Trevithick Dredger Engine. The con rod bearing wedges.

by John

Well, if the comments and likes drop off again, I will threaten to take my bat and ball and shut down again.  10 comments so far on this mornings post (I Give in)!  Thanks everyone.  It is very encouraging.

So here is a Trevithick dredger engine update.

Yesterday and today I have been making and installing the wedges which secure the connecting rod bearings.  The wedges are only 2mm thick, and have a 3 degree taper.  They sit in slots also 2mm wide.

The 4 wedges were fairly simply milled out of 2mm thick brass sheet.  Steel would probably have been preferable, but if the brass wedges ever wear out I will make steel ones then.

The slots were milled manually.  I have some 2mm end mills, and I used them in the accessory high speed spindle at 18,000rpm, taking 0.3mm depth each pass.   Even so I managed to break 2 end mills.

This is the end result.


The wedge is below the 3 square nuts.  It pushes on the split bearing.


And similarly the wedge at the cross head end of the con rod.

The wedges have tightened up the con rod bearings, removing slop and noise.   They look a  bit rough in the magnified photo, but in reality are OK IMO.   Each wedge is individually fitted to its slot, so I have engraved them to identify the position for when they are removed later on.

Next job…. make a fitting to admit compressed air so the steam valve opening and closing timing can be adjusted.