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7-1/2" Gauge CP #173 Builder's Log - Part 1

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Discussion starter · #362 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Brakes - con'd:

With the brake shoes done, it was time to make the beams to mount them to. When I scaled up the Hartford Products Fn3 shoe, the beam mounting notch came out to 7/16,so that's what I made mine. When it came time to actually make the beams, I discovered that the aluminum I could get in 7/16 was somewhat limited, so I decided to start with 7/16 x 3/4 6061 bar stock. That meant I had to shave it down 1/16, so I used a fly cutter to take 1/32 off each side.

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Next I made a jig to hold the material so I could cut the profile.

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The beam stock was drilled for the shoe and clevis mounting, and I drilled the holes undersized and tapped them 5-40. That let me bolt them to the jig.

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Then on to cutting the beam profile. Taking 20 mils off on each pass, it took a while to cut through the 7/16 thickness, but resulted in a nice finish on the cuts.

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While each beam was still in the jig, I swapped to a 1/16th corner rounding mill and milled the radius on the outside edges.

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When all the machining was done, I opened up the three holes for a 5-40 clearance.

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Lastly, I milled a 3/8 wide by 15 mil deep slot on each end to locate the shoes. A finished beam...

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Here's a finished beam brake beam with the shoes temporarily mounted...

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I'm going to mount the shoes with 5-40 threaded rod and make some wedge washers and square nuts out of brass. Once that's done it's on to the brake hangers.
 
#363 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Dwight,


It keeps looking better and better each time you post the latest up dates, keep up the beautiful work.



Just wondering, wouldn't it have been better to make the brake shoes out of something a little harder than aluminum? Or make the shoes them selves separate from the bracket so that they would have been easier to replace? I was just wondering on the logic behind the use of aluminum for the shoes them selves rather than something harder such as steel or iron.

Andre
 
Discussion starter · #364 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Thanks Andre!
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Just wondering, wouldn't it have been better to make the brake shoes out of something a little harder than aluminum? Or make the shoes them selves separate from the bracket so that they would have been easier to replace? I was just wondering on the logic behind the use of aluminum for the shoes them selves rather than something harder such as steel or iron.I already answered that on the last page.
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... but if you're referring to removable pads, I don't expect to ever wear these out. The two runs I've made (well over a couple of actual miles now minimum just on the first day) have been made with no brakes at all. They aren't used often enough to inflict any great wear on them, and when they are used, it doesn't take much to stop this thing, so again, little wear will result. While I could be wrong, at this point I'll be real surprised if I ever need to replace them.
 
#365 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Aluminum shoes work very well. On our Allen mogul, we used alum shoes. They WILL wear. But we pulled the public at LALS every other weekend for four to five hours each day and probably heavier trains than you will have with the American. Remember you CAN use the Johnson Bar to control a lot of you speed. I remember when we first got the mogul and we were brand new to running large scale trains, we were running at night. Coming down the long trestle, on a 3% grade with a heavy train, we found that the engine brakes just were not holding the train back. Talked to an old-timer that night and he said to use the Johnson Bar to assist the engine brakes. Just notch it back, past neutral toward reverse. Worked like a charm!
Damn you do fine work! Very nice!
 
#366 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

BE EVER SO CAREFUL.... Putting the johnson bar into reverse while moving forward is a great way to blow a cylinder head off... or bend a main rod.

More than one 1:1 engineer found homself trying to explain why the main rod of the engine was bent into a horseshoe shape...

A better idea would be to increase the valve opening. At higher speeds, the reverser was brought closer to top dead center. This was to reduce the amount of time steam was being admitted into the cylinders. While this harnessed the expansion power of steam over the pressure, it also reduced the back pressure in the cylinder when it went into the exhaust stroke.


By opening up the reverser towards full stroke, the pressure in teh cylinder remains higher, and the amoun t of work needed to exhaust the steam becomes more higher, causing the rods to steal momentum from the wheels, acting much like a diesel's dynamic brake, or the Jake brake on a truck... in effect you ARE down-shifting the steamer.


Keep in mind, my knowledge is 1:1 based, not model, so your ability to use the reverser in reverse MIGHT work without damage... but I personally wouldn't try it with such a beautiful engine.
 
