I have to drill a 3/4 inch hole in 1/4 steel plate stock

March 02, 2019, 06:49 AM

Do I go for the gusto with a 3/4 bit, or do I drill a 1/4 pilot and then finish it out?

I have a drill press, but not a full machine shop.

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March 02, 2019, 06:59 AM

David Lee

I would step it up from a pilot. Block and clamp the work piece for safety. 3/4" Drill can spin that piece of stock in a very dangerous way. Block your work piece. If you got a center punch, that will locate your pilot hole better.

March 02, 2019, 07:03 AM

ffips

As mentioned, block and clamp. Don't be afraid to use multiple bit sizes between 1/4 and 3/4. Lubrication is also a good idea. Let the bits do the work.

March 02, 2019, 07:06 AM

ArtieS

Thanks. I have a center punch, plenty of HSS drill bits, and cutting fluid. I had planned to clamp the stock to the drill press table for safety.

I have drilled steel before, just haven't tried a hole this big before. I need to build a bracket for a bush hog, and 3/4 is the bolt size.

I appreciate the help.

March 02, 2019, 07:16 AM

Cassandra

quote:
Originally posted by ArtieS:
Thanks. I have a center punch, plenty of HSS drill bits, and cutting fluid. I had planned to clamp the stock to the drill press table for safety.

I have drilled steel before, just haven't tried a hole this big before. I need to build a bracket for a bush hog, and 3/4 is the bolt size.

Unless you wish the bolt to be a fitting bolt, your last drill should be a 13/16 inch. Sugwst using a 1/4 pilot then go directly to 13/16 otherwise you can get into nasty vibrations and jamming. And make sure the bits are sharp. If your drill cannot take the step from 1/4 to 13/16, then an intermediate step could be 1/2 inch.

I appreciate the help.

March 02, 2019, 07:16 AM

Outnumbered

Use a step bit. The cheap ones like these don't last really long (10 holes or so) https://www.amazon.com/Vastar-...-Steel/dp/B073JM4D8F or you can buy really nice ones in the $40-$50 range.

March 02, 2019, 07:17 AM

Cassandra

quote:
Originally posted by Cassandra:
quote:
Originally posted by ArtieS:
Thanks. I have a center punch, plenty of HSS drill bits, and cutting fluid. I had planned to clamp the stock to the drill press table for safety.

I have drilled steel before, just haven't tried a hole this big before. I need to build a bracket for a bush hog, and 3/4 is the bolt size.

Unless you wish the bolt to be a fitting bolt, your last drill should be a 13/16 inch. Sugwst using a 1/4 pilot then go directly to 13/16 otherwise you can get into nasty vibrations and jamming. And make sure the bits are sharp. If your drill cannot take the step from 1/4 to 13/16, then an intermediate step could be 1/2 inch.

I appreciate the help.

March 02, 2019, 07:18 AM

egregore

If you want to drill any hole much bigger than 3/8", start small and progressively increase the size. For a 3/4" hole you'll want ~3 steps.

March 02, 2019, 07:22 AM

Elk Hunter

quote:
Originally posted by Outnumbered:
Use a step bit. The cheap ones like these don't last really long (10 holes or so) https://www.amazon.com/Vastar-...-Steel/dp/B073JM4D8F or you can buy really nice ones in the $40-$50 range.

Given his apparent willingness to spend money, why does he not just take it to a machine shop and pay them to do it? Faster, easier, safer, and probably cheaper.

Several years ago I was making a mounting plate for my router table. 1/4 inch thick stock.

Thought about all the work, problems, etc etc.

Took it to a local machine shop where they did the work while I waited, cost me 10 bucks.

Elk

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March 02, 2019, 07:35 AM

tatortodd

If the hole doesn’t have to be pretty I’d use a plasma torch. Faster, safer, cheaper (in terms of consumables).

March 02, 2019, 07:41 AM

ArtieS

Hmmm, there is a machine shop about 5 miles away. I might take it there.

March 02, 2019, 09:22 AM

sigmonkey

Machine shop or step bit.

Progressive drilling with several bits multiplies the number of times you can have a bit hang and if your hand drilling, you are playing "Mechanic Roulette", not a matter of "it", but "when" and how much blood...

I can do all my own work (given the correct tools), but some things are better ROI.

This would be one of those.

I was doing oiling mods on an engine block, one was to enlarge an oil passage from 1/2" to 5/8" x 11" depth along the side in high nickel cast iron with wall thickness of only a few millimeters in some places.

Trying to drill that far by hand and ensure it was true, was more than I wanted to try at home, so I paid my machinist $50 to drill it.

Cost of a bit and the effort, I came out way ahead.

March 02, 2019, 09:30 AM

DEC505

With a drill press I would use a hole saw

March 02, 2019, 09:31 AM

6guns

Go up in steps, use plenty of oil and set your drill speed slow. You won't have any problems.

March 02, 2019, 09:43 AM

Scooter123

Another option would be to use a Hole Saw. I've cut 3 inch holes for hydraulic pressure gages in 3/8 inch steel using a hole saw and hand drill and it's not that difficult. The key is to slightly wobble the drill so the hole is actually cut to a diameter a touch larger that the diameter of the saw. Fail to do this and about 1/4 inch into the cut you'll find the saw starting to bind as the steel heats up. BTW, once tried to enlarge the tapped hole for a locking screw on the ram shaft of a 75 ton hydraulic press by stepping up from a 3/8 hole and darned near broke my wrist when the bit jammed. BTW, hand drill was a 1/2" Milwaukee Magnum Hole Shooter and this drill is capable of producing a lot more torque than one would expect. Should have added the second hand grip to the drill but I was "in a hurry".

Point is don't try "stepping" with a hand drill because you will be dealing with constant jams and even with a low power 3/8" hand drill those jams can add up to some pain in the wrist and a LOT of broken drill bits.

March 02, 2019, 09:45 AM

Balzé Halzé

Always step up to a size that big, unless you're using a hole saw.

March 02, 2019, 09:45 AM

sig operator

What DEC505 said. 3/4" bi-metal hole saw will cut just over size and should work well for a 3/4" thru bolt. Clamp well.

March 02, 2019, 09:48 AM

MaSigchist

Clamp it down well, use oil, pilot drill it - run 250-300rpm with the 3/4 bit.

March 02, 2019, 10:05 AM

PHPaul

quote:
Originally posted by DEC505:
With a drill press I would use a hole saw

Ding-ding-ding! As long as the hole doesn't have to be dead accurate, hole saws are my go-to for anything over 1/2"

I built a scissors hoist for my dump trailer from scratch (using purchased plans) and all the holes were done with various sizes of hole saws.