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Wheels for my Wagons


MikeOxon

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I got something of a shock when I saw the current price of Broad Gauge wheel-sets so that started me thinking about 3D-printed wheels. I realised that I wouldn’t be able to make metal rims but it could be a way of making basic wagon wheels in bulk.

 

Many early GWR wagons used the form of wheel ascribed to Losh and Bell, in which wrought iron spokes were cast into the hub and wrapped around the inside of the wheel rim, to give the characteristic appearance shown in the following illustration from D.K.Clark’s ‘Railway Machinery’(1855)

 

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Losh Wheel Drawing

 

I scaled the drawing for a model of a 4’ diameter wheel and then traced the outlines, to create a DXF format drawing.  I extruded the spokes and rim to a depth of 2 mm and the flange to 0.5 mm, using ‘Fusion 360’, and printed the result with my E 180 printer.

 

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3D-Printed Wheel on Printer Bed

 

As usual, there were lessons to be learned.

 

My first printed wheel had a gap in the side of one of the spokes, which turned out to be due to slight misalignment of one of the oval cut-outs within the spokes, by around 0.1 mm. This was sufficient to make that part of the spoke too narrow to be rendered by the ‘Cura’ software.  Adjusting the positions of the relevant surfaces in ‘Fusion 360’ corrected this problem.

 

Afterwards, I realised that this error could be observed on the ‘Layers preview’ screen within the ‘Cura’ software. A lesson to check the preview carefully before committing a model to print!

 

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Layer Preview showing Printing Error

 

Once the spokes all appeared correct on the single print, I made an array from the drawing and printed a group all together. As each wheel took only about 4 minutes to print, I had a batch of nine in around half an hour, with no further input needed on my part.

 

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Array of Wheels on Printer Bed

 

I was surprised to find that there was still a stray chord of filament between one pairs of spokes in every wheel that was printed – all in the same place – even though I had checked the ‘print preview’ on the ‘Cura’ screen.

 

The ‘penny dropped’ when I selected to show the paths traced by the printer, when moving from one part of the print to another. It was clear that there was a cluster of ‘paths’ causing stray filament deposition at the offending place. It was fairly easy to remove with a scalpel blade although the PLA thread is remarkable tough, even when in fine strands! Another lesson in checking before printing.

 

 

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Printer Travels in 'Cura' Layer View

 

I found that this effect could be reduced or eliminated by moving individual items on the printer bed and checking the preview before printing.

 

Now I have a handful of wheels that just need fitting onto axles. I am pleasantly surprised by the robustness of the finished wheels and by their smooth surface finish, especially considering that mine is a relatively low-cost machine.

 

 

 

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3D-printed Wheels

 

EDIT:  As I mentioned in comments below "I could also try making a pair linked by a hollow shaft, which could rotate around a fixed axle.".  I have now tried this approach, with a clearance hole along the shaft, which I made half the back to back length.  I gently tapped the axle through the shaft to fix the first wheel and then tapped the remaining exposed axle into the second wheel until the halves met - instant alignment!

 

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Mike

 

 

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This is really fascinating. I’ve had some early Losh and Haddan’s patent Polygon wheel centres printed for me which I’ve been using to replace the centres in Gibson wheels. It works to a degree but the printing has to be so spot on otherwise you have a loose fit which is fatal for a wheel. Printing with the tyre on is an interesting idea and I guess if running is limited, they’re likely to wear quite well. Looking forward to seeing them fitted.

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Thank you for commenting 5&9.  I have made the centre holes too small  (1.75mm) and intend to ream them out to an interference fit on 2mm axles.  I'm not sure whether the plastic will be stable enough to maintain a 'hold'.  A lot of my old Tri-ang stuff runs on plastic wheels, so we shall see how they go.  I could also try making a pair linked by a hollow shaft, which could rotate around a fixed axle.

 

I'd always assumed I would need a lathe to make wheels, so I'm intrigued to see if these work although I intend them mainly for static, diorama use.

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31 minutes ago, MikeOxon said:

I could also try making a pair linked by a hollow shaft, which could rotate around a fixed axle.

Interesting idea. William Bridges Adams always designed his wheels to run loose on the axle on his carriages. The idea was that they would have the chance to rotate independently and therefore eliminate any skidding action on curves whereby the outer wheel has to travel further than the inner one but is forced to rotate at the same speed since both wheels are fixed to the same axle. His idea of loose wheels made perfect engineering sense but in practice it meant extra bearing surfaces that were probably quite difficult to lubricate properly...but I digress!

Interesting to see if it works in model form. I suspect the wheel might have the tendency to freeze and drag.

 

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I agree 5&9.  incidentally, I've now designed a 10 spoke version, since this appears on several wagon drawings.

 

Losh_10-spoke.jpg.c11660b98db0593b2f965672c9be236c.jpg

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Very neat. I think you could sleeve the wheels onto the axle and if the axle itself was also free to rotate in the pinpoint bearings it could work very well.

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More great work Mike. I've always liked the look of this wheel design.

 

Out of interest, how easily does the material take paint/primer?

Edited by Mikkel
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Thank you Mikkel, although I feel that what I'm doing is very primitive compared with real 3D aficionados.

 

My broad gauge coaches seemed to take grey rattle can primer very well and it covered the bright blue effectively.  I've ordered some brown filament, so that I can get an immediate 'feel' for my models but they will all need paint protection because PLA is bio-degradeable and sensitive to sunlight and moisture.

 

It seems that I shall have plenty of time to practise when the self-isolation rules come into force in UK.

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