Building Kozo's New Shay locomotive

[Swifty]

I think that you will find the availability of round sizes in brass a lot easier than square or rectangular.

Paul.

 

[SilverSanJuan]

Thanks for the input, folks.

Todd

 

[crueby]

On to the main attraction: Act 1: The Cylinders

Last time I got the blocks for the cylinders shaped down to outside dimensions. Time for the 'boring' part. First up was to chuck the block up in the 4-jaw again, but this time offset towards one corner. The bore is offset to leave room for the steam passages and bolt holes. Since the number one cylinder block is facing the other way from the number 2/3 blocks, all of these operations took some careful checking to make sure I was orienting the blocks correctly (good time to be paranoid - Murphy is always out to get you!). Anyway, using the dial indicator each time, I offset the blocks the same amount in both directions (0.052", as I recall), and then drilled a starter hole for the boring bar.

Using the boring bar, I took the cylinders out to size, measuring both with calipers and checking final size with a test bar of the proper diameter. The last few passes were done with very light cuts, and very slow feed rate.

As you can see in the third photo, the resulting bore was mirror smooth (okay, photo is grainy, does not show it well - tough to get camera to focus in right spot!). The test bar fit nicely in each, if I plugged the bottom of the hole with my finger and dropped in the test bar, it floated down, and I could feel the suction when drawing it back out. Best I've ever had a set turn out - hope I dont mess up later on these!

Fourth photo shows the three blocks so far, in front of the manifold in the positions they will be. The steam chest for the left one will face left, and face right for the other two. You can see how the bores are offset to leave more material on the back wall and the steam chest wall.

Next steps were to make the steam passages. Kozo used a 1.5mm mill bit to cut the outer ones - I dont have one that small, so I drilled a series of 3 holes and used a micro bit in my high speed air tool (like a little dentist drill - I use it for detail wood carving) I connected up the holes to make a slot. For all these drilling operations, I set up the first block in the milll vise, using a straightedge to line it up at the edge of the vise. Then, once I had the position of the holes dialed in on the first block, I could swap out to the other ones and get the same result - saved a LOT of setup time (center/measure once, drill 3 times).





Next photo shows milling out the passage in the center - that one I had a mill the right size for.

With the passages milled from the side, it was time to make the connecting passages. All the passages are at 20 degrees, so I set up the mill vise on the tilting table for them. Again, used a straightedge on the side of the vise to position the blocks the same every time so I could set up once and do all three blocks. Again, triple checking that I had the blocks oriented correctly! Started out with a mill to make a flat at the top of the cylinder.

Then, drilled the passage down till it met the slot cut in the face in the previous step. This was repeated for all three blocks, and at both ends of each block. Due to the offset of the bore, I could do the top hole for number 1 and bottom hole for 2 and 3 in one setup, then readjusted for the rest of the holes.

Next up was to make the passage for the exhaust, which comes in from the back wall of the block and meets the center slot. Again, started with a mill,

and finished with a drill through to the slot.

Last step was to make the steam inlet passage. Unlike many engines where the steam inlet comes into the steam chest cover, for space reasons the Shay has it coming in from the back wall of the block, exitting into the space inside the steam chest next to the valve slider. This was done with another angled hole in the back wall,

and a vertical hole in the steam chest face.

Last photo shows all the cylinders so far. Note how the number one block (on left) is a mirror image of the other two.

Enough for today (okay, some of this was done yesterday) - time to sit back and admire the work so far! *beer* Next up will be to start drilling/tapping all the mounting holes (lots and lots of them).

 

[SilverSanJuan]

Your work continues to impress. You make it all look so easy. Yet I know there is much careful thought and consideration before each operation. Then that wrankling feeling in your gut right before you plunge the tool in that says, "I hope this is right."

Good show!
Todd

 

[crueby]

Your work continues to impress. You make it all look so easy. Yet I know there is much careful thought and consideration before each operation. Then that wrankling feeling in your gut right before you plunge the tool in that says, "I hope this is right."

Good show!
Todd

Oh yeah, I know that feeling! Not so much on early cuts, its that last one on the part!
On one of the cylinders I marked out the locations for the passages, and was about to drill one when I noticed the lines on that part did not look the same as the other, had the dimensions swapped by mistake. Would have ruined it... Close call...

