Primary drive pulley

Today, I got my motivation back and did some more work on the Yamaha Roadstar project. I received some time back the micro belts from SDP. They are a perfect fit, having the same width and pitch as the original kit part.

This is the original kit part - it is molded as one single part with the belt and final drive pulley, requiring painting in different colors to achieve some sort of realistic look. So I decided to make them as separate parts. I have machined the primary drive pulley out of 6061 aluminum. It was not necessary but I wanted to do it anyway, as a learning process. I will have to do it on the custom chopper so better practice with every occasion.

I had to grind a special grooving lathe tool for this job, but since I am planning to do more custom bikes in the future, I will use it more than once. This was the first time I have attempted to grind such a tool and I am very happy how it turned out.

Unlike the kit part, which is supposed to be painted and glued, the machined part will be secured with a micro bolt and nut. So next job is to machine a 2 mm bolt with nut.

Some more photos of the pulley and fit:

Miniature belt drive

These days I have been working on the designing the final drive assembly for the custom chopper scale model. Initially I planned to use a miniature chain drive, by using a kit from Top Studio (see details in an older post). But while working on Tamiya's Yamaha Roadstar kit, I found out that you can buy miniature belts in various sizes, the smallest one being 3 mm width with 1 mm pitch. They are designed mainly for robotics but would look good on the scale models as well. Check out at SDP-SI for their belts offering.

So with this idea in mind, I changed the CAD project to use a belt final drive. I am going to use the 3 mm width x 1 mm pitch belt and will design the pulleys so the belt length matches the models sold by SDP-SI.

One issue that surfaced when I added the belt and pulleys in the assembly was the clearance between frame and tire; the belt and pulley was rubbing both the frame and tire. I had to widen the frame rear to accommodate the new final drive assembly. It doesn't look so sleek as before but is not bad either. The rear fender will have a cut-off for clearing the belt, but I will not model it in Inventor.

One of the advantages of designing the scale model in a CAD software is that you can find such problems early. When working with metal you need to be precise because unlike plastic, once a part is cut it cannot be adjusted too much.

Brake disks for the Yamaha Roadstar project - Part 2

Finally, the brake disks for the Roadstar are completed. It took me two attempts to do them, since I broke a 0.6 mm drill in and couldn't get it out, so I had to scrap the part and start again. The process of making them was as following:

• Installed some aluminum bar stock on the lathe and turned down few mm, to get to the 25 mm required diameter. The plan was to make both disks at once, so I took into account the desired brake disk's and the cut-off blade's thickness
• After that I removed the chuck from the lathe, with the bar stock still in, and mounted it on the rotary table, on the mill. Careful adjustments have to be made to align the spindle to the center of the brake disk. Then I started drilling the holes. I chose a simple pattern only with holes, in order to make it easier to fabricate. Basically there are five 4 mm radial holes, one 4 mm center hole (for the hub), five 0.5 mm radial holes for the bolts and forty-eight 0.6 mm cooling holes. Drilling the micro holes is tricky as the drills can easily break (which happened once) so I had to take my time. Also to make both disks at once, I had to drill deeper holes (around 2-3 mm), which is not really possible with such small drills (they snap easily). So in the end I had to do the disks separately
• After the holes were drilled, I mounted the chuck back on the lathe and cut a 0.8 mm "slice" from the bar. The 0.1 mm extra is needed for the finishing job, since the cut-off will leave a rough surface
• I then mounted the disk on the Dremel and polished the disk with 180 grit sandpaper, reducing the thickness to 0.7 mm

The disks should attach to the wheel hubs with 0.5 mm micro bolts; I intend to buy some from Scale Hardware.

All in all I am content how they turned out. Some photos below.

Brake disks for the Yamaha Roadstar project

I spent most of the past month designing a custom rear view mirror for my real motorcycle. Unfortunately I realized that the parts would be too big for the footprint of my Sherline mill so I put that project aside.

Now I am back to the Yamaha Roadstar project bike I introduced on the last post. Last evening I have started to turn the brake disks. Unlike the real bike, which has two front disks, mine will have only one upfront and one on the rear and it should look like this.

It has 25 mm in diameter (the same as the part in the kit) and 0.5 mm thickness (the kit part has 0.8 mm but looks too thick to me). It will be turned in 6061 aluminum. As you see, the patterns require drilling a lot of holes of various diameters. I am trying to make both disks at the same time and then just cut each one, like a slice of bread :) Might not work though as the tiniest holes are only 0.5 mm and cannot go deep enough (around 2 mm).

Below the stock aluminum bar reduced to 25 mm on the mill. All there is left is to drill the cooling holes, a lot of them...

Another side project

Today, I would like to show you another project I've been working for some time. It is based on 1/12th scale Yamaha Road Star 1600 kit from Tamiya.

The plan is to slam the rear and make add custom wheels and brake discs. I already made the wheels in 6061 aluminum and they are inspired by Harley's Fatboy ones. Think they turned out pretty cool and hopefully they will look even better once I will polish them.

In order to slam the rear I had to make a longer rear shock. I reused some plastic parts from the kit part but had to make most of the parts in metal (aluminum, brass and stainless).

Back to work

Now that I am back from vacation I continued working on the miniature tube bending device. To remind you, this is the device I will be use to bend the brass tubing for the bike's frame (3 mm) and exhaust (4 mm).

Parts are from aluminum and brass. Below a couple of pictures.

Summer break

For the last two months I have been in business trips and in between had the summer vacation. Haven't had the time to work on the project but I will be back at the beginning of September.

Enjoy the summer holidays.