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

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: cbrew, Harold_V

RET
Posts: 960
Joined: Wed Jun 07, 2006 8:36 am
Location: Toronto, Canada

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

Post by RET »

Hi,

When you press the bushings in, its fairly obvious that the center to center distance will increase, with the amount depending on the amount of interference in the press fit. If you wanted to, you could allow for this by boring the holes slightly closer than the "correct" amount, but then you would have to hold fairly tight tolerances on the OD. of the bushings to get the installed distance right. On assembly, the bushings will get slightly smaller, but the rod ends will stretch more than the bushings will compress, thus increasing the center to center distance.

If you need to be really precise, boring the bushings after pressing them in place is a good solution. In practice, making the whole thing a bit sloppy is probably a good idea and this is one of the areas where that may be required.

Not that I can claim to be an expert by any means, but when building a locomotive, there are places where "sloppy" is OK, especially when you consider that in a lot of cases, model tracks require more flexible springing than the "real thing" may need. My experience says that as long as the locomotive suspension is flexible enough to allow the wheels to follow the track no matter what it does, the locomotive will stay on the rails. I must admit I have seen one or two videos where even the "real thing" bounces and rolls around like crazy but still stays on the track.

Very impressive, both in the workmanship displayed and the logic shown in the planning.

Richard Trounce.
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

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

Post by Harold_V »

Adam,
Thanks for enlightening me in regards to the changing centerline dimension. I must confess, I hadn't considered that possibility.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Johnny O
Posts: 68
Joined: Wed Jul 20, 2011 5:02 pm
Location: Havertown

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

Post by Johnny O »

I like your cnc method, it beats the hell out of swinging these on a rotary table. I use a similar method mounting to a fixture and climb milling into the rod sides and shimming the gap on opposite side. I might try 1144 stress proof or 303 next time. I made my A3 side rods out of cast iron and a set of steam engineer rods from Ti. The use of a spray mister helps also. Thanks for the rod elongation tip, it never occurred to me that the rod would stretch. Patience is a virtue!
Attachments
64680B41-E9DD-4244-AB47-2B7A6E5A0C73.jpeg
0913B38B-B45A-4DE1-A242-9C750D637D1C.jpeg
B8CAB4B3-0418-4887-977B-4139DD27C44A.jpeg
EC7B6C58-977E-4C37-8CD7-A50626790D3B.jpeg
dkellldog
Posts: 14
Joined: Wed Jul 01, 2020 1:13 pm

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

Post by dkellldog »

hello,

Very well described method for rod machining. Regarding tapered rods with flutes, the use of a woodruff cutter causes the entry and exit point of the cutter to not match up well when the two tapers are cut at different angles. This causes a seam at this juncture. Does this call for a hand filing solution or is there a machining tip I need to learn regarding machining fluted rods? Straight is easy, the entry and exit points have me scratching my head.

I am surprised by the change in center to center dimension but I understand now that I think about it. I'm guessing rod center hole growth will be 1/2 of the amount of interference that the two bushings impart to the rod ends, correct?

In my next life, I'll be a machinist, not a marketing major.
User avatar
Builder01
Posts: 726
Joined: Mon May 18, 2015 5:26 am
Location: Erie, PA

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

Post by Builder01 »

Machining the flutes with a woodruff cutter is actually pretty easy, and when doing a tapered rod, where the cuts meet, it is probably less of a problem than you might think. The misalignment is not even noticeable. This photo is of rods done with a woodruff cutter. The flutes are quite rectangular at the ends where the cuts meet, even on the tapered one. These flutes were cut without the aid of DRO. Just a few dial indicators and careful work. You must document exactly where the cuts stop and start, and the depth of each cut. (I hope the photo is clear enough to show this)
DSCN0857.JPG
User avatar
Bill Shields
Posts: 10460
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

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

Post by Bill Shields »

Which is why I loctite bushings in place. :mrgreen:

