"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 » Wed Oct 07, 2015 7:58 am

The steam chest covers were just cut-offs from the same Durabar cast iron blocks I had purchased for the cylinders. They were put in the mill and machined flat on both sides. Then, the tops were milled with a ball-end mill so that they would visually look like the cylinder covers. I suppose I could have just left them plain but I wanted something a little more special, without going crazy. The real ones didn't have fancy brass covers or intricate patterns and neither will mine. Very light cuts were done with the ball mill to prevent breaking it.
Attachments
rough machining steam chest cover.jpg
milling profile on steam chest cover.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 Oct 07, 2015 8:03 am

Finally, the cylinders, steam chests, and steam chest covers needed to be bolted or otherwise held together and that meant drilling 10 holes per assembly in each of the three parts... all hopefully in line with one another! I intended to use 10-32 hardware to do this, so first I laid out and drilled #21 holes in both steam chests. Then, for each assembly, the steam chest cover was clamped to the steam chest and I used the steam chest as a fixture/template to drill through the covers. Extra #21 drill bits were used as pins to prevent the parts from shifting alignment.

The holes for the steam chests and covers will eventually be opened up for the 10-32 hardware but as of right now they are only #21 because I am also using the steam chests to lay out the cylinders.
Attachments
clamping cover to steam chest.jpg
drilling steam chest cover.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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Location: Albany, NY

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

Post by Benjamin Maggi » Wed Oct 07, 2015 8:06 am

Then, the process was reversed and the steam chests were used to drill the cylinders.
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drilling cylinders 2.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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

Post by Harold_V » Wed Oct 07, 2015 2:52 pm

You might reconsider the use of NF threads in cast iron. Not a great idea.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

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

Post by Benjamin Maggi » Wed Oct 07, 2015 2:57 pm

Would 10-28 be better?
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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

Post by Harold_V » Wed Oct 07, 2015 3:05 pm

I think you mean 10-24.
Yes, it most likely would be a better choice, as NC threads are preferred when soft materials with little tensile strength are involved. You stand a better chance of resisting pulled threads if you avoid using NF.

If you decide to stick with NF, make sure your tap drill cuts size. Also, considering you have already drilled holes, you may discover that your choice will eliminate the use of NC, as the hole required is smaller in diameter than for the NF thread.

Cast iron is not known for tensile strength, although if your choice was ductile iron, not cast gray iron, NF might be fine. Still, I'd lean towards NC.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

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

Post by Benjamin Maggi » Wed Oct 07, 2015 3:07 pm

Oops, I most certainly meant 10-24.
"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 Oct 20, 2015 5:43 pm

The next step was "shaping" the square cylinder blocks into something that looked a bit nicer. The prototype ones had the lower outside corner curved back and I thought that would be appropriate here. Anticipating a lot of sawing, a new bandsaw blade was ordered and installed.

After applying blue dye to the lower portion of the rear end of the cylinder, I put the cylinder cover on the cylinder and then traced around the base with a scribe. This represented the very edge of the covers and the line which under no circumstances could I cut to. Then, looked for the shortest distance between this line and the edge of the square cylinder block (about 1/4" and used that amount as the edge of the profile. For the bottom portions of the cylinders, I drew a dropping angled line. However, I was sure cutting to that line would be very difficult because the amount to remove was so thin.

Then, working slowly and by cutting off tiny bits along the way, the shape emerged. I couldn't bend the cylinder as if I was using a jigsaw so I only cut about 1/4" along the profile line at a time and then cut another line from the edge of the cylinder to intersect with where I had just stopped. It took about 10-12 passes to do each curve, made up of smaller chords. In all, it only took about 20-25 minutes per cylinder and the blade cut the metal easily.
Attachments
Cylinders shaped with bandsaw.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 Oct 20, 2015 5:45 pm

Then, the cylinders were taken to a 6" belt sander and aggressively sanded along the cut areas to remove the bandsaw blade marks. It went really well. The only problem was that the cylinder got hot after a while and I had to let it cool down.

In the end, both cylinders were so smooth that I may not even need a cylinder cover to dress them up, unless I want to use brass for a smarter appearance.
Attachments
Sanding cylinder with belt sander.jpg
Finished cylinder.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

User avatar
Benjamin Maggi
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Location: Albany, NY

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

Post by Benjamin Maggi » Tue Oct 20, 2015 5:49 pm

Using a 10-24 tap in the tapping head and then I tapped all 20 holes in the top of the cylinder. Each hole was flooded with lubricant to prevent any nasty surprises. No problems were encountered, but two of the holes on one of the cylinders had obviously broken through to the end holes when drilling and that may prove troublesome. Essentially, the very top cylinder cover mounting holes interfere with the middle steam chest bolt holes. I will need shorter bolts for that intersection.

Then, I took the steam chest and their covers and opened up all of the #21 holes so that the 10-24 bolts could pass through. I started with a 3/16" (0.1875") bit but it was slightly too small so I then changed to a #10 (0.1935") bit which was just right. Keeping a very slow feed rate helped a lot, as the cast iron had a tendency to grab the bit.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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

Post by SilverSanJuan » Tue Oct 20, 2015 8:11 pm

Nice work, Ben. The cylinders look really good.

Todd

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

Post by Harold_V » Wed Oct 21, 2015 12:58 am

Yes, very nice!

Cast iron, as well as most of the copper alloys like to self feed when opening up a hole. You can limit that problem by simply putting a small flat on the cutting faces of the drill. Make the flat parallel to the centerline of the drill. That reduces the rake angle to 0, and solves the problem. If you keep the flat short, the drill can then be restored to original condition simply by resharpening.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

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