"Catherine", a USA "Sweet Pea" engine build

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Thu Jul 02, 2015 5:23 pm

Some holes were later opened up so that the blade of a Sawzall could fit through. Then, the steam chest was clamped in a vice and the holes were all connected. It worked fine though the inside looked like it got attached by a shark!

Some work with the bandsaw then removed the larger areas of unwanted metal around the edges.
Attachments
sawed out steam chest.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Thu Jul 02, 2015 5:25 pm

Then, the piece was put on a surface grinder and rough passes of 0.005” and later finish passes of 0.0025” were taken to bring the thickness of the chest to a consistent dimension.
Attachments
machining on grinding table.jpg
surface ground steam chest.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Wed Jul 29, 2015 4:51 am

The valve stems enter the steam chest through the rear spigots and pass through and are supported by the front spigots. The plans originally called for longer spigots but we decided to shorten them a bit to allow us to use the cast iron we had on hand. We may add extensions to them if necessary.

The steam chests were mounted in the mil and then a boring head was used to turn the spigots round. It was a fascinating machining process that I had never seen done before.
Attachments
Ready to turn spigots.jpg
Turning with boring head.jpg
Finished spigot.jpg
Last edited by Benjamin Maggi on Fri Dec 04, 2015 1:17 pm, edited 2 times in total.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Sep 01, 2015 7:24 am

The original plans for the steam chests called for drilling a long hole through each of the two spigots (one on each end of the steam chest) which the valve stem would pass through. Being typical European/British practice, the stem would be supported on both ends of the steam chest instead of the rear one only. On the end of each spigot, a brass “gland” was to be turned and then bolted to the spigot with three tiny bolts.

For the sake of simplicity, I decided to instead only drill through the rear-facing spigot on each steam chest. This means that the valve stem will only be supported in one place as it enters the steam chest instead of two; however, many steam locomotives running in America do this so I am confident that it won’t be a problem. I may add a cosmetic touch to the front spigot or I may mill it off completely. It wasn’t drilled through to the steam chest so I don’t have to blank it off at any rate to avoid steam loss.

Instead of the glands, which were also specified for the piston rods, I will again turn to compression nuts. These seem much easier to adjust and will eliminate the need for super tiny bolts which may or may not be easy to remove when the time comes. Having chosen this path, I machined the rear spigots to accept the compression nuts.

The steam chests were clamped in the drill press and various checks were done using squares to ensure that the spigot was indeed perfectly parallel to the drill bit. Then, I drilled through with first a 1/4" drill and later opened up to a #G size (0.2610”) drill. My valve stem material is slightly oversize 1/4" diameter SS rod and was binding until we slightly enlarged it.

For the area which we would later tap to accept the compression nut, I drilled down partially for a depth of about half an inch with a 29/64” drill. This was the size required for the 1/2-20 tap, which was done next. Then, all that was left to do was deburr the hole on the inside of the steam chest and it was set aside.
Attachments
11.jpg
Last edited by Benjamin Maggi on Fri Dec 04, 2015 1:19 pm, edited 4 times in total.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Sep 01, 2015 7:27 am

The compression nuts are machined from 7/8” diameter brass rod. Their overall length is about 0.80” but I machined them slightly longer for two reasons. First, it is much easier to shorten something than it is to lengthen it. Secondly, the spigot on the steam chest is slightly too short compared to what was called for and I plan to compensate for that with a slightly longer compression nut.

Then, I turned down the end of the rod to a diameter of 0.515” for a length of 0.600” (which is slightly longer than required, but it can be shortened later). Threads were cut ½-20. Then, the collet was removed from the lathe and put in a square collet holder for drilling the four 3/32 holes which will be used to turn the compression nut.
Attachments
15.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Sep 01, 2015 7:30 am

The compression nut was screwed into the steam chest spigot and the valve stem was tried through the hole. It didn’t fit in nice and smooth so the #G bit was rotated in the hole while spinning the compression nut round and round, which slowly removed little bits of metal that were causing the problem. It took a little time but the results were smooth holes through the nut and spigot that were perfectly in line.
Attachments
16.jpg
Last edited by Benjamin Maggi on Fri Dec 04, 2015 1:19 pm, edited 1 time in total.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Sep 01, 2015 7:34 am

The valves started off as part of some 2” square brass stock. After milling both surfaces (top, bottom) so that they were nice and smooth, abrasive paper was put on the surface plate and the bottom bearing surface was worked over even more. It was also test fit into the steam chest and as a result I did some filing on the sides of the chest to remove any areas that might hit the valve.
Attachments
v4.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Sep 01, 2015 7:36 am

The bottom area was milled away but care had to be taken because again the brass was a bit sticky. As luck would have it, we were just nearly done with the second one when the cutter broke. Thankfully, it was while we were removing metal from the middle and not along the edges which may have resulted in a deformed border.
Attachments
v6.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Joined: Wed Apr 25, 2007 10:38 pm
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Sep 01, 2015 7:41 am

The original plans specified a raised area on the valve which would have a hole drilled through it for the valve stem to pass through. The stem would be threaded in the area that passed through and a nut would be threaded onto the rod, one on each side of the valve, which would secure the settings of the valve. This seemed a little tedious and also meant that any adjustments would require removing the steam chest cover. Instead, we modified the design so that a drive block would fit into the valve and the block itself would be threaded. Rotating the valve rod stem the end would slowly adjust the valve forwards or backwards and the cover wouldn’t have to come off. (In reality, the cover may be off anyways for valve setting but at least it isn’t required now.) The downside is that all adjustments have to be in 1/2 rod rotations as the fork on the other end still had to mate up with the crosshead.

Cutting the slots for the drive block made a mess of the mill, and it seemed a shame to lose so much brass in the process.
Attachments
v9.jpg
Last edited by Benjamin Maggi on Fri Dec 04, 2015 1:20 pm, edited 2 times in total.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
Posts: 1093
Joined: Wed Apr 25, 2007 10:38 pm
Location: Albany, NY

Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Sep 01, 2015 7:45 am

The drive blocks are just steel with a ¼-20 hole drilled through them. They are a slip fit into the valves. I don’t know how much slop should be incorporated here so for right now I will leave the fit as it is.

The valve stems are just 1/4" diameter stainless steel rod that we threaded 1/4-20 on the ends.
Attachments
v12.jpg
Last edited by Benjamin Maggi on Fri Dec 04, 2015 1:20 pm, edited 1 time in total.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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FLSTEAM
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by FLSTEAM » Tue Sep 01, 2015 8:01 am

WOW, this is starting to look like a real engine. Nice work.....

John B.
http://www.ngshay.com/
Shay drawings and castings

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Sep 01, 2015 8:39 am

It took me by surprise too! The cylinders consumed the most time (and they still aren't done yet) but I already feel as though I can start to breathe easier. Messing up parts and having to redo them is no fun, but I would rather redo almost anything compared to a cylinder.

I am sure you felt the same way with your shay's cylinders, or the crankshaft!
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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