machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most. n.b. There is a list of my first 800 posts in my post of 17 June 2021, titled "800 Posts"

Trevithick Dredger Engine. The con rod bearing wedges.

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.


I had decided to cease my WordPress subscription, and cease writing these blogs, recently, and a few readers have very kindly expressed regret about the impending demise of

The annual WordPress fees increased by 23% a year or two ago, and this year they added a domain name charge which amounted to another 25%.  It adds up to about $aud160 each year, not a fortune, but it would buy a handy supply of end mills.  And the price increases are way in excess of inflation levels, and show no signs of slowing.

But more importantly, I do wonder just how much interest there is in the blog.  Roughly 150 people log in each day, and look at one or two entries each.  The “like” button is pressed maybe once each day.  And a comment is entered about once each day or less.  Not very encouraging.  I do wonder if I am wasting my time and money.

So those are the reasons I had decided to stop.

Then yesterday, a friend who I shall call Les, told me that he was very disappointed that johnsmachines was stopping, and how much he had enjoyed it.  He said that he was always pleased to get the notification of another johnsmachines entry, and reading what was going on in my workshop.

Les is paralysed from the waist down, the result of polio when he was a teenager.  He was a champion athlete when he was struck down with the then dreaded disease.  In those days, vaccination against polio was not widely available.  (If you would enjoy a highly articulate tongue lashing, just make critical comment about vaccination to Les.)  Despite the disability, Les worked full time, and was very active in the workshop, and at our model engineering club.  In fact he was one of the founding members of GSMEE, 30 years ago.   He has an incisive intellect, and when he speaks, it always pays to listen carefully.

So when he made that comment about, I listened, and reflected.

And I have decided to continue for another year.

(thanks also to Huib Hoogendoorn, Tim Gee, Brendan Wallace, daredesign, someone, Peter, Jenny, johnf, Ben, and others, who encouraged me to continue).