3/4 and 1" Scale Couplers - Running Off Into the Woods Again

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Carrdo
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3/4 and 1" Scale Couplers - Running Off Into the Woods Again

Post by Carrdo »

As an aside, here is a photo of some 1" scale two piece bronze coupler castings I am also machining.

These castings were purchased some time ago on ebay and appear there from time to time at a very reasonable price.

Couplers such as these are often though to be easier to machine as there are far fewer parts and surfaces to machine vs the A. Grigg type (which I admit do involve a lot of work).

However, one pays your money and makes your choice.

For example, have you ever tried to set up such castings for machining (both the full knuckle piece and the body piece) and have everything square so the parts align properly when assembled and are aesthetically pleasing? Not so easy to do as there is no obvious reference surface where to start (to have everything work out). In addition, both castings are almost totally curved and quite tapered which makes things extremely tricky to hold especially for milling with the significant yanking and twisting forces involved.

It can be done but I had to do a lot of looking and thinking about how plus a bit of luck to get things to the stage shown in the photo. Am not out of the woods yet but now have reference machined surfaces on both parts from which further measurements and machining operations can be undertaken.
Attachments
62 Partially Machined 1 Inch Scale Coupler Castings and Knuckle Pins.jpg
Last edited by Carrdo on Sun Jun 17, 2012 6:59 pm, edited 1 time in total.
Carrdo
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3/4 and 1" Scale Couplers - Running Off Into the Woods Again

Post by Carrdo »

Some further photos. I will make a few comments on each photo.

The setup for the second operation on the coupler knuckle utilizing the first machined surface is shown in the first photo. By taking light cuts, I found that I only needed one clamp which made things much easier to see and to manipulate the end mill.

One only has to machine a somewhat irregular flat around the knuckle.

After years of practice, I can just manage to operate the x and y milling machine table and cross slide handles simultaneously to do this. One's hands have to work automatically while one's full attention is focused on what the cutter is doing. And if you can't clearly see the cutter as it moves around the curve and as well is cramped by the double hold downs .... just try it sometime.

After that one only has to use Riffler files and precision model makers files to obtain a small root radius at the base of the knuckle. All the while not touching or destroying the machined flat in the process.

The second photo shows the drilling and spot facing operations for the knuckle pivot pin. It is a setup NOT recommended as the coupler is not held securely in the vise and the location of the pivot pin hole is by guess and by golly more than anything else. The coupler was set on a couple of parallels and a spacer piece was used to "level" the tail end of the coupler but that was about it.

This is where an irregular work piece having a lot of draft (taper) presents a locating, holding and machining problem (to ensure the pin hole is square in the coupler body and the knuckle piece). The knuckle piece is loose in the body. While drilling, the body did tilt a bit and it had to be repositioned. The knuckle piece also did a bit of wiggle while drilling.

Other than making a custom fitting cradle with positive clamps (which I wasn't going to make), I don't have a good answer to this problem. Quite unusual but luck was with me and the operation turned out as best as possibly could be hoped for.

The third photo shows all of the dental work needed on the internal cavity of the coupler body to have a free fitting knuckle having full rotation. A Dremel tool isn't going to cut it here as the amount of grit and metal dust produced together with the amount of metal to be removed internally calls for a small but heavy duty, high speed, air operated industrial type die grinder.

I employed a number of carbide and diamond coated burrs as well as a number of coarse abrasive stones for this operation. But beware, one has to have a very steady and firm hand and only take light surfacing passes especially when using the carbide burrs as they can buck and kick severely if they dig in. Also, the body cavity was very deep and one had to reach down right to the bottom of it. This meant having a long overhang on the cutting tool so the bearings of the grinder have to be up to the task and fully dust and grit protected.

The last photo is just a size comparison with an A. Grigg coupler.

