Crosshead machining woes

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Dale Grice
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Re: Crosshead machining woes

Post by Dale Grice »

This is a RR Supply heavy mike. The assembly drawing shows the wrist pin pinned to the crosshead. Main Rod rotates on the wrist pin. So I am overthinking bushing material.

Not too keen on silver soldering this big piece. Not enough practice. Guess I should make the bushing a couple thousandths undersize on the OD. Then center punch 120 degrees around the circumference on both inboard and outboard. Clean, slather up with flux and go to town with heat on the crosshead.

I like Dick's idea of "reamed about half the depth of the hole to be a close fit on the piston rod and threaded the second half". However, how do you lock the piston rod after adjustment? Pin it? Or do your adjustment on the piston end and cut off any excess piston rod in the cylinder?

Dale Grice
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Wolfgang
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Re: Crosshead machining woes

Post by Wolfgang »

Dale Grice wrote: Wed Jun 15, 2022 2:37 pm I did not think of the jam nut. Good thought.

But, the real question at this point, what would you use for a bushing in the wrist pin hole?
I need to bore it out and bush it. How big? maybe an 1/8 diameter oversize. What material should I use to bush it? Brass, Silicon bronze, 1144, 1018? Wrist pin is drill rod.

Dale
I'm guessing here that the wrist pin rotates in a bushing in the connecting rod. If so, then the material in the cross head is of no great importance.
Just be sure that the oversized bore in the cross head is in the correct location, in which case a concentric bushing will serve. Methinks a 1/16" bushing wall thickness is sufficient.
Since the cross head is bronze you may wish to make the bushing of a matching bronze, also. I would soft solder this bushing into the cross head. Excess solder may be filed off. The bushing outside diameter should have .002" to .003" diametral clearance for this soldering.
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Bill Shields
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Re: Crosshead machining woes

Post by Bill Shields »

Best pin bushing material is either delrin af or nylatron

Both will take an unlubricated pounding and not wear
Too many things going on to bother listing them.
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Dick_Morris
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Re: Crosshead machining woes

Post by Dick_Morris »

I like Dick's idea of "reamed about half the depth of the hole to be a close fit on the piston rod and threaded the second half". However, how do you lock the piston rod after adjustment? Pin it? Or do your adjustment on the piston end and cut off any excess piston rod in the cylinder?
I'm going to silver solder a shoulder onto the rod, mostly for appearance. Then use a taper pin in the location that the tapered key is on the prototype. I'm hoping that I don't have any need for adjustment, but if I do, it can be done with a shim or removing material from a shoulder at the piston end. I will be using the same combination of reamed hole and some threads on the piston end. The piston end of the rod will have a shoulder, but will also have a recessed jamb nut.

I'll probably try and put a couple of flats on the visible end of the taper pin so it looks more like the prototype's flat tapered key. I've cut high speed steel with carbide tooling, we'll see how hard taper pins are. If necessary, I can even anneal the taper pin as the hardness isn't important for this application.
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Bill Shields
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Re: Crosshead machining woes

Post by Bill Shields »

Loctite
Too many things going on to bother listing them.
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Harold_V
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Re: Crosshead machining woes

Post by Harold_V »

Taper pins are generally not heat treated.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Dick_Morris
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Re: Crosshead machining woes

Post by Dick_Morris »

Harold - Thanks. That's good to know.
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Bill Shields
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Re: Crosshead machining woes

Post by Bill Shields »

There ARE the occasional times when they need to be drilled...😀
Too many things going on to bother listing them.
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