Stuart triple - types of metals to get

[ShedBoy]

That crank looks great.

Brock

 

[Swede]

Agreed, and from solid makes it even better. Nicely done!

 

[rhankey]

Attached is a shot of the completed crankshaft with counter weights. Once again, a camera expert I am not. I chose to make the counter weights from SS flat stock rather than use the supplied castings so they would match the appearance of the crankshaft. I got my first taste of a bunch of hard spots which chewed up a couple cheap end mills. If I find any more hard spots in that bar, I may see if one of our area potters could stick the bar in the kiln when they fire some pottery - I assume a pottery kiln would get hot enough and cool down slowly enough. At some point I will need to cut a keyway slot in the flywheel end of the shaft, but I will wait until later when I know the exact location of the flywheel.

I think it is time to break out the first casting. I think I should machine the sole plate next, then main bearings.

 

[steamer]

I think the sole plate should be a good place to start.

A couple of karma points from me.....multilobe cranks are NEVER easy.

Dave

 

[doubleboost]

:bow: :bow: :bow: :bow:
John

 

[rhankey]

The sole plate and main bearing keeps are now done. The sole plate was my first introduction to working with cast iron. What a filthy dusty mess cast iron makes. But it appears to be a pretty soft and easy material to cut. I also got to use my boring head for the first time, which produced a beautiful finish and perfectly sized hole. Below is a photo of everything that I've built so far loosely bolted together. Everything appears to align perfectly so far.

I think I should make the main bearings next.

However, I have a question... How much clearance should I allow between the bearings and the crankshaft so that there is enough room for oil and a minimum of friction yet not so loose that the crank will rattle within the bearings? Stuart specifies 3/8" for the crank and bearings and they assume the builder knows to adjust dimensions accordingly for appropriate fitting and movement. I machined the crank to .3745" figuring I will need at least .0005" of clearance. The bearings are gunmetal (which I understand to be quite slippery) and the crank is SS 303. is it advisable to machine the bearings to a tight fit, then assemble everything with a fine abrasive to lap/bed the bearings and crank to a perfect fit with the crank chucked to a slow speed drill or the lathe? If so, what clearance should I machine to, and what clearance should I be achieving after bedding such that there is enough clearance for oil? And if I don't need to bed/lap the bearings to the crank, what should the clearance be?

 

[Swede]

VERY nice crankshaft! That engine is going to be a jewel! :bow:

 

[pete]

Rthankey,
VERY nice job so far on that engine. I'm only going from memory and it could be faulty. Years ago Model Engineer did a write up with the full "How to do it" for this engine. If? I remember correctly the author built a simple lathe faceplate fixture, Machined all of the bearing blanks to the exact same size, And then used the fixture to position each bearing for drilling,boreing, and reaming. You then end up with all the bearings dead in line with each other once their bolted down into the soleplate. If my magazines weren't in storage I'd check to be 100% sure of my facts.

As far as what tollerances that should be used between your bearings and crank? I wish I could help you. For the prices charged for the castings and drawings I think that adding those dimensions would be the least they could do. But if it was me I'd email Stuart Turner and I'm sure they would provide that information. The few times I've emailed them they were very good about answering my emails.

Pete

 

[rhankey]

Thanks Pete.

A number of months ago I was able to track down copies of all but one of the articles in Model Engineer on the build of the Stuart triple. Given how new all of this is to me, it was very informative seeing how someone else tackled making the exact same parts I was going to have to be making. I’ve been learning quickly that there are as many “right” ways to make a part as there are people doing this stuff. Despite how new all this is to me, I’m surprised at how quickly I’m finding my own unique ways of making the parts. Perhaps some of my methods might not be the best, as I lack the experience and wisdom and still working with a somewhat limited set of tools and scrap metal.

I did make the main bearings over the weekend. The big relief was that the crankshaft, bearings and crankshaft all fit together perfectly on first attempt. I can’t tell you how much of a relief that was, as I had invested a heck of a lot of time into making the individual parts with no way of knowing if any of was going to fit together before this. The crank turns smoothly, but I think it is a little too stiff for what I think is acceptable, so I will hone the bearings a bit more to get it turning more freely.

