Wood spoke wheel

The Prototype
1927 Star CoupeWooden spoke wheels were pretty much the same but let’s use this one from a 1927 Talbot Star Coupe for a guide.

I brought the photo into Sketchup and based on the wheel dia that I found on line I gathered some basic dimensions.

Fairly Important: I found an online antique tire business. There was a chart showing dimensions of tires from various years – including 1927. It had the dia, width, tread width, profile. Using that, clues from photographs and the size tires used for the 1927 Talbot I came up with these dimensions. These ARE NOT necessairly correct .. but within the bounds of being close. That’s good enough for me since I just want a generic wood wheen that approximates the correct size and dimensions.

Basic Dimensions
Starting Dimensions

Starting Dimensions

To get started I’ve come up with these dimensions:

  • Wheel Rim Major Dia: 20.880″
  • Wheel Rim Minor Dia: 18.000″
  • Wheel Rim Inside Dia: 19.132″ – Why this dia? The plan is to have this printed at Shapeways in FUD (Frosted Ultra Detail). This has a minimum wall thickness of .3mm/.0118″. Multiply that .0118″ x 48 =0.5664″. This is the minimum thickness of the ‘wall’ from the Wheel Rim Minor Dia. Double this – 0.5664 x 2 = 1.1328″ and add to the Wheel Rim Minor Dia – 1.1328″ + 18.000″ = 19.132. [Understand that the numbers shown are rounded up for display. I actually took that 0.0118 and rounded it up to a 0.012 to keep everything above the minimum.]
  • Spoke Small Dia: Most of the spoke length is 1″ dia.
  • Spoke Large Dia: 2.270″ – This is – nominal at best. Where the large dia of the spoke meets another there are curves in two directions – and a 36° slice through those curves. Therefore I started with a dia close and played with it until “it worked”.
  • Spoke Base Dia: 7.345″ – Again – nominal. This is derived from the dimensions of the spoke base, where and size of the curve where the small spoke dia merges into the large spoke dia – number so spokes and so on.
  • Hub Plate: 5.943″ Dia – This was dimensioned from photos – scaled relative to the wheel dia.
Spoke Section – Initial Dimensions
Spoke Section

Spoke Section

Spoke Section[/caption]Next, 1/2 the spoke is drawn, spit down the center, so I can lathe it. Again – many of these dimensions are nominal – and can change. We have –

  • Spoke radius – 0.500″
  • Spoke base radius – 1.135″ (2.270″/2)
  • Length below the spoke base circle – 3.673″
  • Wheel Rim Inside Dia – 0.566″
  • Spoke length enough to extend beyond the Wheel Rim Inside dia – 10″
  • a radius of 0.712″ at the base of the spoke
Lathed Spoke – 1st Try
lathed_spoke_1Finally, I used the ‘Follow Me’ tool to spin the spoke section. This is the spoke as – if it were real – would have looked as it came out of the lathe.

I know I may be going into excessive detail here but the purpose of this is to show how it is done – so you can repeat it.

The next step will be to array this single spoke into a circle of ten spokes and see how close we are.

Spoke Array – 1st Try
SpokeArray1This first attempt shows me that the base dia is too small. A quick use of the tapmeasure tool says that about .0.2″ added to the radius is needed.
Spoke Section – 2nd try
Spoke_Section2I kept all the dimensions the same except for adding 0.2″ to the Spoke’s large end – and adjusted a radius to ti.
Lathed Spoke – 2nd Try
lathed_spoke_2Again .. we spin that sectional view into a 3D object using the Follow Me tool to lathe the spoke.
Spoke Array – 2nd Try
SpokeArray2This time it works pretty well. The rough, obvious flats on the circle can be ignored. I used a 30-segment circle and that is rough .. but .. this entire thing is about .030″ dia and is below the resolution of the printer. So all is good.

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