PM Research #4 Build Log

[abowie]

The main body casting is tricky. It is nearly too big for my mill and completely too big for my lathe.

And it has no easy registration surface to work with.

I used a very large file to smooth off the top rib on the cross slide bore as best as I could. I then set the casting up on the mill bed so that this part was horizontal on the X axis.

Then I tweaked it using aluminium shims under the foot until the foot was as close to horizontal in the Y axis as I could get. I always feel a bit dubious about using the level box, but it is yet to let me down badly. In retrospect, for better accuracy I probably should have used a dial gauge.

Then I machined the upper foot flat and square. Once I had done this I flipped it over and did the other foot using the first as a register. On assembly (see later) I am actually about 20 thou out on the length of the Y axis but the frame sits well on the base and if I want I can drill out the mounting holes in the foot to correct the error.

 

[abowie]

I made a drill extension and drilled the afore mentioned mounting holes.

 

[abowie]

While I was thinking about how to machine the rest of the body, I tackled the cross slide.

Now on the PM1 kit there is a sprue on one of the smaller castings that allows you to mount it in the lathe. You then cut the sprue off when you've finished.

Looking at the combined valve eccentric follower and crosshead casting in this kit, I made a fatal error, and cut off what I thought was a sprue. Unfortunately it was the boss for attaching the valve rod to the eccentric follower. My first mistake, and more later on how I fixed this.

See how nicely that sprue worked?

 

[abowie]

It's really quite a pretty part.

 

[abowie]

I repaired the eccentric follower by drilling the arms and making a new boss. I thought a car main cap design would look appropriate, along with studs and nuts.

 

[abowie]

About this time in the build I found this thread. It was so helpful to be able to read through the ideas and setup for the parts. There aren't a lot of threads on the PM4 /PM6 builds and some of the parts are quite difficult.

I decided to do the valve caps in brass for a little bling, although I did the valve itself in CRS.

For some reason I ended up needing 4 attempts at the valve as I kept getting the OD undersize for some reason that I never did entirely work out.

 

[abowie]

Others have been dubious about the 5 piece crankshaft design, and so was I. Nevertheless I made it to plan.

Everything machined nicely to tolerances, and pressing the main shafts into the flats was fine, but when I pressed the journal into the web discs BOTH of them cracked, and I'm certain I had the press fit tolerances spot on.

More on this later.

 

[abowie]

I read the cautionary tale at the beginning of this post and decided that a steady rest was a necessity for machining the bore. But I have a Workman 6125 lathe and its swing over just isn't big enough to spin the part. Nor will its steady rest fit around the top of the body.

So what do you do when your lathe isn't big enough? Phone a friend!

My brother in law is a diesel mechanic. And he has a HUGE lathe.

Swing over is about 2ft/600mm. The backplate is the size of a manhole cover and weighs about 40kg. I'm 6'1" and 110kg and fairly strong and putting it in place was very difficult.

Here is the frame, dwarfed by the lathe.

After I'd spent some time carefully machining the bore to spec he laughed and pulled open a drawer, which was FULL of adjustable reamers. He had 1" to about 3 1/2" covered. By that stage I didn't need it.

 

[abowie]

Once the frame was machined I was able, by cutting down a drill bit, to JUST drill the holes in the top.

 

[abowie]

Now unfortunately, on to my next, major mistake.

And I apologise that I have no photos.

I came to machine the conrod.

It's a pretty good casting, but there isn't any suitable reference surface that I could find. After a lot of thought I fixed it into a 2" toolmaker's vice, trued it up as best I could and made a light skim cut along one side of the shaft to act as a reference.

I then set out square and concentricity for the face machining and the bores using that skim cut as the reference. This was difficult, and I ended using edge finders etc to try to find the midline.

Unfortunately I was not successful, and have ended up with the crank end being about 35 thou offset sideways from the top end.

It's a pity because both the bores seem to be spot on in terms of parallel and diameter. I have done a trial build, and by trying different orientations of conrod frame and crank I can get it all to go together but it's not good enough to allow me to tighten everything down. If I do it binds.

I have ordered another casting from the ever helpful guys at PMR.

My plan is to machine the shaft between centres this time, as per the video series by GI Customs. That ought to give me a solid centre to work from.

 

[abowie]

I followed Ved's approach to the bearing pillars and caps and machined both raw castings together, then cut them apart. They came out really well.

I wanted to ensure that they ended up perfectly concentric when I bored them.

