Union Pacific Big Boy in 3/4 Inch Scale

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RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Wed May 14, 2014 10:44 am

Hi,

Progress on the power reverse is slow, but its still happening.

As you can see from the pictures, both cylinder bodies are now finished (except for the end cover holes), the valve bodies are almost finished (I still have to counterbore for an "O" ring seal on the shaft) and the valve caps are done, except for silver soldering the supply pipe in one of them. The steel scale gives you an idea of the size of the parts. I haven't made the rotary valve plates yet, but that will be done with the little mill later. The port holes in the valve bodies are located to tenths so the valve plates will work as they should. Don keeps asking me if these units will really work and I tell him yes, I don't see any reason why they won't.

The cap screws are #0-80 and all the holes are put in using the readout on the Bridgeport so everything is accurate and all the parts are interchangeable. Actually tapping the holes isn't as difficult as you might think. Holding everything in your hands gives a good feel for what you are doing while tapping.

For those of you who are interested, I'm working from a series of articles on the four Aces that appeared in Modeltec and the article on the power reverse is quite detailed. First, I design and draw each part of the power reverse in 2D CAD using the Modeltec information and as I draw it, I decide the sequence of operations I'm going to use to actually make the part so I have the dimensions I will need on the drawing. Each part is a combination of conventional and CNC machining. Most of the parts will be made from bronze.

The next part will be the combination cylinder cover and crosshead guide. I've got it designed and I've figured out how to make it; I just have to put the dimensions on, then I can start.

Its slow (especially in the Summertime), but always interesting.

Richard Trounce.
Attachments
IMGA0510a.jpg
This shows how the parts are assembled
IMGA0511a.jpg
This shows the separate little bits
IMGA0512a.jpg
Another picture of the pieces showing the port face on the valve body

SilverSanJuan
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by SilverSanJuan » Wed May 14, 2014 10:54 am

Nice work, Richard. Love the small detail work.

Todd

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Harlock
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by Harlock » Wed May 14, 2014 11:44 am

RET wrote:For those of you who are interested, I'm working from a series of articles on the four Aces that appeared in Modeltec and the article on the power reverse is quite detailed. First, I design and draw each part of the power reverse in 2D CAD using the Modeltec information and as I draw it, I decide the sequence of operations I'm going to use to actually make the part so I have the dimensions I will need on the drawing. Each part is a combination of conventional and CNC machining. Most of the parts will be made from bronze.
Small stuff! Nice job. When I make drawings for myself I always do the same thing - which is make additive dimensions from an origin for use with the DRO. Sometimes if there's room on the drawing without cluttering it, I'll put both the additive dimensions and the usual discreet distance between features for cross-checking.

When I make drawings for the shop at work under our official standards it's the traditional dimensioning.

-M
San Lorezo Flume & Lumber Co. #2 - "Felton"
Live Steam Photography and more - www.mikemassee.com
Contributing Editor, Live Steam Magazine
Webmaster, Allen Models of Nevada

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Fri Apr 03, 2015 9:26 pm

Hi,

Its been a while since I've been able to do anything on Big Boy but I finally got some time to work on it. The power reverse has been put aside for a bit, but I'll get back to it when I can.

In the last month I've been figuring out how to put in the internal piping that is required to supply the turret bushings and building the parts needed. Without this internal piping, any "slosh" or hill climbing would result in water instead of steam in the turret. The piping has to run to the dome, just the way it did in full size.
Installing internal piping (1).jpg
This shows where the piping fitting goes in the boiler
Installing internal piping (2).jpg
This is a closer view of one end of the assembly
Installing internal piping (3).jpg
I filed slots inside the threaded tube so I could turn it with a screw driver
Installing internal piping (5).jpg
This shows how the assembly end looks when disassembled
Installing internal piping (6).jpg
This shows how the steam dome end fits into the dry pipe cap.
The pictures show the parts and after a bit of "finagling, Don & I managed to get the two pipe assemblies in place. As an aside, after trying unsuccessfully for about an hour, we realized that the fittings on the ends needed to be twisted a bit because the bushings on top of the boiler were angled to match the curved top. Once we resoldered one of the end fittings on each tube assembly to provide the proper angle, everything went together easily. The pictures show the construction of the parts and the installation.
Last edited by RET on Fri Apr 03, 2015 9:41 pm, edited 1 time in total.

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Fri Apr 03, 2015 9:39 pm

Hi,

Here are the last two pictures showing both ends of the tubes when installed. If you look closely, The drilled holes at the dome will have wire clips through them to keep the screwed fittings from falling through the holes in the dry pipe cap. You can see the top of the dry pipe in picture number (7).
Installing internal piping (7).jpg
This is how the dome end appears.
Installing internal piping (8).jpg
This shows the turret fittings and a bit of the cab.
The plan is to use 1/4" id. x 3/8" od. Viton "O" rings to seal the external turret pipe connections to the boiler bushings. I still have to figure out the turret design & build it as well as lots of other "stuff," but its getting there.

Hope this helps and yes, Big Boy is still a work in progress, I just don't get a lot of time to work on it.

Richard Trounce.

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Mon Apr 11, 2016 11:10 am

Hi,

I see its been about a year since I last updated this thread. I've been doing other things like stiffening up the CNC mill (it works much better now than it did before).

Here are the recent updates.

Recently I started to put "Big Boy" back together. This is going to be a long, slow process. I started by testing the throttle assembly separately by putting 80 psi. air pressure on it. I found a few leaks; I had to reseal the top plate on the throttle body to stop the first one. I took the plate off, cleaned it and then ran a bead of clear silicone seal around the edge. I put Never-Seeze on the bolts and just snugged them up to hold the plate in place. After about 4 or 5 hours (or overnight), I tightened up the bolts to compress the silicone seal.

A few months ago, I had installed the four longitudinal boiler stays in the boiler, again using silicone for sealing. The bottom one on the fireman's side is hollow for the blower.

After retesting the throttle with 80 psi. I found that two of the top poppet guide plugs were leaking through the TOP of the plug so that I could feel an air cushion when I put my finger on the plug. The air flow was high enough that my finger never touched the metal! When I looked at the plug surface under a microscope, there were no holes visible to account for the airflow! I made two new plugs and that solved the problem.

The poppet sealing "O" rings work very well; they seal leak tight at 10 psi. and as you turn the throttle shaft, you can feel the resistance and hear the airflow increase as the poppets lift sequentially. The short version: It works! The "O" rings will stay in place because the flow is down through the poppet, not up. I've already used this system on the "Boston & Albany" and I've been running that locomotive for several years.

I installed the throttle assembly permanently so the four superheaters extend almost to the back of the firebox.

Next, I assembled the separator plate on top of the dry pipe (that's the disk with the holes in it in the pictures) and installed the dome permanently (with Never-seeze on the bolts in case I ever want to get it apart again). I installed the 5 safety valves (as on the full size Big Boys). When he built the boiler, Gerhardt put in bushings for 6 safeties (3 on each side), so I put a plug in the left rear one, to match the real thing. I made temporary caps for the turret outlets so I could pressurize the boiler and applied air pressure through the top feed. I can hear air leaks, so I will have to find the worst ones which seem to be inside the firebox. Minor ones I will let seal themselves or put a very little bit of "porridge" in the boiler which is an old way of doing the same thing.

Before I can mount the boiler permanently on the chassis, I have to install the insulating brick in its stainless steel box into its position in the firebox. I also have to make and install the centering device on the chassis and design and build the propane control valve for automatic pressure control. Before I bolted the throttle body to the boiler, I also installed the pressure sensing tube which taps off the throttle intake venturi. In the picture, you can see the two plugs in the sides of the throttle inlet, one of which I used for the sensing line. That line will run under the fireman's side catwalk to the control valve under the cab.

Some done, but lots more to go.

Richard Trounce.
Attachments
IMG_0498-A.jpg
Throttle assembly showing "O" ring poppet seats.
Last edited by RET on Mon Apr 11, 2016 7:19 pm, edited 2 times in total.

