Highland Railway Drummond 0-4-4T Passenger Tank

Discussion in 'Kits, Kit bashes & Scratch builds' started by paul_l, Jan 11, 2019.

  1. gormo

    gormo Staff Member Administrator

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    G`day Paul,
    Amazing stuff you`re creating there.........can`t get the gears.......I`ll make my own........Woo Hoo !!!!!
    There`s no stopping you now.
    Just thought of a possible project. :scratchchin:.....you could probably print your own fly wheels if you could get some metal pipe of the correct diameters inside and out and with some weight to it. Then print the inner cylinder for a perfect fit inside the pipe, also with a center hole for motor shaft.........:scratchchin:...what a ya reckon.??????
    Maybe not heavy enough.???
    Anyway Paul..........this pretty to watch.........:thumbs::thumbs::thumbs::thumbs::thumbs:
    :tophat:Gormo
     
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  2. paul_l

    paul_l Staff Member Administrator

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    Hi Gormo

    I was thinking on the lines a series of holes of various diameters (probably 12, 15 & 18mm to suit the most common motor sizes) drilled into 9, 12, 18 and 22 mm MDF. These would be mounted on to 22mm MDF with a hole drilled in each centre to take a piece of brass tube with an internal diameter of 2mm. Probably tin the outer surface before inserting into the base plate hole. Then fill the cavity with either molten white metal or lead. Once cool the tube can be mounted in a drill chuck (a lathe would be better - but if I had one of them I wouldn't be doing this) and the flywheel trued up to the shaft. Then trim the tube to length, and secure to the motor shaft with some loctite - note to self need loctite.

    For the new gear box I have approx 20mm from the front of an 1833 motor to front end of the tanks. The std 1833 only has 8.3 mm of shaft, but I could get away with printing longer gears, possibly even helical gears to spread the load over a larger area.
    The distance between centres of the motor shaft and worm shaft on the current gearbox is 13.8mm in two stages, on the new box I could do this in 1 step.
    I found a youtube video on the maths, so will try and find the video again - I know I should have copied the link, especially when I tried to remember all the formula involved - coffee didn't help either.

    The boss has a list of chores, but as Arnie would say - I'll be back

    Paul
     
  3. paul_l

    paul_l Staff Member Administrator

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    Found it



    Now just need my pad and paper to make notes this time

    If using some form of software generator - there are some online, I'd pick the ISO form (Module), rather than DP, if you watch the video you will see the maths is simpler, and with the CAD software you can define the Module value to any thing you want as your printing your own gears.

    Next up may be to print my own adapter arms for servo's to form a rack and pinion mount and drive for points and signals.

    Paul
     
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  4. paul_l

    paul_l Staff Member Administrator

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    Ok - a public health warning, for those of certain disposition, time to un-cork a bottle of something.

    It's maths time - Platform1mrc's version of home schooling :avatar:

    First up a few definitions

    M = Module (ISO - metric system)
    DP = Diametric Pitch (Imperial - ANSI system)
    Z = number of teeth
    a = Pressure Angle (should be alpha)
    D = Distance between Centers
    PD = Pitch Diameter also known as Reference Diameter of the gears

    Now some formulae

    For ISO

    PD = M x Z - Module x Number of teeth

    For Imperial

    PD = Z/DP - Number of teeth /Diametric Pitch
    --------------------------------------

    Distance between centers D

    Empirical Method
    If you already have the shafts measure from the outer edge from shaft 1 to the outer edge of shaft 2

    D = Distance measured - (radius of shaft 1 + radius shaft 2)
    ---------------------------------------

    Theoretical Method
    To calculate the distance between centres where PD1 is the Pitch diameter for Gear 1 and PD2 is the Pitch diameter for Gear 2

    D = (PD1 + PD2) / 2

    Taking this a little further

    2D = PD1 + PD2

    As we know PD = M x Z

    2D = (M1 x Z1) + (M2 x Z2)

    The Module for each gear has to be the same for the gears to mesh

    So

    2D/M = Z1 + Z2 = Total number of teeth

    therefore

    2 x Distance Between Centres / Module = Total number of Teeth

    To select a set of gearing we can adjust either the Distance between centres or change the Module.

    For example

    Gearbox 1 has a distance between centers of 13.8mm, using a Module of 0.4 we get (2 x 13.8)/0.4 = 69

    So my Total number of teeth = 69

    If I use a 15T gear for Z1 then Z2 = 54T Z Total = Z1 + Z2, and the gear ration 15:54 or 1:3.6

    However

    If I use a 20T gear for Z1 then Z2 = 49T Z Total = Z1 + Z2, and the gear ration 20:49 or 1:2.45

    Working the otherway

    If we wanted a 1:4 gear ratio

    We could have Z1 = 15T & Z2 = 60T

    Using gears with a 0.4 Module we get

    2D = (Z1 x M) + (Z2 x M) = 15 x 0.4 + 60 x 0.4 = 6 + 24 = 30

    Therefore Distance Between centres = 30/2 = 15mm

    Then add 0.1 for backlash.

