Having worked with the whitworth system, the ba system and the metric system since the 1960’s, my opinion is that the current metric fastener system is logical, easier to understand and less confusing than the previous aforementioned.

To me “shoebox” size is quite large for a beginner’s model. The typically suggested beginner’s casting kits like a Stuart S50, 10V or 10H, Clarkson, Reeves sould be smaller and you could get two or three of those in a shoebox. Though with modern CAd and pattern making methods it would not be a lot of additional work to offer engines in different sizes. I see this now in other types of kit where you can buy the same subject in several different scale sas all the supplier ha sto do is click a couple of buttons.

Likewise your price point of £500 is a lot compared to the above mentioned engines at just over £150each. Beginners will be wary of spending large amounts as they would not want to risk mucking up proportionally expensive castings.

I have written a lot here and in my build articles in the magazine about metric being the best bet for anyone new coming into the hobby so agree with that. However if you also want to market your kits at the experienced model engineer, then consider offering just a bar castings package as they will likely have barstock and can use whatever fixings and threads they already have tools for. Yes Reeves and Stuarts only do imperial designs.

What Duncan mentions about working with existing designs and suppliers is something I have already done, see my recent article about the Blackgates Clarkson Horizontal where I completely redrew it to suit metric including adding all the detail missed off the old drawings that a beginner would have found difficult to work out. They can now supply metric drawings and due to my article an build thread got several additional sales.

To attract a beginner you will also have to give them suitable guidance. All the established kits have many build threads and articles as well as a growing choice of instructional You-tube videos. At the very least a full build description with many photos would be needed and could be included with the kit in the form of a USB stick. You also need to get your designs out there just an advert is unlikely to attract beginners they want to see others have made it and are available to help with questions.

Having been involved with other kit suppliers designing new engines, drawings, pattern making and developing the build the main hurdle at the moment is finding suitable foundries that will do good quality small batch or even one off castings. The sure way to put anyone off is to sell them poor castings with defects. I assume you already have a foundry in mind as that would have been one of the factors in working out what your price point would be. I would keep castings to a minimum. Also don’t just design the first engine without thinking ahead, if future additions to the range can make use of the same or slightly modified castings like flywheels and cylinders then that reduces your costs.

Along with that do you have experience designing patterns? Things like Draft angle, minimum thickness that wil reliably pour, shrinkage, etc. Then there is the need to make master patterns from which aluminium or PU working patterns can be made and ideally all mounted onto match plates complete with gates etc as that will keep your costs down – loose patterns cost more to cast due to the labour involved.

You also need consider what equipment a typical beginner has and allow for that in your design. Will you assume they just have a lathe as old designs do. Or with benchtop mills being a lot more common will you assume they have the use of a mill and then what tooling to go with it.

Lastly from delalings with a few kit suppliers ther eis not a lot to be made out of it. If you start having to share your profits with another designer be that a one off payment or royalties with each kit sold then that is going to reduce what you get to keep for yourself. Out of that needs to come advertising, web site, stock, etc.

Maybe I’m just old and cynical, but what struck me is that this is an odd first post on the forum.
The poster has provided no information about themselves in the post or their profile. Not even what country they are in.

Robert.

Why re-invent the wheel? The models are already out there. It is a nice idea but I think you are talking to the wrong people. Most of us are stuck in our ways and while believing that going metric may be a good idea ……

It is very difficult the see the future but the good suppliers’ castings are generally sufficiently oversize to accommodate the required small changes in dimensions. It is quite possible to make a true metric model from some imperial casting kits. One of my two projects is a metric Stuart two cylinder compound engine withe metric fasteners and basic dimensions (i.e. whole number of millimetres). The only problem I have encountered is what do you do with a 1/4″ dimension.

Eventually the suppliers will have to go metric so it should be more fruitful to talk to them than a lot of old model engineers.

JA

If the builder is unable to work to 25.4mm on a metric machine with fair accuracy then the whole project is doomed. Just because the the dimensions are metric will not make it much easier to build and as many imperial drawing give fractional sizes even these have to be converted to decimal. A machinist given a drawing will work to the numbers, what ever they are ?  Noel.

On 20 July 2026 at 10:12 noel shelley Said:

A machinist given a drawing will work to the numbers, what ever they are ?  Noel.

The problem is that most people now coming into the hobby are not machinists, lucky if they did a bit of metalwork and technical drawing at school. What they may have encountered doing DIY or fiddling with cars, etc is also likely to have been metric and any tools they have aquired therfore metric. Many of out suppliers are now only supplying machines with metric handwheel graduations so a lot easier to use those than risk errors converting things they don’t fully understand. Plus metric materials are often cheaper than the imperial ones, same goes for tooling.

On 20 July 2026 at 09:48 JA Said:

……The only problem I have encountered is what do you do with a 1/4″ dimension.

…..

JA

How about making it 6.35 mm?  Good practice in working to reasonable tolerance.