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Mon Apr 11, 2016 12:36 pm

Hi again,

Previously, I had made a shield for Big Boy numbered, "4004". After I made the shield, Union Pacific announced they were going to restore Big Boy #4014 which was in Pomona. I thought it would be nice if the model had #4014 on it instead of #4004 so I've been drawing up a new plate. After some fun & games I'm at the stage where I've started to cut the new shield in the little CNC mill.

When I made the #4004 shield I used a .030" dia. end mill which is finiky enough, but just to make things more interesting, I decided to use a .025" dia. end mill this time to get finer detail, like the inside of the number "4" and the "P" in Pacific. If you look back through this thread, you will see what the first shield looked like (see second picture) and while its a poor picture, you can see the detail on the new one is better.

Milling the last shield wasn't easy (three quarters of an hour per pass with a .002" depth of cut per pass and one broken cutter near the end), but this one is even worse. It looks like it will need an hour and a half per pass with .001" depth of cut. I tried .002" depth of cut with a little over an hour per pass and the cutter broke at the start of the third pass, thus the slower feed rate & less depth of cut.

It is doable, its just going to take a lot of time. I'll add more pictures as it progresses.

Richard Trounce.
Attachments
#4014 Shield(incomplete & reduced resolution).jpg
Shield outline complete and 2 passes finished. Total depth .030"
big boy shield1aa.jpg
#4004, shield close to full depth but fuzzy
big boy shield1aa.jpg (28.44 KiB) Viewed 2182 times

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Sun Apr 17, 2016 12:42 pm

Hi,

I just completed the number and letter milling of the replacement shield. #4004 was the first shield I made and #4014 is the replacement shield. As I said above, I used a .025" dia. cutter for the new one instead of the .030" dia. cutter I used in the original. As you can see from the pictures, the smaller cutter allows more detail in the letters and numbers.

If any of you want to do something similar, you might need to try what I have found out. With the .030" dia cutter, I was able to mill the first shield dry, but when I tried the same thing using the smaller cutter, it didn't work. After breaking two cutters, I quit and thought about it for a day or two before trying a 2 flute carbide cutter (the others were 4 flute carbide) combined with using WD40 as a lubricant. This new combination works just fine.

While the 2 flute cutter may have helped, the WD40 is probably what made the difference. When cutting dry with the 4 flute cutter, I saw that the cutter was pushing a small burr ahead of it and this is probably what increased the force and caused the cutter to break. The cutters always break at the transition between the cutting length and the shank.

Its a slow process, but this is what works:
I used .001" as a depth of cut for each pass, but you MIGHT get away with more. Unfortunately, you won't know if its too much until the cutter breaks. Flood the surface of the shield with WD40 and as the depth increases, the edge of the shield will form a reservoir to hold the oil. The volatiles in the WD40 evaporate, so you will have to add more WD40 several times as each pass is made and at the end of each pass, you have to wipe off the slurry that is left from the cutting process (its not too elegant, but a piece of toilet paper works just fine for this). Using a toothbrush also helps clean the surface between passes.

Now I have to soft solder the mounting bracket to the back of the new shield and paint it. This time the shield background will be "Court Grey" which matches the locomotive chassis colour. If the locomotive is painted black, you won't be able to see all the detail that is there.

This is a hobby not a business, so there aren't any "trade secrets." I pass on what I've learned so others don't have to make the same mistakes.

Richard Trounce.
Attachments
#4014 Backplot Finished & reduced.jpg
This shows the finished toolpath that the cutter followed for each pass.
Big Boy #4014 shield (finished & reduced).jpg
This shows the two shields. As you can see, the new one has more detail.

kvom
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by kvom » Mon Apr 18, 2016 6:22 am

Whats the total depth of the cut? Also, did you just program for 1 pass, and then adjust Z by .001", or did you program for the entire job? Feedrate?

