Adding Sheet Rubber Tyres to a Traction Engine – Part 1

Materials Procurement and Design

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A Bit of History

In preceding pages I explained why rubber tyres were necessary on a Steam Traction Engine with steel strakes like my 6″ scale Little Samson Traction Engine and I described my attempts at fitting sheet rubber tyres and cast rubber block strakes.

Comments from other Little Samson Traction Engine builders/owners with a lot more driving experience than myself dissuaded me from pursuing the rubber block strakes route and my normal local engineering workshop Teera Borigaan who at first quoted me for supplying cast rubber blocks (I had even made a mould to cast them in and made a sample block) declined to source the castings.

Finally – Rubber Sheet Procured

After many months of looking for a supplier of rubber sheet I eventually found one on the Shopee website in Thailand, placed my order and the rubber sheet was delivered to my workshop in two big and very heavy rolls, as you saw in the photos above.

Materials Specification and Quantity

All the rubber is 20mm thick and made from Natural Rubber. The rubber sheets are 1.2m wide, one sheet being 1m long, the second 2m long. Total Area 3.6m².

For those who can read the Thai language, here is the label:-

https://shopee.co.th/product/708273078/29715993678

Product Description NR rubber sheet, waterproof rubber or smooth rubber sheet Made from natural rubber ingredients (Natural rubber), special tough grade. Therefore it is strong, durable, and has high flexibility. Good abrasion resistance and has high tear resistance Our rubber sheets are produced from factories in Thailand. The quality has received ISO 9001:2015 standards, with a complete production process starting from compounding. There is a tire testing room before and after production. And there is a production process that meets ISO quality standards, so customers can be confident that our products are definitely of high quality Usage: Rubber cushioning for machinery rubber mold rubber factory floor rubber sports field flooring Waterproof rubber sheets, etc Product Specs Operating temperature -50 To + 80 °C Hardness 70+/-5 Shore A Ordering Tire sizes are 2, 3, 8, 10, 12, 15, 20 mm thick and 1.20 meters wide. As for the length as desired, for example, if you press to select 1 meter, the customer will get 1 roll of 1 meter length or choose 2 meters. You will get 2 meters of length, 1 roll If the customer wants it to be cut into multiple sheets, the customer can inform us of the size via chat

Next Step CAD Drawings

“What! CAD Drawings?” I hear you ask. “You just wrap it around the wheel and glue it on. No need for fancy CAD drawings!”

Well, let me tell you it’s not so simple as that. If fact there’s a lot more to it. And making CAD drawings forces the designer (me in this case) to consider all details and dimensions. Let me show you what I mean.

CAD Drawings of Rubber Sheet Tyres Applied to 6″ Little Samson Hind Wheels

Hind (Back) Straked Wheels

I did not want to glue the rubber strips directly to the strakes, because I was concerned that:-

• The ride would still be rough as there would be no support between the strakes
• The sharp edges of the strakes might cut into the rubber sheet at the edges of the strakes
• The area of contact between the rubber and the strakes would be 50% smaller than the potentially avalable perimeter of wheels without strakes

Final Hind Wheels Strakes And Rubber Sheet Configuration

The composition and method I am proposing the attach the rubber sheet to the steel-straked rear wheels is described below and seems to follow what is commonly adopted where rubber tyres are retro-fitted to traction engine wheels with steel strakes.

In essence the method of fixing the rubber-sheet to the straked wheels requires a steel band or hoop to be rolled up to fit tightly over the outer diameter of the strakes. The butt joint of the ends of the band will be welded and ground smooth and spot welded to the steel strakes at intervals around the wheel.

For corrosion protection all bare steel on the wheels and the steel band will be sprayed with zinc-rich paint – EXCEPT for the outer surface to which the rubber sheet will be glued.

Next the rubber sheet will be cut into strips and glued to the steel using cyanoacrylate adhesive (‘Super Glue’). Two layers of rubber strip will be applied.

Configuration and Dimensions Of The Components

At the moment my CAD drawings show:-

• Steel Band 5 mm thick. (Nominally 1/8″)
• Steel Band width = full width of the Strakes – 123 mm (4.8 inches)
• Rubber Sheet 20mm thick X two layers = 40mm
• Option 1. Rubber Sheet width = full width of the Strakes – 123mm (4.8 inches)
• Option 2. Outer Rubber Sheet in two separate bands with a gap of (say) 27mm between them

Option 2 of two bands of rubber seems to be what most engines have when the rubber tyres are applied professionally. I don’t know the pros and cons of this compared to a single band.

Unresolved Questions, Issues and Concerns

	Issue	Comments
1	Thickness of Steel Band	Nominal 5mm shown. Is it adequate? Too thick?
2	Thickness of Rubber A) Ride Quality B) Gearing	A) Total thickness of rubber is 40mm. Will this give a good ride? Any other effects? B)Rubber adds 80mm to the diameter of the wheel thereby reducing the gearing of the engine (faster travel for same crank revs). The gearing is already a bit low i.e. a bigger gear ratio is referred not a lower one.
2	Width of Rubber (One or Two Strips)	What are the benefits (if any) of proving two outer rubber bands rather that a single bad the full width of the strakes?
4	Corrosion Protection	Nominal corrosion protection by means of zinc-rich spray paint is shown. In the long term is this adequate to protect the inaccessible gaps between the strakes? Not that the engine is never steamed in wet weather.
5	Choice of Adhesive	A strong case for Super Glue has been presented. Is there any experience in the field upon which to draw?
6	Cutting Rubber Sheet	Cutting Rubber Sheet is difficult without large and expensive equipment. Teera has said that they can't cut it even with their big 20T guillotine. I have had success with a simple hand held jigsaw. Does anyone have any experience I can learn from?

Comments Welcome

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