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Winner Pm Research Engine #7

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tomw

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Jan 24, 2015
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Dear All,

I have decided to post a build log of my attempt at making this engine:
STEAM-ENGINE-7.jpg

from PMRs casting kit. I chose this engine because it is really two engines that have been joined together, giving me twice the opportunity to learn how to do things.

Also influencing my decision is the build log by this fellow: deansphotographica.com. He built his PM #7 engine using Taig equipment with some custom attachments. I am going to be using Sherline equipment (a 4400 lathe and a 5400 mill). I also have a rotary table. Thus, some of the operations will differ from his build. However, the order that I complete tasks will be largely the same as the order he used.

I started this project on August 24th, 2015. Therefore, the first few posts will be catching up to where I am now.

I am very new to machining, having bought my lathe in January, and my mill in March, of this year. Therefore, I am looking forward to hearing peoples comments on my techniques and strategies. Any and all constructive criticisms are highly welcome.

Thank you for following along.

Cheers,

Tom

STEAM-ENGINE-7.jpg
 
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First off, Tom, welcome to the world of hobby machining and model steam engineering. I think that you will find your newfound hobby to be very enjoyable. I for one will be following along on your build as miniature steam engines are one of my favorite subjects.
 
The first part I did was the base. Here is the drawing for the base, and the casting as received.
PM #7 base drawing.jpg

PM #7 base raw casting.jpg


First I took some preliminary measurements to see if any part of the casting was clearly faulty. I was quite pleased with its squareness and uniformity. I decided then to sand the bottom of the base flat, giving me my first reference surface. I did the sanding on my surface plate with 320 grit Aox paper and WD40 as a sanding fluid. I used the figure eight technique, and also rotated the base 90° every 20 or so circuits. I let gravity be the arbiter of how much pressure was applied. This took me about 45 minutes, but I got a bottom surface that was flat with about 90% contact.
Sanding bottom of casting flat.jpg

I then mounted my "big" angle plate to mill table and indicated it to normal of the X travel. I then clamped the base to angle plate and shimmed it so that the short edge marked x above was parallel to the mill table.
Setting up angle plate on Sherline mill.jpg

Facing outermost  drive shaft journal boss.jpg

I then used my 1/2" end mill to face the drive shaft journal boss. I aligned the mill to the boss by eye, such that it would not leave any crust on the "top" (see photo above). The base was then rotated 180°, and the other boss was surfaced.

The center of the drive shaft is the main reference point for determining most of the other features on the base. Thus, I locked my X and Y at this point, as the center of that boss is going to be the center of drive shaft journal. The entire distance from the outside of the right most journal boss to the outside of the left most boss is over 4". To drill the shaft journal and have it be fairly straight is a challenge. I used the approach as outlined by Dean here. Basically, I would center drill the boss, drill it 3/16" through, then put back in the center drill and center drill the next boss in line, followed by another 3/16" drill through, etc. The trick for the further away bosses was to use extra long bits. Unfortunately, I took very few photos of this process. Fortunately, Dean has plenty.

Center drilling first boss.jpg

Drilling 3-16 " in first boss.jpg

Center drilling into second boss.jpg

Using 6" long center drill to drill 3rd boss.jpg


I decided at that point to make a custom fixture/jig for the base that I could mount to my Sherline angle plate (with handy T slots). This is just a piece of aluminum plate that was made square and flat. Of course, making a piece that big square and flat in a Sherline mill took me most of an afternoon! I fit up the base to the plate so I could machine the cylinder mounting bosses. Here, I used shims to get the drive shaft (which I put through my newly drilled journal bosses) level to the table. I did this on my surface plate with a height gauge and some brass shim stock. Once everything was set, I clamped the base to plate. As long as I used the same set of shims, and placed the base in the same place, I could take the base off the plate and subsequently remount it square. You can see in the photo below the black lines on the fixture, and the shims at the bottom right corner of the base, for alignment.

