drilling and tapping cast

I have a NH 327 manure spreader and I'm having problems keeping seals in the gearbox. I put new ones in during the summer and there's water in the box again. There's no easy way to drain the case so I'm thinking about adding a drain plug to the bottom. Is there any special procedures to drilling and tapping a cast housing?
 
Nope nothing special. Be sure you used a pipe tap unless you are planning on using something with a gasket.

Rick
 
(quoted from post at 10:42:06 01/05/13) I was just planning on using a bolt with a rubber
washer.

That will work too. I prefer pipe plugs of the kind thing but the other way works too as long as the gasket seals.

Rick
 
Nothing to worry about unless you decide to really over tighten the threads. Generally the only castings that could be expected to break are those made from Pot metal, or thin aluminum. Use a one wrap strip of teflon tape and all is well. (consider putting a metal or ABS plastic shield over the shaft where the water leaks in. Jim
 
As was mentioned, I like to go slow.
I also prefer to stop and clean flukes of drill/tap periodically.
If particularly tough, I may do 1/2 to 1 turn with tap,
then back it out, clean, and relube.
Using grease, lard, etc on drill bit as well as tap will also keep filings out of internals. Seems I get a cleaner thread cut if I take the extra time to clean--but may just be me and my imagination, lol.
In my experience, if forced too fast or with pressure, it really sucks to extract a broken bit or tap, tho not impossible.
 
When tapping cast iron no cutting fluid is needed. The cast iron works as it's own dry lubricant.
 
Sounds like you may have excess play in your gear box and the bearings. I would be sure to check the end-play and side-play on the shafts before tearing it apart or think about putting a drain hole in it. Because you're really not fixing the problem of water getting in it. You are just making it easier to change the oil by installing a drain.
 
Shops I worked at decades ago....with cast, no lube. Whether cast or steel, slow and steady. I like putting the tap in the lathe or drill press, even often turn it by hand, but don't need to worry about alignment. By hand, yeah, I break stuff!
 
Tightening a pipe plug tight enough to split the cast housing is liken to putting to much mustard on a burger. Ya aughta know when to stop without a stop light.
 
There is one consideration all have overlooked. A casting is not of uniform thickness throughout. Usually a casting that has a tapped fitting has a boss or thickened area where the hole will be. What if you discover that the bottom of the casting is only a quarter inch thick?
 

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