Author Topic: "Robby" a Novel Mill Engine  (Read 24628 times)

Online b.lindsey

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Re: "Robby" a Novel Mill Engine
« Reply #105 on: March 17, 2016, 01:01:39 AM »
That looks good Tim. Maybe just  couple of holes in the nut for a pin type spanner.  How deep is the o-ring groove?\

Bill

Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #106 on: March 17, 2016, 12:27:50 PM »
That looks good Tim.
Thanks.
Quote
Maybe just  couple of holes in the nut for a pin type spanner.
Just what I was thinking. And it occurred to me that if I was too lazy to make the spanner, that sticking the tips of a pair of needlenose pliers in the holes just might work as a spanner.
Quote
  How deep is the o-ring groove?\
Good question. I'll start with what the groove dimensions should be: The o-ring has a cross-sectional diameter of .07. The recommended groove would be .093 wide and .056 deep as measured from the cylinder bore. My attempts to make the groove with a parting tool were less than successful. My groove is slightly deeper and slightly narrower than the recommendation. Still, it seems to seal well in the cylinder without too much friction. If there are problems, I could make another piston (after grinding a proper tool to make the groove).

--Tim

Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #107 on: March 17, 2016, 03:57:08 PM »
You may remember that the cylinder passages are terminated in drilled holes in a flat valve face. on the cylinder. I now had to make a port plate for that face to provide the actual ports that the valve will operate against. The part is simple enough, but the placement of the port slots is critical, and the thin (1/32") brass used requires care in clamping. I started by clamping a scrap of tooling plate to the mill bed and milling a recess to locate the plate.


Note that by running the corner of the recess off the edge of the tooling plate, I eliminated the necessity of milling a square inside corner. The brass plate had been squared up on the sides which meet the sides of the recess. The other 2 sides are cut oversize and will be milled off later in this setup.


The locator recess allows me to move a single clamp around as needed to access the perimeter of the plate. I used a parallel to spread the clamping force.


I first drilled for 4-40 threads, then drilled only through the brass for 4-40 screw clearance, then tapped 4-40 into the tooling plate. A clamping screw could then be placed.






By moving the clamp around and repeating the process, I drilled all mounting holes and provided for enough clamping screws to proceed with cutting the port slots.


Cutting the port slots.




Then I milled the two unfinished edges to size.


The cast iron steam chest is a part which has not been documented here. I made it one day while "in the zone" and in the shop without a camera. I had left the outside edges unfinished. How convenient that I now had this ready fixture with the correct holes tapped for clamping to finish the job.

One thing to notice about the otherwise nice steam chest is that there is an unintended center drill in the upper left corner. Harmless enough, and it will be hidden by the cover, but another mindless and maddening mistake. The steam chest still needs the male portion of the packing gland turned on the right end as pictured. It also needs the steam inlet port drilled and tapped.



Thanks for watching!

--Tim

Offline sssfox

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Re: "Robby" a Novel Mill Engine
« Reply #108 on: March 17, 2016, 04:25:01 PM »
Tim,
wouldn't it have been easier to drill through holes in the steam chest and use one set of bolts, sorry screws, from the cover to the cylinder instead of a two stage attachment?

Just asking,
Steve Fox

Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #109 on: March 17, 2016, 04:37:49 PM »
Hi Steve,
That would have been easier to build, but I want to be able to take the cover off without disturbing the placement of the steam chest. I'll want to time the eccentric, for instance, by removing the cover. Since the valve rod goes through a hole in the chest, I want the chest to stay put once I have aligned it, to prevent jamming of the rod. That is at least my reasoning.

A good question, by the way.

--Tim

Offline zeeprogrammer

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Re: "Robby" a Novel Mill Engine
« Reply #110 on: March 17, 2016, 09:26:36 PM »
Nice to catch up here.

I hadn't seen a 'round' nut before (that I can recall), and I understand the idea of a couple of holes for tightening it.

