Author Topic: Pennsylvania A3 Switcher (Kozo)  (Read 135813 times)

Online Kim

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1425 on: December 02, 2021, 05:25:31 AM »
Thanks Chris and Don!  :cheers:

Kim

Offline cnr6400

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1426 on: December 02, 2021, 12:38:51 PM »
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Online Kim

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1427 on: December 03, 2021, 11:45:44 PM »
Thanks CNR!

Chapter 17.9 Link Blocks

Next up is the Link Block. This is a teeny-tiny piece that slides up and down in the expansion link.  It would appear to be a very simple little item other than that the link bracket slot is an arc, so the shape of this block needs to be a little arc segment to match the radius of the expansion link.

Kozo recommends that this piece be made from bronze.  All the bronze I have is in rods.  I just happened to have a 1 piece of round 932 bearing bronze that Id cut a chunk out of for something else.  So, I used that and cut another slice off of it for this.  Interestingly, the thin slice I cut (about 0.90 thick was my goal) did an amazing curl.


I carefully bent the thin slice back to a flattish shape.  I used the vise some then I moved to this little V-block.  Working carefully, I was able to get it quite close to flat.


Then I sticky-taped it to a flat surface and shaved a few thou off of both sides to get my desired thickness (5/64).


Then I sticky-taped the blank to an aluminum jig that Ive been using and clamped it to the rotary table so it was positioned with the correct radius.
Next I drilled two holes one for the center of each of the link blocks.  These were drilled #53 (tapping size for 1-72) clear through into the jig block.  Then I drilled a clearance hole (#49) just through the bronze.  Then tapped through that hole into the aluminum jig, which allowed me to add some additional clamping using #1-72 screws.


This chart shows how Im planning to cut the link blocks.  Ill be using the rotary table to sweep the arcs, then set specific angles on the RT for the top and bottom edges.  I used lots of fancy trig to figure out what the angles would be.  Ive never done this before using angles on the RT to cut a part to width and length.  But it seemed to work adequately.  I was able to get within a couple of thou at least!



With the additional clamping screws added I swept the top arc.


Then I did the lower arc.


Next, I set the RT to my calculated angles to cut the top of one of the link blocks.  Since I want the edge of the blocks to intersect the center of the arc I had to offset the mill by 1/32 (since I was using a 1/16 mill).  And with this offset, I did the top of the other block too.


Now, to do the bottoms of the link blocks I had to offset the axis 1/32 in the opposite direction.  Then set the angles and make the cut. With that done you have the completed shapes of the two link blocks.


The only thing left to do is to ream the holes to 5/64.  To do this I removed the clamping screws and relied solely on the sticky tape to hold things in place.  At this point theres only a tiny square of tape holding it there.  But it worked and nothing pulled up from the table.


And here you have the two link blocks.   Guess I need to clean them up a bit.  That black gunk you see on the parts is sticky-tape residue.  I just need to get it cleaned up.  But they are quite small!


I was fairly pleased with my cutting to length by angles experiment.  The part was supposed to be 0.171 long and in the end, I measured 0.169.  So, a couple of thou short, but it's plenty close for this.  The length of this part isnt that critical I think. The width is more so and that was done using standard DRO methods, so that came out fine.  Besides, Ill be milling the arc in the expansion link to match these parts anyway!

A tough part completed.  Now Ive got a bunch more curved parts up next with the expansion link itself.

Thanks for stopping by!
Kim

Offline crueby

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1428 on: December 04, 2021, 12:23:55 AM »
Definitely some tiny parts, nicely done!


 :popcorn: :popcorn: :popcorn:

Offline Craig DeShong

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1429 on: December 04, 2021, 12:36:27 AM »
Nice work   :ThumbsUp:
Craig
The destination motivates us toward excellence, the journey entertains us, and along the way we meet so many interesting people.

Online Dave Otto

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1430 on: December 04, 2021, 01:28:40 AM »
Nicely done Kim!

Dave

Offline cnr6400

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1431 on: December 04, 2021, 12:53:07 PM »
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Offline kvom

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1432 on: December 04, 2021, 01:28:18 PM »
Remember you want a nice sliding fit in the expansion links, so when machining the slot start a bit small and sneak up on the width.

Online Kim

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1433 on: December 04, 2021, 05:54:12 PM »
Thank you everyone!  :cheers:

Remember you want a nice sliding fit in the expansion links, so when machining the slot start a bit small and sneak up on the width.