Like the crank, I built the bearings a little differently than the author suggested. He temporarily soldered the halves together and built a jig that mimicked one of the sole plate webs to use as a boring jig. I saw insufficient benefit in gluing the halves together so didn’t. And I saw no point in building a boring jig when I could use one of the webs of the actual sole plate as a boring jig. I simply mounted the sole plate vertically on a right angle plate, and used the top most web as my jig. Seemed far simpler and ended up with the same end result of all four pairs of bearings being perfectly aligned. Prior to boring, I also stamped each half so it was very clear which halves belong together and which went on top/bottom. As I mentioned previously, I need to hone the holes in the bearings a little more to sneak up on what feels like just the right amount of clearance. I’m sure more seasoned builders would know exactly how much clearance is needed and got there in one step. I’ll take longer to get to that end goal, but I’m probably going to end up at the same result.

I may wait with final honing of the bearings until I make and install the flywheel, as I think turning the flywheel will give me a better feel on what is loose/tight enough. I ordered a keyway cutter and broach this morning, as I don’t like the idea of using the specified set screw to attach the flywheel to such a smooth small diameter crank.

Unless folks here know, I’m going to have to contact Stuart at some point with respect to the placement of the eccentrics. The IP cylinder eccentric is clear, as it is in two pieces in order to mount it in the middle of the shaft. But for the other two eccentrics which simply slide on the ends of the crankshaft, it is not clear which is for the HP and the LP cylinders. One of these has a 30% angle while than the other two (including the IP) specify a 15% angle.

Here’s the what I have with bearings installed.

Robin

 

[pete]

Robin,
Obviously your method worked very well. Yeah different equipment, experience, past results make a large difference for how you do any job.

I'm guessing you turned your crank between centers with center drilled holes drilled off set for each crank throw? I'd be interested how you set that up to get each end of the crankshaft blank drilled for those centers and exactly the same for each end of the crank. That's not exactly an easy job to get every thing perfect to get the crank throws correct and in the right position for the degrees of rotation. Over and above making a finished straight crankshaft from solid, The machining setup is just as hard if not harder to manage to do accurately also. Your engine is on a list long enough I may never get to it, But I am interested in how you did it.

Pete

 

[Dan Rowe]

However, I have a question... How much clearance should I allow between the bearings and the crankshaft so that there is enough room for oil and a minimum of friction yet not so loose that the crank will rattle within the bearings? Stuart specifies 3/8" for the crank and bearings and they assume the builder knows to adjust dimensions accordingly for appropriate fitting and movement. I machined the crank to .3745" figuring I will need at least .0005" of clearance. The bearings are gunmetal (which I understand to be quite slippery) and the crank is SS 303. is it advisable to machine the bearings to a tight fit, then assemble everything with a fine abrasive to lap/bed the bearings and crank to a perfect fit with the crank chucked to a slow speed drill or the lathe? If so, what clearance should I machine to, and what clearance should I be achieving after bedding such that there is enough clearance for oil? And if I don't need to bed/lap the bearings to the crank, what should the clearance be?

I have a few Stuart casting sets and your question made me realize that I also do not know the answer on how much clearance to add to the bearings for the oil. For a full size engine I would look in one of the engineering books on my shelf. I am looking forward to see more progress on this engine.

The crank looks just like a 3 cylinder Shay locomotive crank Which had all the eccentrics keyed to the shaft. This is why I am really interested in calculating the angle of advance as it is set on the crank with no easy way to change it after the fact. Shays had a split center eccentric but it was still keyed on the shaft.

Dan

 

[rhankey]

I'm guessing you turned your crank between centers with center drilled holes drilled off set for each crank throw? I'd be interested how you set that up to get each end of the crankshaft blank drilled for those centers and exactly the same for each end of the crank. That's not exactly an easy job to get every thing perfect to get the crank throws correct and in the right position for the degrees of rotation. Over and above making a finished straight crankshaft from solid, The machining setup is just as hard if not harder to manage to do accurately also. Your engine is on a list long enough I may never get to it, But I am interested in how you did it.

Pete

Pete,

Sorry for the long post, but this is how I turned the crank:

Centre drilled each end - I mounted the bar in a 3 jaw chuck and supported the other end with a steady rest, as the 1.5” bar was too big to slide into my 5C headstock.

Centre drilled each of the throws – I mounted the bar in the lathe between centres. My headstock lock pin just so happens to engage at 3 perfectly equidistant positions per revolution, so I simply locked the head stock, and scribed both ends of the bar with a cutting tool at the same time, then moved to the next headstock lock position. This ensured both ends were perfectly aligned to one another. I don’t have a drill press, and the bar was too long to drill vertically in my mill, so I used my mill with the head rotated horizontally to drill the three centre holes on each end for the throws.

