Home made Spade Drills ?

[G.A. Ewen]

I would like to try making some large spade drills. Am I likely to have any success using oil hardening flatstock for the inserts? My drill press is a very old 18" swing monster that I converted from flat belt drive to auto transmission-V belt drive. It turns about 40 rpm in low gear. The drills that I would like to make would be from 1 1/4" to 2 1/2" in size. Thanks in advance for any input and suggestions.
George.

[SGW]

Seems like it has a pretty good chance of working. You speak of "inserts." What are you using for the main body of the drill and how are you going to attach the inserts?

You'll need to use pretty good steel for the body of the drill. I think "mild steel" would bend the first time you tried to use the drill.

You may be able to use something like pre-heat-treated 4140 for the body and shaft. That ought to stand up to the cutting force without turning into a pretzel.

[Kerry.S]

Yep I would use a piece of P20 or 4130 4140 what ever you have on hand (P20 is a modified 4130 tough stuff)
If you can only heat treat with a tourch I would use A2 instead of O1. A2 would get harder with a high toughness along with better resistace to brakeage.
Kerry

[G.A. Ewen]

SGW, on pages 52 & 53 of the new KBC Tools catalogue you can see what I have in mind and if you check the prices you will see why. ( ALLIED spade drills and holders )

[Thrud]

George

I see those on ebay on a regular basis up to 6" diameter. For what they sell for on ebay, it is not worth making them. It is worth regrinding them though! They last forever if you don't break them. The holders show up often as well.

[Cass]

I have made spade bits by sawing a slot in the end of mild steel rod and brazing in a piece of a blade from a 10" table saw. The reason for doing it was the need for a spade bit with a 30" length when I wanted to build a so called "butcher block" table top. I drilled small holes in each strip of wood before gluing things together and after gluing I used the long spade bit more as a reamer to enlarge the holes and get a straight enough hole to install all thread rods to bolt the laminated top together. Worked fine although the brazed in blade later broke/chipped as the brazing/quenching I did resulted in a very hard/too hard condition in the high carbon saw blade material. Quick and easy to make whatever size you need. If you use a piece of cold rolled about 1 inch in diameter you can turn it down to fit you drill press chuck. Should work for up to 2-1/2". You could use a piece of pipe and braze a broken taper drill shank in one end and a piece of cold rolled with the slot/blade in the other end. Minimize the amount of hardened material sticking out from the shaft to avoid broken edges.

[G.A. Ewen]

Thrud,
I'm getting kind of leery with regards to Ebay. By the time I pay the differance on the dollar, duty, shipping and handling ect. i'm not sure that it's worth it. Besides, I like making tools. Steam or IC engines don't appeal to me right now, maybe in the future. Building garden tractors is my other passion. I posted this question because I have never used oil hardening steel before. Will they be tough enough to drill mild steel?

[wierdscience]

Had a job once where I had to waste out some 3"holes from nothing on a b-port mill,I drilled a 3/4"hole and made a boring bar 1"in dia. and turned a 3/4"pilot on the end,I then drilled a cross hole to fit a 5/16"tool bit at the start of the pilot,secured it with a setscrew and ground the face and bottom of it for positive rake and set it with a mike for 1"offset from the 1"shank,cranked the mill up at 80 rpm and let the pilot do the work,in about 1 minute I went trough 2.5"of colled rolled steel,nice wide shaving in one piece,nice and smooth.I got the idea out of an old Audel's machinist manual from about 1910,those old guys knew their stuff!

[Thrud]

if you want o roll your own, then I would suggest a tougher steel thatn the "O" series, either the "A" or "D" series should work fine. "D" series is often used for precison tools, broaches, and cold forming dies & rolls. It should be treated as an air hardened steel as it can fail in threaded, thin, or sharp inside corner sections when oil hardened. D-3 can be oil hardened but this is rarely done.

T-15 would make an excellent spade drill as it has outstanding red hardness. I do not know how well it would hold up as a spade drill - fracturing from stress is my only concern with it. I doubt this is a problem as it handles interupted cuts extremely well, but the cutting edges are usually supported by the toolholder. In a spade drill the wide blade supported only at the center might flex and break I do not know if it would even happen, but I thought I should point it out as it could be the only detraction from this excellent cutting tool steel.

If you have trouble locating any T-15 http://www.arwarnerco.com/ can sell you either Vacuum Crucible or APM T-15 in nearly any size.