Thanks for the advice, Kvom.  I appreciate it.  I'm going to go out and start working on that right now!  ;D

Kim

Offline Admiral_dk

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1434 on: December 04, 2021, 10:00:22 PM »
Oh man - they are easy to put into the assembly the wrong way (or at least trying to do so) ....
It's not easy to see what way the sides curve with so little amount of metal left ....

I have seen a number of Walschaerts valve gear from an early age - sometime in real life and many times in books - but these small details you just made, are some of the things one never thinks about when looking at the assembled gear.

Still following and enjoying your journey and description + progress Kim - thank you :cheers:

Per

Online Kim

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1435 on: December 04, 2021, 10:48:23 PM »
Thanks Per!

Oh man - they are easy to put into the assembly the wrong way (or at least trying to do so) ....
It's not easy to see what way the sides curve with so little amount of metal left ....
Yeah, I've thought about that too! But in person, if you look closely, you can see which side is wider than the other, so you can tell which direction to put them in (I hope!  ;D)

Kim

Offline Roger B

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1436 on: December 05, 2021, 07:44:02 AM »
Those are some tiny parts  :praise2: I'm surprised, but happy, that the sticky tape kept them in place  :)
Best regards

Roger

Online Kim

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1437 on: December 06, 2021, 12:29:17 AM »
Thanks Roger!
Yeah, that sticky tape is actually pretty amazing stuff!  I used it a lot with woodworking and I'm finding that it works pretty well for machining too.  I was quite impressed that it held those itty bitty parts. Of course, it was only reaming it out a few thou, so not too much force, but still, there was VERY little surface area to adhere to!

Kim

Online Kim

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1438 on: December 16, 2021, 05:51:40 PM »
Its been a while since my last update, but Ive still been beavering away on my parts!  I had this idea that Id wait till I completed the parts before I posted.  Not sure it was such a good idea, cause now I have many posts worth of work to catch up on!

So here goes

Chapter 17.10 Expansion Links and Trunnion Plates

The next parts are the Expansion Links and the Trunnion Plates. These parts need to be made together.  Not only do they share a lot of common machining operations, but it really helps to have all the parts as youre doing this.  I actually interspersed operations between these parts more than it looks based on what I show here.  But even then you can see where I use the Trunnion Plates to mark up the Expansion Links in one place below.  Im sure it could have been calculated mathematically, but it was much easier this way!

On with the show!

Starting with the Expansion Links, these are the curved parts that the radius rod slides around in as the Reverse Lever moves the radius rod up and down to adjust direction and steam cutoff.

The expansion link blanks were cut from 0.080 sheet steel on the bandsaw.


However, the Expansion Links are supposed to be 5/65 thick, which is 0.078.  So I double-sticky taped the blanks down and skimmed a thousandth off of each side.


After sticky-taping the two blanks together I drilled three #49 holes.  Two of these will be used with #1-72 screws to hold the parts in the jig for machining and then will be widened to be #2-56 through holes. The last one is the lever arm that will connect to the eccentric rods (which we have yet to make). That last one was reamed to 5/64.


To facilitate cutting the arcs I drilled and tapped the 1-72 holes in the Rotary Table jig which was set concentric to the center of the RT.


Then mounting the blank pair on the jig I proceeded to mill the arc that the Link Blocks will ride in.   In this picture, I just completed milling this slot and Im using my favorite pair of tweezers to move the link block around to make sure its a close sliding fit.  Side note:  I was deathly afraid of having that little link block go flying across the room never to be seen again!  I tried to be super careful.  But I just had to test the slot before I could say it was done.  Luckily, I didnt lose the itty-bitty part.  But I sure worried about it. And Ive still got many chances to lose it yet!


With the slot cut, its time to cut the lower radius in the part:


Before cutting the top radius, I drilled a hole where I wanted my arc to stop.  Dont want to cut off the lever arm!


And then proceeded to cut the arc.


After taking off the scrap chunk I cut the angle across the top of the expansion links.


And thats as far as I could go on the expansion links till I made some progress on the trunnion plates.

Offline crueby

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Re: Pennsylvania A3 Switcher (Kozo)
« Reply #1439 on: December 16, 2021, 05:59:08 PM »
 :popcorn: :popcorn: :popcorn: