Drilling a big hole in small steel plate

Screw it down on a scrap of lumber.

"Richard J Kinch" wrote: Screw it down on a scrap of lumber. ^^^^^^^^^^^^^^^^ This is the best idea in the list, if you juat want tio get the job done easily. Make sure the wood is long enough and slender enough to hold in one hand, to prevent rotation, while feeding the drill with the other.

There's Greenlee chassis punches that will do this in a jiffy and leave nice clean edges, downside is that for a couple holes they're outrageously expensive unless you can find some used or surplus. A sheetmetal shop should have punches that size, might take some sucking up/doughnuts/six pack for them to do it at a reasonable cost, though.

Alternative, Unibit stepped bit. Think the company is Irwin-ed now but the major hardware chains carry them now. Also kind of spendy, $14-20 range, but will also cut cleanly and leave fairly smooth edges. Screw your piece to a wood block and drill it that way. Beats getting your hands sliced up when(not if) the drill grabs and you get the whirlaway.

Stan

Unibit stepped drill bit makes this pretty easy to do if you use the piece of wood behind the metal as was suggested by others. then you are only drilling a small amount with each step.

Doug

If I want a hole much larger than I can drill, this is what I do. Mark the centre of the hole using a centre punch, then score a line around the circumference using a pair of dividers. Then, inside the first circle, score another circle with a radius about 1 mm smaller. Then use a small drill (say 3 mm) and a drill press to drill a ring of holes, nearly touching, inside the smaller circle. Then take the metal plate, put it in a vice and use a punch to knock out the circle inside the small holes you've drilled. Then take a half-round file and carefully enlarge the hole until it meets the first line you scored. You can make quite a neat hole this way if you're patient. I've often used this method to make mounting holes for switches, etc.

Chris

But a Greenlee punch is available to punch the 15/32" hole with a key tab to keep the switch from rotating in the hole.

And a 15/32" Greenlee chassis punch without the key would use about a 3/8" drivescrew, IIRC.

Enjoy, DoN.

also check out the step drill bits - real slick - and expensive too. makes short work of hole making.

My Greenlee 1/2" is a 1/4" bolt.

Mart> Ig's concept of a "big hole' is a little different than ours : ) >

One thing - Greenlee chassis punches are measured using the bottom cutter. e.g. the hole size it punches is the punch size.

Knockout punches by Greenlee - are for the Electrical trade - and are Conduit inside sizes. e.g. a 1/2" Knockout is for tubing with ID 1/2". It punches the outer size that is larger than the marked size of 1/2".

I bought a nice set of Knocks and couldn't use them. 1972. Had a nice handle system...

Martin

On something like that, I make it long enough to hold up against the column. It is far stronger than my hand and won't break under extreme conditions. Martin

Costco carries a set of them at a reasonable price. Chinese quality I expect but might be ok for low usage. Karl

I agree with DoN for home. For work, I design the entire enclosure with all holes larger than a 1/4" or so, and send it to Saginaw Controls down the road. They plasma cut the entire sheet, including tabs for standard controls, and then bend it up and weld it. This works especially well in stainless (I do a lot of sanitary stuff), which is a pain to punch with a Greenlee.

By the way, I told one of the older electricians about the trick I learned here to NOT centerpunch stainless before drilling, use low speed and lube. He was amazed at the improvement.

Pete Keillor

On second thought, I'm not sure whether its plasma, abrasive water jet, or what. Would plasma work on stainless? It is CNC.

Pete

I'd have to look. Most of the ones I use are 3/8 or the larger hydraulic ones.

As I see it, he's got 2 holes to drill, he's probably not going to buy a punch or unibit (he said he may not even have a 15/32" twist drill). The hole is probably going to be distorted if he uses a twist drill, so he might as well drill to 3/8" and hand work from there . I like your other idea of using a tapered hand reamer, but he may not have one of those, either.

And truth be known, in an emergency I've used a spur tipped spade bit : )

The hole may still be distorted, though. Much nicer results when the work piece is clamped between 2 pieces of wood (or steel)...

.===snip---

I'd use a hole saw. They sell sets at Harbor Freight on the cheap. Clamp the sheet metal piece in a sandwich of wood on your drill press table using two C clamps. Set drill speed low and feed with frequent backups to clear chips.

Plasma loves Stainless. Turns the edges blue and brown. Beautiful. Deposits chrome balls - that have oxides on them under the cut area. But yes - cuts like a dream. Really any conductive or semi-conductive material. Plasma is a current - high burst of electrons that blast a heat spot and the air pressure blows out the molten metal.

Martin

I have never seen 0.5" OD hole saws...

i

Spot weld cutters are that size hole saws and come larger/smaller.

Center pin is spring-loaded. I have a diamond dust set (Ebay vendor mistake) with a 1/2-incher. Similar to: