printing inaccurate lengths (160sp)

[artbot]

i do a lot of low pass (1, 2, and 4 pass printing) on metal. lately i've had
wild swings in the print's length. i usually blame this on the metal slipping
in the machine. but i didn't have this issue in the past.

today i printed four large blueprints (on 40lb white butcher paper. very
lightweight, "slipping" impossible) the size of the image was printed at 1 pass
30 x 360, a 40" x 106.5". my blueprints came out:

104.875"
106.75"
107.00"
106.75"

i reprint the one that came out 104.875" and this time it comes to 106.7".

i can accept .25" over 100" because the media comp' is set for .060. and the
paper is not straight and flat when measuring.

but what can cause these sudden 2" short outcomes? lately i've almost ruined
some very high dollar pieces because one pass didn't line up (i overprint each
of my pieces about 4-6 times). my overprints have to come to the same length or
the register will be lost.

thanks in advance!

aa

 

[SightLine]

My guess is Feed Comp has gotten way out of wack. That will do it everytime. Might have to reset the baseline feed comp in the service menu where you print the test, measure then input the actual size. Be sure to first set user feed comp to zero before setting the baseline.

Any adjustments to feed comp will affect the length regardless though. I've had it be enough that on print/cut jobs the cutter cannot even find the reg marks the print had gotten so long. It's the one catch of using feed comp to eliminate banding that I've found.

 

[artbot]

i'll look into that. i've just dialed in my feed comp and left it for more than a year. and i've never done a baseline (i'll be learning something new today). but for intermittent length differences... that's so odd. if a printer doesn't "know" what an inch is, it seems it would just be dead wrong but perfectly wrong to the thousandth of and inch between two prints. could the rip be to blame? or an x motor? ...if the media comp' adjustment just dials in but doesn't get the goblin out of the issue?

 

[MikePro]

my guess at the intermittent distance issue:
are you taping your print to the take-up roll? That's where you might be adding the extra "slip" at different intervals.

 

[artbot]

i never ever use the take up. last night since i had 40' of blueprints i just wound it manually on the take up so there was a lot of slack. this happens with large aluminum sheets hovering on the tables. like i mentioned, i used to blame it on roller slip. but my tables are very dialed in. a sheet of aluminum almost requires less torque than a roll of media.

note: to those that use tables on your hybrids, a flat table isn't the best way to feed mildly flexible material. the sheet should head very slightly down hill going in and slightly up hill going out. notice on an old hp deskjet how the printer "cups" the sheet. the act of bending a sheet causes the "trough" of the sheet to be flatter an straighter. for heavy sheets you can even lean your entire printer downhill. did that years ago and gravity is better than any gripped feed.

 

[SightLine]

I guess it coudl be the RIP. One thing to check is maybe if it is consistently off by a consistent amount over a set length. I know Flexi has a function on the machine setups called "Output Size Compensation" where you can adjust for this at the RIP level.

The machines themselves will also have a function for this as well though as a baseline type adjustment. It will print what it thinks to be some specific size square - then you measure the print and tell it what the actual printed size is. This sets it's baseline size compensation. I'm not 100% sure if this is the baseline feed comp or not but there is a function to set size compensation up. Could very well be a failing motor or the RIP or something else though.

 

[artbot]

thanks for all the input. i think i've got some diagnosing to do this afternoon. plus i will put a ruler at 100" down the right side of my print so as i over print i can monitor when or just how the feed is malfunctioning.

 

[artbot]

i did the 500mm size test thing in service mode. and for the life of me i couldn't figure out how to do the adjustment. the manual made no sense to me at all. basically i'm running 502mm long instead of 500mm. so that tells me nothing. if anything, it should have come up short.

can someone in human english explain the 500mm procedure to me. as in step one, step two. if this, then that? etc.

aa