Turn each of the throws – I did all of this on the lathe. I mounted the bar between appropriate centres for the throw, but rather than driving the bar with a lathe dog, I used a slightly longer handmade centre in the collet closer and a 4 jaw chuck. The centre aligned the bar, to which I snugged the 4 jaw chuck. The 4 jaw chuck was meant to provide greater rigidity to the bar, and thus reduce/eliminate chatter. I started with the middle (IP) throw, then did the throw closest to the chuck, then flipped the bar and did the remaining throw now closest to the chuck, thus always working as close to the most rigidly supported end as possible. As I finished turning each throw which I cut using a parting tool (it was a pretty deep and narrow slot), I mounted the bar back in the centre holes to the bar and checked and corrected any run out that was found. I had to make minor bending corrections. Then I crazy glued in three precisely cut spacers around the edge of the gapping slot so that the bar would behave like I hadn’t carved most of the material away already. I’m not sure this next step was necessary, but I also chose to tape a couple well sized boring bars to the bar by the tail stock end to act as counterweights. I repeated the cycle for each throw.

Turn the main shaft - With the bar mounted between centres and using the 4 jaw chuck as a driver I started by turning down ½” to a few thou over final diameter at the tailstock end. Then I removed the chuck, flipped the bar and mounted the freshly turned stub in a collet, and turned a similar nub on the other end too. I then turned the section of the shaft closest to the headstock to finished size, while supporting the other end in a tailstock centre. I then slid the finished bar all the way into the collet, leaving me a much shorter bar between the collet and tailstock centre, and turned the next section of the shaft that’s between two of the throws and is closest to the headstock. Then I flipped the bar and repeated the same from the other end. When coming from the other end, I double checked that the already turned portion of the bar was perfectly centred, and made minor bending tweaks if needed, otherwise the completed crank will bind when mounted in the bearings.

Cut the flat parts of the journals – I removed the crazy glued spacers and took the bar over to the mill. The milling work was quick and easy work.

I thought I was going to use a steady rest more than I did, but it really wasn’t needed. If the crank had to be much longer, I might have needed a steady rest when turning the crank around to turn the second outbound main section of the shaft, as that is the only time I felt like I needed to be a little lighter with the cuts. My completed crankshaft tested to <.001 of dead straight when I was done which I was plenty happy with.

Robin

 

[pete]

Robin,
Very clever and thank you for the time spent answering my question. It's very much appreciated.

Pete

 

[rhankey]

I have a few Stuart casting sets and your question made me realize that I also do not know the answer on how much clearance to add to the bearings for the oil. For a full size engine I would look in one of the engineering books on my shelf. I am looking forward to see more progress on this engine.

The crank looks just like a 3 cylinder Shay locomotive crank Which had all the eccentrics keyed to the shaft. This is why I am really interested in calculating the angle of advance as it is set on the crank with no easy way to change it after the fact. Shays had a split center eccentric but it was still keyed on the shaft.

Dan

Dan,

I have tossed around using keyways to mount the eccentrics too (Stuart specifies set screws), but I'm a little scared at the thought of finding that I need to rotated then a little later on. And I would have to use an end mill to cut keyway for the IP eccentric as it is wedged tightly between a throw and a bearing. If I can think of a way of temporarily locking the eccentrics in place with glue so I can test run the engine, then I might feel perfectly at ease with keying the eccentrics into final position. With Stuart's eccentrics for forward and reverse being milled from one piece of metal, it would seem to my inexperienced mind that I really can't make any adjustments anyway, as adjusting for one direction would be at the expense of the other direction of rotation. I will have to think on it a bit more. I don’t know if the eccentrics for your locomotive are made any differently than Stuart’s.

I will keep posting periodic updates in this thread to the on-going build. It might take a while for me to complete the engine, and I've probably hijacked my original thread title.

Robin

 

[steamer]

The old rule of thumb is. 001" / 1 inch of diameter should work just fine.
Dave

 

[Dan Rowe]

Robin,
You are correct if both eccentrics are made from the same piece of stock there is no adjustment that can be made they have to be fixed to the crank in the proper location. You could consider a taper pin for the IP cylinder and keys for the HP and LP.