 

[crueby]

Bunch more done on the cylinder blocks today - started out with drilling the holes for the cylinder end caps. There are four 3-48 holes at each end. To get them all lined up properly, and also to make sure the holes in the caps get drilled to match properly later, a jig was made (one thing Kozo shows in his book is great use of jigs - a real time saver, plus it ensures repeatability of placement on multiple parts). I took a piece of brass plate and bored a hole in it to match the bore of the cylinder. With the piece still in the 4-jaw so the hole was centered still, holes were drilled on the rotary table at the distance needed for the mount holes (all sized for tapping at 3-48 ) . (okay - that was annoying - try putting the numbers 3-48 followed by a close paren and period without it turning into a smiley! Like this: 3-48). Extra space solved that one...). Then made a pair of stepped blocks for either end, with the narrow part of the step also matching the cylinder. Note that I made the top end cap deeper than needed - will show why later in this post. With a bolt running down the center, the pieces all sit on the cylinder block the same way each time (markings on the plate show which way to turn it to line up with the front edge). The first photo shows the jig in use, with the block held in the vise, but the vise just handheld on the table, so the drill would self-center in the hole.

Second photo shows the jig sitting next to the block to show the parts. Just a few minutes to make, but with it I was able to drill all the holes in both ends of the blocks, accurately, in just a few minutes - no more measuring/marking/etc needed. The same jig will be used later to position the holes in the end caps - they will be drilled at the tap size, then redrilled to open them up for clearance on the threads.

Next up was to make a drilling jig for the mount holes for the steam chest. There are 8 holes (all 2-56) in this jig. The same jig will be used to drill holes in the cylinder blocks, the steam chest frames, and also the steam chest lids. With the jig, all will line up correctly (as long as I position the jig right way up each time, I guess!).

Next photo shows the jig in use, clamped to the cylinder block over the face with all the steam ports on it. The clamps I am using have copper jaws, so they wont mar the surface of the bore (not clamped too hard, just enough to hold).

Fifth photo here shows the progress so far - all the holes drilled/tapped (took some breaks during the tapping process - tired fingers leads to broken taps at these small sizes). The two jigs are shown in front.

Last step was to round over the front corner of the blocks on the side away from the steam chest. There are no passages in this area, so no need to keep all that material - in the real thing this would have been cast that way. The end-cap drill jig played another use here, as an arbor to hold the block in the 3-jaw chuck on the rotary table. This is where that deeper end of the jig came in handy - made enough room to grab it in the chuck while holding the block out a little from the jaws so I would not hit it with the end mill. I took off the corner in a series of light cuts, down to the point where the curve blended into the remaining side.

In the right block in the seventh photo you can see the surface left - not bad, but not too smooth. I got out my diamond-surfaced lapping plates (use them for sharpening my wood carving chisels), and used that to smooth down the faces of the block. With some oil on the plate to float off the removed brass, I held the blocks down and ran them back/forth while slowly rotating them through the curved face. Couple minutes and it left a nice polished surface. Then I did the same on the other flat faces of the block, which smoothed out any protrusions left from drilling/tapping. I spent some careful time on the face where the steam chest goes, to get a nice flat polished face for the D-valve to slide on.

Last photo shows the complete cylinder blocks and steam manifold, ready to make the steam chests....

 

[jschoenly]

I'm jealous of your progress but really enjoying it take shape! Keep it up!

 

[SilverSanJuan]

Seriously impressive! The cylinders really look nice. Great technique on cleaning up the machined surfaces.

Todd

 

[crueby]

Thanks guys! Learned a lot on this project, makes me want to go back and redo so much on earlier engines. That would get in the way of all the other stuff I'd like to build though... Sigh. So little time, so much swarf to generate!

 

[petertha]

I was waiting to see how you were going to go about lapping the brass cylinder bores, but looks like you got your desired finish by boring & finishing alone. So how does that come together on the piston side, ie what kind of rings or packing run best in brass bores in a steam environment like this? Another question, what sort of max temperatures do boilers & parts see in model steamers? (can you tell I'm more a gasser suck, squeeze, bang, blow kinda guy?)

 

[tms6401]

Excellent work as usual. You make this look so easy.
Tom

 

[crueby]

I was waiting to see how you were going to go about lapping the brass cylinder bores, but looks like you got your desired finish by boring & finishing alone. So how does that come together on the piston side, ie what kind of rings or packing run best in brass bores in a steam environment like this? Another question, what sort of max temperatures do boilers & parts see in model steamers? (can you tell I'm more a gasser suck, squeeze, bang, blow kinda guy?)

On previous engines I lapped the bore with diamond paste on an aluminum rod just under the bore diameter, and gotten excellent results, with good compression. Usually I used steel pistons with no rings, but for this one the book calls for Viton rubber o rings, which can take pretty high temps (some people use the in ic engines). I don't know what max temp the engine sees, have to defer that to someone with more steam experience than me.

 

[crueby]

Excellent work as usual. You make this look so easy.
Tom

Thanks! You are not seeing the shelves full of wobbly, leaky engines I did over the years...!

