I've made a few upgrades to my machine to improve performance. All were done without any changes to the machine frame, just swapping out components.
1. I changed the drive ratio on the X axis to 1-1 by putting a 42 tooth pulley on the motor and a new longer belt. that gives me a reliable 40 IPM rapid on the X, with as much as 60 available, but I like to be conservative.
2. I changed the drive pulley on the Z axis to a 24 tooth ( original was 18) giving me a 3-1 ratio instead of the 4-1 original. Changing the pulley was all that was necessary, as the original belt was long enough. That improved the Z rapids to 20 IPM- I could get 30 on the downstroke, but not on the up- I'm working on a gas strut add-on now to see if that helps.
I think the motor could run a 36 tooth pulley, making the ratio 2-1, but because of the diameter of the pulley, it would require modifying the motor mount and the sheet metal cover and going to a longer belt.
3. While doing the Z modification I also added a belt adjusting device which made it a bit easier to set the belt tension- once again just making a couple simple parts, without modifying the machine frame.
4. I added and ESS ( Ethernet Smooth Stepper) unit to the machine, because other forums reported that it improves the speed and smoothness of the steppers as opposed to the factory parallel port setup. They were right about that, the steppers are smoother, but unfortunately the ESS does not support the P.I.D. function of mach 3, so maintaining consistent RPM for threading and CSS is not possible. The people at ESS say they are adding this function soon, but I would wait until it is included before investing in one.
5. I modified my faceplate so that I can swap back and forth between the 3 and 4 jaw chucks quickly. Once again it only required some hole drilling.
I have some other ideas in mind, including changing from V-Belt drives on the spindles to tooth belts and making a 5C collet closer setup.