Fine or coarse thread in cast iron?

My 17" Drill Press has a slope between quill assembly and casting. As someone suggested I can drill and tap a couple of holes in casting and put some brass screws against quill assembly to take out slope.

My question is if cast iron will hold fine threads and won't chip out pretty soon? Will I be better off with drilling oversize hole and putting in some thread repair inserts like HeliCoil?

Thanks, Alex

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Coarse threads in cast - a good insert wouldn't hurt.Particularly if the bolt will be turned fairly often.

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clare at

some brass

Usual practice is coarse threads, but unless you're talking about very small threads, use whatever is most convenient. Don't worry about a thread insert unless you'll be making constant adjustments, and even if that were the case, you can always Helicoil when the thread actually wears out.

Ned Simmons

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Ned Simmons

In addition to what others have said, at work the rule of thumb for threads in cast iron is to have the screw depth to twice that of the screw diameter. I.e. M5 screw should be 10mm in the cast iron. M24 should be 48mm in the cast iron. Adjust your counterbore to match your screw (if using SHCSs). Using this simple rule, I've never seen a screw pull out. The head is more likely to come off. You can do the math if you're interested.




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Robin S.

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JR North

Ned sez: "> Usual practice is coarse threads, but unless you're talking about very

Good reply, Ned. Also worth mentioning is another poster on this idea (Gunner I think) said the holes should be in a 120 degree pattern so as to achieve even radial distribution of adjustment.

Bob Swinney

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Robert Swinney

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