A few months ago, I wrote to the Third Hand Column in the Home Shop Mechanic (HSM). Explaining the difficulties I had drilling 3/4" holes upside down under my Case Tractor. Within 2 weeks after that issue got to me I had 5 replies! Some of the guys had more than one idea. Many of them recounted problems they had had, or horror stories about others. I received both phone calls and letters. Since I had not published my address as part of the article all of these guys had trouble getting to me. Fortunately I live in a small town, so I did receive 3 letters with only my name and city/state in the address and one more forwarded to me by HSM. One guy used the Internet to get my phone number!
My first reason for writing this article is so that you HSM will print it as my way of saying thanks to all the friendly people who took their personal time to help. I do want to note that I am not personally recommending any of these ideas, since the user needs to evaluate them for safety and viability.
But my second reason is to pass on all these good ideas. It is amazing to me to see so many different solutions to this problem. There is something in here for everyone who might ever be faced with these needs. Here are my mentors and the basics of each idea:
Start with a small pilot hole, open it up to about 3/8". Then, grind the rake angle of the full size drill bit to Zero degrees (or even a bit negative). This idea works because the drill bit's web is not engaged in the metal since the pilot hole has provided clearance and the zero rake keeps the big bit from digging in.
Use a magnetic base drill. Attach a flat plate to the work first if needed.
Use a high speed steel hole saw. Drill a 1/4" pilot hole first and replace the drill bit in the hole saw with a solid 1/4" pin to provide accurate centering.
Use 3 or 4 flute core drills to open up smaller pilot holes. The core drills don't catch and dig like 2 flute twist drills.
Use tapered bridge reamers to progressively open up the hole to the finished size.
Use the Cole Drill, which is the hand powered drilling machine described in the Machinist's Third Bedside reader. I can identify with this one since as a blacksmith of some skill, I like using the blacksmith's "Post Drill" which is also hand powered.
Start with a small pilot drill, say 1/8th, then move up by eighth's, using DoAll cutting wax (which holds better than oil). Rent or buy a right angle drill. This design will lessen the difficulty of alignment and reduce the effects of twisting when the drill bit hangs up.
If you have a bench size drill press, turn the head upside down and (ocate it under the machine that needs the holes drilled. (He had to drill holes under a tractor, just as I had to).
After telling one particularly serious horror story, Lee said that the guy finished the hole with a die grinder and vowed to never drill a hole bigger than 3/8" for the rest of his life!
Use a "Third Arm", a long wooden handle through the handle of the drill motor and attach the handle to an immovable post. The idea here is to poke one end of a 21/2 foot long wooden handle through the D handle of a large drill motor to keep the drill motor from twisting. The other end of the long handle is notched and pinned to a heavy steel bar which is anchored to the piece to be drilled or wedged into a handy location.
(To HSM: I have included Mr. Vincent's letter and his drawing so that you can improve on my summary and print if you desire).
Norm suggests pressing drill bushings into a sizable plate and clamping the plate in place over the site of the hole to be. The drill bushing will help keep the drill straight and reduce binding. He also suggested working up to the final size in several increments.
In closing, I want to thank all of you for your help and HSM for this very useful column!
Just read your letter in "Third Hand" looking for solutions to drilling large holes, free hand with big dangerous drill motors. I have been a "Truck Frame Mechanic" for 25 years and have seen a lot of "Horror Shows" when it comes to drilling. I've seen a drill pick up a 5'10" 250 Lb. man and throw him ten feet from where he was reaming out a 1/2" hole with a 33/63 drill bit, no injuries that time, just a broken bit.
Another time a guy was drilling mounting holes for an auxilliary fuel tank, after the body was on. No big deal! If you know how to drill in tight places. Well, he came over to ask how I would go about it, so I said I would use the step process or use the drill reamers in my tool box, and take it slow and steady, well he didn't do either.
After I came back from lunch, I went over to see how he was doing; one finger was cut wide open, his safety glasses were broken on the floor and his face was bruised up. I asked what happened.
He said he didn't want to take all that time to switch drill bits, so he started with a pilot hole then to a 33/64 drill and the big boy electric drill 3/4" Milwaukee with extension handle. He said he put his right shoulder against the D-handle of the drill for pushing power, well that would put his head near the truck body and the drill extension handle! Not a good place to be! He then started to drill the third hole when the bit got stuck, Then he said he moved some how and the drill started to rotate back and forth while hishead was being beat up between the handle and the truck body cross members. He was lucky that was all that happened to him!
So, I asked how did he get to finish the other hole. He said he used a die grinder to finish it! Well, I finished the installation of the fuel tank, because he refused to drill anything bigger that a 3/8" hole ever again!
Well, enough stories! A solution to your problem is a "Third Arm". Years ago an old blacksmith showed me how to drill holes in truck frames any size hole, and any position. He called it his Third Arm. It is made out of steel and wood. Check out the diagram on the next page. The adjustable part is made from 20" x 1" x 1/4" flat bar stock, at one end is three ears welded into place to form a Tee bent slightly that will hook under the side of a frame or a bracket. The bar has 1/4" holes drilled every 1" on center. The other part is made from wood (oak or maple) something strong about 32" x 1" x 1-1/2" shaped on the band saw. Slot one end to slip over the 1/4" bar stock so it can move freely, then drill a 1/4" hole through the wood handle in the middle of the slot so a cotter pin can slide through it and the bar so the bar can pivot. The other end goes through the drill's D-handle and has a notch in it to hold on the drill somewhat straight, the rest is used for leverage, put it under your arm (arm pit) or your knee or your leg whichever position is comfortabla for you. Then start drilling. It will take some time to get used to it. I have used it for all sizes of drills and with a 1" Black and Decker drill motor, a unit that will twist you up quick if you let it.
Another way is to use high speed taper drill reamers. They have sizes from 1/4" -1 ".
Well, good luck with either way you try.