Technical Drilling hardened steel…

Use a split point cobalt drill. You probably ran drill to fast and heated the surface in the hole. Now it’s hard A/F once you get through that with a good drill and slow rpm I think you will get through it. Here is a chart to give you some idea. Use the 30 fpm. Carbide will probably bust when you come through the hole and catch when hand drilling. May need it to get past your hardened surface in hole though. Would be best to do it in drill press or milling machine with quill lock snug so you can still move it but it will keep it from grabbing rattling when you break through and you can get a lot more pressure on it. A lot of this is what others have said. Lot of good suggestions here (bob396) good luck.

 

Here's a reference to a post I hade in 2015. It's good information and I made it after spending a lot of time researching it after I realized that I didn't have a good grasp of the different type of drill bits. (HSS,****anium coated, cobalt coated, carbide, etc., etc., etc.)

https://www.jalopyjournal.com/forum/threads/drill-bits.1001779/page-2#post-11297172

I should note that I did buy the drill index mentioned at the end of the post. I still have it and it has served me well during these last 8 years. The drills are still sharp and work well except for the 7/64" bit that I broke in an over zealous session in my drill press.

 

When I run into hardened steel I remove the part and anneal it with my oxy-acetylene torch and then it drills easily.

 

Something I remember from Jr. High metalshop, the heat mostly leaves the process in the chip. If your not making a good chip, you are making friction and dulling the tool. When you are drilling, you should get a nice coil from each flute. If you are getting lots of little chips, it's probably chatter. I will slow down and push harder until I start moving metal. Sometimes you have to put more effort into it than seems prudent, if it makes a good chip, you are better off. I also remember "Take your all purpose ball-peen hammer and strike your blows" and "Cool your tool". Mr. Czyczons, great shop teacher. Mike

 

some times I drill holes with a torch

 

I’ve drilled spring leaf center bolt holes with a sharpened masonry bit, slow speed and cutting oil.
In a drill press.

 

Firstly, I was running my drill too fast, secondly, I’m going to pull the bracket back off the car and use my drill press…

 

First I'd like to clear up something. The brackets are not "hardened steel" per se. All steels have a certain amount of temper or hardness, but generally speaking "hardened steel" is steel that went thru additional heat treating and the addition of other things to make it hard. A 1010/1020 grade of steel is relatively soft for steel and is what is used for the production of many parts. Move up in grade to a 4130 or greater and the steel will become somewhat harder due to the things added to it. As you change grades the hardness as well as other traits of steel will change because of the added ingredients. Those steels can go through additional heat treating to make them even harder, but should not be considered as "hardened" in the technical sense. I say this because when you get into things that really are hardened, drilling isn't always possible. The part you are drilling is harder than the drill bit.

I have to doubt that bumper brackets are actually hardened as that means they will usually break instead of bend when a force deflects them. Trying to drill a hole to its full size will often prove frustrating, so I always put a small pilot hole thru first. Then I often drill an intermediate size hole and finally finish the hole to size. A larger drill bit will often dull because the wider surface at its tip can't get a bite into the metal and just rubs. Then we speed the drill up and press harder and make it duller. One of the worse things we do is hold a drill at full speed while trying to start a hole. You can also work harden the metal you are attempting to drill by letting the drill rub against it.

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If you have an oxy/acy torch you might try heating the brackets where you want to drill and let them cool naturally. Then try a small drill bit (maybe 1/8) for a pilot hole. Then a 1/4 and then the final size.

 

Use a Masonry Bit and turn it slow with cutting fluid. This will also work on Chrome pieces if you are very careful.

I found this tip on the HAMB many years ago and used it to drill into my freshly chrome plated bumpers on my '54.

So to whomever posted that years ago I say THANK YOU!

 

I have tried to start with a small bit. I was probably spinning it too fast…

 

That was us with the stock cars until someone came up with a garbage-picked drill press. We put a cord on it... holy*****, it worked. Anything fussy prior to that I took to work.

