Bog's Paddleduck Engine

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kvom:
I finally got all the parts made that are needed to try to get it running. I started to assemble everything, and discoivered that one of the threaded holes in a crosshead that connects the piston rod is crooked. :bang: No way it can ever work the way it is.

One option is to make another crosshead. But I'm wondering if there is a way to fill the hole and redrill it. Calling John! :bow:

bogstandard:
Kirk,

The normal way would be to drill out the offending hole oversize, silver solder a little bar of brass in it, then just redrill and trim everything up so that it looks nice.

If you can get a little bit of the same metal into the original but enlarged holes, you can rescue almost anything.

I don't know if you have read the article, but this shows just how to do it. In an hour or so, you should be able to see the finished article after rescue.

http://madmodder.net/index.php?topic=1370.0

Hope this helps.

John

kvom:
I was thinking it was something along that line. The hole is about .25" deep, threaded 8-32 and hence ~.160" in diameter.

Once I drill it out, how much solder needs to go with the plug? Am I trying to get the solder to flow all the way down the sides of the plug, or just around the top?

bogstandard:
Make the plug slightly smaller than the hole, say 0.002" to 0.004".

Dip the plug into your liquid flux, paint a bit of flux down the hole, and push the plug down into the hole. If you make the plug longer than the hole is deep, you can always trim it back afterwards. Cut up one coil of solder wire so that it fits around the plug on the surface, it doesn't have to be a super close fit (if you are repairing a tapped hole, use two coils, so that the threads are filled up as well), as long as it isn't too far away from the hole it has to go down. Heat up the main part of the job and you should see when the solder flows down the gap. Take away the heat, let it cool down for a few seconds then quench and pickle for a while.

Dress up the the part to get it looking like it was before the bad hole was put in, then redrill and tap your new hole in the correct position.

All you are doing is filling up the bad hole with metal, then remaking the part from before you made the mistake.

John

kvom:
I followed the recipe, and it worked like a charm! :thumbup: Although I was irritated that I needed to do this, I'm glad to know the technique for future use.

Since the hole was both off center (at one end) and angled, I was reluctant to just drill it out, fearing that the drill bit would just follow the hole. Since I have some 1/4" brass rod, I decided to use a 1/4" endmill centered on the new hole and encompasing the old. After a slight chamfer, I did the SS thing. Once I had milled the plug level with the top of the crosshead the repair was practically invisible.

Rather than risk doing the same error again, I clamped the piece in the vise such that the crosshead guide bar chucked in the mill would go straight into its hole, thus ensuring that the new hole would be parallel. After drilling the new hole, I also used the mill to tap it. That's what I should have done in the first place.

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