    OK time to finish the beverage

    Coffee break over - guess who forgot to press the post button :facepalm:

    For my gearbox 13.8 mm between centers will work, and maybe even with a 1833. Coupled with the Roxey 40:1 worm / wheel, from the above calculations I have 69 teeth to play with. 23T / 46T will give 1:2 ratio and 80:1 overall ratio or 28T /41 gives 1:1.46 or 58.6:1 overall.

    Me thinks a couple of test prints are in order.

    I'll be back

    Paul
     
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  5. paul_l

    paul_l Staff Member Administrator

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    And the result is

    upload_2021-2-25_17-16-25.png

    This version has the 28T / 41T combination giving a 58.6 : 1 ratio

    Without the spur gears

    upload_2021-2-25_17-18-41.png

    Showing the bearing on the worm shaft

    And from the rear

    upload_2021-2-25_17-19-51.png

    Just got to sort the print out - probably much later for that.

    Paul
     
  6. paul_l

    paul_l Staff Member Administrator

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    A little more work done

    As the gear ratios can be changed here are some of the ratios that can be achieved

    upload_2021-2-25_22-38-1.png

    The gearbox body

    Front, not the worm shaft id off center to allow for the boss on the wormwheel

    upload_2021-2-25_22-43-48.png

    The rear view this mount is to suit an 1833 Standard Mashima motor.

    upload_2021-2-25_22-45-7.png

    Almost ready to print, just need to complete the gears, I'm going to make 23T / 46T (80:1) & the 28T/41T (58.6:1)
    If I go for less than 21 teeth then it's advised that you may need to open the gap.

    upload_2021-2-25_22-53-29.png

    I'll post up pics when the print has completed

    Paul
     
  7. paul_l

    paul_l Staff Member Administrator

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    And the print is ready to be sent to the printer

    upload_2021-2-25_23-15-32.png

    4 gearboxes and 4 sets of gears, approx 3 hours to print

    I'll report back tomorrow.

    Paul
     
  8. paul_l

    paul_l Staff Member Administrator

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    Some good and bad news

    The bad newsTwo gearbox prints failed


    These were the two prints in the center - so probably means either the FEP want tightening or the lift height needs to be bigger, as the supports on the other two prints were ok.

    Next the motor needs moving more into the mount, two reasons
    a). the M2 x 4mm screws don't protrude beyond the mounting face plate, and
    b). the motor shaft is only 8mm long, and only protrudes beyond the mount by 5.5mm, so moving the front motor bearing to the front of the motor mount I should get the full 8mm.

    The Good news

    Two motor mounts were good, bearing alignment apears good.


    and the gears printed perfectly., and meshing was good


    Just need to make the alterations and print again

    My bearings and 2mm shafts are due to arrive on Tuesday - ooooo the pressure is on

    Paul
     
  9. paul_l

    paul_l Staff Member Administrator

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    and were off

    upload_2021-2-26_14-58-0.png

    Only 3 hours to wait

    Paul
     
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  10. paul_l

    paul_l Staff Member Administrator

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    Forgot to mention the changes to the print settings were

    Increase to lift height for the print from 8mm to 10mm, and increase the exposure from 2.2sec to 2.4sec for normal exposures.

    upload_2021-2-26_21-15-22.png

    All four mounts printed ok and were all around the central area so if an issue was to occur Murphy should have struck.


    Just going through the curing process at the moment

    Paul
     
  11. gormo

    gormo Staff Member Administrator

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    Holey Jumpin` Catfish Paul,
    You didn`t tell us you were a Maths Master as well. You are working through a very high level of amateur engineering here which is honestly very, very impressive....:thumbs::thumbs:
    I think from now on I will have to call you " The Professor ".........:scratchchin:

    Quote .........Professors are usually experts in their field and teachers of the highest rank.Wikipedia

    :worship::tophat:Gormo
     
  12. paul_l

    paul_l Staff Member Administrator

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    Aye but all I did was cut and paste and take notes (and watched the video's several times).

    Actually now the prospect of making a gearbox doesn't feel that daunting, and the software + 3D printer make up for a lack of skills.

    Now that I have the larger printer making the loco in O gauge is easier, however I could have done all of this in 4mm / ft on my original Photon. And although it's taken me two years since this thread was started to get this far, it's been a great learning curve, with a goal to spur me on (sorry about the gear pun).

    Whether these gears are capable of withstanding the forces involved I will find out, searching on ebay there are sources of small spur gears, I may just have to adjust the designs to suit to be able to get metal gears. OR follow Andy's suggestion of trying Shapeways to see how Metal printed gears would turn out.

