1.75” Minnie traction Engine

[dnalot]

Having recently completed a “Clayton Steam Wagon” I decided I like big projects that take some time to complete. While building the Clayton I acquired the original book on the Minnie designed by Leonard C. Mason in 1969 in 1” scale. And a set of drawings in metric by Arthur Droves. The metric drawings were very helpful in that they were very detailed and had exploded views of the parts.

I decided on the scale based on the limits of my machines and a piece of 4.5” copper tube I had in stock. With an expected weight of 90 pounds it’s also the largest I can lift.

Step one, draw all the parts to the new scale using “Draftsight”. So that took a while but I now fully understand the plan. As I made my drawings I acquired most of the materials I would be needing for the Minnie.
The first thing I did was build a fixture to hold the boiler and a rotating platform for it to sit on. The fixture will come in handy for holding the engine during assembly but first it will be used to mount the boiler to the mill for a lot of drilling.

The boiler is the biggest expense and probably the most difficult part of the build so that’s where I will start. It’s not easy to heat up 30 pounds of copper to 1180 degrees for silver soldering. I love pounding on copper. It is amazing how easily it forms and how close to the final shape & fit you can get by hand. Everything else about copper sucks.

I am planning on an operating pressure of 80 Lbs so I tested the boiler at 200 PSI. I would like to say I had no leaks but you know that never happens. I had a few and fixed them before moving on to the next step.

Overall length 15.5” width 4.75” height 8.25” Weight 30 pounds. Material; Copper

Well its a start.

Mark T

 

[Herbiev]

Wow ! Very impressive work. Will be following with great interest. is that a pneumatic scaler you are using as a riveting gun?

 

[dnalot]

is that a pneumatic scaler you are using as a riveting gun?

Hi

I am a licenced Aircraft mechanic and that is my short stroke riveting gun, been using it since 1974.

Mark T

 

[bmac2]

Hi Mark
Great work I’ve got my chair pulled up as and the kettle on. I like those little spring clamps on the water jacket I don’t think I’ve seen them before. Being your short stroke gun is from 1974 would it be safe to assume that it isn’t stamped “Made in China”?

 

[Jasonb]

You are off to a good start, did I see you have fitted a clack bush inplace of the boiler mounted pump which is a wise thing.

J

 

[dnalot]

I like those little spring clamps on the water jacket I don’t think I’ve seen them before

Do a google image search for "cleco" and you will find a wide variety. The are used by aircraft sheetmetal workers. They are small but very strong. McMaster-Carr has a few.

Mark T

 

[dnalot]

I see you have fitted a clack bush inplace of the boiler mounted pump

I wanted to mount the pump lower so it would not have to lift water to get primed.

Mark T

 

[dnalot]

Being your short stroke gun is from 1974 would it be safe to assume that it isn’t stamped “Made in China”?

Made in England actually.

Mark T

 

[dnalot]

Next up cutting the gears. Never tried that so I expect it to be challenging.

The original model called for gears made of steel. I plan to use as little steel as possible to avoid rust over the long term. The smaller gears I will make from silicon bronze cut from round bar stock. The three larger gears I will need to cast planks for. I have salvage Aluminum Bronze for that. Thirteen gears in all. From 1” 12 Tooth to 6.8” 82T. Five of the gears are for an added feature the original model lacked, a differential.

Using my CNC router I made a indexing disk that I will use for all my indexing needs for this model. I designed and built a fixture for cutting all of the gears. With a spread in diameter from 1” 6.8” and several different hub diameters the fixture turned out to be a bit of work. The mandrels will also be used to turn the gear blanks to the correct diameter. The round blob next to the indexing ring on the fixture is a 6 pound lead half round. It takes out most of the fixture’s vibration and ringing. The pitch for the gears is 12, the depth of the cut is .1853”. I didn’t think my little SX3 mill could handle that in one pass but it did very well. I recently upgraded its lead screws with ACME Ultra smooth threaded rod and self-adjusting nuts in anticipation of this job.

Link to mill upgrade

http://www.homemodelenginemachinist.com/showthread.php?t=24448



Cutting the first gear was a lot of fun. After that it was just a lot of repetitious work. I cut at a rate of about 40 teeth per hour. With my home made fixture it took longer to set up a cut than it did to make the cut. I only needed to cut 367 teeth so I took my time. To sum it up, the hardest part of making gears is paying for the cutters.

The steering worm gear set I purchased.

Mark T

 

[cr4k3r]

Very nice indeed sir, the gears are well finished and cut. I will follow this to the end, your work is beautifull. Keep the pic comming.

 

[dnalot]

With the gears cut I am now able to measure them and mark out the mounting points for the four shafts on the horn plates. The horn plates and specter plates are made of steel. The shafts are made from drill rod. I made several modifications to the plan here. I opened up the hole for the crank shaft so the crank could be removed without taking the horn plates off. And I joined the bushings for the drive axle with a tube. The new axle housing will hold the bushings in alignment and help tie the horn plates square to one another. I also made the Specter plates with formed edges to add a little style. (The axle housing and the bushing supporting the flywheel have bronze bushings pressed in, the other shafts run in brass bushings)

I used a fixture to hold the boiler square while milling the stays that would be the mounting points for the Horn Plates. And I used double back tape to hold the horn plates together for shaping and drilling to assure the proper alignment of the holes. The method paid off with great results, when assembled, everything lined up nicely and the gears meshed very well. It only took a little filing on a few teeth to get everything turning smoothly and there is surprisingly little backlash in the gear train. I added a differential, requiring 5 additional spur gears. It’s a simple setup but works well.

