User login

Fine Tuning for Fine Details

(December 2012) posted on Tue Dec 18, 2012

Use these pointers to start making the adjustments needed to produce high-quality work.


click an image below to view slideshow

Clamshells Many clamshells have little or no provision for adjusting alignment of the press head. The only option here is to shim the pad or support, or to loosen the bolts connecting the carriage rails to the rear drive housing and use what little slack there is to make a change. Neither is ideal. Ensure that both rails are equally spaced from the body of the press, in the front and rear, and adjust the press table using the leveling screws from underneath.

Some clamshells have adjustable front-head supports. Threaded locators with conical ends on the head nest into a cone-shaped bushing on the frame. These hold the front register of the head to the frame steady during the print, but they can also be used to truing the rail housings to the frame, front to back. You can then make fine adjustments to the table. Also check your table for flatness and, if possible, adjust for that, too. if you have a good straight-edge available that is long enough, place it diagonally across the table to assess flatness in both directions. Also use the edge to check for flatness from side to side and front to back. Check for bow and for high and low spots across the face.

Four-post These flatbed presses are slightly different from clamshells, but in some regards, they can be simpler to adjust. First, check the table for flatness and verify that it is in good condition. Reciprocating tables have little provision for leveling that can take care of deformation. Check the rails on which the table rides for straightness. You can set a long, straight stick or rod across the rails at each end and sight them for parallel, or you can watch the table bearings as the table moves to see whether they stay in contact with the guide rails along the entire area of travel. At the very least, ensure that the bearings are solidly in contact when the table is in-board in the printing position.

Measure the amount of misalignment by using the squeegee to check distance to the table at the ends of the stroke. Once you know the required adjustment, remove the press’s side covers to see that it is in the down, or printing, position. Once you’ve confirmed that the press’s power is off, examine the posts that lift the head. In typical designs, the lift chains attach to the bottom of the posts with threaded connectors. These can be used to adjust the position of the head at each corner.

If a threaded connector has been used all the way to the end, connected to a chain, and you need to adjust further in that direction, then you likely have a case of chain stretch. Removal of a link may be required. If so, contact the press manufacturer for special instructions. Otherwise, loosen the locking nuts and adjust the connector to bring the head into parallel with the table.


Terms:

Did you enjoy this article? Click here to subscribe to the magazine.