    Motor secured in the place and motor gear on the shaft, the worm shaft is just placed in position. Note the boss on the gear makes sure the gear is clear of the retaining screws.


    Paul
     
  13. gormo

    gormo Staff Member Administrator

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    Well Paul,
    I am an ignoramus when it comes to the properties of resins, but looking at the thickness in those gears, I reckon they will perform just as good as metal gears.
    Most nylon / plastic gears in model locos are only thin wafers compared to your versions, therefore, I reckon the increased surface area will result in a very sturdy gear. The thickness also removes any wobble that you might get in a thin gear wheel, so if everything meshes well, it should be quite a smooth drive train.
    You would need an extremely heavy load ( a couple of house bricks ) to break those suckers...:thumbs:
    :tophat:Gormo
     
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  14. paul_l

    paul_l Staff Member Administrator

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    Fingers crossed Gormo

    Now I wonder what It will look like together

    upload_2021-2-27_11-26-38.png

    I've added the firebox and ash pan - a bit of guess work as I only have a side view to work from.

    upload_2021-2-27_11-29-20.png

    mmmmmm :scratchchin: do I make the motor mount part of the chassis, whic means I could replace the axle bush with a ball bearing

    Adjustments to the firebox could be made to allow access for the 5mm reamer from the rear for the alignment of the worm axle which wouldn't be seen.

    What do you think ?

    Paul
     
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  15. jakesdad13

    jakesdad13 Staff Member Moderator

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    It would stiffen up the chassis as well as making fitting of the gears simpler. Would it be a big job to print one off to see? I like the idea of using ball races for bearings, I guess it make for a smoother running engine.
    As the printed gears mesh and turn would there be excessive wear on the teeth compared to metal? Could you use a plastic friendly grease on them? On my lads old Tamiya R/C car, when I built it I used the supplied grease on assembly on the gearbox and that's got plastic gears.

    Pete.
     
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  16. Andy_Sollis

    Andy_Sollis Full Member

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    What kind of cure time with the UV are you putting on the gears?
     
  17. gormo

    gormo Staff Member Administrator

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    Weighing up the pros and cons.........I lean towards building the motor mount into the chassis provided it still gives you reasonable access to assemble or disassemble everything.
    A more rigid chassis is a definite plus.
    On the other hand, a removable motor mount allows you to create a new mount at a later date, if you decide to change the motor type or re-arrange the gearbox.
    The chassis as it is,may accept additional bracing between the plates if you have room to drop it in.
    :tophat:Gormo
     
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  18. Andy_Sollis

    Andy_Sollis Full Member

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    I agree.. when it’s a prototype, I’d make it removable so you can tweak.

    once finalised, you can then always reprint and fix it in.
     
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  19. paul_l

    paul_l Staff Member Administrator

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    Here goes version 1 then

    upload_2021-2-28_0-21-24.png

    I could fit 2 bearings per side if wanted.

    And will take 5 to 6 hours to print

    upload_2021-2-28_0-24-2.png

    Andy - Cure times for the gears, I have cured them with the supports in place and given them 2 blasts of 4 mins with an hour between blasts.

    Now to find some resin the same as in the tank

    Paul
     
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  20. paul_l

    paul_l Staff Member Administrator

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    Most of the mornings chores done - still got the dog to walk

    Time to check the printer.


    Generally looking good, apart from the rear


    I may have to raise the print further from the print bed to allow the supports to better form and add extrat supports for the undercut.

    upload_2021-2-28_10-31-6.png

    However, the backend still has to be worked on as it has to have the relief cut outs as per the front to clear the fillets on the body, and the bogie mount.

    The frames in the axle area have printed correctly



    With the supports removed the shpan can be seen - still needs clean up.


    And the motor mount looks good


    with supports removed


    And with the body added


    Curing the chassis at the moment, then will try and ream out the holes for the bearings (I have a 3/8ths reamer for the wheel bearings on order so will either wait, and if it arrives before the bearings jobs a gudun, if not them I will use the broaches and taper reamers, afterall it's not the final chassis and I want to test the motor drive - once the bearings arrive I have all the bits to build the drive chain down to the worm shaft.

    Next up will be to sort the plunger pickup locations, then the bogies.

    For the bogies my initial thinking is to have a pivot point on the chassis for the bogie compensation to move side to side, and the bogie side frames / axles allowed to pivot (a few mm) for fore and aft movement.

    I've just ordered some compression springs from amazon 6mm OD 10mm long. The mount between the bogie and chassis will have the compression spring between them and a screw to set the ride height. Fingers crossed it will work.

    And the dog won't wait any longer :facepalm: :avatar:

    Paul
     

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