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  1. #1
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    RP3700 Master Skew

    I am fighting a maddening issue with my RP3700: excessive master skew.

    Masters go on perfectly straight, measuring 26mm from the edge of the near side of the master to the metal frame on both the lead and tail ends. But, no matter what, the trailing edge quickly drifts. it will be at 25mm by about 20 prints, and at 23mm by around 100. If 3mm drift isn't bad enough, it just gets worse from there. It is happening to all of my drums and no matter what I do, I can't seem to stop it.

    Here is what I have tried so far:
    • flipping the pressure roller
    • scraping the excess dried ink from the pressure roller
    • replacing the pressure roller (though with another used one from my parts machine)
    • increasing the amount of master material under the clamp.
    • decreasing the pressure using the print-pressure adjustment in TM
    • increasing the pressure using the print-pressure adjustment in TM
    • adjusting the parallelism of the pressure roller
    • changing the internal squeegee pressure on a drum (though its an issue with all of my drums)
    • readjusting the whole print-pressure assembly (removing the rear gears, cams, etc. similar to retiming)


    Ive also tried taping the master on the clamp, trailing edge, and far side to prevent it from drifting, but that only really seems to slow it down and I start to get wrinkles in my image where the master is pulling against the unmovable tape.

    The clamp-side doesn't seem to move, staying at 26mm,.

    I tried to be as thorough as possible before writing in, but now I'm at a loss. Does anyone have any Hail Marys for me?!

    Thanks in advance!


  2. #2
    Just a fellow wanderer 2,500+ Posts Iowatech's Avatar
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    Re: RP3700 Master Skew

    Sounds like you have already tried most of the stuff I would have suggested and more, and as you said that happens on any drum you try, that pretty much rules out the drums.
    In this case it appears you've got some defective master material. It's likely all the rolls you currently possess are from the same production lot and could be defective too, but you might try a different roll or two just to make sure if you haven't tried that already.
    That's a pretty old machine, so I don't know if authentic Riso RP master material is available any more, but if it is try a new batch of that next if you can afford it.
    If that's not an option, see if the place you get your master material from has a usable warrantee replacement plan for defective supplies (that's the exact minimum, if they can't do that even they don't believe in their products) and have them replace the master material that is causing problems.
    Or if there's a different distributor you can use, you might see if their master material works better.
    Good luck!


  3. #3
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    Re: RP3700 Master Skew

    Thank for the idea, Iowa - I hadn't even thought that the master material itself could be an issue. It's OEM RP riso masters, manufactured in 2014 according to the box.

    Here is another observation I forgot to mention. while the master is straight along the drum, its a actually not straight across under the clamp - the master material is 3mm higher on the far slide of the clamp then in the near side - so perhaps this is the master settling on the drum - straightening out under the clamp as it prints? is that insanity?

    why would it be crooked under the clamp, but perfectly straight on the drum itself?

    is there a way to adjust the master's parallelism as it enters the clamp?

    EDIT: i put in the other roll i had (from the same box) and the VERY first master it made, without being cut by the machine on the lead edge (just the factory deckle) was very even under the clamp - but the second master (this time cut by the machine) had the same unevenness as every other master. Is it possible for the cutter unit to be out of square? I can't see any any point where you would even adjust it...

    Last edited by mixedfeelings; 09-05-2016 at 04:42 AM.

  4. #4
    Just a fellow wanderer 2,500+ Posts Iowatech's Avatar
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    Re: RP3700 Master Skew

    Quote Originally Posted by mixedfeelings View Post
    Here is another observation I forgot to mention. while the master is straight along the drum, its a actually not straight across under the clamp - the master material is 3mm higher on the far slide of the clamp then in the near side - so perhaps this is the master settling on the drum - straightening out under the clamp as it prints? is that insanity?

    why would it be crooked under the clamp, but perfectly straight on the drum itself?

    is there a way to adjust the master's parallelism as it enters the clamp?
    Well, the image burned on the master would have to be not parallel the same angle of the master under the clamp, so that's unlikely to happen all of a sudden, but as I have never seen your machine it isn't insanity. You might try running mode 253 for ten seconds or so, theoretically that should run a few inches of master material into the drum cavity. Then if you have a decent straight edge you can check to see if the master material is aligned with the guides it is coming out of. Then run mode 250 which should cut the master and you can check if the trailing edge of that master strip looks better than the leading edge.
    The information I just shared probably has very little to do with the problem you described in the original post. For what it is worth, I still think that is probably being caused by defective master material, especially after all the things you said you had already done to to fix that yourself. So, I'm sorry if this was a waste of time.


