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Drilling 3/4" hole in 1/8" thick 303 S/S

berol

Aluminum
Joined
Jan 5, 2006
Location
Florida
Not sure how to proceed with a 3/4" demming bit in a drill press. Do I center punch and go at it with the 3/4" bit or work up in stages of smaller bits. If in stages what size steps would you suggest.
 
I'd be inclined to use a multi-cutter bit or hole saw. Keep it moving and use cutting fluid to keep it from work hardening. If you're committed to the SD bit, drill a hole to clear the web, then drill the piece making sure it is extremely well clamped.
 
Run about half normal steel cutting speed, lots of pressure, but be ready to back off as it breaks through. This is going to be no fun due to the thin material. Your hole is probably going to come out lobed instead of round and it's going to try to grab. Hole saw or rotobroach or even a punch (ironworker) would be a lot easier and will give you a rounder hole.
 
An old trick taught to me about 30 years ago........

Assuming drilling is the method to be used (mill is out of the picture?)

Once hole location is directly under spindle, part must be fastened down to table...don't allow it to move around.

Drill a small starter hole, say 3/16
Open it up to 1/2"

Chuck up the 3/4" drill and adjust for correct RPM ; on the low side.

Take a paper shop towel about 6" square, fold it over 3 or 4 times. (ends up about 1 1/2 x 3 or 1 1/2 sq)

Don't turn on drill yet. Place folded towel under bit and apply firm pressure down to capture the towel between the bit and the 1/2" hole.

Give it a few squirts of cutting oil. While still holding down pressure, turn on drill and push firmly, letting the drill cut through.

A foot switch is indispensible for a drill press, if you don't already have one.

You'd be surprised how well this works and avoids the chatter ususally encountered.
 
If you are drilling just a few holes and are committed to the twist drill, you might consider sandwiching the material between some 1/2 inch aluminum. Then centerdrill and drill at 60 SFM with coolant.
 
First choice, Punch it.

Second choice, drill with a 1/2" drill and then follow with a 4 flute core drill.

Most likely you don't have either, so the S&D in the drill press. Drill your starter hole, say 3/16" (should be slightly larger than the web thickness). Now get two pieces of 1/2" mild steel scrap, and drill 3/16" holes in them too. Use the drill in the drill press as an alignment pin sandwiching the stainless steel between the two mild steel plates. Clamp the whole mess as close to the 3/16" drill as possible and still have room for the 3/4" drill to spin. Change drills and slow your drill press as slow as you can go, proceed with "extreme" feed force...you can usually slow most drill presses down to a usable speed in stainless with a lot of force. This does two things, it keeps the rpm low to avoid burning up the drill and keeps you under the work hardened surface. If the drill spins up fast, the work hardening gets worse, the drill dies, and it's all ugly from there. The sandwich effect keeps the drill centered and on the margins, and should keep from having a triangular hole when your done.

Steve
 
Thanks much for the great suggestions, The qne with the paper towel was really interesting. What a great idea to have a forum like this to help out. Can't get over how helpful everyone is. Thanks again!
 








 
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