Pennsylvania A3 Switcher (Kozo)

[cnr6400]

 

[Kim]

Thank you for following along Achim and CNR,
I really appreciate people watching to make sure I'm not doing anything too boneheaded! 
Kim

[Kim]

Here’s the tie plate after some clean-up.  You can see that the feet stand a little proud (1/64”) of the bottom of the tie plate.  That will come off here soon.


But first, I drilled the 3-48 mounting holes to mound the tie plate to the chassis.


After this, I shaved down the feet and took a very light skim off of the bottom just to make sure things were completely even.  I also took this opportunity to shave the feet down to size (I’d left the length a little oversize before).


Next we have to cut a very small relief angle in the bottom of the plate in two places. Kozo specifies 55^o, though I doubt the angle is really that critical.


Because it’s just to make sure the tie plate clears the rims of the drivers.  It’s important to clear the drivers for sure!  But I’m not convinced that the 55^o angle is super important to that!   Here’s a shot to show you what that little clearance cut was for (see the little tiny notches right over the rim of the front drivers? - that's what I just cut.)


Now I need to drill the holes to connect the yoke guides (3 on each side):


And tape them 3-48.


The final op for this piece is to take the curve out so that it nests with the boiler well.  I know you could just hacksaw and file this out, but I want to do it on the rotary table.  To do this, I drilled a couple of holes in the piece that will be removed.  These are tight clearance for 10-32 screws.


And finally, I drilled some matching 10-32 tapped holes in a piece of aluminum that I use for a rotary table jig.  It already has some nicely placed 1/4" holes in it.  So I used one of those holes, and measured out with the DRO, and placed my holes.  Unfortunately, I did my calculations wrong.  This should make a 1.875” radius arc, instead, I’m getting a 1 3/4” arc.  But after being frustrated with myself for a bit, I’ve now figured out that I can use this anyway. All I need to do is shift the jig over 1/8” on the RT before I start. And I should be golden.  The locator hole doesn’t really have to be at the center – that was my original intent, but my poor math prevented that from coming true.  But it shouldn’t matter.


Anyway, we’ll see if my jig-save works tomorrow.  I’m done for today.

Thanks for taking a look!
Kim

[kvom]

You'll need to attach "feet" to the yokes as well.  Make these oversize so that you can adjust their thickness to get the attached guide bars horizontal and parallel.  Once the bars are good the crosshead fit can be adjusted by the slippers.

[Roger B]

It all goes round and goes along     

The first big step     

[Kim]

Yes!  Quite exciting for sure!  Thanks Roger 
Kim

[Kim]

You'll need to attach "feet" to the yokes as well.  Make these oversize so that you can adjust their thickness to get the attached guide bars horizontal and parallel.  Once the bars are good the crosshead fit can be adjusted by the slippers.

Thanks for the warnings, Kvom.  I appreciate the insights from someone who's been through this before!

I have been thinking of how to do the yokes to keep things all parallel and aligned.  With your input, I think I have a pretty good plan. (Famous Last Words!)

Kim

[Kim]

Well, I ended up re-doing my jig.  While I might have been able to just slide the jig 1/8” from the center of the RT it would have had to have been slid in a straight line – parallel to my direction of offset.  And I had no way to guarantee that other than eyeball.  And if it was off from the offset axis then my arc would be off-center.  I didn’t want to chance that.  The cost to drill & tap a few new holes was very small too

With that done, I centered up the rotary table with the coaxial indicator (cool tool alert!)


Then centered the jig on the center hole using a 1/4" gauge pin.  While the jig was held on center with the gauge pin I clamped things down with a bunch of hold-downs.  Then spent 45 minutes re-arranging them and swapping them out for shorter ones in order to find a way that I could get the mill to cover the entire sweep of the arc.

Once I finally had that, I used 1/4" drill to chain drill around the edge of the arc.  I moved it in 0.020” from the final dimension and will clean up that last 20 thou with the end mill.


Then moving to a 1/4" 2 flute end mill I proceeded to complete the arc.  Then I widened the arc those last 0.020”, with the final pass being a few thou climb mill.  It left a really nice surface on the arc.


And here’s the final tie plate.  I’m pleased with this!


Now onward and upward to the guide yokes themselves.
Kim

[crueby]

Very nice boat cradle. I mean tie plate!

[Kim]

Very nice boat cradle. I mean tie plate!

Hey, it does look like that, doesn't it? 

[steamer]

His prints have always entranced me.    They are so nice, and clear and well presented!

That saddle looks awesome Kim....even if its only for a boat......



jk


Dave

[90LX_Notch]

Nicely done Kim.  Parts like that always look easy at first.  Then reality sets in.


-Bob

[Kim]

Thanks Dave and Bob! 

Dave, I have made a few model ships and have some cradles that really were for ships.  But you've made the REAL THING!  I'll bet you had bigger versions of that cradle for your boat! 

Kim

[cnr6400]

 

[Kim]

Thanks CNR! 
Kim