Highland Railway Drummond 0-4-4T Passenger Tank

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

 

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

 

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

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

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

 

And the result is



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

Without the spur gears



Showing the bearing on the worm shaft

And from the rear



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

Paul

 

A little more work done

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



The gearbox body

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



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



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.



I'll post up pics when the print has completed

Paul

 

And the print is ready to be sent to the printer



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

I'll report back tomorrow.

Paul

 

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

 

and were off



Only 3 hours to wait

Paul

 

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.



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

 

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

 

Fingers crossed Gormo

Now I wonder what It will look like together



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



mmmmmm 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

 

Here goes version 1 then



I could fit 2 bearings per side if wanted.

And will take 5 to 6 hours to print



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

 

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.



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

Paul