Wheels by cutting and turning
Method
There exist several methods to produce a spoke web on the milling machine or lathe. But the most succesful method I tried until now is by using twin cutting blades. This method was described by Bill Newton on the Scalefour site but has now disappeared. The method I use is adapted to the required smaller diameters and accuracy needed for our scale. The first trials existed in making a length of spokecenter rod. This can then be parted into slices for wheel centers. Bill's method existed into first making slices and solder these into a rod that was made into spoke centers. However cutting up such a rod into slices is easy if the V's between spokes are filled with shellac, the whole center can than also be changed into a smaller diameter if required. This circumvents the soldering of slices into a rod. However getting a wobble free wheel when fitting the spokecenter with a (1mm) stubaxle turned out to be difficult. The way out of this is cutting individual spoke centres with an integral stubaxle. Due to the small depth of the spokes of just over a mm lining out the whole lot is not critical. This method is what the photo's below are showing.
The first shows the result just after finishing the last spoke. We see a part of brass with a disc and raw stub axle having a slightly larger diameter than required. The disc is already made into the correct diameter for the wheel required. The saw blades are in this case 25 mm in diameter. Of course smaller cutting blades mean less waste and more rigidity thus better results. In between the blades is a 0.2 mm spacer. The spacer can be thinner, I also tried 0.15 mm with succes. The number of spokes around the circumference is divided with a rotation table or any similar means. The wheel in question is a trial for a 13 spoke wheel such as found on the NMBS type 29 of american origin. The metal for the spokes can be anything, I tried Nickel Silver and brass, but steel or bronze would possible too.
setup of wheelstub and saw blades
The spokecenter for a 9.5mm 13 spoke wheel
This second photo shows the resulting spoke center and stub axle. The spoke center is cut off with a slitting disc and mounted in a rod that is produced into a wheel. This can be steel or NickelSilver. First turn a hole to required dimension and then fit the spoke center by soldering. I used solderpaste. After that the stub axle can be brought up to diameter and the tyre finished. The wheel is cut off and the center of stub is finished. One of the small improvements would be to do it otherway around and use the stub of the spoke center as stub axle, not only because of saving 3.5 mm material but also the outside finish of the spokes is slightly smoother than the inside finish of the spokes. Also wheels which require a specific center with spokes that follow a curve from rim to center instead of lying in a flat plane can be processed first that way.
Photographic results
FLM bogie with 2 replacements trials
Here we see a R-T-R bogie with replacement wheels, all 5.3 mm diameter 9 spokes. The left one is according to drawing specs, the right one with a calculation error resulting in a too thin tyre but really showing its spokes.
Three wheels comparison
Comparison between home made wheels and the 6mm 10 spoke of the 2 mm SA in the center.
Comparison of different techniques
A small collection of wheels, from left to right top 5.3mm 9 spokes , 9.5 mm 13 spokes still without web, 8.5 mm 15 spoke lasercut wheel, 5.3 mm 9 spoke, in front 8.4 mm 16 spoke on basis of FLM halfproduct. The differences in time for the various methods are not significant. Producing a spokecentre costs about 10-15 minutes depending on the number of spokes. The turning of the rims takes most time resulting in about 3/4 hour for a complete wheel for a small series. Most of the time is eaten away by measuring. Time can be gained by optimising the tooling required for producing the tyres, such as boring the hole in one go to the required dimension and accuracy and for producing the tyres. The wheels can use some grid blasting to remove the remains of solder paste that sometimes clings as small particles in corner that are difficult to reach.
copyright: Henk Oversloot
date: 28 jan 2003
