1.75” Minnie traction Engine

[dnalot]

Hi

The flywheel was cut from a 1.5” by 8” round of cast Iron I purchased from McMaster Carr. The material was very nice cutting without any hard spots. It took a few hours to rough out the shape on the lathe and a quite a few hours doing the mill work. Very little filing was needed and the final texture was added by sandblasting the spokes and hub. After sandblasting the part was placed in the bucket for “Parkerizing”. After that the flywheel was mounted to a shaft and turned to its final diameter and the rim sanded smooth.

Mark T

 

[dnalot]

Hi

Time to make the crankshaft. On my last two engines I turned the crank one piece. This Time I have opted to assemble the crankshaft and silver solder the parts together. My camera had a low battery so some of the photos were not usable. Sorry about that.

The shaft was made from .5”, 8” long drill rod. And the webs were cut from 12L14 steel. I fit the shaft to the web with a close fit. After that I removed about .003” from the shaft where the web will ride, leaving a small shoulder to hold the shaft centered in the hole. A .125” hole was then drilled through the edge of the web at each joint for feeding the solder into the cavity between the shaft and the web. I mounted the shaft to “v” blocks to support the shaft during soldering and clamped the “v” blocks to a straight piece of heavy metal. The main shaft runs through the webs during soldering but gets cut away afterward. After soldering I let the assembly cool completely before I took it out of the "v" blocks and cut away the unwanted section of rod between the webs. A little filing and sanding and a quick dip in the Parkerizing bucket and the part was done.

I placed the crank in the lathe to check for straightness. The crankshaft is 8” long and I had a deviation of .0036” at the midpoint. I slipped the eccentrics and the shift gears onto the shaft and fit the assembly to the engine. It turns butter smooth and the flywheel has no wobble. I’m a happy camper.

 

[dnalot]

Hi

The engines cylinder assembly was cut from a 3”x3”x4” block of brass. The original model was made from a casting that included the saddle. Mine required the saddle to be made separately and silver soldered to the cylinder block. And like the original model the cylinder sleeve was soft soldered into the block. The most difficult operation was fitting the unit to the boiler to be in line with the crank, at the proper height, plumb, and square to the barrel of the boiler. To keep from getting chips into the boiler while I drilled and taped the holes for mounting I pressurized the boiler to about 15 Lbs with air. At this point all of the holes have been drilled and tapped, all of the steam passages have been milled or drilled and the stuffing boxes are complete. The bore is 1.187” and the stroke is 1.75”. Having 2 power strokes with each revolution yields about 50CC displacement.

Next to do is producing all the motion parts.

Mark T

 

[robj.brown]

Wow nice work

 

[dnalot]

Hi

Before moving on to the motion parts I aged the completed components of the engine and mounted it permanently to the boiler. Followed by mounting the motion plate and its saddle before pressure testing.

With that done the boiler was wrapped with a brass sheet insulated with .125” of ceramic insulation. The wrap is held in place with three nickel plated straps.

There are three stuffing boxes on this engine. An 1/8” a 3/16” and a 1/4”. I am using O-rings for seals that are 1/16” in diameter (actual .070). The rods passing through them are polished S.S. The well these seals sit in are very easy to cut and the system seals very well without binding. I start by reaming the hole for the shaft .001” over and then use an end mill .125” larger in diameter than the shaft to cut the recess for the O-ring.

I started with the piston & rod and the cross slide. The piston is brass and the cross slide is fabricated from brass and bronze. Once I had these parts installed and moving smoothly I measured for the connecting rod and made it from a 1/2” square piece of steel. The strap is made of steel as well and is located in place by a tapered pin. Bushings are made from PTFE impregnated material. I must have located the engine on the boiler nice and square because the connecting rod when installed moves smoothly. The hole in the spectacle plate was a little off so not everything went to plan.


I now have a good start on the motion parts for the steam box valve. Most all the control linkage parts are made and have been fitted to the model. After I post this note I’m off to make the valve. On my next post I hope to be able to post a video of the first run on air.

 

[Herbiev]

Looking great so far. Keep the pics coming.

 

[dnalot]

Hi

The stack required a tapered tube. I didn’t think I could roll a smooth looking tube so I Made a tapered mandrel and used it to stretch a length of copper tubing. The base of the stack and the crown I cast using the lost foam method. After silver soldering the parts together I left the part as is as the heat gave a very nice finish.

Mark

 

[dnalot]

The control rods for the steam chest valve were made from brass in several separate parts and then silver soldered together. With those parts in place the engine was ready to run. So I ran it for the first time.. Sweet. She purrs like a kitten. Smooth and powerful and the reversing mechanism works well at most any speed. With the engine mounted directly to the boiler the response time to changes in the regulator were crisp.

 

[dnalot]

The sight glass I made from some modified plumbing parts. It doesn't' show in the photos, but there is a pipe plug in the end opposite the valve for inserting the glass tube. I will replace the “T” handle on the valve with a wheel. Simple cheap and it works well..

 

[dnalot]

The water pump is one area that I have deviated from the plan. It had been reported that the original pump did not work well. The original was mounted on the boiler well above the water tank. I relocated the pump to the side of the right horn plate with the pickup tube level with the bottom of the water tank. The pump is a complete redesign. Also changed is the location of the return line valve. The original had it mounted on the outside of the water tank. I have mounted it inside the tank. The pump is working and will pump a lot of water quickly and has no problem forcing water into the pressurized boiler.

 

[10K Pete]

Great engine, Mark. I don't think I ever thought about how many gears are in
one of those machines. Amazing work. Can't wait for the video!!

Pete

 

[dnalot]

Every steam boiler needs a whistle. So I crammed one in.

 

[dnalot]

Hi

The oil pump on the original model looked like it was tacked on as an afterthought to the rear of the motors head. The arm that drives the ratchet was slaved to the rod that drives the steam chest valve.

I have relocated the oil pump to the specter plate and the rod that drives the pump is now driven by the water pump’s eccentric. The reservoir on the original was square mine is round and the internal pump is of a different design. The eccentric that drives the pumps piston is turned by a ratcheting action. The ratchet is accomplished with a one way bearing. It takes from 10 to 20 revolutions of the crankshaft to cycle the pump one revolution, depending on the hole you pin the arm to. The pumps piston is .09375” with slightly more travel. There is a check valve at each end of the copper line to prevent steam pressure from escaping.

 

[Mark Rand]

Automatic oil pumps, when fitted, were normally rectangular and were often mounted off a bracket on the back of the cylinder and worked by the valve rod.

I've got a picture in front of me of Alchin's 7NHP Royal Chester showing that she had one like that when delivered from the factory.

Having said that, one on the spectacle plate would be a bloody sight easier for the driver to reach in the morning for filling it up.


PS. Thanks for the wonderful write up. I've got a set of 1" Minnie bits waiting for me to get started on them and your work is a great encouragement.

Regards
Mark

 

[dnalot]

Automatic oil pumps, when fitted, were normally rectangular and were often mounted off a bracket on the back of the cylinder and worked by the valve rod.

Good to know. Thanks for your comments.. It has been a rewarding project, so don't let your bits go to waste.

Mark T

 

[dnalot]

This is almost the end of this thread. I have but one thing to do before declaring this project completed. As you can see the chain for steering is way too big. The chain I originally used was the correct size but had no strength and broke easily. I ordered a replacement but it will be about 10 days before I get it. After I replace the chain I will stage the model for photos and a video and post them.

The past few weeks my camera has not been working well and I have now replaced it. Unfortunately, I have lost many of the details of how some parts were made. In this post I am showing the 50 feet of cable spooled onto the drum, a guard for the gears made from .020” brass and the ash bin assembly installed.

Mark T

 

[dnalot]

Hi

Well it's been a fun build but the model is now completed. I have posted a few final photos and a short video in the completed projects section. Here is a link

http://www.homemodelenginemachinist.com/showthread.php?p=279090#post279090

Mark T

 

[dnalot]

The link in the post number 57 is dead. here is one that works 1.75" Minnie Traction Engine

Mark T

 

[Tug40]

I just looked at this thread for the first time today.
In post #1 i saw what appeared to be cleco pliers & lo & behold actual clecos.
Haven’t seen those since working for Lockheed Aircraft in the late 60s.
Went to the garage, looked in pliers drawer & yup, I still have a pair.
Small world.

 

[dnalot]

In post #1 i saw what appeared to be cleco pliers & lo & behold actual clecos.

Yup still have them and still use them. And I still have my safety wire pliers. Spent many years working as a licensed A&P mechanic before switching to marine mechanic where I could make good money. Ended up owning and operating a small boat manufacturing company. (both the boats and company were small)

Mark T