Crank axle

The crank axle is more complex, but not too difficult to make.  Recently I've made a new crank axle for my 3½" 'Mona' steam locomotive. This is the same working procedure, it is only a bit bigger.

In fact, it only consists of three different parts. 

The first part is the same as the coupled axles. These coupled axles are a simple affair to turn with the aid of a collet of 16 mm. For 5" gauge a standard is 117.5 mm back to back. 

The excentrics

A round bar, which was first turned to the correct outside diameter, is then set up in the independent four-jaw chuck. The excentre stroke was scribed with the height gage, and a center was drilled on the drilling machine first.

The axle hole is bored out with a standard boring tool

After that, a set up in the three jaw chuck is used to turn the diameter of the excenter. 

The parting tool was only used for a limited depth, because it was not possible to support the material.

The rest was cut by a hand hack saw. The back was faced, holding the excenter in the jaw. A piece of thin brass protects the surface of the excenter.

There was just enough material to make an extra spare part. 

Scribing a line trough the center, with this center finder. 

This way the location for the 3.5 mm hole could be marked.

drilling and..

.. taping M4

The crank webs

In the milling machine, the holes for the axle were bored and reamed

A quick test fit, to check that the holes are nicely aligned.

Roughly milling the radius on the webs

After milling they were filed to shape, with the aid of filing buttons. 

The crankpins are glued. Cleaning the surfaces was done with brake cleaner spray. This works very well; the Loctite then cures fast; within 30 seconds. 

The second web is glued in position on the axle. A gauge strip of 10 mm is used to keep them aligned.

The major components of the crank axle.

Center drilling the location for the roll-pins on the milling machine 

The first crank is shifted on the axle and glued at 15.75 mm from the end. 

After curing, the second is glued on. A clamping set up is used on the milling table, and with the aid of magnet blocks it can be set to 90 degrees. 

I had to look at the drawing several times, to make sure that the right-hand web is leading.

This is not that important, but is a general practice by British locomotives to have the right-hand in the motion leading. 

After the glue has fully cured (about 24 hrs), the holes are drilled 3.1 mm, for 3.3 mm roll-pins.

The roll-pins are pressed in. I'm not sure if the pins are needed, with the crank axle of the 3½ Mona they were not installed and so far no problems. But then again this is a bigger crank axle on 5" gauge.

The last stage is milling out the axle between the webs. By the axle that I recently made for the 3½" Mona, I did cut it out with a hack saw and filling. This is a quicker option.

The last thing to do was to set the excenters. Their position was determined in Solidworks. In the drawing, the angle can be measured as a distance to the axle center. This value can be set on the height gauge. By turning the excenter and carefully touching up, they can be set and locked.

The complete crank axle.

Driving and coupled wheels for the Y14

 As an intermezzo in building the boiler, some machine work was nice to do. Turning the driving and coupled wheels is a straightforward turning job, but requires some planning in set-up and sequence to machine the several faces. 

The wheels were bought in England from Mark Wood,  in the days before the Brexit customs rules made this very difficult.
The wheel castings are of excellent quality and are fine cast. Mark did some special research on the prototype Y14 locomotive so that they are very close to scale.

Update:  Mark told me today that: 

Just after Brexit I had problems with long customs delays and even parcels being returned to me - that was with DPD.  Now I use UPS and pay the local duties in advance and parcels have been delivered to Europe in about 3 days from posting. 

So this gives a good prospect for future model locomotives. 😀 Take a look at his website, because he offers many wheel castings. 

First the backside is faced, so there is a reference plane to start with. 

With all the wheels faced, the outer flange had to be cleaned up. But the jaws of the chuck were too deep to give enough clearance. So some aluminum strip was bent, so it could be clamped over the inner jaws. 

This made it possible to give just enough clearance. 

Gripping the wheels on the machined outside rim, the front could now be faced.

The bosses are 3,5mm outside the rim and could also be faced. 

Then the backside could be finished and faced to the final thickness of the wheel. 

In the same setup, the wheel is bored for the driving axle. By doing this in one setup, the hole and backside are dead square to each other. This way the wheel will run without a sway. 

Because the spokes are close to scale (and therefore thin), the wheel was clamped between two aluminum disks. With three bolts the disks are screwed together. 

Now the rim could be turned to the final diameter of 133 mm and the flange could made.

It's a job that takes some steps for each wheel. Every step is done for the six wheels, before changing to the next set-up.  So a lot of set-up time: clamping in the three-jaw chuck and between the disks and changing the lathe tools, was involved.  A few evenings behind the lathe were needed. 

For the flange, the top-slide was set to 18 degrees. 

Finally, a small radius was made on the flange. 

To drill and ream the crankpins, a set-up was made in the milling machine. A short stub was mounted on the milling table from which the center of the wheel was positioned.
The stroke of the crankpin was done first with a center finder used on the stub, setting this to zero and then moving the Y-axis to 26,5 mm.

With a small piece of round brass, that was turned to the same diameter as the boss, the correct position of the crank could be determined by turning it over around the center, after which the wheel was locked down with the clamps. 

  

With two clamps the wheel was fixed to the bed. The hole was centered, pre-drilled with a standard drill, drilled with a three-lip drill and then reamed. 

The small brass plate under the wheel is used as protection for the milling table, in case a drill or reamer is going too deep. 

The backside of the crankpin hole is countersunk, so a screw can later fix the crankpin.

The axles are a job that could be done by using the collet. 

"On its wheels" (well, without the hornblocks yet)