Enigma wrote:This is all very interesting to read. But in practical terms, how much variation in design is possible? For example, how about flat fronted spokes as per Barclay wheels? One of their 'standard' sizes was 3'5" which is a bit of an oddball but I suppose 3'6" (which is a tyre size that would probably be more obtainable) could do at a stretch.
It depends on how much time someone wants to put into doing the CAD to get the variations, flat fronted spokes should be easier to draw than oval ones. I have 3'3" and 3'6" rims but nothing in between.
But would Colin provide the same service given that these wheels could be seen as being in competition with him?
I think Colin takes the view that P4 wheels are a very small part of his business and he needs to make his money in other directions.
I'd also like to ask how the axle holes will be dimensioned. Similar to Gibson wheels ie a push/interference fit? Does the plastic being used have the slight inherent 'flexibilty' to allow this?
This is where things get interesting. There would be relatively few problems printing a Romford type wheel, but if it's finescale that's wanted then the limits of the printer and the materials start to come into play. If the wheels are to have the same sort of interference fit with the axle as injection moulded wheels then a resilient plastic is needed. Today this is usually ABS. FDM printers, that use spools of plastic wire, can use ABS, but as far as I know, very few of these machines can produce wall thicknesses down to 0.5mm, which would be needed for a tapered spoke. The other common printers like the jetted type ( Shapeways' FUD etc) and the liquid resin machines (SLA and DLP) use photoacrylic resins which in their common form is too hard and brittle to use with an interference fit. This means that a glued sliding fit has to be used with all the problems of concentricity and squareness to the axle. Oh, and most photoacrylic resins creep, meaning that within some time after printing, maybe 3-6 months, the bores close up enough to stop the axles being inserted. This is probably not what is needed when sales are made to customers that habitually salt away kits and components to use in the future.
Anyway Here are a couple of photos of work in progress. The light speckles are filings from removing the support pips. The wheels should have gone into the ultrasonic before I took the photos.