Need Help!- problem in mach 3 mill z axle over heat's

[gothdragon]

my problem is my z axle is over heating and it's only my z axle
I well explain the best I can so please bar with me

this is a home made cnc.
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probotix 3 axle kit
24 Volt 6.5 Amp Switching Power Supply

motor is
166 Oz In. Hybrid
1.8° /200 Steps Per Rev.
2 Amps Current Per Phase (Uni-polar)
6-wire Uni-polar or Bi-polar
NEMA 23 Frame

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now here is my problem

this or uni- polar motor's . but the z axle over heated the uni polar board so I had to use one of my bi polar board's 4 wire setup motor or 6 wire
the motor can be used as uni or bi

{ this board I have the bi polar and uni polar chip's or not connected to board
they or ran with a cable so I am runing both uni and bi }

was working ok but the motor over heated after 3 min run and I mean
3ed degree burn over heat

I thot I fixed it in the motor tunning but I guess I was wrong
now I burnt out the bi polar chip and need to order a new one

this only with z axle set up in mach 3 and I feel it is something I am doing inside mach 3
I do know that uni polar and bi polar have deferent setup but I don't no nothing about bi polar setup's so im asking for help

also I can not seem to get the z axle to line up with the y and x axle
if I make something the timing is off
the z axle seem's to acked like it's getting back lach before it hit's anything
and no sign's of backlash

also noted I am using home depo screw's they or y 3/8 8 ft x 3/8 4 ft and z 3/8 1 ft sorry no acme screw I do not recommend this to no one


p.s I am using spill check sorry for english grrrr german here

[gothdragon]

if you need info on where i got this board and mmotor's at here is the link it has all the info on what i am runing so you can better help me with
3-Axis CNC Stepper Motor Driver Kits

and the bi polar chip is SideStep Stepper Motor Driver - Bipolar Stepper Motor Driver

the board is great for someone new like my self just lost on this z axle thing othere thin that everything els works great