How to duplicate measurements from one piece of material to another?

Question

I am not sure if this is the right place to ask this but. I have an offroad skateboard from MBS. I bought their brake system which comes with a circular piece of aluminum. Pictures attached.

You can see that on the circular aluminum brake part (don't know the proper name), it has 5 holes drilled. I called the company and they said they have CAD files and it is done in mass. I don't have those CAD files and I am not a CAD expert, nor do I have a machine to cut it.

I want to know the best way to measure (with basic relatively inexpensive tools, if needed I'll buy more), and replicate those holes with high precision on the sprocket. As you can tell, this is going to spin, so any measurement that is a little bit off is going to make the sprocket wobble.

The sprocket is not the same exact size as the aluminum brake part.

I am not looking for measurements. I am looking for how to measure. Not the fish itself, but I want to learn how to fish.

Answer 1

I would go either of two ways : one to mount both pieces rigid on a shaft and line centre punch the sprocket or two find or borrow (machine shop...) a pillar drill to get perpendicular and mount both parts so they rotate and centre punch again.

There is also the (old school) possibility of using compass and dividers.

Answer 2

I am confused about why you have the gear? The center of that gear does not look like it will fit on the axle where the brake disk is.

If you are planning on cutting the center out of the gear and the 5 holes, I might mount it in a drill and clamp the 2 together. Spin the part with the drill in a vice or something until you an see that they are lined up correctly then you can spray paint through the holes in the brake disk to mark the gear. Depending upon the precision you need you can drill press then mill until the paint is gone.