The right voltage for my Stepper Motors in order not to lose steps

[jhonansaro]

Hi there
I have put together a 3 axis router CNC machine. It is a 4 meter By 2 Meter long machine. The machine has 4 Leadshine stepper Motors (Model 86HS45 4.5 N.M --- 637 OZ-In --- NEMA 34), The motion system for Y and X axis is Helical rack and Pinion (spring loaded with 3:1 Pulleys). The Drivers are Leadshine M880A with Electrical Specification as follow:
Min current of 1.8 A --- and Max 7.8(5.6 RMS) A
Supply voltage --- Min 24 VDC --- Max 72 VDC --- and Typical 68 VDC
The Machine is working fine in Short Runs. It can actually cuts 16 mm MDF in one Pass without any Difficulty. But In Long runs (Over one Hour) For example when is Cutting a Relief Like a Lion Heads and so on, IT Loses some steps and when it moves to its zero Position it is off target by few mm mostly in X Direction. I am wondering what would be the probable cause or Causes?
I have some questions on its Voltage supply.

1. My power Supply is a Hittachi 32 A --- 57 VDC. I think I am OK with Current, But as far as the Voltage goes as you can see My Driver Typical Voltage requirements is 68 VDC, and my PS has a Max of 57 VDC, Could this be the cause of the problem?

2. Can I add a 10 or 15 VDC --- 10 A in Series with my Original PS? And If I do so, Wouldn’t this sort of burns my Smaller PS?

3. I am also considering of Upgrading my motors to a Higher NEMA 34, Like 86HS85 with holding Torque of 8.5 N.M --- (1203 Oz-In ), On this issue what do you think of Stepper Motors with Brakes? Are there any better for my machine? And How about the Closed loop Steppers? And If I use them do I need to change my BOB?

Regards
Jhonansaro