Driver machining order

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Re: Driver machining order

Post by RET » Tue Oct 15, 2019 8:24 pm


LBSC and Lester Friend gave a similar sequence which still makes sense today. Remember, both of them were talking back in the days where very few people had a mill of any kind, usually just a drill press and a lathe (usually either a South Bend -American or a Myford - English). Also, remember, Harold is always worth listening to.

The sequence is: 1. First hold the casting in either a 3 or 4 jaw chuck by the wheel tread (back out) so that the tread and flange run as true as it is practical to get them. Face the back off flat and true to its finished dimension.

Next, 2. turn the casting around and mount it on a faceplate (machined face to the plate) so the wheel tread runs true. Clamp the wheel to the plate using the flange. Be careful not to tighten things up too much or you might break the flange! Machine the front of the wheel to its finished dimensions including grooves to represent the tire and counterweight mountings. In the same setup, drill the center hole and bore it to size.

3. Mount the wheel on an arbor and machine the flange and tread to their finished size and shape.

4. Either make up a fixture with a pin that is a close fit in the wheel bore with a bushing at the crankpin radius so all the crankpin holes can be made the same using the fixture, or make a different fixture that mounts on the mill table and holds the wheel (by the bore) so that the mill can be used to bore all the crankpin holes to the same radius.

When doing this, it helps a lot if you set up a mini production line so you run all the wheels through each step in the process at the same time.

You can use the key method of quartering, but alternately, you can also mount the wheels (and crankpins) using the dutch key method. This has the advantage of being able to remove the wheels or crankpins at any time in the future and putting them back on again if you need to change bearings, etc. or for any other reason (for those of you who don't know, look up "Dutch Key").

In all of this, remember you are making a locomotive, not a watch, so some play is both necessary and desirable.

Hope this helps a bit,

Richard Trounce.

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Re: Driver machining order

Post by SteveR » Tue Oct 15, 2019 10:18 pm

Well, I did mine a bit different than everyone else, but they seem to function correctly. The procedure that I wrote down was for my Allen Consolidation and goes like this.

Mount driver face out in 4 jaw chuck with inner edge of the rim centered as well as possible. This will define the cleanup groove.

Make sure the front of the spokes are in the same plane as well as possible. With the Allen drivers, they are pretty consistent with the back face, but this is not always guaranteed. Since this side of the spokes will be showing, this part needs to be correct.

Turn down the front OD of the flange to 6.75" to rough.

Face the wheel rim face so that the #2 spoke is 0.25" from the face. This will also define the OD of the counterweight =5.025 or counterweight arc length =4.280".

Face the counterweight so that it is 0.25 or 0.125 from the wheel face (depends on which driver it is).

Face the hub so that it is 0.125 from the wheel face (Allen dimension)

Groove the rebate groove around the ID of the rim.

Centerdrill and Drill 7/8 and then bore to press fit axle

Remove and turn around to do the back.

make sure faces of 4 jaw chuck are even within 0.001 with tape and shims, then mount front of driver on top of 1/4" keys taped to shims
(If I was going to do a lot of these, I think I would try using soft jaws)

Face back to thickness.

Turn down the OD of the flange to 6.90 to rough, then mount on a mandrel to turn the profile or add tires.

Good luck.
12x36 Enco Lathe, 9x42 Bridgeport, SMAW, O/A, Miller MIG w/gas, "Tools to make things"
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1" FEF in progress
1" LE Pacific "Project"
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Re: Driver machining order

Post by SteveM » Tue Oct 15, 2019 10:32 pm

I made the attached "shoes" for my lathe before I had a chuck dedicated to soft jaws.


Came in handy when I discovered how reamers can leave a taper is the tailstock is not perfectly aligned.


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Re: Driver machining order

Post by JTolan » Wed Oct 16, 2019 12:24 am

For what its worth. I've always done the finishing pass when the whole axle is together. Keeps things true. Also, I face the back of the wheel in the lathe, then center drill in the mill the center of the hub, then place in a four jaw using the center drill hole, then perform the rest of the operations. Often castings are rather funny shaped, and dont clamp concentric in a dependent chuck. Just drilling the hole straight way in the lathe can result in having a wheel that looks off center, which aesthetically is bothersome and can result in vibration at high sleeds :).

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Re: Driver machining order

Post by neanderman » Mon Oct 21, 2019 12:32 am

ChipsAhoy wrote:
Mon Oct 14, 2019 8:55 am

Put the drivers on the axles (along with all the items required on the axles) with the intent never to be removed again
Turn the complete tread, flanges, front and back faces between centers.
If you've ever seen a wheel lathe, that is exactly how they do it on the 1:1 scale -- on the engines and cars.

Wheel lathes have two compounds that move in unison.

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Re: Driver machining order

Post by gwrdriver » Tue Oct 22, 2019 7:47 pm

The problem with turning the front and rear faces of a rim on the axle (in models) is that often there isn't enough stiffness in the axle and spokes to avoid deflection which can create harmonic chatter, even if taking the weensiest skim cut.

An on-the-axle skim on the tread usually goes off without problems, except that I put generous fillets on my wheels (using a "spoon" bit) and when I get to the fillets I've found that in order to eliminate the little bit of harmonic chatter that occasionally appears, and my slowest spindle speed won't quite get rid of it, I simply draw the wheel around the last turn or two by hand which does the trick.

The other thing I do is to spend whatever time it takes to do three preliminaries to get the relationship of the front rim to spokes right. First, I make sure the spokes are running true and aren't "swash-plating" in relation to the wheel face. This is usually an "averaging" process. I make sure the inner edge of rim is running as truly concentric as the casting will allow. Also sometimes an averaging process. And lastly I make sure the faces of the crank hubs and rim are at the proper depth relative to the spokes and their fillets. Then I closely rough the rim face which tells me exactly how much the backs can/must be taken down. To me the proportions of the fronts matter, the backs not so much. Before leaving the fronts I turn a chucking step on the rim front edge to provide a witness for when I turn the wheel around. Once the wheel is turned around THEN I begin the usual process of facing the back, boring for axles, etc.
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