Only managed to do one so far as my nerves have had enough.
Attachments
63 Second Machining Operation on Knuckle.jpg
65 Drilling and Spotfacing the Coupler Body Casting for the Knuckle Pivot Pin.jpg
66 Internal Dental Work Needed on Coupler Body Casting.jpg
67 Size Comparison Three Quarters and One Inch  Scale Couplers.jpg
Last edited by Carrdo on Sun Jun 17, 2012 7:00 pm, edited 1 time in total.
Carrdo
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3/4 and 1" Scale Couplers - Running Off Into the Woods Again

Post by Carrdo »

To finish these couplers, one has to make the coupler lift pins (now mostly done) and to locate and drill the coupler body for them.

This involves the interesting operation to generate theoretical (but real) center lines on the coupler bodies. The theoretical center line is shown on the coupler drawing and the coupler pin hole is referenced (dimensioned) to it.

It is the classic case of producing a center line on a part or casting which has no reference surface. One runs into these situations a lot in model locomotive construction.

It looks so easy on paper until one actually has to do it.

Guessing is never good so here is how I do it.

The object here is to create a true center line on the shank of the coupler which tapers differently on both sides of the casting and once generated to continue this center line to a normally inaccessible point on the coupler body (the coupler lift pin boss in this case).

To start, pick any two points spaced at least an inch apart on the top surface of the shank and carefully (using a graduated rule and eye loupe) find and lightly mark half of the coupler shank width at these two points. It's better if you have 3 points on a long piece but I usually get away with using only 2.

One must not have the part move so if you can secure it as shown in the photo (with soft compressible jaws if possible), the operation will be made immensely easier.

Then carefully scribe a line through these two points.

Since one cannot extend the generated line easily to the lifting pin boss with the first setup, the coupler was then transferred to the milling machine vise (or any vise with a flat top) and the coupler shank center line was picked up using a vernier height gauge and eye loupe as shown in the second photo.

One can make light test marks with the height gauge scriber to verify that the center line is level and the scriber tip bisects the center line. It is just slow careful work and light tapping with a plastic hammer.

The reach of the vernier height gauge was then used to continue the center line onto the lifting pin boss. Since the drawing indicated the center line of the lifting pin boss was to be 1/16" higher than the shank center line, this was easily accomplished .

I also have made a sloped "Z" type scriber for the vernier height gauge so that it can reach up and over obstructions as one will find this is also needed in locomotive layout work.

As stated many times before, mostly preparation work and a little bit of thinking.
Attachments
68 Generating a Centerline Along the Shank of the Coupler Body.jpg
69 Picking up the Centerline and Continuing it to the Lifting Pin Boss.jpg
Carrdo
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3/4 and 1" Scale Couplers - Running Off Into the Woods Again

Post by Carrdo »

Drilling the coupler body for the lifting pin.

Another by guess and by golly operation. I hate these types of situations but I didn't have a good way to ensure the coupler body was totally square in the vise (and not tilted or rotated slightly in 2 directions i.e back to front and/or side to side). Had to use/trust the casting surfaces which are never straight, flat, square, etc.

One thing, one has to do all of these machining operations at one setting i.e. center drill, undersize drill, drill, ream and spot face without touching anything to have a straight and on size hole. Even though the lifting pins were collet machined, they must have warped slightly from machining as the pins needed to be eased slightly to produce an easy slide fit.

Next comes some even trickier bits to machine; i.e. the knuckle tail pieces to ramp into and lock smoothly with the slot in the lifting pins. Am not certain at this point whether it is even possible to do it by machining rather by slow hand filing and careful carving of the metal with an electric die grinder.
Attachments
71 Drilling Coupler Body for Lifting Pin.jpg
73 First Installation of the Lifting Pins .jpg
Carrdo
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3/4 and 1" Scale Couplers - Running Off Into the Woods Again

Post by Carrdo »

A casting now looking like a coupler. I love the look of cast and machined metal.
Attachments
77 Couplers Closeup.jpg
xinumike
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Re: 3/4 and 1" Scale Couplers - Running Off Into the Woods A

Post by xinumike »

Don....the couplers really look great!

Will you use them on the Little Engines Northern and Tender?
Carrdo
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3/4 and 1" Scale Couplers - Running Off Into the Woods Again

Post by Carrdo »

The 3/4" scale couplers (if they ever get finished) will be used on the Northern and the NYC Hudsons. I also said a while back that I would market a few of these but first I want to have a stronger lifting pin than on the originals. I have the design for it but this has to wait until an expensive piece of tooling shows up.

