Also make sure your end mill is secured well particularly if you are using an up-cut spiral bit. This type of bit will try to ‘pull’ itself out of the collet/grip and result in a varied cutting depth shown in the Friend cut photo. The cutting depth increases as the bit slips through.
kindly show video how it’s used.
thanx-
Hello
I’m facing the same problem … A few months ago this problem started …
I tried everything.
I completely disbanded and rebuilt the mechanism
Testing the time when the z axis will be shifted to 5 mm it will move 5 mm. But the final result of the work is 5.4 mm
Did you solve the problem?
YES … it was a loose set screw… I went got a different one like AngusMcleod suggested in the above pic.
I also used Blue Loctite to secure it…
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Exactly … put in little screws like these instead of the cheap set screws… add blue loctite also
Fixed it instantly…
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Of course I’ve gotten these little screws … but the engine ax has a cut where sits screws … how to move around Pulley?
But maybe the placement has other screws marked with a green marker
If the set screw have sligthly loosed or is worn the shaft can rotate a few degress off in each direction. To ensure proper connection take the pulley off and add blue Loktite or similar thread locker compound to the shaft AND set screws. Replacing the set screws with longer / larger head ones is also worth considering.
Dont assume - check and verify 
I have the same problem as BrianScheibach…
Why is your acme screw sticking way up, out of your Z-axis?
I’m sorry, I can not understand you?
That is not supposed to stick way up in the air like that.
Is that the old M8 screw?
Ohh, good question!
If so, it may not be set properly in the SetUp. That could account for it not moving the Zaxis correctly.
Several months ago it worked properly.
Then the problems started
When not in the mode of operation and I move the Z axis up or down, for example 20 mm it performs 20 mm.
Only when performing work and cutting any surface, the result is 20.4 mm 