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Joined: Oct 2000
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Here's a old pump that I have to rewire. The Cover plate screws have rusted in place, and the Cover plate itself was not water-tight and was hanging from one screw. I just reached out to move it and the screw broke off. I'm not sure if I can re-tap the holes because this is solid cast-iron and I think it would destroy my tap & drill bits (although I have not tried this yet).

Have any of you run across this, and if so, what did/would you use to seal up the built-in j-box? I have all sorts of water-tight cover plates in my truck but need to fasten them somehow. Thanks in advance for your suggestions!

- Electric-Ian

Joined: Jan 2003
Posts: 4,391
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Drilling and tapping cast iron is no particular problem.

You will actually be drilling out the screws which will be a (most likely) mild steel.

A sharp bit used at a slow speed with oil will be fine.

The goal is not to let the bit get to hot or you will lose the edge on it.

When tapping use tapping fluid or penetrating oil, turn the tap in until it get tough to turn, back it out to clear the chips and turn it in again.

Repeat going forward and back with the tap until you are done.

I would use the cover that came with it and seal it with gasket material (at auto parts stores) or silicone.

It would be good to buy some brass or stainless steel screws to put the cover on with so this will not happen again.

At the least put some "Anti seize" compound on steel screws


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Jul 2003
Posts: 394
B
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Double the info on tapping. When you tap cast iron, you don't get nice spirals like in steel. The cast kind of crumbles out of the way of the tap into fine, abrasive dust or chips. If the hole is vertical, it'll fall out fairly well but if you are going horizontal, back out completely a couple of times and blow out the crud. Slow and easy is the rule.

Joined: Dec 2001
Posts: 18
E
Member
Thank you iwire & Big Jim. I retap almost exclusively galvanized boxes which has never been a problem. I'll try out your suggestions and am sure it will work fine.


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