  5. #5
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    Re: RP3700 Master Skew

    I actually found another OEM roll from another batch (this one from 2013), and it's doing the exact same thing - so I don't think that bad masters are the problem after all. It was definitely a good thought, though!

    I ran about an inch of the master (from the 2013 roll) as you suggested and folded it in half so you can get a sense of the crooked cut and what the skew is like under the clamp:

    crooked_cut.jpg

    It really seems like these two issues must be related, somehow. but I just don't know.

    I did some digging around the cutter this weekend to see if there is any place to adjust it, but there doesn't seem to be. I also cleaned all of the master making rollers, for good measure, but like everything else it has had no result.

    what an annoying situation!


  6. #6
    Just a fellow wanderer 2,500+ Posts Iowatech's Avatar
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    Re: RP3700 Master Skew

    Thanks for the picture. If you used the modes I suggested to feed the master for that, that takes the thermal head and the write roller out of the process, and if the part of the picture that shows the single thickness of master material was the lead edge, you might want to check those. As in trying a new or working write roller (they get a depression from the master material after tens of thousands of masters have been run that can cause master feed problems and need to be replaced), or make sure the downward travel of the thermal head isn't obstructed on one side (I've seen that happen exactly once, due to a tech who shall remain unnamed not routing the thermal head's data wiring harness correctly (d'oh.)).


  7. #7
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    Re: RP3700 Master Skew

    Use 11x17 paper and run the checkerboard test pattern. After it is made pull out the drum and measure the front and rear parallelism of the burned image to so some point on the clamp plate (like the lead egde of the clamp plate- no need to open the plate). If it is square or within tolerance I'd order a new Pressure Roller. They aren't cheap but that is touching the master on every single copy.

    It's been a while but I don't think the RP's cut the master perfectly square anyways. All that really matters is if the image is square on the drum. You could also lighten up the amount of pressure being applied.

    Just my 2 cents as you have already done so much


  8. #8
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    Re: RP3700 Master Skew

    I think I may have found my own hail mary - sort of. I measured the hight difference of each side of the Pressure Roller holder, pressing them both as far down as they could go and one side was 1mm higher than the other. so I loosened the large post that attaches the pressure roller holder assembly and adjusted it. This has mostly mitigated the pulling of the master - its still there, but 2mm of movement over hundreds of prints vs 100. This is enough to get me through my current project while I search for the ultimate cure.

    As far as the image on the master - it starts out fairly straight at the top, clamp side. I have put in an order for new OEM roller. My machine only has about 500,000 clicks on it, so it seems a little early to replace the pressure roller - but it won't hurt either. As you say, it touches every print...

    Is there another way to lighten the amount of pressure? I always run the machine at the lowest density, and I have the TM setting at -46

    Is there a way to adjust skew in the burned image apart from replacing the write rollers, or is they pretty much what causes that?

    Thanks so much for your help, I REALLY appreciate it!


  9. #9
    Just a fellow wanderer 2,500+ Posts Iowatech's Avatar
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    Re: RP3700 Master Skew

    Quote Originally Posted by mixedfeelings View Post
    I think I may have found my own hail mary - sort of. I measured the hight difference of each side of the Pressure Roller holder, pressing them both as far down as they could go and one side was 1mm higher than the other. so I loosened the large post that attaches the pressure roller holder assembly and adjusted it. This has mostly mitigated the pulling of the master - its still there, but 2mm of movement over hundreds of prints vs 100. This is enough to get me through my current project while I search for the ultimate cure.

    As far as the image on the master - it starts out fairly straight at the top, clamp side. I have put in an order for new OEM roller. My machine only has about 500,000 clicks on it, so it seems a little early to replace the pressure roller - but it won't hurt either. As you say, it touches every print...

    Is there another way to lighten the amount of pressure? I always run the machine at the lowest density, and I have the TM setting at -46

    Is there a way to adjust skew in the burned image apart from replacing the write rollers, or is they pretty much what causes that?

    Thanks so much for your help, I REALLY appreciate it!
    Thanks for letting us know what helped.
    I don't think the write roller is the main culprit in this case, it can't cause the master to move after it is in place on the drum.
    There is a gold colored screw underneath the shoulder screw that holds the front pressure roller bearing in its place. While I've never done this, I've heard that loosening that screw and tweaking the bracket ever so slightly will adjust the pressure on the front of the roller only, which might help. IF YOU CHOOSE TO DO THIS, IT IS INSANELY IMPORTANT THAT YOU SCRIBE THE POSITION OF THE SCREW IN ITS BRACKET BEFORE YOU LOOSEN IT! That way, if this doesn't work you can return everything to the default position.


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