Trevithick Dredger Engine Guide Bars

by John

I was discussing the guide bars with a very experienced modeller, and he finished with some advice….  “make them either very accurately, or very sloppy, otherwise you will have problems!”

The guide bars and cross-head

Well, I decided to shoot for “very accurately”.

I made the cross-head bar, and silver soldered it together.

All seemed good.  Just the guide bar bushes to be made and Loctited into position.  After a soak in sulphuric acid and tidy up.

So I made the bronze bushes, drilled them in the lathe to 9.5mm, then reamed them to 10mm.  Or so I thought.

But when I fitted them to the 10mm guide rails, they were very, very sloppy.   Checked the guide rail diameter… 9.99mm.  Checked the reamer 10.07mm!!  Chinese reamer.

So I searched my reamers and found 2 more.  Another Chinese one measured 10.04mm.  Another was a Sutton, made in Australia.  It measured 10.00mm.  I reamed a test piece, which fitted the guide posts perfectly.   So which reamer did I use?   Guess.

I made some more bushes and Loctited them to the cross-head.  Then drilled and reamed them, carefully, accurately.  This time the fit on the guide bars was snug, perfect.

Is there a point to be made here?  You better believe it.