Textile Mill Diorama

[mklotz]

Marv, do you remember when we bored the tapered holes in the spindle of our PMR engine lathes? I bought the #4 taper reamer to represent that Morse Taper. I think we used it on the drill press quill as well, but I never thought I'd be using mine again.

And here is a #4 taper pin in the crosshead of the mill engine!

I remember it well, John.  In addition to mimicking Morse tapers at 1/12 scale, they work well for making self-aligning structures.  That might be handy for building the engine in a bottle I've been nattering about in another thread.

[J.L.]

Hi Marv,
Must find that thread.

Now that I've got an engine that is progressing nicely, I thought I would go back through the files and have a look at the development of the diorama since the project began.

First Photo: Feb. 2, 2018
Second Photo: April 10, 2018
Third photo: July 26, 2018

[Kim]

Wow! That really compresses a lot of work into three easy photos!
Beautiful work at every stage John.
Kim

[J.L.]

And so begines the slide valve.

On page 29 of this thread, Tug forwarded a tip given to him by a former member, George 'KBC'. Instead of threading the valve rod and nut, the valve rod is kept smooth with a nicely fitting holein the valve nut to suit. This allows infinite adjustment of the valve. The nut could be easily adjusted back and forth with a hex headed grub screw.

Bill mentioned that allowing the valve to 'float' a bit was also important. I would not want to lock the valve itself to the valve rod. Its four tangs give it some play in the nut.

So I'm going to give it a try. Notice in the photo that the end of the valve rod has a flat filed on it. This is to prevent hydraulic lock in the tail rod guide.

[J.L.]

Thanks Kim.
John

[b.lindsey]

Still checking in regularly John. The valve sub- assembly is looking good. Anxious to see how the grub screw adjustment works out for you as well. Since you are still using the nut, that should allow all the "float" you need. I had thought previously that the nut would be eliminated with just a straight holes though the valve slide, hence my concerns.

Bill

[J.L.]

Thanks Bill. Your three PMR#5 pictures posted on July 4 (reply #139) tell the story of the slotted slide valve and rectangular nut.

A quick question - how deep did you cut the square recess for steam exhaust; 3/32", 1/8"?

I guess depth isn't too important unless you cut into the meat for the four tangs on the ohter side!

John

[J.L.]

The plans call for a 7/8" square slide valve giving a 1/16" lap.

Looking good so far...

[b.lindsey]

John, I looked and the recess is 1/16" as noted in the plans for the PMR #5.

Bill

[J.L.]

Thanks Bill.  I found the depth dimension on another sheet of the plans. The depth is 1/8".

It's interesting how things change. When the original drawings were made in 1946, there was no valve nut at all. A central flat was filed in the valve rod that dropped down into the slide valve's forks. Imagine. Not much room for adjustment or strength there.

Also the cavity in the bottom of the slide valve was rectangular; 1/2" x 5/8".

Winter's 1992 drawings show a modification to the threaded valve nut. The cavity was also drawn square; 1/2"x 1/2" or whatever the distance is between the inner edges of the ports.

This little part is trickier than you would think.

I understand you made a second one out of bar stock. If I screw this cast one up, I may be doing the same.

John

[J.L.]

The recess has been milled.
I'm finding the circular saw very handy lately. It gives a clean, controlled cut.

[J.L.]

I think the grub screw in the valve nut is going to work. It certainly will be infinitely adjustable.

It's ready to party! Mind you, it's not hooked up to anything yet...

[Admiral_dk]

Looks like you nailed this perfectly John - all coming together nicely so far 

Best wishes

Per

[J.L.]

Thank you for your kind words. 'So far...' is the operative word.

A considerable amount of time was spent machining the valve rod guide. I like the casting's spine and backward bend as it reaches out from its pad.

I had no idea that I was going to be able to clamp the entire assembled engine on its side in the milling vice to drill the threading holes.  A scary moment...

[b.lindsey]

Really nice work John!! That should work well though it still seems the steam chest cover has to be removed to adjust the valve rod .

Bill