A website dedicated to the construction of an accurate 1/2 scale replica of a 1937 Aero Douglas Motorcycle

The
rims are commercially available for pit bikes and are 10" diameter.  They are slightly overscale and have 8 less spokes than the full size motorcycle BUT they are very close and accept fully road legal tyres which are also overscale but look the part.  The Hubs are machined from solid and the cast iron brake drums are fitted to them as per full size.  They are fitted with deep groove ball bearings and are oiled from a grease nipple in the centre of the hub between the spokes. 



Rims

It appears that pit bikes (whatever they are) use 10" diameter wheels and would take road legal tyres.  Now, I doubt I will be able to just purchase one off the shelf as there are so many things to consider - number of spokes   - the way they are laced - if they look close enough to the original wheels etc.  BUT they are the correct profile for the road legal tyres so can be used as a guide if i have to make them from scratch.  There is a possibility that I will have to modify the rims to suit my application.  The hubs will of course be made the same as the full size bike's and and spokes will be made similar -  using quality heavy duty cycle spokes as a base. 

I bought a used pit bike wheel from fleabay, im very suprised to say that it looks really good.  The second photo is of the full size wheel to show profile.  This rim is second hand as there was no point in purchasing new if it was going to be disgarded later. 

I then bit the bullet and decided to purchase two new wheels, once again the internet was searched and the cheapest place was on fleabay again.  These will require lots of modifications to be suitable.  More to come later....




Hubs


The wheel hubs are identicle front and rear with the drive from the chain and brake drums being transmitted through a tapered spline.  The material used was 'some aircraft stuff' kindly donated by my mate Mr. Dawson Esq.  The two blanks were roughed out at Les' house on his roundhead colchester bantam...oh the joys of power feed and flood lubricant!  I have no idea what the material is except that it finishes to a high standard and is fairly tough to cut.      


The end with the taperd spline was machined first.  This was basic turning along with the 10 degree taper, the threading is done later.  A modified parting tool was used to machine pretty much everything else including the inside faces of the hub and any undercuts.  Due to the ML7's somewhat limited topslide angle of rotation, two clamps were used to hold it in position to do the 6 degree angle on the outer face of the spoke flange.  The later Super7 does not have this problem.  At this stage one end is left unfinished and the hub is still solid.




The screwcutting was done next in the standard manner using my spindle handle allowing me to retract the tool at the correct moment, giving a perfect run-out right up to a shoulder.  The thread is 0.75" 26tpi BSB and was cut using a slightly reground chaser from a coventry die head. 

Once the thread was complete and the previously made gauge nut fitted a treat, the hub was drilled and bored for the bearings.  Now that the bearing housing was machined the hub can be removed from the chuck FOR THE FIRST TIME.  This meant that everything so far is running dead true.  An aluminium split collet was made from an offcut, firstly bored, a groove made for an old o-ring then its position in the chuck marked using a punch.  This will allow me to replace the collet in the same place giving me a greater chance of accuracy.  Chucks never run true again, no matter what people say. The collet was split with a hacksaw, each mating segment marked and the burrs removed.  An old o-ring was then used to keep the
segments together just to make life easier. 

A dial gauge was used to check for any run-out and the collet was adjusted to suit.  The outer end was then finished in a similar mannor to the first end.  Support via a live centre was not required to the reduced overhang of the job due to the collet.

A simple jig was made to hold the hub vertically to drill the holes in the dividing head.  A long series drill bit, along with extreme care, was used to drill the 36 holes for the spokes.




The final stage was to cut the splines.  These splines are a apecial 90 degree spline due to them being formed on a taper.  The taper is 10 degrees but the splines cannot be cut at this angle due to the differing diameters.  You would have too many splines on the smaller diameter and too few on the large diameter...........


The shaping tool was used to cut the splines, and becuase it uses the topslide, it can be swivelled to the required angle.  The tool was a 90 degree tool used on its side.  Because the myford has a 60 tooth back gear and 60 splines workes out nicely, the index plate was used so index every spline, but the dividing head could've easily been attatched. 

A test block was cut first to ensure that the set angle is right so that the crests of the splines stay parallel as mentioned above.  Well, it wasn't but it meant that I had 30 tries to correct the angle.  Once the angle was correctly set and the remaining crest of the splines were coming out parallel, the aluminium split collet used in their initial manufacture was re-used to hold them true with any innacuracy being brought into line with newspaper and tightening different jaws. 


There are 60 splines in total being 22thou deep.  The splines have come out well and finsh off the hubs.