Loss of precision

[Peter Martins]

Hi we are cutting a sheets of printed circular images on a summa s160t

Media about 54"
Diameter of circles about 50mm

We're losing tracking as it proceeds through the print- the cut circle is moving away from the printed circle. It's about 3mm out

We professionally fix a lot of designjet printers. So not afraid to tackle it. Though we have not much experiance.

We are not sure where to go with it.
Suspects are
1) motors
2) encoders
3) pinch wheels
4) y axis spindle wear
5) belts
6) wear somewhere (where?) In through system.

Don't think its Media.

Before we start trying all those things and working through the list though there may be some help here.

Thanks for reading.
Bristol inkjet ltd

 

[MikePro]

new to summa tangential plotters, as we recently replaced our mimaki cg130's.
Uncertain if it applies to cutting via printed registration marks, but for general plotting, I believe calibrating your length tracking may be the solution.
...for print&cut, reducing drag on the material or slowing down your feeds has always been my best remedy. Keeping my batches in 4ft lengths, and everything comes out fine, but if I go beyond it then i notice cuts start drifting as the weight of the sheet/roll repeatedly tugging/shoving on the plotter.

 

[swordguy3222]

The only time I've seen this on our machine is when the feed calibration on printer was off, sometimes media change causes that with different thickness's, or you need to calibrate your cutter. We do ours every Monday morning, or before large job that we need to be precise. We also try not to make our prints with a lot of cut more then 3 feet, 4 feet at the max. The longer the print, the more the feed distortion can be.

 

[Peter Martins]

Just checked the summa spec
Its 0.2% which is disappointing.

We are about 1500mm between the corners, so 3mm is within the spec of the machine. That is really underwhelming.

I'll check calibration.

I am fairly sure the cutter are more accurate when new.

Due to our inexperience and the age of the machine we are only to willing to believe its wear.

I asked summa directly but they were little help referred me to the UK disti. I'm reluctant to ask them for reasons I'd rather not go into.

But if I did I fear the response would be spend a load and get little benifit and or it not suppoted buy a new one.

We will emerge from this with a huge revulsion of these things having failed to sort it, or I hope and more likely fairly valuable skills and a range of our own 3rd party parts like belts, encoders
It depends if we have the time to pursue it to a conclusion.

 

[cornholio]

As a Summa tech for 30 years I can tell you, that 3 mm in 1500 mm is not the norm. If it's a Opos job, length calibration has nothing to do with it.
Check for clean tracking marks on the media back first. I had a problematic medium printed on a HP 800 that was so deformed, that it was impossible to get it perfect. Changed the vinyl and it was spot on +-0.1mm.
When your tracking marks aren't good, try another material. If still not good, you'd need to replace the feeding rolls.(it's one rather expensive part, because all the rolls need to be exatly the same and are combined at the factory)
It could also be a jumping timing belt, if the problem arises suddenly in the job. Mark the belt and pulley before job start and check after.
Long jobs can be cut with Opos Paneling. Set the Opos marks not more, than 400 mm apart in the feed direction.

 

[Rayd8]

yeah i set the opos marks at 200mm, cost more time to start the cutting job but this small change together with using oposxy in combi with my HP Latex has greatly improved accuracy. hth T.

 

[Snydo]

It's probably the media, one trick that I do with more "affordable" media is place the far left outside pinch roller well inside the crop marks, this helps keep the media more stable/flat as it feeds.