Muncaster Grasshopper - Work in Progress

[kvom]

After a lot of time standing at the lathe, I completed all 8 stays.  Here are the 6 nearest the cylinder in their approximate positions.



Because the vertical stays are relatively unrigid, they must be braced by the diagonal fixed stays, and for this to happen the brackets at the bottom must be screwed to the tops of the rails.  The brackets must be positioned so that the bottom cross shaft is orthogonal to the long axis of the engine, and hence force the top cross shaft to be as well.  Then the middle stays that attach to the beam will be able to swing smoothly as the beam moves.

This setup allowed me to determine the position of the brackets resulting in a rigid structure.  I used a transfer punch to mark one of the four holes needed to attach the brackets.  Then it was off to the Bridgeport with the stays removed but the rest of the assembly still in the small vise.  This allowed me to locate the punch mark for the first hole and then to locate the others to ensure that the holes on each side form a rectangle.  I spot drilled these points, and then removed the beams to drill and tap 5-40. 



When reassembled we have this.



To further address alignment I need to turn my attention to the crank and conrod, plus finishing the piston rod end.  Then the beam itself can be assembled and mounted.

[crueby]

Complex set of bits to get all right, very nice!


 

[b.lindsey]

Tedious work but a beautiful result Kirk. And the pictures, as always, are excellent too.

Bill

[Dave Otto]

They look very nice Kirk!

Dave

[Craig DeShong]

Still following along Kirk, this project is really starting to shape up!   

[kvom]

Very cranky today so to speak.  Attacked the crank today starting with some ground low-carbon steel bar 1.5x.5x2.5".  Fairly vanilla CNC ops all using one 1/4" carbide endmill do do both profiles and holes.  Larger hole is .626" to fit the crankshaft, and smaller is 5/16", the closest to the 8mm in the drawing.  Finishing the outer profile required making some soft jaws around the two bosses.

[kvom]

Fitting the conrod to the crank so that it's centered on the long axis requires a spacer on the crank pin that is to be determined when the time comes.  And since I don't have a flywheel yet the diameter of the crankshaft through the flywheel is unknown.  For these reasons I have a temporary crankshaft and crank pin.  To fix the crank on the crankshaft is a temporary set screw that will be replaced by a pin in the final assembly.  The crank pin is a length of 5/32" drill rod that is close to the 8mm specified by Julius.



As drawn in V1, the crank pin and end of the conrod could not actually be built.  Solidworks makes it easy to move one piece of material through another, but physics is not cooperating.  So I have designed a simple rod end that will be used on both ends of the conrod and on the end of the piston rod.  The first stage in making these is cutting 3 sets of profiles from a single piece of 1.5x.5x4.6" steel bar.



They will be 10mm thick, and with 12mm bearings installed will clear the 14mm separation of the two halves of the beam.  I machined the profiles 11mm deep to accommodate later machining once the halves are joined.  Next the parts are cut free on the bandsaw.



And then the remaining waste stock us milled on the manual mill.

[kvom]

Continuing with the rod ends, I set the vise stop and DRO in order to do all of the drilling and tapping to connect the halves of each of the three pairs.  Just had to remember to keep the ground side against the fixed jaw.



After a bit of work, I had these:



Then drilled and reamed the conjoined pairs .499".



Then I could clamp each firmly onto a piece of 1/2" brass rod and face turn to bring the thickness to 10mm.



Then I made the first two bearings from some .77" 660 bronze rod.  I'll finish the third bearing next time out and start to think about the conrod,

[kvom]

Short work session today.  First off was to "fabricate" a temporary conrod that I'll use to verify the length and spacing before making the real thing.  The temporary rod is just some 1/4-20 threaded rod onto which 2 rod ends are screwed.  The plans call for a 205mm spacing between the bearing centers, and the rod I started with was a good deal longer.  So with the following "set up":



I positioned the 5/16 drill bit over one end until it could enter the bearing, zeroed the DRO, and moved to the other end to do the same.  The DRO reading:



So I needed to part off 81mm from the rod.  After doing so and repeating the measurement:



The rest of the afternoon was machining 3 spacers from 1/4" drill rod, each 14mm long and tapped 5-40 in both ends.  This job was a bit more tedious than it might have been as these are for spacing the two halves of the beam, and I wanted them to be as close to 14mm as I could.



As you can see, I'll need some more small screws from AME for this part.

[kvom]

Proceeding further with the beam, I need to attach it at 5 separate points:  piston rod, conrod,  middle stays, end stays, and the pump.  Each of these has 1/4" holes drilled through both sides of the beam.  To make the connections, I decided to use 5/16" rod cut in 14mm lengths for the center section, each drilled and reamed .251".  Through these will be passed 1/4" rod.
 Doing it this way makes it easier to hold the center section length more precisely, and is much easier than turning each connection from a single piece of drill rod.  Once the lengths of the 1/4" rod are fixed, the two pieces will be loctited. Note that the 5/16" diameter matches that of the rod end bearings, which were reamed .001" over.



After taking the previous picture and verifying that turning the crank resulted in motion that looked pretty good (i.e., the holes for the piston rod end seemed to move straight up and down, I decided to prolong the shop session by cutting the piston rod to length and threading the end.  After attaching the rod end to the rod and the beam, I was pleased to see that turning the crank caused the piston to move up and down in the cylinder without too much effort (little sticky at the top), and that the piston travel was nearly perfect (the edge in each direction barely touch the bottom of the steam ports.  Given that the temporary conrod isn't precisely straight, I'm encouraged  by the motion.

[crueby]

Nice!   

[zeeprogrammer]

Wow! Not sure how I miss some posts but I sure missed the last few.

Looks great! 

[Craig DeShong]

Yowza !   

[Jasonb]

Coming together well. Probably best to check for tightness with the top cylinder cover in place as without it as in the photo the piston rod can lean sideways if the linkage lengths are out.

[kvom]

I remade both the piston rod and the the conrod using thread milling to ensure straight threads.  Upon reassembly the middle stays no longer match up with their connections to the beam.   

I need to remeasure everything to see what might have happened.  Length of piston rod won't matter, so length of conrod is a suspect.