I suspect that is is the LP that has the 300 for the angle of advance. If you know the lap of the valve which can be calculated from the drawings the sine of the angle of advance is (lap+lead)/(1/2 valve travel). Hey I just worked that out in my valve diagram thread.
http://www.homemodelenginemachinist.com/index.php?topic=15939.msg163740#top

Dan

 

[Dan Rowe]

Robin,
The other thing about the eccentrics if made from the same piece of stock is the Hp and Ip cylinders face the same way so both eccnetrics are the same hand. The Lp cylinder faces the other way so if the Hp/Ip eccentric is right handed then the Lp eccentric is left handed. I know this because I made two of them the same way for a 2 cylinder Shay and there was no way I could flip one around to work the other cylinder correctly.

The main reason I am atracted to Shay locomotives is it is really a marine engine that got lost in the woods. All Shay cylinders were Hp cylinders other than that it was a typical marine engine on a locomotive boiler.

Dan

 

[rhankey]

Robin,
The other thing about the eccentrics if made from the same piece of stock is the Hp and Ip cylinders face the same way so both eccnetrics are the same hand. The Lp cylinder faces the other way so if the Hp/Ip eccentric is right handed then the Lp eccentric is left handed. I know this because I made two of them the same way for a 2 cylinder Shay and there was no way I could flip one around to work the other cylinder correctly.

The main reason I am atracted to Shay locomotives is it is really a marine engine that got lost in the woods. All Shay cylinders were Hp cylinders other than that it was a typical marine engine on a locomotive boiler.

Dan

Dan,

I just scanned your thread on computing valve timing. I'll definitely need to give that a much closer read when it comes time to make the eccentrics and valves. If I do deviate from set screws for attaching he eccentrics, I think I'd prefer to use keys even for the IP where space on the crankshaft is very tight over taper pin.

I just checked the Stuart drawings with respect to your heads-up on the left and right handed eccentrics. Unless I am missing something (having not carefully read your valve timing thread yet), I think all the Stuart triple eccentrics are same handed. I say that as all appear to mount to the crankshaft the same way around, and the drawings for each are identical other than one having 30deg vs 15deg, and one being split. And in checking a hi-res photo of a completed engine from Stuart's website, it appears the eccentric rods all attach in the same way too. I'm not seeing where the LP is reversed in orientation or in operation to that of the other cylinders. Am I missing something?

Robin

 

[Dan Rowe]

Robin,
The eccentrics might be a little different than on a Shay. First I am thinking all D slide valves with outside admission. The thing to check for the eccentrics is ALL the ahead rods connect to the same side of the link and ALL the astern rods connect to the other.

If they are all D slide valves the angle relationship will be the same to the crank pin of the respective cylinder. Which rod is closeer to the connecting rod might be different than a Shay. My tale was only ment as one way to goof up.

When you say 30 degrees and 15 degrees is that the angle to the axis for each eccentric or it is it the angle between the eccentrics? A sketch would be helpful. The thread on valve diagrams will tell you how to calculate the lap with the drawings.

Dan

 

[rhankey]

Robin,
The eccentrics might be a little different than on a Shay. First I am thinking all D slide valves with outside admission. The thing to check for the eccentrics is ALL the ahead rods connect to the same side of the link and ALL the astern rods connect to the other.

If they are all D slide valves the angle relationship will be the same to the crank pin of the respective cylinder. Which rod is closeer to the connecting rod might be different than a Shay. My tale was only ment as one way to goof up.

When you say 30 degrees and 15 degrees is that the angle to the axis for each eccentric or it is it the angle between the eccentrics? A sketch would be helpful. The thread on valve diagrams will tell you how to calculate the lap with the drawings.

Dan

Dan,

I have attached a side view of one of the eccentrics for clarity. As i mentioned previously, the other two are the same, except they are 15deg and the IP one is split to mount it in the middle of the shaft. I have also included a photo from Stuart's website of the completed engine. so you can see the location and arrangement of the valve ports and the valve linkage. As you guessed, the HP and LP valves are on the outsides, but despite that all three eccentrics face the same way. I very much appreciate the heads up, as it could have been very easy for me to have not noticed if one of the eccentrics was reversed from that of the others.

With all this talk of the eccentrics, I think I might work on them and the flywheel next, and thus complete everything that attaches to the crankshaft. With more thought overnight, I'm now leaning heavily towards keyways for all three eccentrics. The same jig I intend to make to machine the eccentrics should also make it easy to nail their alignment to the crankshaft too. I'm also thinking it would look better if I made the eccentrics from SS rather than the supplied cast iron blanks.

Robin