#367 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

I NEVER threw the bar into into FULL REVERSE. On a small engine like I'm talking about, you won't blow a cylinder head OR bend a main rod. You're explanation was much better than mine. What you do have to be careful of on a model, is the tendency to have steam lift the slide valves off the ports in the steam chest. Even a model can be damaged that way! You should have put a caveat with my explanation to use finesse when using the Johnson Bar along with a gentle touch to the throttle AND to do these things WAAAAY before you need to. Plan ahead so to speak.
 
#368 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Posted By Gary Armitstead on 20 Sep 2010 01:39 PM
I NEVER threw the bar into into FULL REVERSE. On a small engine like I'm talking about, you won't blow a cylinder head OR bend a main rod. You're explanation was much better than mine. What you do have to be careful of on a model, is the tendency to have steam lift the slide valves off the ports in the steam chest. Even a model can be damaged that way! You should have put a caveat with my explanation to use finesse when using the Johnson Bar along with a gentle touch to the throttle AND to do these things WAAAAY before you need to. Plan ahead so to speak.
What could cause of the slide valves to lift off the ports in the steam chest? This happened to my engine once, but it happened seemingly out of nowhere. About 3 weeks ago I let my friend take my 1" pacific for a run, and while going uphill the steam suddenly started going straight to the exhaust. Someone suggested that the slide valve lifted from the port, so I let the engine sit for probably 20 minutes. It had about 20psi left afterwards - enough pressure to see if the problem was still there - and everything was working normally. It was both the first and last time i've had the problem.
 
#370 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Dwight

Sorry about asking the same question twice, I looked at the shoes bolted to the beams and thought "why aren't they removable and why aluminum" so I asked the question my only excuse was I had a brain fade. Again I apologize for the same question twice.

Andre
 
#372 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Fly-cutting is what stripped the gears in my mill. I figured if I was taking a big bite it would stop the head (and possibly break the gear train) but I didn't think it would do so when I was just barely scaring the surface on a first pass to see if I had everything aligned. The "interrupted cut" done when fly-cutting is really hard on the machine; your's is obviously much better made than mine. I hesitate to even try it anymore.

I have rounded a rectangular aluminium bar on my lathe without problems (well, except for the hideous noise and shaking tools off the bench!) and I think the gear train is very similar in my mill and lathe, so I am not real sure what happened on my mill.

At any rate, what you have made is looking REAL GOOD. Congrats on it all.
 
#374 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Dwight....back in one of your messages discussing Mach3 and your larger Mill, dated 8 Sep 2010, you said "For one thing, it runs under Windows, so all my Acad drawing, g-code writing, and machine execution can be done on the same machine. It also runs on my notebook under USB control, so the computer takes a lot less space and is completely portable. I can draw parts and write code on the couch in front of the tube, and simulate the machine operations and debug right then and there. When everything is correct, I can carry the notebook out to the garage, plug in the milling machine, and I'm off and running".

So, when you stated that it, (the Mill)" also runs on my notebook under USB control"....does this mean your new mill's driver board doesn't require a parallel cable to be connected to the computer?

I'm about to add a 4-axis CNC capability to my Sherline 5400, but not Sherline's upgrade. I have only found driver boards that require a parallel cable for the interface with the computer. I happen to have a spare notebook (USB only) on which I currently do all my CAD work and really like what you described.

Any driver board brand names would be appreciated.

Thanks
 
Discussion starter · #375 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Howard - the driver box I'm using came equipped with the SmoothStepper board, which sits between the actual driver board and the computer. The SmoothStepper board takes input from Mach3 via the USB port and generates the correct parallel signals for the driver board. It's also powered by the USB port, so no additional power source is required. Works pretty darned well.
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#376 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Posted By Dwight Ennis on 21 Sep 2010 06:16 AM
Thanks Semper. What kind of milling machine was/is it?

I used a new carbide tool in the fly cutter and was taking off 10 mils per pass, three passes per side, and one last pass of 1 mil for finish = 0.031" per side.
The mill is a Cummins (now known as ToolsNow) 7877 Mini-Mill (R8 spindle). Just like several other brands all made from the same basic design (Grizzly, Micromark (original one they sold), Homier) mostly made by Sieg.

