Author Topic: Being creative with the Atlas Shay...  (Read 1746 times)

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randgust

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Being creative with the Atlas Shay...
« on: December 14, 2016, 11:12:31 AM »
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OK, so as I sit here studying the new version - with the smaller motor.

One of the things Atlas did was pick probably the longest truck-to-truck wheelbase for a two-truck Shay that ever existed.  If you could shorten that up a bit, all kinds of things could be done in the geared locomotive world.   With the old motor, probably not possible.  With the new motor, well..... now there's some space in there, and the Bachmann 44-tonner motor of the same case design is three feet shorter.  Hmmm.   Particularly if you took out a flywheel.

Most of everything hasn't changed much.   But in trying to determine if there's any creative possibilities with that chassis, I've run into a real rock wall here on two specific issues.

First - the design of the 'flyworms' and their mounting onto the motor looks like an invitation to disaster to attempt to remove.    It looks to me like the worm and flywheel are one brass turning, and it looks to me like it is probably only drilled as deep as the flywheel portion; i.e. there's no way to either remove it without damaging the motor as there is no shaft sticking out of the worm end.  And, even if you did get it off, I suspect there's no drilled shaft hole in the worm itself.    The only way I can see to get that flyworm off might be to put a hemostat clamp on the motor shaft as a heat sink and do a fast heat with a torch to see if the flyworm could be heated and expanded off the shaft.   One of those 'you only live once' moments.    Still wonder how it was assembled to begin with.  Anybody else looked at this?

Second - the modulus on the worm/worm gear appears finer than anything I've ever seen anyplace else, which is great for slow speed but makes it fairly impossible to substitute anybody else's worm as an alternate solution to the Atlas.   Has anybody found another worm that fine a pitch that would work?   The Bachmann brass worm on the 44-tonner is a considerably heavier pitch.

I'm not criticizing the design in any way as it runs great as-is, just I bought a second one to tinker with and this is about as much of an assembly puzzle as my old Hallmark Northern where the wheels were put on after the frame was soldered up.   I don't give up easily, either.   

This is the only design I've seen with inside-bearing wheels, 36" wheels, and a 56" truck wheelbase (more or less) - which was very typical of all geared steam but that wheelbase, wow.   That's way too long for anything but that late-version Shay it's on.


Chris333

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Re: Being creative with the Atlas Shay...
« Reply #1 on: December 14, 2016, 01:59:03 PM »
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This is the first I've heard about the new motor.

I do remember on the old version there were some people who had a hole at the end of the worm and some who didn't.

narrowminded

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Re: Being creative with the Atlas Shay...
« Reply #2 on: December 14, 2016, 02:00:22 PM »
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Randy, you could back in to the pitch by measuring the worm gear that the worm mates with.  It would be a reasonable assumption that it's a metric standard.  And one additional note to keep in mind is that there is no dictated standard to worm diameters although they tend to be in a close range and chances are good that a manufacturer has picked one as his standard size.  And in fact, several manufacturers seem to have chosen that dimension as their standard, evidence some known worm interchangeability between manufacturers.  But there's nothing in the modulus standard that dictates this and they can be different.  And further, if we were working with true worm gears that partially envelope the worm, this would matter, but we're not.  What WILL happen in our applications where they just use an angle modified spur gear, is the tooth angle will change slightly as the worm diameter changes but I think it's safe to ignore that in these very little, low load applications and again, evidenced by some of the cruder old stuff that just ran straight spur gears into worms and got away with it.  But what is now revealing itself is why many of the older gear trains were noisy running and it can be in this but also in the involute shape required on worm and spur gears for smooth meshing not being addressed in the tooling.  It makes for a noisy running gear and if it was really sized and loaded as a bigger application would be, would be very short lived in service.  But we get away with it.

You can determine a metric gear outside diameter by counting the number of teeth, adding two teeth, and multiplying by the modulus.  An example might be to determine the OD of a 14 tooth, .3 mod gear.  It would go as follows:  14 + 2 = 16.  16 x .3 = 4.8.  So, 4.8mm is the diameter of a 14 tooth .3 mod gear. With that basic method in mind, just divide to back in.  4.8mm divided by 16 (14 teeth +2) = .3 (mod).  That's it.  When measuring the gear OD do it carefully and try to get the crest (not spanning two teeth) of two opposite teeth to get the most accurate measurement possible. 

You will likely have some decimal places that get out of hand but if you look at them in actual size changes will find that they are well within some pretty fine tolerances and therefore can be dismissed as tolerance error, your very small measurement error, or the like. 

Many N scale trains use .3 mod gears so thought it was a good example.  That's probably what that Bachmann is.  I've also seen .25 mod which is visibly finer.  I'm working with english in my endeavors and am currently down to 120 DP (diametral pitch) which in metric would be about .2116 mod.  It's also that easy. :)
Mark G.

narrowminded

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Re: Being creative with the Atlas Shay...
« Reply #3 on: December 14, 2016, 03:03:55 PM »
+1
If you needed to get that worm/ flywheel combination pressed off you could drill in from the end to make it a through hole.  The exact shaft size or perfect center wouldn't be mandatory as it would give you access to that shaft end but the closer, the better.  Very careful set-up in the mill or make a bell shaped fixture for the lathe. 

If you had drills or a reamer of the worm OD you could make a one time use fixture pretty easily in the mill.  The idea, absent much gory detail is, a piece of scrap stock gripped in the mill vise and overhanging on the end for access to it from underneath, drilled in place to the OD of the worm at an arbitrary but now known number, slip the worm up in, and it will be square and on center of the just drilled/ reamed hole.   Carefully spot drilling and drilling at each step and the tightness of your machine will dictate the success or failure.
« Last Edit: December 14, 2016, 03:05:33 PM by narrowminded »
Mark G.

nkalanaga

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Re: Being creative with the Atlas Shay...
« Reply #4 on: December 15, 2016, 01:04:58 AM »
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Is there a "flyworm" on both ends of the motor?  If so, could you put a plate between one and the motor, thick enough not to bend, with a slot for the shaft?  If you can, make a "puller" from similar material, with a similar slot, and put that behind the other flyworm.  Clamp the first plate in a vise, and pull on the second, being sure to pull straight along the shaft.  I wouldn't recommend pulling with pliers, make some kind of fixture with a screw or "come-along" type puller.  Since the shaft goes clear through the motor, there won't be any stress on the motor, regardless of which end releases first.  Either you get the pulled end, and motor, with the fixed end coming off, or the pulled end comes off, and the motor stays in the fixed end.

They would probably press both ends on at the same time, and if everything was aligned right, they'd both bottom out without damaging the motor.
N Kalanaga
Be well

narrowminded

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Re: Being creative with the Atlas Shay...
« Reply #5 on: December 15, 2016, 01:12:31 AM »
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A new worm could be made relatively easily if that's the stumbling block.  A sample would be needed for measurement.
Mark G.

cbroughton67

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Re: Being creative with the Atlas Shay...
« Reply #6 on: December 15, 2016, 09:46:51 AM »
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@randgust , can you post photos of the new motor and "flyworm" assembly? I'm not familiar with the Bachmann 44-tonner motor, but I do know the Bachmann S4 motor is quite small, and the worm gears are the smallest I've seen. Maybe these could be substituted for the Atlas parts to get around the flywheel issue entirely. But, I can't say without seeing the new Shay setup.
Chris Broughton
MMR #650

Darwin was an optimist.

randgust

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Re: Being creative with the Atlas Shay...
« Reply #7 on: December 15, 2016, 10:20:00 AM »
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This is the old mechanism with the old motor.

http://www.spookshow.net/loco/files/atlasshaymech.jpg

Worm pitch and size is unchanged.   The newer motor is smaller, and I also think the shaft diameter is now smaller.

But the real issue here is that the flywheel and the worm look to be one continuous brass part, and only the flywheel portion appears to be partially drilled for the motor shaft.   It is not drilled all the way through the worm portion.

I'm not sure, and until you try to get it off there you really won't know how deep it's drilled.   And getting if off looks to be difficult if not impossible.  I've taken off a lot of flywheels and have pullers, know the drill.   This is different.  If I knew the shaft actually went INTO the worm portion, I'd try the torch to heat it up and expand it off the shaft. 

I'll try to get some dimensions on that worm portion.  Also note that Atlas doesn't sell any of that separately - you can get the motor assembly with everything on it, but no parts under that.

I'd think the way to go would be with a different worm, same pitch (if it can be found), possibly mounted on a Bachmann 44-tonner motor (dual shaft) to get a far shorter wheelbase potential.  If the shaft went THROUGH the worm, you could set up end bearings around the truck.

I'm still wondering if Kato or somebody also uses a worm pitch this fine - when they went to finer-pitch gears on some of their newer diesels.

randgust

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Re: Being creative with the Atlas Shay...
« Reply #8 on: December 15, 2016, 07:48:54 PM »
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OK, took several tries to get a decent shot of this.

This is the Bachmann 44-tonner motor perched on top of the new Atlas Shay chassis.  Those of you that have one will notice the immediate difference in the motor and mounting bracket, and the new LED board instead of the spindly LED sticking up back there.

Look at the 'flyworm' and you can see what I mean.  Long turning, one piece, no end hole or protruding shaft.   And a very, very, fine-pitched worm.

A Kato 11-105 worm is at the bottom, and that appears to be the same pitch as the Bachmann worm.   Thought of that today, nope, won't work.

« Last Edit: December 15, 2016, 07:50:25 PM by randgust »