How to drill 3/4" Hole with 15" Drill Press (1/2" chuck)
I need to put a 3/4" hole in 1/2" mild steel plate. The trouble is, I won't be able to get in the shop for about 2 weeks, so I will have to do this with a Clausing 15" slow-speed drill press. The hole does NOT have to be precision by any means, but it must be drilled (torch and cover is not an option).
I have lots of vises/tooling to keep the plate from spinning and the drill will do 250RPM. However, it only has a 1/2" chuck. What would you use to drill it? Drill a guide hole and then use a bi-metal hole saw (eugh...)? Is there a 3/4" jobber's bit with a reduced 1/2" shank? Some kind of rota-broach like thing? Whatever I get will probably just be used for this one-off job...
McMaster Carr number 2933A33 will get you what you want. They are known as reduced shank or silver and deming bits. If you drill a pilot hole that takes out most, but not all of the center web on the 3/4" drill it'll go easier too.
Yup. Silver and Deming drill. But - predrill about 10% larger than the chisle tip (web). 2/3 the drill thrust when drilling from the solid is required to force the chisel tip into the metal. Pre-drill and save a bunch of stress and strain. You don't have to step is out in small increments. Predrill then procede with the on size drill.
Last edited by Forrest Addy; 07-23-2012 at 11:44 PM.
Does your drill press have a Morse taper spindle?
You guys are the best -- I had spent over an hour flipping through the Mcmaster catalog and I didn't see what you all found. Thanks for the help.
My drill has the Jacobs 33 Taper. I plan to vise/clamp the work VERY well and go slow with lots of cutting oil -- hopefully won't see a proble
My local Ace hardware sells the reduced shanks if your in a hurry and can't wait for ups. I always wondered why they are called silver and deeming. Anybody know... Forrest?
agree with everyone on the reduced shank drill - no idea why they're called silver and deming drills either! I would use a 3/16" or so for the pilot hole at full speed and you should be able to drill the 3/4" at the same speed if not a little slower depending on how rigid your drill press is. One thing to remember with pilot holes is not to drill to close to your finish size or the 3/4" drill might just do what it pleases and go oversize on ya.
Don't overlook annular cutters.
A 3/4" hole saw can trepan through 1/2" plate easily.
Even using a battery drill. Just use a sharp one and
use oil with it.
I beleive the original company that made reduced shank drill was Silver & Demming.
Originally Posted by lowCountryCamo
the other good thing thing about SD drills is they are all 6 inches long. no need to crank the drillpress table up/down as you switch bits.
see link for SD history
VintageMachinery.org - Silver & Deming Manufacturing Co. - History
"I would use a 3/16" or so for the pilot hole at full speed and you should be able to drill the 3/4" at the same speed if not a little slower depending on how rigid your drill press is."
Not unless you want to burn up the corners of your 3/4" drill, instantly. A 3/16" HSS drill in steel should be running around 1500rpm (about 70ft/min). A 3/4 drill running that fast is going to be running 300ft/min... about right for aluminum. The 3/4 drill should be run about 350rpm in steel. Running fast is going to be bad enough, but with a little flimsy underpowered 1/2" drill press, you are not going to have enough power to give it a proper feed rate, so the drill is going to be half rubbing, which will create even more heat than burying it in cold uncut metal.
Chuck 3/4 drill straight or taper drill in lathe, turn 1/2" shank.
Around here if you walk into a tool supply place and ask for a "Silver & Demming" drill you'd mostly get blank stares. Ask for a "Prentiss" drill and you'd get what you were looking for. Try to find a drill with 3 small flats ground on the shank. Use them in a good chuck and they work pretty well but I have lots of these with torn up shanks because the chuck just couldn't hold them. In my opinion they're only good for "emergency" use...
I believe you can buy Silver & Deming drill bits with 3 flats machined on the 1/2 inch shank so that the jaws of your drill chuck can clamp on the flats and not spin in the chuck when drilling the 3/4 inch diameter hole.
OK i been tasked. The following text can be found verbatum in a dozen sites. I don't know where it originates or who to attribute it to. I assume it's credible.
Silver & Deming History:
Silver & Deming evolved from the 1854 founding by Albert R. Silver and John Deming of a company to make agricultural machines. They made a variety of machines primarily aimed at wheelwrights but eventually moved into drilling machines. They came up with the large-size twist drill bit with a turned-down shaft that someone could use in a chuck smaller than the bit's cutting diameter; however, they did not patent the idea and it was soon copied by other companies. The term Silver & Deming drills continues to be used as a generic term for this type of drill bit.
All drill bits for a post drill have 1/2'' shanks even the little ones.
But they only have one flat on them.
An enormous amount abuse and damage has been inflicted upon the lowly
1/2" capacity drill press by using S&D bits. I remember when I was younger
watching my dad trying to monkey hump a 1" drill bit though some steel
brackets for a bumper he was making. It was a good drill press (a Buffalo
Forge) but it was still only a 1/2" capacity bench top model. Chatter to
high hell and the chuck fell off a few times. At a young age watching this
I knew something was not right with this method. But at that age, dad
was always right (I guess). Now of course I know better. I own a large
(4 Morse) Cleerman upright drill. I believe it could drill at least a 2" hole
with ease. I guess I did learn something growing up. Maybe it is "Do as
I say, not do as I do". I think all parents say that at some point.
It is satisfying to hear a smooth running drill just slicing through steel.
And the slight sizzle sound that coolant makes coming off a drill that
is really ploughing through some thick steel.
Another option is to use a 4-fluted core bit. They can be a little hard to track down, but many used machinery dealers will have some in their used tooling section. Do a web search for core bits, and you'll find them. I have a set that I've left in morse taper, and a smaller set that I've turned the shank down to 1/2". Since they are multi-flute, they cut very smoothly with no chatter, but they do need higher feed pressure and they like cutting oil. One web site I checked had a 3/4" for $ 82, but I usually pay only a few dollars at a used machinery dealer since most people don't know about them.