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Mon Apr 18, 2016 11:11 am

Hi kvom,

What you see in the cutter path picture is for one pass only and I just do multiple passes of the same thing, at .001 thousandths depth of cut per pass. Using the WD40, I could probably take .002 thousandths per cut, but I've broken enough cutters already. At the feed rates I'm using, one pass takes about an hour and 45 minutes. Its slow, but it works and I don't have to be there to babysit it all the time. Remember, while what you see is only for one pass, there are over 1600 lines of code to produce that single pass and every time the cutter goes up and back down, you have to tell it the descending speed for the final approach and the horizontal travel speed.

As the "G" code program comes from the CAD package, the horizontal speeds are well over 200 inches per minute, ie. commercial travel speeds, so all of this has to be edited and adjusted to suit the capabilities/limitations of my machine. On my machine, G0 (max travel speed) is only 24 inches per minute so the steppers don't miss steps. I know they don't, because after the hour and 45 minutes, the dials come back to exactly the same position they started at, cycle after cycle.

The descending feedrate is .03" per min while the horizontal feedrate is .6" per min. The maximum spindle speed is only a little over 3,000 rpm so that limits things. If the speed was higher, then I could boost the feedrate. For this cutter size, I would like to run at about twenty thousand rpm. Maybe one of these days, I'll build/buy a better spindle which can handle heavy cuts as well as high rpm.

Since the cutters don't really like to plunge cut, the descending feedrate has to be a lot less than the horizontal. Again, as I said above, you won't find out if the feedrate is too high (or the depth of cut) until the cutter breaks, so I tend to err on the cautious side.

With the original #4004, the final depth was .030"; this time I went deeper so the final depth is .045". While I think the deeper cut looks fine, I could have stopped at a shallower depth. You have to gauge the depth by eye because you can't measure while the work is in cutting position (yes, I could have measured by moving things in manual mode, but I didn't think of it at the time).

The real shield casting pattern is made up of cut out letters and numbers, 3/8" thick fastened to a 3/8" thick base, so in full size the letters are deep and stand out well and I wanted to duplicate that effect in the model.

If someone wanted to do the same thing in 1/8 size, it would be much easier because you could use a .050" dia. cutter which is much stronger.

It sounds as if you might want to do the same thing. Hope this helps and best of luck if you do.

Richard Trounce.
Last edited by RET on Sun Apr 24, 2016 9:45 am, edited 1 time in total.

kvom
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by kvom » Tue Apr 19, 2016 7:20 am

If I were to program that job I believe I could shave off a good deal of the run time by "isolating" the letters into separate areas and clearing the rest with a larger tool. The carbide engraving cutters I have are a 80-degree flute angle and a bit stronger, but I haven't tried one that small as yet. When I did my number place (1.5" scale) I used a 3/64" endmill, about twice the size of yours.

Nice job and it looks great. Anyone who undertakes a Big Boy gets my admiration.

RET
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Re: Union Pacific Big Boy in 3/4 Inch Scale

Post by RET » Sun Jun 05, 2016 9:59 am

Hi,

Well, the shield is finished and painted. It looks like I was lucky the first time, because when I put the white on this one, I smeared it and had to redo it several times to get it right. Live & learn.

Now I've started on the centering device. I could probably get away with not doing it on the model since the smokebox saddle slides on a teflon shoe, but its on the full size locomotive, so it should be there. It will also help to keep the smokebox "face" exactly where it should be when running. The centering device is a complex assembly of a number of separate parts so its going to take a while to make and put together. As I've said before, having all the original Big Boy drawings on CD is an invaluable asset.

Here are the initial pictures. By the way, to give you an idea of the scale, the holes in the tabs are tap drill size for #2-56 thread. In case you are wondering about the cap screw, I put a 5/16-18 threaded plug inside the collet to make sure that the part would stay put under cutter pressure. The last thing I need is to have the part chewed up because it slipped in the collet.

Richard Trounce.
Attachments
Big Boy Centering device end machining.jpg
This shows the setup in the mill to cut the "ears."
End machining detail.jpg
Closeup of one of the finished end pieces (except for hand filing).

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