My brother shows up with a drill index he got at a garage sale. They LOOKED good... he chucks one in the drill press, goes to drill something in 1018 steel, the drill bit BENT like it was made out of Silly Putty.

 

The best advantage of carbide tools, whether they are drill bits, end mills or lathe tools, is that they remove heat in the form of a chip. The chip itself should show it was "hot" like a toasty potato chip, but not blue and angry looking.

I was lucky to have had decent shop teachers over the years.

 

Good advice here as well. The newer "split point" drills have a 135 degree included angle, they used to be almost exclusively known as "aircraft drills". A lot of them were extra long to reach into places to do riveting. I started seeing the short type around 1982 in tool catalogs.

True that a drill will tend to break when it breaks through a part. Canned CNC drill cycles were designed to lessen this from happening.

Then there are "parabolic" drills. They are made to drill a straighter and more accurate hole than conventional drills. They are inherently weaker that conventional drills, using them hand-held is a***** shoot whether they will break or not. I only use them in my mill.

 

How does a good metal file bite into the brackets the brackets?

Yeah, those angle iron bed frames I've been scoring from beside the road on trash day for several decades are sometimes surprisingly difficult to drill or saw.

I would have thought making the legs 0.25" longer legs would have been cheaper way to add bend resistance in heavy duty service.
Harder steel deflects the same under a given load. All steel has petty much the same "E" or modulus of elasticity.
If it has higher 'yield strength" it just may take a heavier load to make a permanent bend.

 

Totally agree with this approach. By heating the metal once more you’re annealing the metal which will reduce the hardness and return some ductility to the martensitic bracket. Allow it to air cool no quenching after heating.

 

i found the easiest way is to punch a pilot, drill a very small hole ( LOTS of oil) then drill bigger, and bigger, and bigger.

 

Lots of good advice above. Dan Timberlake suggested the file test if the file skates across the steel the steel is in the 60 Rockwell c scale HARD if you have an end mill capable of plunge cutting I would try it in a drill press with some cutting oil. To truly anneal the steel you need to heat to approximately 1450 degrees f and allow to slowly cool wrap kao wool around the part or bury it in vermiculite or pearlite (available at hardware stores in the garden center) let it cool overnight. To get to 1450 to 1535 heat the steel until it’s between cherry red and tangerine orange ,you determine this temp with a magnet ,when the steel becomes non magnetic it’s at temp. Those brackets may be made of 5160 spring steel and you may have work or air hardened the steel. If all else failed you a oxy torch to blow hole and grind to size as stated above.

 

I needed to drill 10 holes 3/8" in diameter in angle iron today with the hand drill. I had guide holes in the steel plate they were welded to that I drilled on my drill press without issue. Drilling the holes in the angle iron was brutal.

I could switch bits, do larger and larger holes, but the bits would only work for 1-2 holes then not drill. I had almost all my drill bits out and was getting frustrated. The answer was the step bit. Once I had a pilot hole, the step bit did the rest easily.

 

Those HF step drills have surprised me on a few things. I'll wrap tape around it once I establish a size I'm after.

They just may be TiN coated which I started to see on lots of drills past 1984. It was strictly an aircraft thing when it was becoming popular, but they hold an edge a lot longer than drills and end mills that lack it.

 

Yeah, mine are not harbour freight but a higher quality brand and are TiN coated.

 

If you ever take the time to examine the tips on drill bits, you will see that they use more than one angle on them. The web area in the center also varies and the wider it is, the harder it is to start a hole. Generally people use too much rpm and not enough pressure. Thats one reason a drill press works so much better. It multiplies the pressure and usually is set for a slower speed than full throttle on a hand drill. I'm not a big fan of the coated drill bits because many companies put the coating on poor quality bits that dull quickly. Once the coating wears off the tip, you are down to the cheap bit that dulls. If you resharpen bits, the tip will always be without the coating. There may be some higher quality ones available, but I just try to buy ones that don't have the shiny coating and I bought a drill doctor so I can keep them sharp when they do dull.