The 1" scale couplers are for the 1" scale Yankee Shop Atlantic which also is sitting here waiting to be finished - it needs a tender as well.

Have just spent the budget this month on the Yoder and Ashton Walschaerts valve gear books as I want to draft it out out to see how it compares with the Hoffman NYC Hudson design which I now have but don't ask me questions about that.

I agree, the Don Ashton information is excellent.
Carrdo
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Re: 3/4 and 1" Scale Couplers - Running Off Into the Woods A

Post by Carrdo »

After a long time further work on the 1" scale couplers.

The photos are self explanatory so I don't need to go into the details.

The drilled holes in the knuckle head don't have any practical operating function. They were only there in the prototype as core holes as coupler knuckles were cast hollow. If the knuckle had been cast solid no person could have ever pulled the knuckle open by hand - it would have been just too heavy.

Locomotive coupler design and manufacture shows engineering at its best. The coupler/knuckle has to be incredible strong but light as possible and lock and unlock flawlessly every time under every operating condition and in every weather condition known to man.

I still have to machine the knuckle tail pieces. More tricky machining. I can't figure this out on the drawing from what is shown. Either it is wrong or I am ...

If anyone has or can take a photo of an operating knuckle (tail piece) similar to what is shown in these photos in model scales I would appreciate it. The Al. Grigg couplers have completely different tail pieces to these 1" scale couplers.
Attachments
79 Milling Knuckle Piece Head to Final Width.jpg
80 Setup for Drilling Core Holes in Knuckle Head.jpg
81 After Assembly.jpg
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LVRR2095
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Re: 3/4 and 1" Scale Couplers - Running Off Into the Woods A

Post by LVRR2095 »

Carrdo wrote: The drilled holes in the knuckle head don't have any practical operating function. They were only there in the prototype as core holes as coupler knuckles were cast hollow. If the knuckle had been cast solid no person could have ever pulled the knuckle open by hand - it would have been just too heavy.
.
Don....it is not so much that they would be too heavy to open...it is that they would be too heavy to carry!
When I was a fireman and learning to run freight trains...I have to admit that I learned about train handling by breaking a knuckle. Once you have helped carry a knuckle back 50 or so car lengths to replace the one you broke....you learn to be careful! The hole that is in the end of the knuckle (vertical hole) is the same size as a broom handle. On every engine you have a broom for sweeping the cab floor....but mostly it is there to use when clearing switch points of snow or debris. The broom handle is put through that vertical hole so two people can share the burden of carrying the knuckle. Believe me....when you have to carry a knuckle a half mile or more....you REALLY appreciate that second person!
Keith
Last edited by LVRR2095 on Wed Sep 12, 2012 8:48 pm, edited 1 time in total.
Carrdo
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Re: 3/4 and 1" Scale Couplers - Running Off Into the Woods A

Post by Carrdo »

Here is the drawing of the coupler knuckle and tail piece. Does it make any sense to you? Can someone sketch it out in 3D?
Attachments
IMG_0537.jpg
10 Wheeler Rob
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Re: 3/4 and 1" Scale Couplers - Running Off Into the Woods A

Post by 10 Wheeler Rob »

I have a pair of unmachined 3/4" scale couplers. Is there any way I could get a copy of the machining drawing, the one posted is a partial print.

Rob
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Re: 3/4 and 1" Scale Couplers - Running Off Into the Woods A

Post by LVRR2095 »

Don....the print shows 3/32" holes in the knuckle only going part way through. The hole should go all the way through.
They are not core prints. In fact I have carried more knuckles that I would have cared to...and not one was hollow.
Now you will have to make a tiny little snow broom with a handle that will fit through the hole.
Aside from the hole making the knuckle easier to carry...the hole is there to intentionally weaken the knuckle at that point.
If you have slack action that will cause a seperation, you want the knuckle to be the "weak link" and break at that point, as the knuckle is easier to replace than a drawhead is!
Keith
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