Pennsylvania A3 Switcher (Kozo)

[Kim]

The Trunnion Plates surround the Expansion Links and provide the pivot point for the mechanism.  They have the same radius as the expansion links and have the same two mounting holes.

The trunnion plate blanks were cut from 1/8” x 5/8" 1018 bar stock then double-sticky taped together in pairs.


Each pair was then drilled for the #49 mounting holes and a 1/8” reamed hole in the middle.  This middle hole will eventually hold some pivot pins.


I then moved the trunnion plate pairs to the same jig, same holes as used for the expansion links, and did the same operations to cut the inside arc, the outside arc, and the top.  But THIS time I also cut the bottom to length (which we didn’t do for the expansion links).


Now, here’s where I used the trunnion plates to mark up the expansion links.  I made a 9/32” filing button for the rounded end of the lever, but to get the right shape on the bottom of the lever arm I used the trunnion plates and just marked a straight line to the intersection of the trunnion plate and the edge of the link – if you look close, you can see the scribe line there.


Then some disk sanding and filing later, the final shape of the lever arm is revealed!


The last operation on the expansion links is to square up the inside of the milled slot so that the link block can slide all the way to the ends.  Here again, I was very afraid of losing the little link blocks.  Then I finally realized that I had some extra material that is exactly the same radius and width as the link blocks (extra length that had leftover when I cut off the real parts!) so I started using that for these fitting operations.  In addition to being less concerned about losing it, this part was much longer than the actual link blocks making it easier to hold onto.  And I could hold it with forceps without worrying about scratching it.  This ended up working quite well and was far less stressful!


And after widening the two upper holes to 2-56 clearance size, here are the completed expansion links.


That completes the expansion links. Just the trunnion plates to go...

[Kim]

Now, back to the Trunnion Plates!

The next thing to do here is to carve out the cavity on the underside of the plates.  To do this, I made yet another jig with holes placed such that it would hold the part at 17^o and 31 ^o up, and 17^o and 31 ^o down – four different positions.

Here's how I used the jig: For the first edge, I used position #1 (note that the numbers are in a bizarre order, but that is correct).


To make the lower part of that edge, I used position #2:


Then for the other side, I used position #3.


And of course, for the final edge on the far side, is position #4.


Not hard, but a lot of moving parts around in a jig – for four different parts.

Here’s the point where these four parts become two pairs of parts.  One set is tapped 2-56, and the other set is drilled for a 2-56 clearance and countersunk.


This shows the four trunnion plate parts (two of each kind, though you can’t tell it because some of them are upside down).


And this is mostly what they will look like when assembled.  The fork of the radius rod will slide between those slots and hold the link block between its fork in the slot in the slot in the expansion link in the middle. 


But wait! the trunnion plates are not done yet!  We still need to add the pivot pins!

So, off to the lathe to turn four little pivot pins:


Then silver solder them in place:


And after a clean and shine, here are the completed set of trunnion plates!


And this now brings us up to date!

Still, many more parts to go on the valve gear!

Thanks for checking in and sticking with me through this long series of posts,
Kim

[Kim]

Thanks Chris!
Kim

[RReid]

Great looking little parts, Kim! I don't know how you can do such nice work and still remember to document the details as you go, but I'm glad you manage to.

[cnr6400]

 

[Kim]

Thanks, CNR and Ron!

Great looking little parts, Kim! I don't know how you can do such nice work and still remember to document the details as you go, but I'm glad you manage to.

I don't know what I'd do without the camera in the shop!  It's just my habit now to do an operation, take a few pics, then set up for the next one.   I still forget the camera from time to time, but I can usually recreate the scene.  Maybe you notice some of those irregularities?  Like taking a picture of "drilling" when in fact, you've already tapped the hole?  Or that sort of thing 

But I so enjoy sharing.  And I tend to learn more when I show more detail because then people can mention better ways (or safer!) of doing the same thing.  And I learn!

So, it's kind of self-serving, isn't it? 

Kim

[crueby]

It also comes in handy on later projects when you need to make the same kind of part, and can't remember how you did it before!

[Don1966]

Moving along very well Kim….



Don

[Kim]

Thanks Don! 
Kim

[Kim]

It also comes in handy on later projects when you need to make the same kind of part, and can't remember how you did it before!

Very true!  I've used my build log many times to refer back to what I've done! 

Kim

[Roger B]

Looking good        What's the grooving tool you are using for the 'four little pivot pins'?

[Kim]

What's the grooving tool you are using for the 'four little pivot pins'?

It's the Warner grooving tool: https://www.arwarnerco.com/Cutoff-and-Grooving-s/169.htm

I think Little Machine Shop sells them too (in the US).

I've got the 3/8" version, and here I'm using a 1/16" HSS insert.  I really like this little cutoff/grooving tool.  I use it quite a bit!

Kim

[cnr6400]

Groovy man!   

[Kim]

I actually got this completed before Christmas but haven’t had a chance to upload till now. So here goes!

Chapter 17.11 –Link Brackets

The next parts up are the Link Brackets. These mount onto the guide yokes and will hold the previously made Expansion Links at the pivot pins.

The link brackets were made from a length of 1/4" x 3/4" 1018 bar.  The first thing I did was to shave the 1/4" thickness down to 0.200” per spec.


Only the mounting surface of the brackets are 0.200” wide.  The main part of the bracket narrows down to 5/64”.  To narrow it, I used a 1/4" carbide end mill.  This gave me the required 1/8” radius where the part widened to 0.200”.  Since I was going to be doing this four times, I made a removable stop setup from some 123 blocks and a parallel.  I could push the bar out to hit the parallel and tighten the clamp down, then slide the parallel out of the way.


Here’s what it looked like with the narrowing maneuver completed.


Next, I cut the narrowed end off the parent stock so I could make the next one.


With four of these nascent bracket blanks I needed to square up the cut end and bring them to a specific length.


Now, using the newly formed base as the datum, I drilled and reamed the 1/8” hole for the pivots exactly 3/4" out, and centered exactly on the part.


And using the DRO set exactly the same, I drilled and tapped the mounting holes in the end of brackets.  These holes are centered on the width, but most importantly, they are located the same distance above and below the pivot hole we just drilled.  But by using the same settings on the DRO, I am guaranteeing this.  Far different processes than Kozo uses, but he wasn’t assuming the reader had a DRO.  I believe I can be far more accurate using this procedure than the way he described.


Now for the most complicated operations – cutting the angles on the sides of the brackets.  Luckily, this is not that critical, it’s mainly for looks so the accuracy isn’t as important.  I calculated the angles to be 15.1^o so I just rounded down to 15^o and used that.  It seemed close enough.

For the first side, I made this setup – it’s the bracket with a bunch of packing all set on a 15^o angle block.  The actual bracket is sandwiched between a piece of brass and a piece of aluminum and backs up to yet another chunk of aluminum.  The piece in the back keeps the part from sliding down the angle block and the brass shim and aluminum packing allow the vise to clamp down on the bracket since it is narrower than the 1/4" wide angle block.


Just to check my setup I removed the aluminum block so I could make sure the angle was coming out in about the right place, and not TOO close to the hole.


With my checking out of the way, I went ahead and cut the side down.  I took many small passes since there really isn’t much of the bracket being held in the vise.  But it seemed to work pretty well.  The additional piece of packing you see sticking out at a jaunty angle on the right was added partway through to hold the back 1/8” aluminum packing in place.  It actually isn’t clamped in at all and would jump around terribly during milling. That wedge helped significantly.


Here are all four brackets with one side angled.


For the second side, I changed the angle block to 30^o.  I also had to re-arrange all my packing.  I did a much better job of it this time   The short parallel sticking out of the vise on the right can be removed after the vise is clamped down on the part.  And when that is removed, the angle block can slide over to the right to help get it out of the way so I don’t accidentally take a bite out of it!


And here they are after the second side was angled.


Finally, I made a 9/32” filing button and rounded the ends of the brackets.

Here’s the completed angle brackets:


The next part will be the return crank.

Thanks for stopping by!
Kim

[Admiral_dk]

Still doing the small details Kim 

Per