Machining side rods for a 1.5" scale 2-8-0

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amadlinger
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Location: Central NJ

Machining side rods for a 1.5" scale 2-8-0

Post by amadlinger »

Hi all,

I thought I would share something that so many of us have to go through at one point or another in life: making side rods. These are for my 1.5” scale, 7.25/7.5” gauge Boston and Maine K8b 2-8-0. Truth in advertising, I actually machined these two years ago…

Many years ago on my first locomotive (Little Engines 0-6-0 AC&G #26, a photo of which is in the LE catalog) I used 1018 low-carbon steel for the side and main rods. In the intervening years, I have had a very hard time keeping them rust-free, even with regular wash-downs with WD-40. I also had a lot of challenges with warping during machining, so hoped a change of material might help both problems this time around.

After consultation with Andy Pullen, I elected to go with 303 stainless steel – this turned out to be a fantastic decision for ease of machining and an excellent finished appearance, while still being relatively strong (thank you, Andy!). I sourced pickled & annealed “true bar” from Speedy Metals during one of their semi-annual discounts – it is extremely important to specify “true bar” as otherwise most suppliers will provide material that was sheared to size. True bar has square corners, flat edges, and is what you need for clamping on a milling machine (unless you want to make your life infinitely more difficult).

Step 1 was to bore all holes in the raw bars and drill/tap all the oil/grease holes. The bars were too long to fit in my vise, but no problem – I supported the ends with machinist jacks. Note that I drilled/tapped an ample number of 8-32 holes around the perimeter of each bar to be used in subsequent steps.
Part1.JPG
Step 2 was to rough out the excess material using an indexable insert milling cutter with the bar held horizontally in the vise.
Part2.JPG
Step 3 was to mount the bar in the mill, using the 8-32 holes, to an aluminum fixture plate I made up for this occasion. I first roughed, then re-oriented the bar to use a 5/8” dia x 2-3/4” long solid carbide end mill to finish the cut. It’s an expensive stinker, but the solid carbide end mills are worth the money for the superior surface finish and minimal flexing during cutting, which results in great dimensional accuracy of the machined parts.

Two important notes here: First, by machining all the stock off of one side at a time, you are GUARNTEED to have warpage in the part. That is why the robustness of the fixture plate and ample 8-32 holes around the perimeter are critical, in order to pull the material flat for machining. These rods had a full 1/8” to 3/16” warp after unbolting from the fixture in this first step. Second, if you make sure that the center of the rod is in the dead center of the raw bar of material, the rod will eventually end up being straight when the opposite side is machined. Knowing the second point, I did not bother to rough out both sides first and the rods did indeed come out dead straight after machining the back side in step 5.
Part 3.JPG
Part 3B.JPG
Step 4 was to machine a pocket on the ends of the rods that have “forks”. By machining this as a pocket, the bar was much more dimensionally stable during machining, although it did require the use of a rather long ¼” dia solid carbide end mill.
Part 4.JPG
Last edited by amadlinger on Thu Jan 07, 2021 10:31 am, edited 1 time in total.
amadlinger
Posts: 174
Joined: Sat Jun 23, 2007 8:18 pm
Location: Central NJ

Re: Machining side rods for a 1.5" scale 2-8-0

Post by amadlinger »

Step 5 was to flip the rod over and machine the back side. I used a ground plate as a shim to pull the material evenly and solidly against the aluminum fixture plate. Again, after this step the rods were dead straight and required zero manipulation to flatten them.
Part 5A.JPG
Part 5B.JPG
Step 6 was to mount the rod directly to the bed of the mill using the t-slots and cut the profile. I was lucky here that the rods were short enough that I didn’t need to clamp down the center of the side rods during the profiling step. The main rod was much longer and did require clamping down in the center. I should probably also mention that this is a 2.5-axis CNC Bridgeport, so the only effort in milling the profile was programming the machine to do it for me :-)
Part 6A.JPG
Part 6B.JPG
Part 6C.JPG
Part 6D.JPG
amadlinger
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Joined: Sat Jun 23, 2007 8:18 pm
Location: Central NJ

Re: Machining side rods for a 1.5" scale 2-8-0

Post by amadlinger »

Step 7 is to machine/install the bronze bushings. I use plain Alloy 932 bronze with the spiral grease grooves, available from McMaster in many sizes – or otherwise for the odd sizes machine the grooves using a small slot cutting endmill and helical interpolation on my mill. As Bill Shields has mentioned, there are some outstanding engineered plastics that make great bushings, but the bronze has worked for me trouble-free over the years so that’s what I went with again.
Part 7.JPG
Step 8 (not shown) is to clamp the rods back in the mill and bore out the bronze bushings to their final size. I would note that it is important to do this back on the mill (as opposed to using an adjustable reamer, for example) because the spacing between the bushings will increase due to the forces of the press fit. I have found this to be a non-negligible difference, but is easily corrected by boring to final size.
Final.JPG
The whole process took a few months to complete, but I think it was well worth the effort – check out the photo of the side rods in their “native habitat”. The model grease fittings shown are from Howard Gorin (The Machinery Works), although SuperScale used to offer them as well.

I would love to hear how other folks do this work. Specifically, I know that some folks have rod blanks waterjetted to the rough profile first, and then machine them. I am curious how exactly folks hold the rods for machining if you do it this way.

I hope people find this interesting and welcome any questions.

Sincerely,
Adam
Berkman
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Re: Machining side rods for a 1.5" scale 2-8-0

Post by Berkman »

Thanks for posting.

For step 6 did you have to flip the rods over to finish the profile?

Using LE 0-6-0 cylinders as a basis for your build ?
amadlinger
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Location: Central NJ

Re: Machining side rods for a 1.5" scale 2-8-0

Post by amadlinger »

Hi Berkman,

No, the profile was done all from the same side, stepping down in 0.050" increments at 0.005" oversize and then doing a final, full-depth finishing pass to clean it all up at the same time. The sacrificial aluminum shims underneath the rod ends kept it off the bed of the mill.

In the photos of the finished rods, i did zero additional surface finishing after machining except for deburring (no Scotch Brite or abrasive cloth), so the surface finish you see is how it comes out. I find it absolutely remarkable how well a sharp, solid carbide endmill works in 303 stainless.

The cylinders are from my own patterns, true to the B&M design with Cattail Foundry in Lancaster, PA pouring the metal.

Sincerely,
Adam
Andypullen
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Re: Machining side rods for a 1.5" scale 2-8-0

Post by Andypullen »

Thanks for the kind words Adam!

The rods look great!

I've done dozens of waterjetted rods. Typically, I use 2 vises with aluminum soft jaws machined to the waterjet profile. I will program the finish dimensions and mill the outside profiles and interpolate the bores. Lowering the spindle on the ends where the eyes are. After that I make a simple fixture to bolt the rods to with close fitting pins in the eyes to narrow the thicknesses. Usually, cut and flip. Like you said even cuts are pretty easy. You may have to straighten after each cut, but that's not a big deal.
12513 front rod in mill2.jpg
1013141615.jpg
Eccentric rods have to be pulled out and straightened unless you use a wider piece of material and mill the vertical profiles first.

Berkman,

My 2-8-0 is using Little Engines Pacific cylinders. Adam's cylinders aren't Little Engines. The castings are very different.

Andy Pullen
Clausing 10x24, Sheldon 12" shaper, ProtoTrak AGE-2 control cnc on a BP clone, Reed Prentice 14" x 30", Sanford MG 610 surface grinder, Kalamazoo 610 bandsaw, Hardinge HSL speed lathe, Hardinge HC chucker, Kearney and Trecker #2K plain horizontal mill, Haas TL-1 lathe.
amadlinger
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Location: Central NJ

Re: Machining side rods for a 1.5" scale 2-8-0

Post by amadlinger »

Hi Andy,

Quite a clever way to do it, nicely done!!

