Technical Drilling hardened steel…

Hey guys, with my ‘40 Olds I got both bumper brackets, and only the front bumper. Not interested in mounting one up front so I decided to put the front bumper on the back brace. Problem is that only the center bolt lines up and the side bolts don’t even hit the bracket. The rear bracket only has the center hole so I have attempted to drill two holes between the ones on the bumper to add stability. I bought an inexpensive set of carbide drill bits that right through the bumper but stopped dead on the hardened steel bracket. Any advice would be appreciated…

 

Remove bracket get it in a drill press. Drill a pilot hole with coolant (cutting oil)

 

Plasma cutter

 

Center punch where you need to hole and bring it to your local machine shop, what seems like a major job with a hand drill is 15 minutes on a Bridgeport, and 11 of those minutes are setting it up in the vice.
If it has to be done on the car, do whatever you can to get some rigidity in the drill and consider buying a high speed steel spotting drill. They cut slower but can let you get away with more
As said above, keep it cold, I like Moly-D as a cutting fluid

 

The only way I have found to get through hardened steel is a pita.
I have had luck using a mini die grinder and a pointed carbide bit.
I tried for hours trying to drill a hole in a bed frame rail ... "hardened steel" I made my drill bits 3" shorter but never got anywhere.

With the mini die grinder it took a few minute to create a hole and a few more to widen the hole out to the size needed. .... I actually completed my task.

 

Carbide drill (expensive) or carbide burr in a dremel (cheap)

 

Wouldnt think they would be that hard.
That would just make them brittle.
Could try a torch and anneal just where the hole needs to be.
Dont quench. Could get glass hard.
Too much speed will knock the sharp off carbide.

 

Too much speed makes too much heat , slow down use cooling fluid

 

1/8" pilot hole first, with cutting oil. Then with a slow speed drill and an expensive carbide bit drill your hole with lots of cutting oil.

 

Get better drill bits and go slow.

You said the bit stopped dead. Did it actually stop, or just stop drilling? I ask because those would be two different issues. If the bit stopped dead, sounds like you need a pilot hole. If the bit stopped drilling, a drill press and a better drill bit (diamond or better) will probably be your best bet.

 

M32 Cobalt drill (NOT Cobalt coated). A little expensive, but affordable. Slow speed and constant controlled pressure. (Think drill press.)

 

You can use a cheap carbide masonry bit from any hardware store to drill tough steel like springs

 

I've built a couple sets of 1/4 elliptic rear spring setups ny cutting some Posie front springs in half. I took them to the machine shop I used and while he did it twice he recently tole me to find another way to do the holes. Metal was to hard for drilling and it ate the bit so ti required lots of sharpening. How to drill hardened steel Wet and Slow with a Carbide bit..

 

May try one of those uni bits. I've had luck with those drilling in bed frame angle iron.

 

I can't imagine that dog biscuit to be that hard, or why you'd want holes in it?

 

Well, the other driver behind you owns the bumper and brackets, so strength isn’t a concern, just support.
Take it out, center punch , torch red and drill asap.

 

Make your brackets out of mild steel. That bumper is just for decoration anyway. ​

 

It looks like your stock front bumper has only outer holes and a center bolt hole. From your explanation, the center does go thru a cross piece which attaches to the outer brackets that bolt to the frame. If your wanting only 1 hole on the the bracket to line up with the hole in the bumper I’d mark where you need the hole, remove the frame brackets, and take them to a shop which has a hydraulic punch press. We had one at our power plant.
Do your frame brackets look like these? The pair are extra 40 Chevrolet rears. The 40 Chevrolet bumpers are the same front and rear.

 

If you are stuck & absoultely have to drill the hole NOW, take the necessary drill bit & regrind the point angle from the customary 118 degrees to a flatter 130 degrees, use a cutting oil(or grease) drill RPM VERY slow & lots of pressure! yes, it's a PITA, but it's doable(That's how we did it in the pressure vessel shop I worked in : the main problem was getting the rookies to accept the need for SLOW speed & LOTS of pressure!)

 

Sorry guys, lost internet connection today and just got it back. Some good suggestions here, and will try some of them. The drill didn’t stop, it just stopped cutting metal. Just bought a new set of carbide bits, tried a couple of them (with cutting oil of course) with no results. My Olds bumper brackets are different than the Chevy brackets and don’t match or interchange. I will see what I can do tomorrow…

 

Will definitely try a slower speed!

 

I use my plasma to punch a center hole straight through the piece, then put it on the drill press using a low speed, lots of pressure and ATF for cooling and cutting oil. It really works great. If you're good with a plasma torch, you can carefully blow your center hole then work it out to size. I do that a lot. It won't anneal the brace. I can remove the inner race on a press fit axle bearing without leaving a mark on the axle using my plasma torch. Barely warms the axle.

 

Start with a small bit, low speed and cutting oil, then step up in very small increments, the faster you drill the more it work hardens

 

Thing is, a small bit needs to turn faster than a large diameter bit. I don’t have the numbers in my head, but turning a small bit slow is not the answer, most likely a solution to a broken bit.


Edit: to add, spinning a larger diameter bit too fast, is how and why the will get dull. Look up speed and feed charts

 

I was just drilling stainless and small bit slow definitely worked over going fast, just my experience

 

Could be for SS. Speed and feed charts are available for many different materials.

 

Interesting thread. Years ago a neighbor brought home some scrap metal bits from his work and asked me to drill some holes in them with my drill press. Some drilled perfectly fine, like you would expect steel to drill and some pieces of "mystery metal", the drill bits wouldn't touch it, I mean I don't even know if they left a mark.

Totally useless info but just saying, "been there"

 

RPM = cutting speed x 4/tool diameter. This looks like spring steel, so I'll give it a machineability of 50 (same as cutting speed). Diameter, I'll use a 1/2". So you are in the 400 RPM range.

Definitely a pilot drill is needed (anything over 1/4" gets one). Cobalt drills will do the trick. Also coolant and take your time. After I get a good pilot hole, I chamfer it close to the final drill size. I'll step up the sizes too, for a 1/2" hole I'll go 1/4", 3/8" then the final size.

 

Carbide drills in a hand drill, usually not a good idea. They can shatter. The old carbide-tipped ones were a better bet.

 

Cobalt drills are the way to go, these are something like 5% cobalt, really nothing exotic, just a better choice that takes the heat. I still have a # drill index with all short screw-machine cobalt drills. Also a plethora of loose cobalt drills.