed or molded one would be best.

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    I see you point Zahnrad and I don't know enough about printing to address that method... Did re sharpen an 18" diameter knurling cutter on a cincy #2. Catching the rise and fall then grinding in 4 facets using another dull for the index, Then blending with a custom made hone to chop peaks. Was not perfect but beat sending 3000 people home for a week or so.
    Last edited by michiganbuck; 01-03-2015 at 05:08 PM.

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    I'm not a salesman, I just happen to work at a company that uses and sells this technology. In this application I think it would be great. You can talk all you want, but I have actually printed gears in Nylon with the FDM process and used them successfully. They work well, not the same as a machined gear but 80%. As stated in my first post, if this is acceptable then it sure beats machining one.

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    Quote Originally Posted by avongil View Post
    In this application I think it would be great.
    Based upon what?


    Quote Originally Posted by avongil View Post
    They work well, not the same as a machined gear but 80%.
    80% of _what_? And what is this based upon?


    Quote Originally Posted by avongil View Post
    As stated in my first post, if this is acceptable then it sure beats machining one.
    Okay. Let's explore that. How much to make one? And let's explore the steps involved while we're at it. Please do not omit your time creating your model either. Ready? Go.

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    With knowing the pitch diameter and being able to hold perhaps +- .002 I think a printed gear might work (or a time). First choice the manufacturers gear for perhaps 40 or $60 as a guess.

    two examples

    http://www.dyersonline.com/ap-produc...FTFp7Aod0QIAVg
    https://www.google.com/webhp?sourcei...82445091642137

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    Why so hostile to 3D printing?

    1 - the limited info in this post and the original material being delrin.
    2 - Mechanical properties of reguar nylon vs printed (the spaces between layers and adhesion between them)
    3 - to model, i'd use mcam since it has gear.dll to draw the profile. Some people have better faster software. - 15 min.
    Save as STL File. - 1 min
    Open in insight and print - 5min
    Wait for machine to finish - 2 hours
    take off machine - 1 min

    Less than 30 min of hands on time. Mostly modeling.

    Price - I could find out on wed exactly, im guesing around $75 - 125
    I'd personaly want this one printed in nylon since I think it will hold up the most.

    Im assuming you are not up to date with 3D printing. It's an option.
    I speak from experience. I have done all the above steps and made working gears. The times are correct.
    14x 28tooth and 14x 11 tooth gears for around $100.

    Is it the best option? Not if someone will machine it for less than that, but you can't beat the speed and convinence and sometimes even cost of 3D printing gears.

    All the hobby printers use 3D printed gears. They are printed mostly out of junky PLA and they work great. Printing a Nylong gear on a $150K FDM printer makes for quite a good end product.

    I suggest you try it before bashing the idea.

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    Quote Originally Posted by pressfit1 View Post
    I'm in need of a plastic helical gear for a motor home slide out.. had a fellow on here offer to machine one for me and it looks like I may get him to do it.. on another forum someone suggested getting one printed.. would a printed gear be strong enough to hold up? I know nothing about this.. the gear is 2.300 in dia. .480 thick and 88 teeth.. thanks!
    Have one made. Printing will not hold up for the process you can afford.


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