newbie question - drilling big holes in steel plate

You will kill a normal hole saw pretty fast with that thick of a bar.

What you want is a rotabroach.

You can also use a flycutter. You need to clamp the workpiece securely on the table. There is an adjustable cutting tool on an arm. Cutting all the way through thick material is tricky, as it often causes chatter. You may have to move the cutting point in and out to open up an annular ring before advancing deeper, and then make a finishing pass at the final diameter. If your drill chuck is not securely attached, it may come off at a bad time.

Jon

I use hole saws in this thick of material quite often - they last for me. I'm not saying it's the fastest - just that it works & the saw lasts as long as you use cutting oils.

If by 'bar' you mean flat, rather than round stock, yes. The least expensive and most readily available home shop type tool that I know of to do this would be a fly cutter. Chucks in drill press, has pilot drill and adjustable arm perpendicular to axis of drill, lathe type single point tool is held parallel to drill and appropriate distance from drill. With care, patient appropriate speed and cutting fluid you can cut holes several inches (like 6, anyway) in diameter with one of these. Even places like home depot have cheap ones, tho' if you go this route I'd suggest getting the beefiest one you can find.

Mickey

I think I would chain-drill around your hole and then clean up with the Armstrong milling machine (a round file). Buy a new top quality file with a handle - splurge, it will be maybe $5. I used a brand new round file the other day for the first time in my life (hey, I've acquired a *lot* of used files in my day) and oh man did it cut!

Grant Erw> I'd like to drill a 1 5/16" (1.3125 inch) hole in a 1 inch thick mild steel

How big is your drill press chuck and how much horsepower does it have? I may have a drill this big I could grind the shank down for you.

Gunner

"To be civilized is to restrain the ability to commit mayhem. To be incapable of committing mayhem is not the mark of the civilized, merely the domesticated." - Trefor Thomas

Dave, I often have to drill holes that are that large and larger. When I do not have the correct drill, I drill to the closest size smaller and then mount a boring head for a milling machine. The boring head that I use has a number 3 morse taper shank. Even though I do not have an automatic quill feed on my drill, a steady hand and patience does a perfect job. Steve

An APT Multi-Tool would be the perfect tool for your application. Specifically designed for drilling large holes with low horsepower machines lacking rigidity like most drill presses andr mag base drills. I have never used one for 1 inch thick steel, but I see no reason it would not work. Basicly it is an interchangeable blade spade drill with a pilot. First drill a

3/4 inch hole with a conventional drill bit (or multiple steps working up to 3/4 inch.) The 3/4 inch pilot on the Multi-Tool is guided by the initial drilled hole. For bigger holes there are 1.5 and 2 inch interchangeable pilots so the hole can be done in multiple steps, but you will not need that for your 1 5/16 hole. I have a spare set, but many of the blades can use touching up. I have been trying to get around to sharpening the blades so I can list it on ebay, but I have not had my surface grinder fired up for a while.

Mill

Here's one that some machinists will recoil at, but with a steady hand a good result can be gotten:

Cutting torch, fine tip. Turn the material on its side and pierce a hole through the middle. Then clamp the material flat with the hole overhanging the edge of a welding table, and carve your hole to its final dimension. Dress it with a high-speed rotary rasp.

Fast, lots of fireworks, cool hissing sound as the steel burns. Voila!

If you only have one or 2 holes and you have lots of patience, the hole saw will work. You'll need a very slow spindle speed (50 rpm?). A helpful trick that I would suggest using is to drill a 1/4" hole through the plate right on the edge of the hole saw's path, so the chips and oil will drain out of the groove made by the saw teeth and allow fresh oil to enter the cut. Use dark cutting oil, not fluids like tapmagic whivh will evaporate from the heat.

On Sat, 14 Feb 2004 22:07:24 -0500, "Dave in MD" vaguely proposed a theory ......and in reply I say!:

I have drilled 1.25" holes in steel on a press using a normal 1.25" drill bit in the chuck. Works. Not cheap. BUt I had a few to do, and will have more. However, lots of cooling or cutting compound is a good idea, along with working up to the size and taking it easy on the larger holes. My press runs at 200 RPM lowest, and it was pushing it. I would say 400 RPM is way too fast.

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