In reality, if things are so tight that you have to worry about this change...your loco is going to have a lot of trouble running on uneven track.
Too many things going on to bother listing them.
User avatar
Greg_Lewis
Posts: 3014
Joined: Wed Jan 15, 2003 2:44 pm
Location: Fresno, CA

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

Post by Greg_Lewis »

Builder01 wrote: Mon Sep 12, 2022 3:53 pm Machining the flutes with a woodruff cutter is actually pretty easy, and when doing a tapered rod, where the cuts meet, it is probably less of a problem than you might think. The misalignment is not even noticeable. This photo is of rods done with a woodruff cutter. The flutes are quite rectangular at the ends where the cuts meet, even on the tapered one. These flutes were cut without the aid of DRO. Just a few dial indicators and careful work. You must document exactly where the cuts stop and start, and the depth of each cut. (I hope the photo is clear enough to show this)
DSCN0857.JPG

Ditto. I came back with some emery cloth wrapped around a bit of wood that fit into the flutes and cleaned up any remaining hints of multiple cuts. You do have to have all brain cells working when making the cuts, though. Lock yourself in the shop and turn off the radio and the telephone.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
dkelly@rmce.com
Posts: 27
Joined: Sun Apr 03, 2022 1:32 pm

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

Post by dkelly@rmce.com »

Everyone,

Thank you for the information and the quick response. I'll radius the corners of the end mill slightly and start machining, The rods on Builder01's engine look very good. his gives me a visual target of how my rods should look.

Bill, I'm a huge fan of Loctite as I use the 609 product to secure the bearings, wheels, axles and journal boxes together so the lateral movement of the axle boxes controls side to side movement of the drivers. I will use plastic backed metal for the rod bearings so rod growth due to bushing fit will not occur. What clearance in an axle box slot causes pressed in bushings to bind? Must be an awfully tight fit up.
User avatar
Bill Shields
Posts: 10460
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

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

Post by Bill Shields »

If you plot out one axle at top of travel and the next at bottom, you can calculate the hippotimus of the triangle.

If you do not have at least that much clearance, plus slop for oil film and accumulated tolerances between the axle boxes and frame...you gonna find yourself in a bind.

Remember you have to think in 3d since as the axles go up and down, they also go left and right as you go around tangents....and you can have the left hand box up and the right hand box down on the same axle...all on a wavy track that would send Amtrak off in a ditch were it scaled up.

In general, after all is built and runs smooth on the stand, I drill the rods out to the next size and wait as they wear in and start to clank. :mrgreen:

THEN it is ready to run on a bad track....and there are lots of them out there.

Remember . We are building locomotives not watches.

There are places where precision is important and there are places where being one step above a blacksmith is just about correct.

Having the center to center distance is important.

Making the bearing fits too tight is a common mistake.

My personal favorite is a bearing inside a bearing running on the axle pin. Oil space between each. Gives a lot of oil dampened float and minimizes wear and clank because the dual oil films accommodate the differences needed.
Too many things going on to bother listing them.
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

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

Post by NP317 »

Watch videos of full sized steam locomotives (with the sound up) and you will hear the rods clanking, especially when the locos are drifting.
That illustrates the required clearances to accommodate all that 3D motion in the running gear.
Same required for our smaller locomotives.
Watch makers might have difficulties making our locomotive designs actually operate...
RussN
10 Wheeler Rob
Posts: 1546
Joined: Tue Mar 21, 2006 2:44 pm
Location: East Hartford, CT

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

Post by 10 Wheeler Rob »

I have found that if you Loctite the bushings in the center dimension dose not move since they are a slip fit before applying the retaining compound.

I have also had issues with the inside of bushing getting slightly smaller when pressed in. This was very noticeable when I made some Delrin bushings.

Rob
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

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

Post by NP317 »

I have always pressed the rod bushings into position and hand reamed (if still required) to the needed large clearances.
This has worked for hundreds of miles and any years. No bushings have required replacment yet.
RussN
Post Reply