 

[crueby]

Got a start on the steam chests today. Started out by cutting down/milling square to length some flat bar stock - had to take a couple mm's off the side but thickness was good. This bar was enough to get all three valve chests out of - it was cut into thirds, each squared up to length with the mill.

Then chucked it up in the 4-jaw on the lathe - first centered it then offset to the side so that the valve shaft will be far enough from the side for the D-valve to fit.

After that, turned down the end to form the boss for the o-ring holder (the valve shaft is sealed with an o-ring, with a holder ring going into the hole in the end). The hole in the end was drilled for the o-ring size, then a smaller hole farther in for the valve shaft.

Turned the block around, and drilled/tapped a hole in the other end for the oil pipe inlet fitting - the axle pump on the front truck pumps oil up to the steam chests (the way it is ratcheted, the pump only delivers a drop of oil every so many turns of the wheels).

Next step was to drill/tap the hole for the set screw that keeps the o-ring holder in place. since it was so close to the main part of the valve chest, I had to dig out my smallest center drill to start the hole,

then drill for the 2-56 thread.

Next photo shows the valve chest so far, with the center marked out for the opening which will be milled out after I get the other two chests up to this point.

 

[crueby]

Continuing on the steam chests, set up in the mill and drilled corner holes for the opening in the center of the chests. Easier to accurately locate these holes and mill to them than to mill blind and try and match the edge locations.

After the holes were all drilled, switched to an end mill and cut out the center section, taking three passes to go the full depth. In the second picture you can see the block cut out from the center.

Third photo shows all three steam chests so far - ready to drill mounting holes.

With the steam chest clamped together with the same drill template used for the cylinders, making sure the orientation is correct (stamped numbers on the chests to match them with the cylinders), drilled through with a 2-56 tap size drill.

Then, removed the template and clamped the cover plate on the steam chest, went back and drilled out the holes to a 2-56 clearance size, going through both the chest and the cover - in this case, the steam chest acted as a drill guide for the cover. I had tried clamping up the chest, cover, and guide all at once, but it was too hard to line up properly - this worked out just as easy.

Last photo shows all the engine parts so far, with the chest/cover/cylinder all bolted together on number 3 (right end). Naturally, no matter how many screw sizes you have, you always need an in between length - had to cut down some 3/4" long ones to fit. Which Murphys' law is that one?

Anyway, great progress this week - next up are the cylinder heads and steam chest stuffing boxes.

 

[SilverSanJuan]

Very nice. You're making quick work of this. Are you going to polish the mating surfaces?

Todd

 

[crueby]

Very nice. You're making quick work of this. Are you going to polish the mating surfaces?

Todd

Yes - only takes a few minutes, and lets me use thin (sometimes no) gasket.

 

[crueby]

With the valve chest bodies done, on to the head caps: turned them down from brass bar, with a step on the end that matches the cylinder bore. Then parted them off - used the steady rest for the first ones since the bar was sticking so far out from the chuck.

The rest of the bar was used to make the stuffing boxes - again, turned the end down to match the cylinder bore (they have protrusions above and below the flange - in the next photo it is the bottom side with the larger protrusion showing). Then, drilled for the piston rod and also a larger diameter hole for the o-ring.

Third photo shows making the upper step, and parting off from the bar.

With the caps/boxes turned to shape, last step was to use the same drill template from the cylinder blocks to drill the mounting holes in them. The stuffing boxes also get a cross-hole for a set screw in the bottom protrusion.

Next couple photos shows the engine assembly so far. Really taking shape quick with just the first few parts.



And then a couple photos of it test mounted on the side of the boiler...

 

[SilverSanJuan]

That just adds a whole other level to the loco. And, I have to keep reminding myself of the scale of those parts.

What is the process you'll use for polishing the mating surfaces of the steam chests?

Todd

 

[crueby]

That just adds a whole other level to the loco. And, I have to keep reminding myself of the scale of those parts.

What is the process you'll use for polishing the mating surfaces of the steam chests?

Todd

Same as with the outside of the cylinders - I have a pair of diamond lapping plates (two diff grits) that I use for sharpening my wood carving chisels. They are flat steel plates covered in diamond particles - can get them at most woodworking suppliers.Some oil to float off removed particles, hold it down firmly and slide it back/forth, making sure it does not rock. I get much better results with this than with files. I learned the diamond plate/followed by diamond paste sharpening method from an old boatbuilder. Gives a really quick result, with mirror finish. On the chisels, I put the paste on the bottom of an old woodworking plane - nice and flat, and the steel is softer than the chisels so it holds the grit - you want a plate softer than the metal you are lapping. For these parts, the diamond plate should be plenty.