Kozo A3 in 1.5" scale

[kvom]

Right now the springs have no camber and the axle boxes sit midway in their range. If the weight of the boiler, etc. pushes the frame down too far, then I can add camber to the springs to raise it back.

 

[Lesmo]

That's a nice looking bit of kit you are making there, the progress of which I have been following with great interest. I like the video of your maiden run, which can be watched lying down. Very thoughtful of you.

Cheers

Les

 

[kvom]

Over the past two days I've been working on the tie plate, a part that mounts to the frames and provides support for the yokes that in turn support the valve gear. The initial machining was manual, with only the final radius cut (needed to clear the boiler) done on the CNC mill. For this operation, the aluminum fixture plate was drilled to match the mounting holes in the tie plate, plus two additional to retain the scrap part. Here's the assembly at the conclusion of the final op:

The two "feet" are screwed into the bottom notches to allow mounting to the frame, and then the two yokes can be trial fit.

There is a bit of interference between the bottom of the yoke and the driver flange needing to be relieved:

Kozo shows a small angled notch for this on the 3/4 scale, but I wasn't sure it would be needed at 1.5.

I also went out to the RR this afternoon with the chassis to test it out with the side rods attached. Here's a couple of short videos:

[ame]http://www.youtube.com/watch?v=ym6Rl_eTRIQ[/ame]

[ame]http://www.youtube.com/watch?v=rkIadM9Ncu8[/ame]

 

[Bernd]

Love those video's Kvom. Thm:

Bernd

 

[kvom]

Today I took 5+ hours to get the first crosshead guide in place. As a novice builder, I struggle with knowing where fit and tolerances are important. But since I've had problems on stationary engines with crosshead guides, I decided to see how tight I could get.

Kozo shows soldering the yoke mounts and then machining to fit. I wasn't going to do it that way for several reasons, among which is the problem I had already soldering on the yokes where I couldn't get it hot enough. Also, the yoke was going to be modified from plan because of the width/gauge issues, so I prefer to do a fit "in place."

The yokes had 2 1/4" reamed holes for attaching the mounts, so my first task was to machine 4 of these from some 1" round brass stock. The mount body is .75" long, with a 1/4" diameter spigot for attaching to the yokes:

Lots of manual milling later, I have this:

The guides need to be parallel to the frame side as well as the frame bottom. I tried a number of ways to ensure the first parallel to the frame side, but eventually hit on this idea. I knew the distance of the bore centerline from the frame as well as the width of the guide, so I could compute the distance of the inner edge of guide from the frame. I then used gauge blocks to position the bar laterally.

the height gauge gave me the vertical distance at the cylinder end, and also the height of the mount top edge, so now I knew how deep a "notch" to mill in the mount. The final result with the first lower guide in place:

Measurement with a depth mic shows .004" vertical difference between the two ends; I'm satisfied with that result.

The upper bar will be a lot easier since I just need to make it parallel with the lower, via a parallel and some gauge blocks to get the needed measurement to make the upper mount. Even though the guides hold the mounts very tightly against the yokes, I'll loctite them in place.

 

[steamer]

Cool use of round stock. Did you index them about the pins while machining them?

Dave

 

[kvom]

I used a .25" 5C square collet block to hold them for the first light cuts on 4 sides. With the 4 flats centered on the pins, I could just hold them in the vise and take equal cuts on each side.

 

[kvom]

Since I lack material for the rest of the guides (and being burned out on them for the moment), I decided to make a start on the crossheads themselves. With the steel oblong I squared up a few weeks ago, I set up for the CNC mill. I had only .08" at the bottom for clamping with the vise, so was obliged to use soft jaws. Following Kozo's technique of initial machining of both crossheads from the same block, I first did roughing passes to get to here:

After the finishing passes, I had this:

The next step is to turn two round discs to fit into the heads forming a round-end pocket for the end of the conrods. These discs will be silver-soldered, after which the side of crosshead will be cleaned up with a facing pass. I'll have to see if my MAPP torch can heat the assembly enough for soldering.

Still lots to do on these afterwards.

 

[kvom]

This weekend I finished the other 3 crosshead guide bars and their mounts. For now they look pretty good, but we'll see if any adjustments are needed when the crossheads are finished.

I did the measurements with the frame on 123 blocks and surface table assuming that the cylinders are parallel to the bottom of the frame, which was the datum for the cylinder mounting holes. If that proves not to be exactly the case there is some play in the piston rod travel via the packing gland/bushing.

 

[kvom]

With only a few shop hours available today, I proceeded with the next step in the crossheads. I needed to silver solder the disks forming the pocket for the main rod end, but the MAPP gas torch couldn't produce enough heat. So I used my small Henrob oxy-acetylene torch for the first time. Then I cut the two pieces apart and face-milled both sides.

There are still quite a few operations to go on these parts.