But why 'round'? Why not just a regular nut? (No implication that it should be something other than what you did...just wondering.)
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #111 on: March 17, 2016, 10:41:48 PM »
Hi Carl,
The idea of making the "nut" round is that it will fill the cavity I bored in the piston. Any space left at the end of the cylinder when the piston is at the end of its stroke is "dead volume" and could be considered a negative aspect of the design. Does it really matter in this little engine? Hardly, if at all. I'm just doin' my thang.

--Tim

Offline sssfox

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Re: "Robby" a Novel Mill Engine
« Reply #112 on: March 17, 2016, 10:56:36 PM »
I've seen nuts like this before, but can't recall where.  I think it must've been on a camera.
The only use I can recall now is on Leigh woodworking jigs.  They use this design to adjust the depth of a tapered bushing to change the clearance.

You can see the design here:
https://www.leighjigs.com/ugs.php

The threads are on the outside.   Come to think of it, I think the other ones I remember had the threads on the outside too, not that it makes a difference.

Works for me.

Offline zeeprogrammer

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Re: "Robby" a Novel Mill Engine
« Reply #113 on: March 17, 2016, 11:26:11 PM »
Does it really matter in this little engine? Hardly, if at all. I'm just doin' my thang.

Works for me.

I thought it interesting and cool.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline Art K

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Re: "Robby" a Novel Mill Engine
« Reply #114 on: March 20, 2016, 03:21:08 AM »
Tim,
I got behind, I think I missed your posts, now I'm all caught up. Things are looking good and coming along well. See you at names.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline chrisinestes

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Re: "Robby" a Novel Mill Engine
« Reply #115 on: March 20, 2016, 05:18:52 PM »
I've been a lurker here mostly... Signing on to this thread will get me coming back more often.

Cool looking design... Maybe one day I'll be good enough to tackle something like this.

Thanks for taking the time to document the build.

Chris

Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #116 on: March 21, 2016, 08:18:49 PM »
Thanks Art, see you at NAMES. Look forward to seeing where you are on the Val project at that time.

Chris, thanks for checking in and glad you're watching.

--Tim

Offline tvoght

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Re: "Robby" a Novel Mill Engine
« Reply #117 on: April 27, 2016, 01:15:17 AM »
My write-ups for this project took the back seat to productive shop time as the NAMES show crunch set in. Sadly, not only did I neglect the write-ups, but I forgot to photograph much of what was going on.

 I'll do what I can to catch you up.

I showed where I was on the steam chest back when I showed the port plate. Here's a quick review of the chest as I showed it then:


I managed to make the steam chest cover from scrap cast iron I sawed off to make the cylinder. Here you see one side of the scrap plate milled flat and drilled for screws. I outlined the outside dimensions of the cover with a 1/8 inch endmill.
I then sawed near the milled lines leaving some for cleanup. Finally, back at the mill I cleaned up the other side, and cleaned up the saw lines at each edge using the previously milled outline as witness.



I mounted the chest on the cylinder with the brass port plate, and with the cylinder mounted on the frame, I could then use a drill bit through the valve rod guide to mark the exact location for the valve rod hole in the chest.


With the rod location marked, I centered the mill's DRO on the mark and drilled the rod clearance hole. I then cut away excess material around the packing gland boss.


I used an inward-facing tool in the boring head to cut the boss round concentric with the drilled hole. The boss was threaded for the packing nut using a die holder in the same setup.




Thanks for watching.

--Tim

Online b.lindsey

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Re: "Robby" a Novel Mill Engine
« Reply #118 on: April 27, 2016, 01:30:05 AM »
Nice to see an update Tim. The steam chest looks great.

Bill

Offline Don1966

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Re: "Robby" a Novel Mill Engine
« Reply #119 on: April 27, 2016, 01:12:26 PM »
Beautiful work Tim and glad to see progress........ :ThumbsUp:


 8) Don