So I made up a mandrel that fitted the bores with 1 thou clearance and spaced them the correct distance apart on the casting referenced from the drawings.

 

[abowie]

I mounted the base onto my mill bed using two vices.

I referenced the side of the pillar with a gauge to get the bore perfectly vertical. I centred the cutter on the bore using an edge finder in the bore.

Then using a newly purchased 5/8" reamer, I bravely cut the bores.

The resulting surface isn't perfect; there was some chatter that has left very shallow grooves, but it is a really good fit for the crank. I wonder if I had used a straight flute reamer whether the result might have been better.

I have decided that I deliberately made the grooves to aid with oiling...

 

[abowie]

Back to the crankshaft. I did what Ved did, and fused the parts together with TIG.

One positive of this is that with the crank bolted down into the pillar blocks prior to welding it has turned out perfectly true.

Sadly it looks ugly.

So I have bought a big chunk of cast iron, and I plan to make a one piece centre section, then press shafts into it.

I have cut the rough shape on the mill, but I don't have a long enough cutter to do the journal so until that arrives it's sitting in my 4 jaw on the bench, waiting.

 

[abowie]

So this is where I am at present.

I've made most of the rest of the simple parts like the valve linkages, rods , piston and rod etc etc.

I still haven't done the eccentric because my 4 jaw is occupied. But I'm probably 95% done.

To those reading this thanks for your interest, and to Ved and the others of you who have helped with advice and ideas thank you so much.

 

[abowie]

I thought the crank caps would look better with nuts and studs. Several burned and sanded fingertips later..

 

[abowie]

I did a little bit of painting. Clear lacquer for the flywheel. I cut the keyway using the "cutoff tool in the lathe toolholder" technique.

I may yet hand paint the spokes red.

I have used brake caliper paint for the red. It is really good on the raw cast iron.

I sandblasted the castings for my PM1 kit, but just degreased the current ones.

I'm toying with the idea of using silver on the base and maybe the cross slide, although I may blue that and the eccentric +/- the follower.

 

[Eccentric]

Wow, that is a big steam engine. I really enjoy the PM research kits.

 

[abowie]

Yes. It stands 19" high and is a full scale model of a unit you could buy in the 1890's. Presumably to power your butter churn or something.

 

[abowie]

Rather than machine the base in the lathe, I did mine on the mill. There are a couple of pics of it above where I am boring the crank.

I have a set of very old, very large files that I bought at a garage sale.

These are really good for truing up rough castings.

I blued up the underside of the base and then filed it flat until it didn't rock when placed on my mill bed.

Then I clamped it down to the bed and trued it up using the long edge of the cavity in the centre as my X axis. The casting was rough and upsetting my dial gauge so I placed a piece of flat steel along that edge and held it on with magnets so I had a smooth surface.

I decided to clamp it on the rough top casting first to drill the 4 holes that allow it to be mounted to a solid surface.

Then I moved the clamps one at a time so I could mill the top flat and drill and tap the other holes. With a DRO on a mill this is just child's play.

 

[abowie]

I had ordered a couple of big pieces of HSS in order to finish the rod journal on my replacement three piece crankshaft. Because of the amount of stick out needed (about 3") I wanted something as rigid as possible.

The larger of the two, 20x20x180mm arrived on Friday, and it is HUGE! I intended to use it only to rough out the basic journal diameter from the really rough octagon I'd produced on the mill.

I had to machine out one of my quick change holders to 20mm to hold it. It was slow going but I managed to produce a nice round 5/8" diameter.

Now I had to decide how to machine the journal to final diameter. I simply don't have a tool that is long and narrow enough to make the cut while being rigid enough.

I had also ordered a 16mm square piece of HSS but that still hasn't arrived. The crank has been taking up my 4 jaw chuck and I want to get it done and out of there.

So I decided to make up what was essentially a giant parting tool.

I milled up a 20 x 10 x 150mm piece of mild steel as a mount, and cut a 40mm long 10mm slot in one end. I then TIG welded a piece of 10x10mm75mm HSS blank into it, and sharpened the end.

Unfortunately the the 30mm or so sticking out snapped off in short order. So I ground the end of the mild steel to a point so the HSS was sticking out, shaped the HSS to form a cutter, and it performed flawlessly. I was able to get a very nice consistent 0.499" diameter on the journal and got the 0.560" width spot on.

So now I can chuck it up in the 3 jaw, centre drill it for the crank journals and finish it to final dimensions.