With the Horn Plates installed and the gears turning smoothly there are now multiple ways to proceed with the build. I have been working on the side making Smoke Box parts so I think I will turn my full attention to completing the front end next.

Mark T

 

[bazmak]

Beautiful,i am very impressed and will follow with great interest.
You say you have tested the boiler to 2.5 working pressure,i assume hydraulic
Will you be getting it retested with certification ??? regards barry

 

[dnalot]

Will you be getting it retested with certification

Probably not. I will fire it up once or twice and put it on a shelf to look at after. It is smaller than the threshold for required inspection in my State.

Mark T

 

[RonGinger]

Very interesting differential- I did almost exactly the same thing with my MINNIE. I enlarged mine slightly, to 125% of the drawings if I remember correctly. My first attempt at the differential had trouble with the shaft that runs through the big 'bull' gear. Because the gear was relatively thin the shaft didn't get enough support. I made a second version with a couple pins inserted and gears that rode on the pins. It was much more successful. I have never hauled anything with mine, simply ran it on air and only let it move a couple feet.

I never did post any photos of the differential, but here is a link to a few photos of my MINNEY- note I mis-spelled the name because I didn't really follow the plan completely. http://plsntcov.8m.com/minnie.htm

 

[dnalot]

Because the gear was relatively thin the shaft didn't get enough support.

I had a similar problem with stability of the drive sprocket when I built the Clayton Power Wagon. For this build I was very careful to fit the bull gear closely to the axle shaft. Then the bull gear rides between two gears that were silver soldered to their axles and then faced on the lathe. The left gear being mated to the long axle and the right one being mated to the short hub/brake drum. The bull gear tracks dead on square and turns easily.

I could not get your link to work but with a little searching found the page. This link should work http://plsntcov.8m.com/minnie.htm

That is a very nice looking model.

Mark T

 

[ddmckee54]

If you look at the properties of both links, you'll see why the first one doesn't work.

The first link is "http://http//plsntcov.8m.com/..."
The second link is "http://plsntcov.8m.cov/..."

You just can't trust computers, I swear they all have dyslexic keyboards.

Don

 

[dnalot]

I have had to take a break due to surgery but at long last I’m back in my shop. Boy I sure missed fiddling about in my shop, it sucks to get old.

I had a 4” long piece of copper tube left over so I will be using that for the smoke box. The base for the smoke stack is a very odd shape and I elected to use the lost foam casting method. I roughed out the shape using sandpaper and then buried the foam part in green sand for casting. The part was cast from old cartridge brass that is not very good for casting. I did get a suitable lump of metal for my efforts. A little sanding with the drum sander and it fit snugly to the smoke box. Next I chucked the part in the lathe to do the machine work. From there on it was hand sanding and filing to get the final shape, and a bit of buffing to make it sparkle.

The door and its mounting ring “jam” were turned from a single cast piece of stock. After silver soldering the hinge bits, I nickel plated the ring. After fiddling about getting everything to line up straight and square I riveted the smoke box parts together.

Next I fabricated the perch for the front axle. This was a simple brass fabrication job with a turned bronze part to receive the yoke. After riveting the assembly to the smoke box I painted the smoke box with heat resistant paint. The paint on the firebox and smoke box are the only parts I plan to paint. Everything else will be left metal. Steel parts will be ether blackened (shiny or matt) or nickel plated (shiny or matt)

The front axle yoke I made from steel. I have deviated from the plan here, providing for a thrust bearing, and giving the part more of a cast look. I also provided a spring system to stabilize the axle. Both the axle and the yoke have been nickel plated.

I am now working on the wheel hubs and have them mostly completed. I will probably leave the rest of the wheel assembly to later as I’m still not decided on how I will go about making the rims. I have resisted using any aluminum on the model but at this point I’m thinking a cast aluminum rim would be cheap and easy. If I go with aluminum I would anodize the part and then die them black. I have made the patterns for casting but I’m thinking I might try making a tool for rolling the rims from brass flat stock.

Mark T

 

[Twizseven]

Mark,

That looks very nice. Out of interest what paint are you using. I assume that if you intend to fire the boiler and run on steam then you have used a heatproof paint. I have a 1" scale Minnie I bought nearly complete but it has been painted in cellulose car paint. I reckon the second the boiler gets fired the paint will bubble and peel off. I either have to decide never to fire it or to strip down completely, remove the paint and repaint in some form of heatproof paint.

Colin

 

[dnalot]

Out of interest what paint are you using

The painted parts are made of copper so I used ferric chloride to etch the surface and then painted with a paint intended for painting an engine block that was rated to 500 degrees and is oil resistant. I hope it will work out OK.

Mark

 

[Twizseven]

Mark,

Thanks for info. It will be some time before I get around to it.

Colin