 

[Lesmo]

Hi Kvom

those look very neat, a really nice job, but as I know nothing at all about these engines, I can't figure out where and how these parts fit. Maybe I should be patient and all will be revealed. ???
Keep up the good work

Cheers Les

 

[kvom]

Third operation on the crossheads: use the CNC mill to profile the rear face.

Then I used the facemill on the Bridgeport to bring the thickness down to .75" with the pocket centered.

Les,

These parts link the piston rod to the main rod. The piston rod will screw into a threaded hole on the left, while the end of the main rod will slide into the pocket on the right and be fastened by a pin that will drilled through the center of the crosshead. The flat top and bottom will slide between the guide bars that I installed a couple of posts earlier.

 

[kvom]

More work on the crossheads including an "O $hit". First task was drilling three lateral holes: 3/16 reamed for the retaining pin, and two 5-40 tapped holes to mount the link bracket.

Then I drilled and tapped the front side 5/16-24 for connecting the piston rod, but then discovered that the threads weren't straight. I had started the tap with the mill spindle, but apparently didn't get enough turns to ensure straightness. Plus it was a crappy carbon steel tap (I should know better by now). So I'll order a HSS tap before doing the other. For this one my plan is to bore out the hole to 3/8", then drill and tap some 3/8 rod on the lathe and press it into the crosshead.

I spent the rest of the afternoon making the cross pin that connects the crosshead to the main rod. This simple-looking part took a lot longer than it might appear. The center is drilled 3/16 to accept a Gits ball oiler, tahen 3/32 to 4 cross holes that will allow oil to reach the bronze bushing in the rod end. The threads are 5/16-24, and the inner side of the crosshead will be countersunk to avoid any protrusions that could interfere with the side rod.

Next shop session I'll try to make the second one come out as good.

 

[kvom]

Today's plan was to make the link brackets and union links shown on page 104. These are simple CNC profiles, with the holes drilled on the Bridgeport to serve to attach to a aluminum fixture plate. Here's the setup for the link brackets; all holes and screws are 5-40.

A few minutes later:

Then it was back to the Bridgeport to enlarge the single hole on each to 5/32.

Test fit for to the crossheads, where I discover that the crossheads should be mirrored wrt the brackets, and one set is on the top of the crosshead. grrrr. The union links are shown as well, along with the second crosshead pin that I made yesterday.

I think the simple fix for the bad holes is to loctite a SS screw in each and mill them flat, then drill and tap new holes in the correct position.

My order from McMaster came in just now, so I should have a good 5/16-24 tap to try threading the piston rod attachment properly.

 

[kvom]

Today's project was to finish the combination levers (p. 103, fig 17-9). These had 4 main machining setups. First was to mill lengths of 1/2" square bar CRS down to ~.410" square, drill the 3 holes 5/32", and mill the recess flat where the union link connects. A small aluminum fixture plate is then drilled with matching through holes so that the prepared stock can be attached with 6-32 screws and nuts. The left hole is indexed from the plate's edges so that the machining zero point can be located for the CNC mill.

The second op is then to mill the profile. Here I used a .25" carbide endmill, .125" DOC at 7IPM and 4000 RPM: conservative F&S.

Now the fixture is mounted vertically in the vise, and the "cutout" is machined, again with the .25" carbide endmill. This cutout is needed to clear the main rod.

The final op is to cut the slot where the end of the radius rod lives. Here I used a .125" carbide endmill, .05" DOC, 3IPM, 4000 RPM.

And the final parts:

The radius rods will be done in much the same way, although needing a longer fixture.

 

[stevehuckss396]

Nice looking parts!! You are really knocking this thing out of the park. Looking forward to the next set of pix!

 

[Lesmo]

I was pleased to see that the crosshead (Oh $hit) was easy to overcome and did not require a remake. That’s the sort of setback nobody wants. The build is all looking very good so far, and I can’t wait to see it running under its own power.

Cheers Les :bow:

 

[kvom]

Yesterday I machined some raw stock to size for the radius rods, and today I started to machine them. The first went in the scrap bin, but lesson learned for the second. Following the same process as for the combination rods, I first did the "top" profile:

Then the "side" profile:

Finally the slot:

And a bit of fit up to show how the valve parts done thus far fit together:

 

[Lakc]

That looks like a heck of a lot of fun. Your doing a lot to combat my near total ignorance of steam locomotives. Thank you! :bow:

 

[kvom]

After making the second radius rod yesterday, I decided to tackle the expansion links (p.106). These are each comprised of three pieces screwed together with 8-32 screws. I did each of the three pieces in pairs from one pieces of steel for each pair, using the same fixture plate for each. The holes for mounting to the fixture were drilled on the Bridgeport prior to moving to the CNC mill.

The radius rod does fit but is a bit tight at the ends, so some sanding/filing will be needed eventually.

The next step will be to make the 1/4" round for the center holes in the outer plates' these pins will fit the brackets that attach them to the yoke and allow them to pivot.