Hello folks, in the last episode of the 6CI steam engine project I had just finished the two outer halves of the crankshaft. I am now ready at this point to build the crank pin and join the two halves in unison. The crank pin is made of the same Cold Rolled Steel (CRS) alloy as the crankshaft outer halves which is super easy to machine.
Remember the arbor that I made for turning the crank discs? Well that steel is now needed for the crank pin. I coated the remaining CRS rod with “Dykem” red layout fluid which helps better indicate where scribed lines are on a workpiece. I use the stuff quite often now and I am finding more and more uses for it every day.
Using my calipers as a bit of a scribing tool I layed out the cut lines on the crank pin blank. It was then an easy job to just cut up too the scribed lines with the lathe.
To cut the narrow inside cuts of the crank pin I used a High Speed Steel or HSS “parting” tool. This tool is normally used to make narrow deep cuts into a workpiece, usually to part the piece into smaller lengths. In this case I used the parting tool as a unidirectional cutter to shape the crank pin’s inside surface.
Now that the crank pin had it’s basic shape I decided to “grind” the inside face in preparation for fitting of the connecting rod later (not shown). I used 330 grit sandpaper to clean up the mating surfaces while the piece was still on the lathe.
The next step was to use the parting tool to cut the crank pin away from the rest of the CRS piece.
Ahh, and now the final product :0) I had cut a lead on both ends to help to facilitate the press fit into the crank discs. Hopefully my careful matching of the crank disc holes to the newly cut pin will pay off when pressing the halves onto the pin.
I used a nylon faced hammer to carefully start the press fitting of the crank pin into the two halves (not shown). This is to help align the halves before committing to the full press. I then used a “V block” tool that I had made earlier for one of my other projects to help true up the assembly before pressing. A dial indicator helped show where the discs were off in alignment. You will notice the set of 5/8” ball bearings used to eliminate friction while turning the crank for inspection (below).
Now after some careful tapping of the hammer I was able to get the crank pretty darn true with little runout if any. Of course that may change when I push it all out of shape with 12,000 pounds of force!!!
The crank was positioned into the shop press and carefully eased into it’s final form. It took a lot less pressure to seat the crank pin as it did with the two outer shafts.
After the press I mounted up the crank assembly on the lathe to see how the crank was effected by the force (not shown). I used the nylon hammer to carefully fine tune the crank’s outer shaft opposing the lathe chuck to remove any runout or wobble. I then rechecked the crank on the V block setup to confirm my adjustments.
All in all the crank was pretty darn true, about .003” out on one end of the shaft (runout). I’m sure with a little more tweaking I could have worked out the small wobble but I was nervous to, fearing I would screw the whole thing up if I tried :0P At this point I decided to call the crank finished so I could move on to the next part of the build.
The next step was to machine the base of the engine. This is the largest casting of the kit but requires the least amount of machining. All I had to do was surface the mounting bosses for the crosshead frame and pillow block bearings. Once the surfaces have been “decked” or milled I can lay out the mounting holes and then drill and tap them to complete the job.
First I used a Dremel tool to clean up the outer edge of the casting for a more “finished” look. You can see the rough edges of the casting below.
As with all parts that will be machined from a casting you will need a reference or starting point on the casting that will not change throughout the phases of machining. This is important as all of the dimensions that you will need for future machining operations will be taken from this point or plane (in most cases). Sometimes the prints will indicate the starting point at which you will be measuring off of and sometimes you have to determine what parts of the casting will best reflect the prints version of the finished part. In this case my starting point will be the actual bottom of the base casting. Unfortunately the base has a rough finish and cannot be trusted as a true finished surface. To fix this problem I used my belt sander to flatten the bottom edge of the casting so it could be used as a true starting point for measurement. FYI - The bottom of the base could have been milled flat but it wasn’t necessary as the tolerances needed are not that critical.
Now that the base was “flat” I could use it to properly gauge the elevation of the milling head to deck the bosses. I set up the milling head to be 2.510” off of the table and then surfaced the bosses.
The indexable carbide end mill that I used worked amazingly well on the cast iron.
Now that the bosses were surfaced properly I could lay out where the mounting holes would be drilled. This part of the build is very important to get right as a misalignment will spell disaster. The pillow block bearings must be perpendicular to the travel of the connecting rod. The crosshead frame must also be perfectly perpendicular to the axis of the crankshaft. Careful measurement is critical at this point!!! The centerline of the base is the most important aspect of the layout and unfortunately you do not have a flat surface to “transpose” the bearing side of the centerline mark to the crosshead frame side. To solve this issue I used a straight edge and an extra pair of hands to hold the ruler edge between the bearing bosses (with the help of my calipers). I then scribed out the centerline of the crosshead frame to be axial with the base. To get the centerline of the crankshaft perpendicular to the frame I used a precision square and measured off of the frame’s centerline. All of the measurements were fairly easy after these baseline marks were made. Once the hole centers were cross haired I could double check the symmetry or squareness of the layout by cross-measuring various hole centers with the calipers. If the holes are the same distance from each other diagonally then they are generaly symmetrical. Once I was sure the base was layed out correctly I used a center punch to finalize my drill locations.
I like to use a smaller drill to pilot a hole before the finished size drill is used. This makes the finished hole more axial and reduces chip build up in the flutes of the larger drill. Using a 7/64” pilot bit I pre-drilled all of the mounting holes in the base as seen below. The mounting tab bosses were also drilled out with a 7/32” drill bit.
I chased out the pilot holes on the pillow block bosses with a #25 (.1495”) drill bit. The crosshead frame holes were then drilled out with a #7 (.2010”) drill in preparation for tapping.
A 1/4-20 tap was used on the frame’s mounting holes and a 10-24 tap was used on the pillow block holes respectively. Cutting oil helped the process greatly.
Once the holes were cleaned with solvent they were checked by installing the mounting screws.
Now that the base was complete I could get my crankshaft supported by the pillow block bearings. This kit is designed to used a set of cast iron bearings to support the crankshaft which is a practical design. The use of an oiler hole on the top of the bearing caps will keep the cast to cold rolled steel surfaces lubricated. However I am not a big fan of this setup due to the wear characteristics of this combination. I am planning on adding a bronze sleeve to the pillow block to ensure smooth running of the engine (more on this later).
To get started on the pillow blocks I first needed to separate and “shape” the castings for machining. Using my band saw I removed the caps from the blocks as seen below.
I used my grinder to carefully remove the casting seams from the blocks. You can see the difference from the right block to the left one in the vise below.
The parts were now ready for machining.
This is another perfect example of finding the “starting point” on a casting for proper machining. In this case the pillow blocks will need to have a flat surface to reference to when milling the tops. This is why I chose to mill the bottoms of the castings first. I measured the casting so the mounting “tabs” on the bottom of the block would be equal thickness when the milling process is done. This will properly orient the block on the table for the next machining process.
The bearing caps were also milled at this time. I took into consideration the thickness of the cap’s mounting tabs when I surfaced the bottom of the caps as seen below.
The tops of the bearing blocks could now be surfaced to the right elevation. I followed the prints and topped out the blocks at 1.375” high.
From this point on I will keep the blocks as matched sets so they can be custom fit to each other, I numbered them accordingly.
Well that’s about it for this episode of the 6CI project. Please join me again when I finish the pillow block bearings and get the crankshaft in place!!! Till then be safe my friends!!!