Sincerely,
Adam
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Benjamin Maggi
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Re: Machining side rods for a 1.5" scale 2-8-0

Post by Benjamin Maggi »

Adam,
Those rods look fantastic. Admittedly, I am happy that my engine only has 4 total drive wheels so I don't have to make complicated rods like yours. But, the end definitely justified the means in this case!
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"
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Harold_V
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Re: Machining side rods for a 1.5" scale 2-8-0

Post by Harold_V »

amadlinger wrote: Thu Jan 07, 2021 9:43 am – it is extremely important to specify “true bar” as otherwise most suppliers will provide material that was sheared to size.
That's excellent advice. Shorn material has extreme stress introduced by the progressive cut of the shear. Narrow pieces will even be twisted after the shearing operation. Wider material may remain somewhat straight, but when it is relieved (by machining), the part tends to twist, which is not good when you're trying to make a long, slender flat and straight object.
Step 1 was to bore all holes in the raw bars and drill/tap all the oil/grease holes.
Would you please comment on your rationale for creating all the holes first? It's no secret that the parts are going to move when you machine the profile, and that's going to have a profound effect on hole perpendicularity, and even location, depending on the amount of movement one experiences. It's common practice in the shop to make holes the last operation, so they can be placed where they're desired and be perpendicular to the finished surface.

I can understand roughing the large diameter holes (common shop practice), leaving enough material behind to take finish cuts when the profiles are completed. That assures that the bores are perpendicular and on proper location. It sure could save a lot of misery that could result from bores ending up at an angle due to movement from stress relief. I would also do all the small hole drilling ONLY after the profiles were completed, but that's me. It need not be others.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
amadlinger
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Re: Machining side rods for a 1.5" scale 2-8-0

Post by amadlinger »

Hi Harold,

For sure, all it takes is one (bad) experience to forever ingrain in your mind that "true bar" is the way to go. I find myself confirming that for all materials these days, even cold rolled steel.

Great question on the holes, a lot of thought went into the decision to do them first since, as you say, that's not typical practice. There were a number of factors, but ultimately it was a bit of a gamble that paid off. As we know, the critical dimension is the spacing between the holes (lengthwise), and the length of the rods will be relatively stable, at least well within the margin that can be trued up by finish boring the bronze bushings afterwards.

Major perpendicular misalignment would mean that the rod warped on me more than was acceptable, requiring straightening anyway to correct (as mentioned, I did not have this issue). Minor perpendicular misalignment is actually a secondary concern here because, as the locomotive goes down the track over undulations, the crankpins likely won't be perfectly perpendicular anyway so the overall system design has to be able to tolerate it. The rods are long and thin enough that they do flex a little, as well.

As for the small oil/grease holes, that was a practical matter: the geometry of the rods doesn't provide a great way to indicate the locations lengthwise after the profiling step.

Sincerely,
Adam
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Harold_V
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Re: Machining side rods for a 1.5" scale 2-8-0

Post by Harold_V »

Thanks for your polite response.
I would suggest to you that regardless of the need for rods to be able to correct for irregularities, boring the final diameter after the profile was completed would be in everyone's best interest. Boring the inserts is a solution to correct for errors is a solution, but it complicates any future replacement. By making the rods properly at the outset, replacement brasses are made simply by machining them so they are concentric.

I'm not refuting that your method works. It's just that there is a way to ensure easy future maintenance, whereby the proper rod spacing and perpendicularity is not lost when the brasses are replaced, and that is likely going to be needed at some point in time.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
amadlinger
Posts: 174
Joined: Sat Jun 23, 2007 8:18 pm
Location: Central NJ

Re: Machining side rods for a 1.5" scale 2-8-0

Post by amadlinger »

Hi Harold,

I fully appreciate and concur with the sentiment, but as stated I did not have any issues with spacing or perpendicularity in the bores after profiling.

The only error induced was when the bronze bushings were installed, which did noticably alter the center-to-center spacing. I was quite surprised by that.

Sincerely,
Adam
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