Bespoke, not re-profiled, tyres - commission offered

andrewb

Western Thunderer
Morning all!

Is anyone able to help me by creating a set of bespoke tyres for a 7mm project I have underway? I'm experimenting with 3D CAD while also exploring what modern 3D printing materials are commercially available to create exact miniature replicas of loco wheels with the resolution, rigidity and toughness needed in 7mm scale. But I do not have the skills nor the tools to turn my own metal tyres.

Those of you with very long memories will remember that I have a Parallel Boiler Royal Scot project trickling along (See An Anniversary Royal Scot, now on page 5 of this forum) so won't be surprised that the wheels in question are destined for this fine loco. I visited the archive at NRM just after Christmas and photographed the plans for its 6' 9" main wheels, recreated in CAD then modelled in 3D. I'm not quite there with it - there are significant challenges 'reverse-engineering' into computer-speak some curves and profiles that were lovingly hand-crafted by highly skilled artisans in the pattern shop - but I'm getting close enough to be thinking about getting some tyres made. As much as anything, the final details of the 3D printed bit in the middle will depend on the precise dimensions of the solid, turned metal bit on the outside!

Here's a screenshot outlining the requirement:
 

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andrewb

Western Thunderer
The dimensions are simply converted from the imperial measurements on the plans - hence the ridiculous micron accuracy! I also don't fully understand whether the 3" tyre thickness (1.75mm) is strictly necessary in model terms: if it could safely be taken down to - say - 1mm, that gives me an extra bit of material on the rim to aid stability further. So anyone able to help - please let me know what the real-world dimensions should be. Likewise with the front face - I'm currently working on a design assumption of this needing to be 0.5mm.

I'm thinking tyres made from steel would be ideal. Nickel silver comes a close second.

Please let me know if you can help - either with the job itself or pointing in the right direction. Many thanks
 
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richard carr

Western Thunderer
Hi Andrew

The S7 wheel profile is based on this

BS276:1927 Contour A, as specified in British Standard 276:1927 Contours for Locomotive Tyres (for British Railways 4ft 8-1/2in Gauge).

You can find the details here

S7 Tyre Profile - Scale 7 Group

Your profile looks pretty close to this and scaled down I doubt will be any different, so an S7 form tool will give you the correct flange profile.

I'm sure someone like Colin Dowling (Eastside Pilot on WT) can do this for you.

You have done the hard bit getting the centre right.


Richard
 

andrewb

Western Thunderer
Many thanks Richard - yeah, I meant to have added that the flange profile as drawn was intended as indicative (hence no dimensions), and fully intend for the S7 Tyre Profile to be used. But I'm thick-headed with a cold and completely forgot!
 

Lancastrian

Western Thunderer
Andrew,

Excellent work. I could have saved you a trip to the NRM as I have copies of the Royal Scot wheels too !

Ian
 

Len Cattley

Western Thunderer
Hi I also have the Royal Scot drawings from the NRM, a few years ago I met a chap who was doing wheels from drawings that was CNCed from drawings from the NRM (it was at the Bristol show) I can't remember his name though. Perhaps Mickoo from this parish can remember?

Len
 
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andrewb

Western Thunderer
Thanks Ian, Len

One drawing I forgot to ask for during my visit was for the bogie wheels (can’t remember the diagram number and currently away from my sources. But it was from, I think, 1905). Do either of you guys have a photo you could share?
 

Len Cattley

Western Thunderer
No but I will use S7 boogie and tender wheels as they do both sides not like Slaters. I want to do the Rebuilt Scot in the future are you going to do CNC them or cast them?

Len
 

andrewb

Western Thunderer
Plans at the moment Len are to explore what modern 3D printing can offer - new products on the market seem to show potential to offer the strength and stiffness required. But my aim is to recreate the centres digitally with sufficient accuracy to that I could switch to CNC or casting easily should they still not have sufficient grunt!
 

andrewb

Western Thunderer
I can’t use the S7 bogies - they are for the Stanier rebuilds. I need the old fashioned 3’ 3 1/2” ‘Fowler’ pattern:(
 

Len Cattley

Western Thunderer
Hi Andrew, do you know that Elliot 84A of this parish was talking about wheels in 2018 have a look in the post
"New O gauge wheel sets"
he might be able to help.
Len
 

andrewb

Western Thunderer
Thanks to both - found and read. Looks like Elliot 84A is more into complete, machined wheels, while I’m just looking for advice on tyres.

In particular, if I assume a front face thickness of 0.5mm (vice prototypical equivalent 0.474) and reduced the tyre width to 1.5mm (vice 1.75) - which would allow me to print slightly deeper rims for increased stability, would I be at risk trading the stiffness of the tyre?

PS - watching the England Wales match in the foyer of a hotel in Austin Texas - there are some confused locals here too... :))
 

simond

Western Thunderer
Andrew,

At the loadings we experience, I’d be surprised if stiffness of a steel tyre is an issue once it’s made. Making it will require some solidity, but that doesn’t have to affect the finished part, and a few hundred grammes per wheel doesn’t seem too challenging. Not that I’ve calculated anything, you understand...

if I’ve understood your question correctly, you want to trade some of the (steel) tyre thickness for (plastic, or whatever is cast from it) rim thickness.

Intuitively, this seems entirely reasonable. However, if you’re going to investment cast the wheel, and fit a turned rim, you’ll want to turn the wheel OD anyway, so you’ll surely cast it oversize, so your moulding, or 3D print will be oversize on diameter anyway, I guess?

does this help, or am I barking up the wrong tree (or perhaps, just barking...)

Atb
Simon
 

andrewb

Western Thunderer
Thanks Simon - that helps enormously! Instinctively I feel the trade is worth doing too. Just wondering if there was somehow a ‘standard’ for 7mm scale wheels and tyres. I’d like to add a little to the wheel rim depth as it’s scarcely 1mm at the moment, even though the trial print seems pretty tough already.
 

andrewb

Western Thunderer
So, to ‘cut to the chase’ as the saying goes, I’d like to commission a fellow WT-er to produce a set of tyres for me, to S7 standard, so I can complete this project. If anyone is in a position to take this on, could they please PM me and we can thrash out the details. :)
 

andrewb

Western Thunderer
I’ll need to double check Mike, but as far as I can tell the S7 store only goes up to a 6’ 8” wheel, so any Slater product of the correct size 6’ 9” would be FS and need re-profiling.
 

Dog Star

Western Thunderer
You have nothing to lose by speaking to David White and asking him if he can produce a batch of tyres for you... although he might ask you to take what gets produced in one shift - tyres in free cutting mild steel, S7 profile, scale width and diameter.
 

Podartist79

Western Thunderer
Dear Andrew,

I think this is an incredibly interesting project as I’d like to do something similar for a Schools Class loco, as no directly correct wheel exists in the Slaters range for the drivers (I discovered on WT - informed by very knowledgable WTers).

I’ve spoken to Alan Buttler of Modelu about this and he’s already provided wheel centres in 4mm scale that have worked successfully. Also since then he’s got hold of tougher/stronger materials that would hopefully be even better suited to this task of creating wheel centres.

I just need a drawing of a Schools Class driving wheel now!

best wishes,

Neil.
 
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