Pennsylvania A3 Switcher (Kozo)

[Kim]

Chapter 31.3 – Glass Tube and Gland Nuts

Today I made the glass tube and the gland nuts.

However, before I started that, I had two more plugs that I had to make. Guess I missed these yesterday.  The one on the left is a plug for the top glass tube connector - that tube has to be open so you can insert the glass tube, then you plug it up with this plug.  The one on the right is for the bottom of the brass column.  Having a plug at the bottom of this allows you to drain the water out of the sight glass.  Having the column open also allows you to drill the steam passages. But being able to drain is the important reason (I’m saying anyway ).


Now, on to today's main event.  I made the gland nuts first. These are a little more complex than your standard union nuts.  First, you drill through with a drill that is 0.008” larger in diameter than your glass tube.  Since my tube was 0.238”, I used a letter D bit which is 0.246”.  Nice that the letter drills worked out so close for me, isn’t it?  To make a spot for the O-rings, Kozo specifies making the hole 0.125” larger than the OD of the glass tube.  So for me, that was 0.363”.  The closest drill I had to that was 23/64” or 0.3594”.  Pretty close -within 0.004”. The next closest was “U” at 0.368”.  I chose to go under by 4 thou rather than over by 5.  Probably six to one, half a dozen to the other…


And finally, I drilled and tapped 7/16”-24.  This is a very thin nut - there is only room for about 4.3 threads.  Even a bottom tap has several threads of taper on the tip of the tap. So I got TWO bottom taps and ground one to where the taper was almost gone completely. I tapped with the un-ground bottom tap to start with, giving a full thread or two. Then  I followed it up with my ground off tap. This gave me at least 4 full threads!  I was pretty pleased with that.  I wouldn’t want to thread much with this severely ground tap, but it worked to clean up those last couple of threads so they were usable.


I then cut the nut off (with appropriate chamfering).  And made a second one.

Finally, I needed to cut the glass tube to length.  Cutting glass always scares me, but this worked out pretty well.  I put some tape on the area where I was going to cut. This not only allowed me to mark my cut, it also served to help keep the glass chunks under control, should I break it.  I then used a carbide tipped scribe to scratch around the glass tube, scoring it nicely where I wanted it to break.


I then VERY GENTLY placed the part in the soft-jaw vice with the scribed line right at the edge of the jaws.  There was minimal pressure on the glass, and the tape helped protect the tube too.  Then I winced and did a quick snap right at the edge of the vise.  Magically enough, the tube broke right where I wanted it to!  And it was mostly a clean break.  I did it a couple of times and picked the best one.  Then I cleaned up the ends on a fine grinding wheel (with the tape still in place).


And here are all the parts I made today


It took a bit to figure out how to assemble it.  I started by wedging the o-rings in the bottom of those nuts in the flat that was made for them. Then I threaded them in place, leaving them very loose.  Next, I worked the glass tube down through the o-rings and gland nuts till it was in place. Then carefully finger tightened the gland nuts.  And finally, put the top plug in to close it all up.

And here it is, all done.  Even seems to hold air!  I’m getting some leaking around the manifold – don’t think my blank plugs are holding well.  Or maybe it's my gasket?  But the sight glass didn’t seem to leak, as best I could tell.  Probably should do a hydro test.  And maybe I will eventually. But not today.




And that wraps up Kim’s day in the shop.  Thanks for stopping by
Kim

[crueby]

Nice!  For cutting the glass tube, I've always used a triangular needle file and scored around the tube with that, less pressure than using a scriber tip, just normal filing action. The tape and the rest are the way to go.
 

[Kim]

Nice!  For cutting the glass tube, I've always used a triangular needle file and scored around the tube with that, less pressure than using a scriber tip, just normal filing action. The tape and the rest are the way to go.

Interesting... I originally tried a small triangle needle file but it didn't seem to be biting into the glass at all - didn't seem like I was getting a score line.  Maybe my needle files are just too old and dull?  Or maybe that's just me that's getting old and dull 

Kim

[cnr6400]

  I've also had good luck with scored line / sharp file / snap method for cutting glass tube. Deep score and a hard snap are needed for thicker glass. Drop of oil sometimes helps, but I have no idea why.  Paging Bill Nye, come in Bill Nye....

[crueby]

A lot depends on the file - many of the needle files don't have teeth on the corners. I've got a couple sets, one of them is fairly smooth on the corners, other has teeth there. Or, as you said, could be just dull. Nice thing about the file trick is that you dont have to put as much pressure on a small curved surface as with a scriber. If you have a diamond coated file, that is the best choice since it will cut glass nice and evenly.

With either tool, and after snapping it, vacuuming right away to catch any glass dust is a good idea.

[Firebird]

Hi

I bought one of these little gadgets. £6 - £7 on eBay. They work really well.



Also after cutting I heat the end of the tube with a small torch and that removes the sharp edge.

Cheers

Rich

[Firebird]

sorry about the over size image I forgot to re-size it

[scc]

Nice job Kim 

[Kim]

Thanks Terry!

That looks like a nice little tool, Rich!  If I were doing any amount of glass cutting, I'd have to pick one up!

Kim

[Kim]

Chapter 31.5 – Blower Valve Parts

The next item to focus on is the Blower Valve.  This is a valve that allows you to send some seam directly up the smokestack to help increase the air drawn through the firebox.  From a big-picture view, the valve will take steam from one of the bushings on the backhead of the boiler and send it through a little tube to another bush on the backhead which is plumbed straight through the boiler to the front, where the blower is positioned under the smokestack.  Most of this pathway already exists, but the control valve and a bit of plumbing to get the steam to the blower bush on the backhead remain to be done.

The first thing I’ll be making is a round handle for the blower valve stem.  I’d originally specified in my BOM to use 3/32” brass sheet for this. But on some reflection, I chose to make it from a slice of 9/16” diameter brass rod.  I think this worked out much easier than the sheet route.

Starting with the rod, I faced it and started to part off a 3/32” wide disk, but didn’t finish that job.  I wanted the disk to still be connected to the parent stock for a while as it’s easier to hold this way.  With the disk defined on the end of the rod, I rounded the edge with a file and drilled a 3/32” center hole in it.


Then I moved the rod over to the mill and mounted it in the spin indexer.  Using a 3/32” ball nose mill I cut 12 notches around the perimeter – every 30^o.  The spin indexer made this a cinch!


Back to the lathe, I trepanned a little out of the middle using a 3/8” end mill, then finished parting it off.


Now, back to the mill where I found the center of the valve wheel using a gauge pin, then proceeded to drill four holes to open up between the spokes.


I considered leaving it like that – with the holes.  But Kozo’s drawing shows more pie-wedge shaped openings between the spokes.  So I used a tiny diamond needle file to open them up some.   Looking at the results, I probably should have stopped while I was ahead, with the round holes.


I may try to even things up a little more tomorrow when I’m feeling a little fresher. Or I may just leave it so it doesn’t get worse!  I’ll sleep on it for a bit.

I’m just not that good at freehanding things, you know? 

Thanks for checking in on me!
Kim

[cnr6400]

  Great looking valve handle Kim! I wouldn't worry about the openings being exactly to drawing (they look just fine to me, in any case). One way to take viewer's eyes away from the openings though might be to paint the handle centre a dark colour. Just food for thought.

[Kim]

Thanks, Jeff. 
And a great idea on painting the 'spokes' of the handle. That's a viable option!

Kim

[Prowler901]

Not sure what you're on about,  Kim.  The handle looks great

Todd

[Roger B]

What a wonderful little hand wheel   

[Kim]

Thank you Todd and Roger!  Appreciate the support! 

Kim