Clamping base to custom fixture-jig.jpg


I then took a skim cut of the cylinder mounting bosses to make them flat.

Taking a few skim cuts on cylinder mounts.jpg


After that, I removed the base back to the surface plate, and using my height gauge I marked the vertical position of the cylinder mount through-holes. Using a steel rule, I then found the center of this line on each boss and center punched it. The base was then remounted to the angle plate on the mill. I then used my long center drill bit and a .010 feeler gauge to find the center of the drive shaft and set my Y axis to zero on my DRO. Basically, I brought the center bit towards the shaft until I could just feel resistance as I moved the feeler gauge. The amount of resistance is about what I would use when setting points on a distributor (for any young-uns wondering what are points and distributors, ask an old guy). I then subtracted .010 and half the diameter of the drill bit to find the center of the shaft.

I did this complicated bit of metrology because I could not get my edge finder even close to the shaft.

Finding center height of drive shaft.jpg

Marking drive shaft center on cylinder mount bosses.jpg

Finding drive shaft datum.jpg

I apologize for the fuzzy image. And for all future fuzzy images. A drawback of using an iPhone camera and not focusing.

Once the shaft center was found, I used a wiggler to find my center punch marks on my the cylinder bosses. Using a center drill and then a 1/64 under bit, I drilled out the cylinder mount through holes. The entire rig was then flipped around, and the holes were reamed to size. I had to flip it around, otherwise I did not have the vertical clearance on my mill for the reamer.

Center drilling cylinder mount boss.jpg

Drilling cylinder mount hole 1-64" undersize.jpg

Reaming cylinder mount holes to size.jpg


Until next time:

The base so far.jpg


Thank you for following along.

Regards,

Tom
 
Terry, thank you for the welcome. I am definitely enjoying myself.
 
Upon re-reading my previous post, I forgot to mention that once the drive shaft bosses were drilled 3/16", I used a 3/16" drill rod to check that the drilling operation resulted in a straight bore. I then went back, and with a 15/64" long drill, through drilled the bosses. I then reamed the bosses 1/4". Again, this is the same approach as taken by Dean of Idaho.

Unfortunately, at the time I was not thinking about making a photo log of this build. Thus I don't have photos of the final drilling and reaming operations.
 
Hi Tom,
Nice work and careful planning, I like your Jig It will help a lot as you go along.
Thanks for taking the time posting your project. .you have me hooked.
Brian..
 
In this post, I go through finishing most of the machining on the base casting. The first task was to remount the base flat on the mill table and use an indicator to get the drive shaft parallel to the table (x-axis). I did not need a jig here, as it mounts easily with some strap clamps directly to the table.

The first thing I wanted to do was finish machining the cylinder mounts. The thickness of the cylinder mounts is determined by the distance from the face of the mounts to the horizontal center of the crankshaft (drive shaft). Thus, I found the center of the crankshaft using an edge finder and set the Y axis on the DRO to zero.

Finding the center of the drive shaft.jpg

Finding the horizontal center of the crankshaft.

I then put in my trusty 1/2" end mill and cranked forward on the Y axis 3.25"+.25" and made note of the DRO reading. I then cranked a little further and touched off on the face of the cylinder mount. I need to take about 60 thou off. I did this in 20 thou passes, using a spindle speed of around 400 rpm. Deeper cuts produced unsatisfactory vibration, a drawback of such a small mill. The last pass I made was 5 thou, at 700ish rpm and a very slow feed to get a nice finish.

Milling the face of the cylinder mounts to final size.jpg

Milling the face of the cylinder mount with a 1/2" end mill.

Cylinder mounts milled to final size.jpg

The faces are completed

Mmmm, smooth.

Now it was time to mill the crosshead ways. The reference data for the crossheads are the vertical centerline of the crankshaft and the horizontal centerline of the cylinder head mount through-holes. To find the vertical centerline of the crankshaft, I brought my end mill toward the top of the crankshaft as I moved a small bit of paper back and forth underneath it. When the paper was grabbed by end mill, I knew the end mill was .003 above the shaft (the paper is .003 thick). I could then crank down the z-axis .128 and set my Z axis DRO to zero.

To find the horizontal center of the through-holes, I placed the shaft one of my end mills into the through-hole (which are 3/8 dia). The fit of the end mill shaft was very tight in the hole. I then used my edge finder and a little arithmetic and voila, the center was found.
miracle_cartoon.jpg
Obviously, I had to repeat the above to find the horizontal datum for each cylinder mount. One center was used as the X axis 0 on my DRO, the other center I recorded carefully on a torn piece of oily paper which I frequently placed under my stool (the kind you sit on, not the kind you give as a sample to your doctor when you have giardia).

Finding the center of the cylinder mount hole.jpg

Finding the horizontal center of the cylinder mount. That is a 3/8" shank end mill in the hole.

Before proceeding with milling the crosshead ways, I decided to clean up the oiling points on the top of the crankshaft journal bosses. I positioned the cutter horizontally by eye. The final height was determined by the first boss I milled. These were just careful plunge cuts.

Cleaning up the oil cup mount points.jpg

A very clear shot of some strap clamps.

The rest is pretty basic milling. The important bit for me was keeping track of where I was in three dimensions relative to my reference points. You may notice that I milled the outer edge of crosshead rails. This is not what is called for, but I think it makes a neater appearance. If I was a tiny foreman running a tiny factory, I would have wanted it done this way.

Milling the top of the crosshead way rails.jpg

Smoothing the tops of the crosshead guide rails. I am using a 1/4" end mill.

Milling the crosshead ways.jpg

Milling the crosshead ways to the correct width and depth using a 1/4" end mill.

I then drilled the mounting holes for the crosshead caps and the oil cups on the crankshaft journals. The placement of the holes for the caps is relative to the centerline of the cylinders and the machined face of the cylinder mounts. The oil cup hole placements were determined by eye in the x axis and on the horizontal center of the crankshaft. I then tapped all the holes. The oil cup holes were tapped 2-56, and the crosshead cap holes tapped 5-40, per the drawing.

More crosshead way milling.jpg

Center drilling the mounting holes.

Tapping 2-56 for oil cups.jpg

Tapping the oil cup holes for 2-56 threads. I am using my tapping rig*, a very handy piece of equipment.

Crosshead rail mountings are tapped.jpg

Crosshead cap holes are tapped for 5-40 threads. I think those are pretty darn smooth crosshead ways.

So, after all that, I ended up with a base that was largely machined except for the holes needed to actually mount the cylinders. As I figured out later, I should have done these now. Dean of Idaho did them later, but I think that is because he does not have a DRO, which makes finding the hole positions on a bolt circle pretty easy.

Until next time:
Crosshead ways are done.jpg

Cheers,

Tom

*I have no financial interest in this company. Just a happy camper.
 
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congrats on getting started, I also am doing the same PM#7 with a Sherline 5400 Mill and 4400 lathe. Question, How did you do the crank or do you have the extended axis on your mill as my stock one is not tall enough to set the thing on it's side and get a drill through it. I'm looking at mounting it on the lath so that I can drill through all 4 post. Second where did you get the long center drill and long bit from.
I have not taken any pictures yet. Keep forgetting phone and don't have a camera. but have less of the main casting done than you do. So I will be watching what you do.
 
Ken,

I did get the extended column. It really makes a difference in what you can do with the machine. If you are heading to Austin anytime soon you are welcome to use my mill to do the crank bores. I think that is the only machining steps you really need the extended column for. Of course, it is pretty handy for other steps as well.

I got the long center and twist drill bits from McMaster Carr. The center drill is part number 2915A35 and the twist drills were part numbers 2986A21 and 2986A24.

It has been a fun build so far.

Cheers,

Tom
 
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