Omas: Repair Of Sheared Piston Guiding Finger

[fountainbel]

Hi all,

 

Today I've repaired an Omas Moma on which the piston anti rotation guiding finger (one piece with the barrel ?) was completely sheared off.

Result being the piston simply rotated when turning the filling knob

At first I expected the guiding finger was part of a ring glued or press fitted in the barrel.

Whatever I tried - heat or US cleaning - I could not move the ring, so it looks it is one part with the injection mould barrel.

Anybody who has the same or a different point of view/experience?

At first I tought in drilling a transversal hole trough the barrel( in the middle of the ring) and installing a HR pin.

However the guiding groove in the threaded piston spindle is rather undeep, and the thread grooves are wideand deeper as the guiding groove , meaning I should mount a 4mm pin with 2 flats, overlapping the threads.

I did not like this approach, drilling trough the barrel wall did not really appeal to me.

Finally I came to the idea fof drilling the existing ring out ( 0.3mm smaller as the piston bore) and install a new delrin ring with a directly integrated guiding key.

So I made me a reaming broach (or reaming needle) to make the bore & the key in one pressing operation.

The ring fits with 0.07mm pretension in its barrel seat

This worked perfectly, the piston now travels smooth & well guided in the barrel.

Francis

 

http://i62.photobuck...bel/Omas003.jpg

Attached a Photobucket link showing the ring on the piston rod & the reaming broach.

Edited June 8, 2010 by fountainbel

[fountainbel]

Hi all,

Just repaired the 4th Omas which was sick in the same bed.

Looks this clearly is a design flow, the piston rod anti-rotation finger in the barrel was again completely worn off .

Francis

[lowks]

I have exactly the same issue. My piston travels up and down now and it cannot suck up ink