LM 2.5, 30x30, SLB, one year old. Intricate 2.5D job. Rough cut, then finish with Sienci 1/4"D1/16" tapered ball nose. Finish Job was over 8 hour cut, so went through the pause/stop/restart sequence as per Sienci instructions, two separate times. First time the restart outcome was a 1/32" deeper cut. Second time was a 1/16" higher cut. Suggestions? Thank you
Did you shut down the mill in between sessions? When you shut down the drive to the stepper motors they will loose position. You would have to re-zero the z axis (I am guessing stepper loosing position is more noticeable for z). When you re-zero you are subject to errors although these errors seem to be more than what I would expect.
No. Kept power on to the PC and the machine throughout. Wonder what I would do if I had a power outage???
Those are good questions. I have an Altmill and I was going to post something like this whenever I get a minute:
Effect on zero when powering off SLB
Effect on zero when closing gSender
I have to rehome the machine when I power cycle the SLB. How accurate is the rehome and are the zeros impacted?
Anyways, that doesn’t really help you so I’ll just watch 
The Altmill has closed loop steppers so the position of the 3 axes should always be known if there’s any drift.
The Longmill has open loop steppers so any drift would not be accounted for. So maybe the weight of the router resulted in the z drift? Or maybe your lumber warped slightly overnight.
cry 
(extra characters to keep the forum software happy)
This is guessing:
When you close gSender, there is a good chance that the steppers are powered down and they will loose position.
Re-homing after a power up should get you within the repeatability of the home sensors so maybe 0.01 mm? (as long as you don’t accidentally knock the home sensors out of position)
If power is kept on, z should not move assuming the configured holding current isn’t enough for the weight of the router/spindle but then you would only see drift in one direction.
The lumber warping is a definite possibility if enough material was removed on one side of the job. Would it be enough for 1/16" … I don’t know but possible.
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1/16" is definitely possible depending on the moisture content of the wood and the relative humidity of the air. And milling also releases stress in the lumber, which will add to the warping issue.
Wait.. we’re supposed to cycle on long jobs? I must have missed that.
I have my gControl and SLB-Ext on a UPS so that ‘hopefully’ I never have an outage or hiccup while running. Eventually I’d like to get a larger UPS system and throw the Spindle & Laser on there as well.
I wasn’t even thinking ‘moisture’ … I was only thinking ‘stress relief’ in the wood. Agreed, moisture content is a different ball of chilly altogether but then it would never occur to me to use wood that wasn’t dry and acclimatized to the environment.
I don’t think so. But I might if I have to pause for several days.
Not moisture. Material is seasoned walnut, 13"x28"x1.3", laminated out of 3 pieces. Job pause was for 2 hours and overnight in basement workshop. Very firmly held on spoilboard throughout. Also, one restart was a higher Z and the other was lower. Wood does not warp one way and then the other. My speculation is either something physical, ie., the mill, or software. Did regular maintenance on mill before job. Checked if router, rails, anything loose - all firm. Returned to all-Zero after stopping job, then backed up number of lines on restart, as recommended.
Next time you pause, put a dial gauge on the z axis assembly to see if there’s any drift overnight. I think Sienci recommends putting a wood block under the router if you suspect any movement.
I would not discount deformation of your work piece due to moisture/humidity and/or stress relief. A dial gauge could indicate that as well.