PM Research #3

Last year on Black Friday I bought this kit from PMR on sale, I just started on it last week and my goal is to have it finished before the next Black Friday sale comes around haha! Forgive me for starting a build thread on what is a very trivial engine for most of you.

So far the biggest challenge has been setups, my mill is rather small and restrictive, but I have been enjoying the strange setups as well. I had spent close to an hour trying to get a setup that allowed me to make the first cut on the bottom of the base before moving to the lathe. The setup seen below actually worked very well, with no wobble after the cuts were made. I also threw a dial indicator on some of the casting surfaces and was surprised that it wound up within a couple thou across the length of the casting; I expected to need some shims since I had the unmachined cross head guides as the reference surface.

The second operation of spot facing and drilling holes for the mounting holes was also easier on the lathe. A single bolt holding the casting to a 123 block clamped in the milling attachment was enough for this.

Then it was onto the cylinder mounting face. This time I didn’t have too much trouble setting it up on the mill. I did however have a hard time figuring out how to fit the tools in there. The mill has a B&S#9 taper, so I have limited collets as they are expensive. I wound up using loctite to hold the drill bit in a piece of drill rod as an adapter to the 3/8 collet.

When it came time for the larger 3/8 hole in the center, the 3/8 drill was too long. A center cutting end mill was short enough to do the job here.

Onto the crank bearings, I made a bonehead mistake and caused the 1/4” holes for the crank to come out oversize. My solution was to make them even more oversized and put a bushing in. The crank casting was a quick set of operations on the lathe.

Not a trivial engine at all. The PM Research sets make into very nice engines. Their plans are pretty good and accurate too. Looks like you are off to a good start. I will be following along. I’ve built 2 PMR’s and enjoyed both builds.

Quote from: Rledoux313Forgive me for starting a build thread on what is a very trivial engine for most of you.

I agree with Propforward, no build is trivial and you've already had to overcome a couple of challenges and successfully corrected an error.....well done! 

I built my 1st PMR engine last year, it was the no.5 and was a really nice kit with quality materials (see below) I'll be following along for sure, keep posting pics, they're great to see 

Over on HMEM  and I believe here, I did a build log showing how I fixtured everything,  including details on the fixtures.  Thus is a fun one build

Prop and Sanjay, thank you for the kind words

55, thanks for the heads up. I will look up your threads

I got a little shop time in today. I started out by creating a nice radius where the mounting flanges meet up with the main portion of the base. When I machined them originally, I left a corner. I wasn’t quite happy with the way they looked so I put it back on the mill and I think the result is much better.

I also got started on the cross head guide. I found the best way to hold it was by mounting it to a plate, which was then bolted to a 123 block held in the milling attachment. I only had brass 2-56 screws, so very light cuts were made. Looking at the photos I realize I could have put a clamp on the left side of the base. I did not have time to get all of the cuts made, so I will throw a clamp on there tomorrow before I make the last of the cuts.

I would really like to get a T slot style cross slide from MLA. Each time I have a setup that sticks out this far I am reminded of that desire.

I'll be watching...

Today I finished up the base. The drawings showed spot faces for the cross head guide bar spacers. I milled them off square, I’m not really sure why. I think it looks ok, but the spot faces may have looked better. I was about to start on the flywheel, but after getting it setup I had a think. Do the direction of the curved spokes matter? Was one direction stronger than the other? Was it just for looks? The side away from the chuck is where I am indicating, and where all of the reference cuts will be made, so it will likely appear to run truer and I would like to orient it so it looks concentric, with the spokes going the correct direction.

I'm not sure that the direction matters, but someone more qualified may be able to assist.

I asked the question about why curved or 's' shaped spokes before and was told it was to avoid failure whilst the metal cooled and contracted after casting; i.e. the shape would allow for some 'give' as opposed to straight spokes - again one of the casting experts they can give a fuller answer and how this situation was ultimately overcome?? 

i read the curve in the spokes was to do with rpm regulation.

I did a little research, and it I am certainly not the first to ask this on a forum. It seems somewhat debated, but appears that the reason you have about metal cooling during casting is the most agreed upon. I then wondered if it matters which way it runs, based on photos and forums having the spokes in a manner that would put the spokes in compression appears to be favored. So that’s what I’ll go for on this model.

The flywheel cleaned up nicely, and runs pretty true by eye.

Today I got the crosshead guides and spacers made. The guides are pretty small and with the draft angles hard to hold onto. My solution was to mill a 1/4 slot in two pieces of aluminum that could be clamped together. With the guide held securely, I cleaned up the bosses where the bolts heads go, and drilled the oil hole. The holes for the bosses I tapped 2-56 instead of drilling for the finished clearance size. This allowed me to hold them in the following operation with the finished bosses as a reference surface. I made a couple clearance slots, and some holes in one of the earlier pieces of aluminum to bolt the guides to it, and hold the block in the milling attachment. After cutting the bars down to size, they went back to the clamping arrangement that I started with and drilled out the tapped holes, to the clearance size. A few minutes to whip up the spacers and I have a completed crosshead guide.

More photos

Looking very nice, making good progress 

Rledoux, the PMR#3 was my 1st build & i assure you it was not trivial to me ;-)
I am enjoying your build thread, especially the use of your milling attachment.
I know their drawbacks, i used an Atlas 10-501 adapted to my SB9C for years.
PMR makes great kits, i’m working on their #1 now.
Have fun!

Thanks guys! After a couple weeks of no progress I was able to get a couple hours in the shop today after work.

I made up the connecting rod, which was two holes and another fixture. I reused the aluminum blocks that I have been using for other parts. By the end of this project there will be more holes than aluminum! The photos are pretty self explanatory on that one.

I also started on the cross head. I got a few cuts into the part, before getting greedy and breaking the end mill  If I feel myself trying to rush or just get through a part, I usually hang it up for that session. Which is what I decided to do tonight as I wasn’t really happy with my planned order of operations on the cross head anyway.

Thanks for reading!

Ryan