C axis "Jumpy" on lathe

[JoBalbis97]

Good morning,

I've been having some trouble understanding machining with the C axis on my mill/turn, was hoping you guys can give me a hand on this. 

I have an Haas St-30Y, using the post provided by the hsm website. When I do, for example an adaptive, when machining, the C axis is VERY jumpy. Doesn't seem normal. Also, let's say I make an adaptive circular pocket feeding at 100ipm from center to outside. When it plunges on center, it moves looking like 100ipm, but as it heads towards outside diameter, it goes very slow, like 20ipm slow. 

Do I have to do something to the post? I've seen machines like mine machining with live tool using C axis it look nothing like mine. The one's I've seen are extremely smooth. 

I'm attaching a program that I ran a few days ago and my post, maybe there's something wrong you guys notice. 

Hope I made it clear enough for you guys to understand. 

[Laurens-3DTechDraw]

Main disadvantage of using XZC code/mode over the G112 is that you cannot use radius compensation on the machine.

G112 supports this, and can output arcs, where XZC-mode needs to linearise those, and to make a nice circular movement with straight lines you need a whole lot of code, which the machine might not like either.

I haven't fully read up but here is a couple of general remarks on jitter/stuttering on C-axis cuts.

Loads of machines have a C-axis break, most machines have two different levels of pressure, one for drilling to keep the C-axis stationary, and one two remove jitter(low pressure). The spindle motor can push through the brake but the brake keeps it stable and stops it from moving all over the place when the force applied to it changes all the time. If your machine has this option please use it as it might make the machine far more accurate(especially belt driven machines)

If your machine has a geared spindle run it in the low gear, as often it is much stronger and more accurate.

[infoXQ6DN]

Has anyone found the fix for this!?!? I am dealing with it on my st20y.