I bought an Amadeal XJ12-300 milling machine, sometimes called a Mini Mill, this is actually a Real Bull milling machine. I bought this as it was cheap, but since buying it I’ve spent a lot of time making upgrades.
Note: the original lower spindle bearing comes apart very easy and the balls spill out and go free – take care if you intend reassembling with the original bearings.
The taper roller bearings make a huge difference to the shaft, it runs smoother and have not measured it yet, but I can see that the chuck is running much truer than it did. Taper rollers are worth the effort of upgrading even if you do nothing else.
I have been using the milling machine for over a year since replacing the taper roller bearings and this is a must upgrade. There is just no play in the spindle and it runs absolutely true.