Little Engines 2.5" Scale Air Pump

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Mike Walsh
Posts: 599
Joined: Sun May 06, 2007 10:14 pm
Location: St. Louis, MO

Little Engines 2.5" Scale Air Pump

Post by Mike Walsh » Sun Jan 25, 2015 5:06 pm

Well, finally got some time after taking care of major tasks on the fleet earlier this winter to start this project.

Mike sent the castings promptly, and there was an issue with the drawings -- which was remedied quickly by Mike. Thanks!

Started off by machining the LH/RH Bobbins as well as Valve Cover Plates. I took care of the LH/RH bobbins, while I taught Kyle how to machine simple parts such as the valve cover plates.

We have a team of younger men who help with running repairs as well as general operation of the railroad. We've been teaching them new skills every chance we get.

Kyle did a great job of machining the valve cover plates -- he even pointed out that I ordered the wrong size material for the plates... The specs call for 1-3/8" wide brass, and I accidentally ordered 1-1/2". Whoops! Just meant a little more practice for him on the mill.

The bobbins were machined out of 303 SS. I could have externally threaded one bobbin, but I decided to tap it and I'll use a 10-32 setscrew loctited in place instead.

I think it all came out well. I just need to machine the screwdriver slots and that'll wrap them up.
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Mike Walsh
Posts: 599
Joined: Sun May 06, 2007 10:14 pm
Location: St. Louis, MO

Re: Little Engines 2.5" Scale Air Pump

Post by Mike Walsh » Sun Jan 25, 2015 5:12 pm

Today I wanted to make some progress on the castings. I wanted to get more done, but encountered a setup issue that required me to think differently.

First, cleanup of one face of the casting was needed. I aligned as best as possible, then started machining away.

Next, center drill, then a large drill bit. I worked slowly as I had to drill through the 2nd side of the face. This face on the inside of the casting is an uneven surface and I didn't want to throw anything off center.

Next, I bored out to 1.5" diameter.

I turned the casting around and chucked it up. Did a light cleanup cut, and checked everything over and noticed the center bore was off about 1/32". I realized that we had an expanding arbor set in the shop, and checked it... Sweet! It should work!

After setting up the arbor, I used the trusty last-word indicator to check the machined face. Within .0005"? Fine by me!

I made sure that the arbor ended INSIDE of the unmachined face about 3/16" as I had to machine about .106" away. I didn't want to hit the arbor.

Once I was done, there was a difference of 0.001" between the two planes. I'm ok with that.

I tore everything down after that and cleaned up shop. Time for mom's birthday dinner.

Looking forward to hearing from everyone else on progress of theirs!
Attachments
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Round and round she goes on the arbor...

Mike Walsh
Posts: 599
Joined: Sun May 06, 2007 10:14 pm
Location: St. Louis, MO

Re: Little Engines 2.5" Scale Air Pump

Post by Mike Walsh » Sun Feb 08, 2015 9:57 pm

Next up... The Steam cylinder!

I chucked up in the ol' LeBlond and did the best I could for lining up the casting...

Started with facing the first side of the casting. I had a few minutes of thinking as I was reviewing the prints and didn't want my mounting holes to be messed up. As a result, I wound up machining more off of this side than the other. Good thing I thought of this as that could have really messed up my operations!

After finishing the first face, I bored out the cylinder. Was aiming for 2.373" to allow for honing, but wound up at 2.375".. D'oh! I'll do the best I can with the honing operation later.

Next, I pulled out the trusty expanding arbor again and set up the cylinder, and that's all she wrote!

Next up -- the air cylinder.... And probably the cylinder head.

I'm trying to put off the valve head til I get more components made up.. That is one complicated bit. I know once I get the head faced off and started, it won't be that bad... But that 1-1/4"-12 thread gets me..

Mike
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apm
Posts: 178
Joined: Sun Jan 05, 2003 12:21 am

Re: Little Engines 2.5" Scale Air Pump

Post by apm » Mon May 22, 2017 6:55 pm

I hope I am not hijacking someone else's build log here but I thought I would toss my own efforts into the mix. I purchased the plans for this air pump and found the plans were less than desirable, and the valve mechanism at the top was far more difficult than it needed to be in terms of overall machining.

At the risk of having to eat my words and admit defeat in the not too distant future if it doesn't work I redid the entire pump in 3D cad where I found my interpretation of the hand written notes would have lead to a complete disaster had I even attempted to make the top manifold to the prints. So I decided to change the design quite a bit and go with two spool valves, the main valve is an outside admission spool with pilot pressure on either side, to drive it back and forth while the pilot valve is an inside admission spool valve. I have included some photos so far as well as a PDF of my redesigned spool type valve head. So far the construction is going a lot easier than I would expect the head design shown in the prints to be.

A big word of caution here, this design is completely unproven, I will be the guinea pig, secondly my drawings are only intended to help me build this thing and may omit key details that are still in my head and worth detailing out. But I do think that this is worthwhile enough to share with others who are considering building this compressor. I am hoping that by going with 2, 4way spool type valves it significantly simplifies the construction.

One other thing to share with others, I probably should have taken more photos but you can see it in the first. Once you machine the base I put the whole thing onto a fixture plate. That thing allows me to move things around very nicely, locate holes relative to the central one, and keep things square. I think it is a must in constructing this part.
Attachments
Air comp 1.JPG
Air comp 1.JPG (30.38 KiB) Viewed 1950 times
Air comp 2.JPG
Air comp 2.JPG (27.03 KiB) Viewed 1950 times
Air comp3.JPG
Aircomp4.JPG
Valve Head_Spool type.pdf
(137.72 KiB) Downloaded 40 times

User avatar
apm
Posts: 178
Joined: Sun Jan 05, 2003 12:21 am

Re: Little Engines 2.5" Scale Air Pump

Post by apm » Mon May 22, 2017 6:59 pm

One other neat little thing here, you can see there is an internal groove cut into the main spool body to allow the steam to travel to each side of the spool. For $45 and change here was a very nice little set of tools I picked up on eBay. These expanding mandrels made holding a difficult part really easy and are such a wonderful buy for what they charge.
Attachments
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brokenheart tools.JPG (26.08 KiB) Viewed 1948 times

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