Homing going wrong

I have homing set up which works fine, and also G28 for work home position, so I home the machine and go to G28 and all works well then I use the probe to set the Z, then press send and as the Z is going down it jerks to the left and towards the front of the machine, I was trying to cut a circle which did not come out round, then when it finished and returned to the work home position, it was about 1/4 inch out, the same amount as what it jerked when going down, I am using Phantomms screw drive but that was working great and cutting perfect circles, so I don’t know what is causing this jerking movement

I checked the X axis calibration again and found it is off by 1/4 inch over 10 inches, and the movement is not smooth, a bit of a pause now and then, it was calibrated a few weeks ago, so it should have been okay, I did have a carve go wrong yesterday where the cutter plunged right through the 18mm mdf, before I got to stop it, would that have done some damage, could it be the stepper motor loosing steps, I don’t want to change the calibration again if that is not the problem

Check all of your electrical connections, then check the calibration again. If the calibration is off, fix it in machine inspector.

I’d also check the set screws on the couplers, make sure they haven’t backed off. If they are loose you would see it slip.

Thank you all for your help
Robert-- I did calibrate again only the X needed doing
Philip–you were right the set screws had loosened a bit, all tight now
Phil–my $1=255
I tried again after calibrating and tightening the set screws, it cuts the circle perfect and the size is spot on, it is still jerks to the left when going down to do the cut and after the cut it does not return to zero, it is slightly off, and goes down deeper, I have added some photos so you can see before and after, in the photos I have dropped the Z down 1 inch from where I have the work zero set at , so you can see it clearly, and when I home the machine again and press G28 it goes back perfectly

to work zero

Yes,I will use blue loctite from now on, I still can’t figure out why the Z moves to the left when moving down to start the cut, and why it does not return to work zero