rgrae
Gandy Dancer
Posts: 2
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Post by rgrae on Mar 2, 2006 3:34:07 GMT -5
Hello,
Just found this place - looks like I'll be here a lot....
(I'm a home-shop machinist, but have never done these types of cuts.)
Broaching and quartering. Most times the broached hole is in line with the crank and the axle keyways are offset to get exactly 90 degrees offset. I've always thought it might be hard to get exactly 90 degree offset on the keyways.
I recently saw a setup where the keyways were in line (no offset and easy to do) and the broached holes were offset from the crank by 45 degrees via a template that had pins fitted into the axle and crank holes.
This way, when you broach the holes from the "front" of each wheel, when you then turn a wheel around and line up the broached holes, the cranks are offset by exactly 90 degrees.
Another way to accomplish the same result, but seems easier to get exactly 90 degrees. Once the template is accurately made, no fidgeting - just cut two keyways inline and broach the holes and Bingo, automatic quartering!
And that's all I have to say on that.....
Richard
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rgrae
Gandy Dancer
Posts: 2
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Post by rgrae on Mar 2, 2006 4:00:07 GMT -5
Actually, there is one more thing I'd like to say.........
Offset error: It assumed that if you use only the X axis to cut the keyways, there is absolutely no offset. That leaves only the template (sorry, I should be calling it a Jig) to be the source of any errors in this.
If the pins in the jig are not loose in the holes and the slot for the broach is not loose, the only place where any error can come into play is that the slot in the jig is not exactly 45 degrees offset from the crank.
Maybe after your most diligent work, the slot in the jig is 44 1/2 degrees offset. Not the greatest, but this error will be exactly duplicated on all the wheels and therefore all will be exactly in "tune" with the others. And therefore, no binding.
And THAT'S all I have to say on that.......
Richard
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Post by GoldenSpike53 on Mar 6, 2006 1:17:15 GMT -5
Hi, Richard. Actually, quartering of axles to 90 degrees is not that hard. How it's done is to take a piece of square stock a bit larger than the diameter of the axle, and bore a hole in it just large enough for a slip fit for the axle. Then drill and tap a couple of holes for some set screws, insert the axle and set screws, tighten the screws down, and the axle will stay in place. With the axle in this jig, lock the jig down in the milling vise and use an end mill of the correct size to cut the slot in one end of the axle. Turn the axle and jig 90 degrees in the vise and cut the other slot. This should provide you with perfectly quartered axles. If someone used your method and ended up with a displacement of 89 degrees (2 x 44.5 degrees), it may not make an extreme difference, but the further off it is, the more it will impact the timing of the locomotive. That can always be accounted for when the timing is set up. The idea behind quartering is that the locomotive will never be in a position where it can't start on its own. There will always be a valve that will be open on one end of one of the cylinders. The other impact would be somewhat aesthetic, since it will place the "chug-chug" of the locomotive closer together so it would sound a little off. I guess it depends on how important that is to you.... Dale
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