[Misc] GR3770 print area and synch

[Guest]

Hello!
I'm back here for a question about the synchronisation of the printing with a riso gr3770. I understand that:
1) the paper feed synch should be set with the disk on the right on the picture (with the little notch aligned just above the sensor)
2) the printing timing should be set with the disk on the left (with the hole aligned with the sensor)

01.jpg

To move those disks, I managed to loosen the paper feed clutch and disengage the belt, I set the disk on the right like in the picture above, so when I fasten the paper feed clutch, it goes down a little and get the proper alignment.
BUT no matter where I set the disk on the left, it always get back to its initial position after one print like in the picture below:
02.jpg

Result: the printing stops too early... It should print until the red line in the picture (this is the end of the sheet)...
limit.jpg

Any suggestion would be very appreciated!!

[Iowatech]

Re: GR3770 print area and synch

On a GR3770, the notch on the right hand disk should align with the lower corner of the sensor. The notch only aligns with the upper corner of the sensor on the GR1700 and its ilk.
To adjust the disk, you need to loosen it with a 2mm hex key (allen wrench). Moving the entire cam with respect to the timing belt will cause timing problems. Probably like what you are experiencing now. Undo what you did and then adjust the disk only.

[psykolio]

Re: GR3770 print area and synch

Hello Iowatech and thank you for your reply!
The best setting I can do is like this:
01.jpg

I've moved the cam on the right without moving the timing belt. The upper margin of the printing area is correct.
I've changed the position of the disk on the left, only with an allen wrench (without moving the cam).

02.jpg

I still have the same problem: it's like the pressure begins and stops too early! Looks like moving the disk on the left doesn't change anything at all...
And on the master:
03.jpg

I don't know what to do. The timing of the pressure mechanism should change when I rotate the left disk, am I correct? I've tried to do it only with an allen wrench, no result. I've tried to disengage the timing belt and rotate the entire cam to align the holes correctly, no result neither...

[Iowatech]

Re: GR3770 print area and synch

The end of the pressure roller engagement is determined by the pressure solenoid releasing the pressure lever, you might try checking the pressure lever position and the solenoid adjustments. If the pressure lever is worn where the solenoid's hook engages it, that could affect that, too.
There is enough pressure between the solenoid's hook and the pressure lever during printing that I don't think adjusting the left hand disk will have any effect on the end of the pressure cycle.
Oh, also, thanks for the pictures, they help a lot. The right hand disk is just a little bit out of adjustment, it should be a little bit more counterclockwise.

[psykolio]

Re: GR3770 print area and synch

Thank you Iowatech! Unfortunately, the problem is still here... I checked the solenoid adjustments (the space between the hook and the solenoid should be 0.5mm according to the manual):
01.jpg

and the pressure lever position:
02.jpg

Is it the proper setting?

[Iowatech]

Re: GR3770 print area and synch

The adjustments in the two pictures look correct. The adjustment in the first picture appears to be perfect. I never used the two lines on the pressure hook as the older Risos didn't have them but the spec was the same, still I think the one on the second picture is OK.
Are there any other drums for the machine other than the red one? If not, or if printing from the other drums doesn't show that problem, there is a mylar ink blocker between the screen and drum body that could be out of position and interfering with ink flow through the trail edge of the master. If there is no ink on the screen where the trail edge of the image on the master is, you might check that.
On average, do you make at least 20 prints per master? I have to ask as doing less than that can cause ink starvation in the drum, which can cause problems like this. Sorry I didn't think of that earlier.