Stuart No. 4 Build

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Stuart No. 4 Build

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smfr:
[Moved from homemodelenginemachinist.com]
Hi Don

Nominal diameter of the flywheel is 4.5".

I built up the courage to cut the keyway in the crank:

and it went smoothly. I had enough room to fit the flywheel and check the depth of the cut, and adjust accordingly.

A test fit:

The flywheel has a bit of play, but I'll be able to fix that when I make the actual key.

smfr:
[Moved from homemodelenginemachinist.com]
Work on this project ground to a halt for a bit, partially because I was annoyed at myself after http://www.homemodelenginemachinist.com/index.php?topic=18463.msg190483, and also because of interior decorating and lots garden work in the spring. But I've managed a couple of weekends in the garage, and the saga of the connecting rod continues!

Here's where we left off when I used a blunt saw, and insufficient clamping to cut the top off the gunmetal conrod casting:

The cut is crooked in both axes. I tried to silver-solder the parts back together, but that was a disaster as well. Not having done any silver soldering before, I didn't practice enough beforehand, and the solder penetration was terrible. So, plan B:

That's a hunk of 12L14 and two bronze rounds. The plan was to build up a conrod with a split bronze bearing from this lot. So, here we go! I have to hold the split bearing and steel together with bolts, so I need some bolt-holes. The end of the steel rod was cleaned up, and holes drilled accurately either side of center:

Then I formed what would become the cap on the big-end of the conrod:

and parted it off:

That insert parting tool actually does a reasonable job on my Emco Maximat "Standard".

The bronze disks also get reduced to the right thickness, and drilled:

Now I can hog out some material on the main part of the conrod, which reveals the ends of the holes drilled earlier, and allows for the bronze disks to be bolted together.

Now I can turn between centers. At this point I'm reducing the overall diameter to what will be the largest width of the big end.

I'm turning both ends to the same diameter at this point, so that I can easily clamp it down to mill some flats later. After a bit of turning we end up with this:

Still a lot of metal to remove!

At this point I realize that the bolt heads get in the way of finishing the taper on the center section, so I take it apart, and locate and center drill at a point which will be hidden under the bearing on the finished part:

Now I can turn this section alone between centers, and form the taper. Hmm, does everything seem right here? Whatever, soldier on!

smfr:
[Moved from homemodelenginemachinist.com]
We stop for a second to admire the work so far:

Now to mill some flats. The consistent diameter allows me to clamp it in some V-blocks:

Clamping down on the thinner center section is iffy since it could pull the rod out of true, but I didn't tighten that clamp down much. By shifting clamps around I could reduce both ends to the same thickness; it was then flipped over, clamped to the table, and the other side milled down. I took it down to the distance across the "Y" of the little end (11/16"). Now we can drill and ream both ends in the same setup, ensuring that they are parallel:

Of course the hole at the big end has its center on the seam between the two bronze pieces.

Next I take off some excess material on the little end, which was a successful slitting saw operation (yay!):

Feeling pleased at the progress, I put it to bed for the night.

Next day, I pick it up, wondering how best to set it up to saw some more off the little end. Then it hits me. The taper goes in the wrong direction! Headdesk. >:( Time to leave the garage and find something else to do for the rest of the day!

smfr:
[Moved from homemodelenginemachinist.com]
Now to clean up the big end with the split bearing. This is where it starts looking more like a connecting rod.

First I made an expanding arbor; chucked up some 1/2" cold-rolled rod, and turned down 1/2" at the end to 7/16", which is the bore diameter of the bearing. Then I drilled and tapped for M6, and countersunk. I'm going to use a countersunk screw to make it expand. I sawed cuts at 90° to allow for expansion (another successful slitting saw operation!).

Now the conrod is attached to the arbor and can be turned. Here I've started to clean up one side.

It's so satisfying seeing the casting and the split bearing merge into one as they get turned down together!

I have to be careful to take the right amount of each side; here again I wish I had some better setup for measuring.

After turning both sides, here's where I'm at:

Sadly I can't test the fit on the crankshaft yet, because the crankshaft journal has a pretty significant radius that I need to replicate on this bearing. I need to think about whether to grind a tool to cut the radius, or do it some other way.

smfr:
[Moved from homemodelenginemachinist.com]
This is almost where I left off last time:

but I've done some hand filing on the end cap, and drilled and reamed what will become the bottom of the yoke. I regret not leaving a bit more material at the small end of the taper, but I think it will be OK. I decided to form the bottom of the yoke because I wanted to shape the shoulders, and to know what the profile will end up like.

I broke out the ball-turner to form the shoulders, turning between centers of course:

It's always a bit of a puzzler to work out the combination of placement and rotation with this thing, and I usually end up doing it by eye.

Next up was cut out the center of the yoke. For most of the material removal, I had the part clamped in a screwless vise. However, as soon as I broke through the bottom, the part loosened and moved slightly; not a big deal but stupid here then decided to just tighten the vise, which squished the Y, pushing the sides of of alignment ;D. Some judicious hand-bending with some 1/4" drill rod through the crosshead pin holes got it back into shape!

So to finish off the Y, I clamped it down securely:

Then it was onto the rounding table to finish off the radius on the end:

The top arm is flapping in the breeze a bit with this setup, and had enough flex that I think it was getting pulled up by the end mill, resulting in a non-square profile. I was able to flip the part over and tidy that up, however.

A bit of draw filing, and the part is almost done:

What remains is still to put a radius on the journal bore to fit the crankshaft.

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