When I broke mine I was just barely scratching the surface of the stock piece, still checking if I had it perpendicular to the mill axis (or parallel to the orbit of the fly-cutter). I am assumming the cutter caught a large-ish blemish/extrusion on the edge of the raw material where it had been roughly treated (dropped on a sharp edge). Either that or the table wobbled as I was turning the crank (due to poor gib adjustment). It just made no sense that it went "bang" and the motor sped up as the fly-cutter slowly reversed about 1/4 turn and stopped. I had just finished smoothing the opposite side of the piece without a problem, taking just a few thousandths off in 4 or 5 passes (I don't remember just how much as I was just removing some scratches that I thought were too deep to buff out and I kept at it, a few thous at a time, until they were gone).

Although I had the replacement gears on hand it still took me a couple of days to figure out how to get the main bearings out of the cast case/housing. My son and I finally decided I just had to pound on the shaft and hope that I didn't damage the balls or races in the process. Putting it back together I was able to pound on the edge of the outer race to get it seated back in the casting. The mill still works and is no noisierthan it was before so I am assumming I did not damage it much. It sure was a complete dissassembly of the main mechanicals; the gear that was broken was on the main spindle.
 
Discussion starter · #377 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Gotcha Semper. I was just curious if it had metal gears or not. I've seen ads in Mirco-Mark saying, "Now with metal gears on the spindle!" which led me to wonder what they used before. I'm real down on using plastic on stress-bearing parts. The door latch on our microwave broke last night - for the THIRD time! The spring which pulls the latch down to engage when the door is shut hooked to a cheap, skinny little plastic tab molded into the door frame. This time I fixed it PERMANENTLY with a 2-56 stainless steel screw and nylon insert lock nuts. That part of the latching mechanism at least will last until **** freezes over!
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Discussion starter · #378 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Making Clevises:

I made a total of ten clevises for the brake system. I opted to use the Sherline equipment on these because (a) they are small and one can sit reasonably comfortably when machining them, (b) they lend themselves nicely to small parts, and (c) I already had all the tooling needed.

The first step was to turn the shape on the CNC lathe...

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The bullet-shaped nose was turned first. The parts were then cut to the same length on a small Harbor Freight chop saw with abrasive cutoff blade and stops clamped in place. While the lathe was still retaining the same settings and coordinates used to turn the noses, and the cutting tool set to 0,0 (dead center), the parts were reinserted and butted up against the tool.

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For those that are curious, this video shows the lathe turning the rear profile of the clevis in several passes. The first half is close up, and the second half is more of an overall showing the working of the lathe...



After all ten clevises were turned to shape, they were reinserted one last time to drill and tap the end for the 5-40 mounting studs. I realize this is less precise than doing it while they remained in the chuck from turning, but this was easier, required less re-indexing of things, and precision of that sort wasn't required here.

The nex step was to move over to the milling machine and slot them for the levers using a slitting saw...

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While still in the vice, the clevises were drilled for a 4-40 screw - tap drill all the way through and clearance drill through one side. Doing this while the part was still in the vice insured the hole would be perpendicular to the slot.

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The last thing to do was to clean up burrs and sharp edges with a needle file and tap the hole. I opted to tap them manually as the clearance hole on one side guided the tap to insure it went in straight.

A finished clevis...

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(Mikey suggested I include a ruler/scale in some of my photos).

Earlier in the week I made 12 square nuts from 3/16 square stock and washers from 5/16 round stock. I intended to make wedge washers to mate with the slanted brake beams, but after cutting one to the required 4.4*, the difference in thickness from one side to the other was so negligable that I just made them all flat. The shoes are mounted with 5-40 stainless threaded rod cut to length.

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A finished brake beam...

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Next up - brake hangers.
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#379 ·
RE: 7-1/2" Gauge CP #173 Builder's Log

Posted By Dwight Ennis on 26 Sep 2010 06:20 AM
Howard - the driver box I'm using came equipped with the SmoothStepper board, which sits between the actual driver board and the computer. The SmoothStepper board takes input from Mach3 via the USB port and generates the correct parallel signals for the driver board. It's also powered by the USB port, so no additional power source is required. Works pretty darned well.
Image

Thanks Dwight....that should do the trick.
 
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