I read this somewhere on the net but it has been a while and I do not remember where I read it.
My mini mill table is 4" by 16" long and with the T-slots that does not leave much room for checking tram.
I found this Honda brake disc on the bay for $15.00 and that included shipping. Now, the thing weights
a good bit, must be over 10 lbs and that is a good thing.These discs are precisely ground and have a nice finish.
The one I bought has a large hub in the center section which I could do without buy my tramming tool that I made
a while back has positions for small diameter testing and larger diameter testing since I always wanted to get a
precision plate to aid tramming.
Any how here are a couple of shots of the setup. Works great.
My mill was the tilting column variety and I have it locked down. I never tilt it.
I made mine quite sturdy using this process:
Reducing Mini-Mill Column Flex (and Column Y-Axis Alignment) - Home Model Engine Machinist
The bar at the bottom is the secret to a fast and accurate tram. If you have the solid column I think it has a built in set of
stops that can be adjusted.