PM Research #3

[55fairlane]

So my wonderful wife & child got me this PMR #3 as an early Christmas present (I have time off at Christmas & need something to keep occupied)
So with no idea where to start, I hit youtube and found a few people building these engines. As I watched, I was stuck with "omg do any of these people have any idea what there doing?" No one is working off a master reference (dimensionbroughtoff all 4 cornersand in some cases guessed at), nothing is true/flat & square, grabbing the parts 4 different ways in a vise, not having any idea if any of the references are going to be correct. So many incorrect clearance, you must run the engine with an electric drill..........my head was left spinning........after lots of thought, I grabbed the drawings, the castings, my calipers and started creating fixtures......let's see that I have gotten done so far,

Here is the casting kit

 

[55fairlane]

Ok let's start with a simple fixture, the connecting rod....the one was simple, a "channel" with a deaper channel on both ends.....only problem, the pattern maker left "divets" in the rod, and they were not close to being on a common center line , nor the center to center distance shown on the drawing, but I did fix that, this part also seemed to be an easy first part .....

 

[55fairlane]

Next on list was make the big end bearing, I used the drawing as a suggestion & made the bearing .005 longer then the rod is wide, then I reamed the bearing to .126, then I made up a one off crank pin , I made it with 4-40 thread (I am ditching all those ugly 5-40 screws)

 

[GreenTwin]

There is a bit of an art to building/assembling model engines, and another art to machining castings.
The only way to learn it is to jump in and do it.
I have had to redo some parts, but eventually one gets a feel for it, and gains the confidence to get it done.
Nice kit there, and jigs, and nice machining work !

.

 

[55fairlane]

Next up is was the crank, I deviated from the suggestion at this point, PM says to ream a hole fir a press fit, and drill/tap for a set screw, ....... I grabbed a chunk of 1 inch low carbon steal.......drilled a ½ hole, chamfered (to clear radius on crank) tapped a #6 -32 .....for a clamp....... dropped the crank in, reamed it to .251, offset & drilled & tapped a 4-40. Next I pulled the part, degreased it, found a piece of ¼ drill rod, tossed the CRS shaft that came with the kit...green Loc-tite the shaft in place, no set screw, no press fit....face the part in the lathe (by holding on the shaft things must run true)

 

[55fairlane]

At this point I figured out my made in the USA GMT vise was several thou outa square.....so as I wait for a warranty vise to show up, I was down to using my 2 inch screwless vise....

 

[55fairlane]

Cross head guides are next.....lots going on here, I started by reaming the parts for pins, assembled the 2 halfs, witnessed the halfs, and from now on the fixture was machined as 1 unit, pinned together. The back of the B half has a 2.007 slot on it, so the fixture locates identical in the vise, the fixture was slotted with a business card between the halfs to give the fixture some crush.
The bottom(s) was cut flat first, the turned over and drilled

 

[55fairlane]

The replacement vise is now on the mill and it's time to tackle the cylinder. The fixture is pinned together & tapped for screws, there is a central slot for the steam chest to register on, the fixture is the same over all height as the finished cylinder, so finding the finished height & keeping concentric is easy, once I finished one face, I will bore the cylinder, bore the spool valve, drill the bolt pattern, turn the fixture and drill/tap the steam chest, turn again finish the cylinder, drill/tap the bolt pattern......then set on the sine bar and drill the steam passages...

..all done in a fixture, easy to pick up master reference surface, should come out perfect