Monotype Pneumatics: Paper Tower air supply

Just for a lark, I tried connecting my Monotype caster to a compressed air supply, and found that the air connection to the paper tower leaked so badly that the (admittedly small) compressor could not keep up. I tried putting a little grease on the connection but that did not help much.

ConnectedThe air supply rises from below the caster table to the top of the paper tower in the tube to the left of the photo and enters into the connector, which is installed over the pivot shaft for the paper clamp. It is held on by a nut and washer which clamp it against a spacer collar. The shaft is hollow with a radial hole (facing away from the camera) to allow the air to pass from the connector through the shaft to the paper clamp. The nut can’t be tight against the connector because the shaft must pivot a bit as the paper clamp moves up and down for each cycle of the caster. I have to wonder what prevents the nut from working itself loose from this movement. I think the nut actually tightens against the end of the shaft (not the connector) and so the nut ans washer are locked to the shaft and rotate with it.

I suspect that the leakage is due to a subtle bend in the riser pipe skewing the connector a bit. Flexing the pipe causes the leakage to change dramatically.

DisconnectedI took the joint apart and found that the spacing collar does not appear (to me, anyway) to be long enough, causing the connector to tighten against the shoulder of the shaft instead. The lengthwise position of the shaft is determined by a groove that the pinch screw of the paper clamp (upper right in the photos) passes through so I can’t just move the shaft in a tiny bit.

I will be doing some careful measuring to try to determine what surfaces should be providing the air seal here. It may, for instance, be that the inside of the connector should be a closer fit to the shaft to provide a seal. It might be possible to find a pair of O-rings to fit the recess in either end of the connector, or perhaps a pair of thin flat resilient washers will do the trick.

This recess on either side of the connector might be able to hold an O-ring.

This recess on either side of the connector might be able to hold an O-ring.

In any case, despite the leakage, I managed to apply some air to the system. I found that many of the airpins were stuck, and even when unstuck some still failed to rise. Several years ago, when I first started work on the caster, I had used an inflating needle to inject air directly into each hole in the table where the paper tower mounts, and the pins worked well then. This makes me wonder if the pipes in the paper tower are plugged with dust. The interior of the tower certainly had plenty of oily dust in it!

Posted in Equipment Acquisition, Repair, and Maintenance, Kevin, Monotype Composition Caster
5 comments on “Monotype Pneumatics: Paper Tower air supply
  1. Antonio says:

    Hi! There is a rubber ring at the right in the second picture. You could see in that pic the place to locate it.

  2. Antonio says:

    Sorry, a rubber ring should be there.

  3. kpmartin says:

    Antonio,
    The rubber rings you refer to might be the parts 6G2 “Connection Washer” which are listed but not illustrated in the Monotype Corp. Spare Parts List Plate 23. It states that there are three of them, but without seeing what they look like it is not clear where the third one goes. These are not mentioned at all in the 1955 Lanston Plate Book.

    Do you know if these are O-rings (with a circular cross section) or flat washers?

  4. Christophe Slychan says:

    I solve the problem with some instant gasket on the tower’s side, and some rubber on the nut side: https://www.flickr.com/photos/elegantandrogyne/25331060243/in/album-72157653482323328/
    But this may not be viable if the joint moves a lot (i.e. you use the traditional ribbon rather than electronic control attachment).

  5. kpmartin says:

    I don’t remember now why I didn’t just find correct O-rings to fit the recess in the stock connector. Instead I made a new connector fitted with O-rings as shown here.

    I’m still mystified by the parts book which states there are three connector washers here (all the same). I could imagine a washer being placed on the shaft before the spacer, but such a washer would need a larger hole that the other two.

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