Drill bit for case harded steel drilling

[pjogrinc]

Old retired gunsmith told me and showed me this one. Had a broken grade 8 bolt stuck in a hardened steel planitary gear. OK, back to the facts. He showed me that no matter how hard the steel is, he could drill it in seconds as if it was butter. Trick is to visit your local dentists office and talk them into giving you the "old dull bits they use for dental work". They will usually just give them to you instead of throwing them out. I don't know what these are made of, but they went right through the grade 8 bolt as it it was cheap steel. He showed me how he drilled receivers for mounting scopes, WARNING, these will cut fast!!

If the dental burr does not cut or cut or cuts real slow, toss it. Ever seen smoke come out of someones mouth while they where having dental work done ?? That's a dull bit!!!

If you can, ask if you can buy a new set, pricey, but worth it.

You can tape these up to the correct diameter for use in a Dremal or put in a pin vese and chuck it up in a drill press.

UPDATE: Just found out that these bits are in 2 classes: Carbide and Diamond. Get the diamond ones. Keep bits cool.

[HollowPoint]

I wish I'd have known that a couple of years back. I've been seeing the same dentist for many, many years.
I'd venture to guess that my routine dental visits have made more than a couple of his house payments or car payments.

I purchased a K31 a couple of years back but, my eye sight is such that I had trouble seeing the iron sights clearly so, I decided to mount a set of old lyman peep sights on in.

I don't know what type of metal this K31's action is made of but try as I might I couldn't even scratch the surface with any of the bits I tried. No matter how expensive the drill bits they all seemed to just wander around the surface of the action where I wanted to drill.

In an act of sheer stupidity I figured that if I held the action in my lap I'd be able to better balance it as I attempted to start my hole because I'd be able to tilt or move it in order to stop the tip of the drill bit from wandering.

That drill bit more or less stayed where I wanted it but it just wouldn't scratch the surface of this K31 action. I guess I pushed down a little to hard because that drill bit wandered right over the edge of the action and into the top of my thigh.

That sucker was so searing hot that I believe it cauterized the hole in my leg because it never did bleed.
I thought my K31 action must have been made of some kind of extra-terrestrial metal because I couldn't put a scratch in it.

Finally wised up and found the Home Gunsmithing website, signed up and asked a few questions.
Someone suggested I purchase a HiRoc drill bit and some carbon taps for threading and I'd be good to go.

We learn these things the hard way. (At least I do) I got the HiRoc drill bit from Midway on a Friday, drilled both mounting holes on Saturday and then proceeded with the tapping of the two holes. (Now the tapping of these two holes was an adventure that would take this thread way to far from its original course.)

This one HiRoc drill bit cost me about $18.00 plus shipping and it did cut through that milsurp action like the proverbial butter.

So, I repeat; I sure wish I'd known about those dental bits back then. I wonder if they're made of the same stuff as the HiRoc bits??

HollowPoint

[machinisttx]

I've drilled out many grade 8 bolts with standard HSS drills. I prefer left hand twist and cobalt for the job, but HSS works just fine if you use it right.

Case hardened rifle receiver? Carbide....

BTW, diamond isn't generally used on steel because the heat breaks the bonding down on the wheel/bit, and because the carbon in steel doesn't agree well with the diamonds.

[MtGun44]

Diamond bits are what dentists use.

However, a grade 8 bolt isn't very hard, it is good strong bolt but not hard. They machine fine
with ordinary high speed lathe bits, drill with ordinary drills like regular steel. I often use
a grade 8 bolt as the basis for some machined part because they machine nicely and make
a good strong part.

Bill

[2shot]

Been in the dental field since 1970. To confuse things more, straight handpiece burr's (shank about 1 1/2" long and 3/32" diameter) are for slow speed belt driven handpieces (speed simular to Dremel). Friction grip (about 3/4" long and 1/16 diamiter) are made for high speed air rotors ( speeds of 35,000 + ). The high speed friction grip cut through nickle based alloys easily, the straight handpiece can too but with some trouble. Diamonds are used and designed for cutting tooth structure and porcelain, carbide burr's are used for cutting gold or other metals including nickle based alloys. Any of the dental diamond burr's will clog when hitting metal, the carbide's will not whether straight or crosscut.

Nickle based alloy's, porcelian and teeth are not hard to cut. None of these burr's do a good job on Titanium but then I don't know where Titanium stands when it comes to comparing it's hardness to hardened steel

In all of these 40 some years I have never tried using them on hardened steel. They may work but I think that there may be better tools for the job.

2shot

And just out of curiosity, how's the tape going to hold the shank of the burr without slipping?

[deltaenterprizes]

Titanium machines similar to stainless steel with carbide.

[2shot]

Titanium machines similar to stainless steel with carbide.

Not with the carbide burr's we have in the dental industry, they will not dent it with hand held handpieces. But then the burr's we use are not designed to cut through titanium. I'm sure that carbide in a milling machine would be a different story.

I think the thing we are all overlooking here is that the title to this thread is "drill bit for case hardened steel drilling". It's been a long time since I had started a tool and die apprenticeship (never finished it either) but isn't case hardened steel just hardened on the outer surface? Once the surface is broken through isn't it easier drilling because it's not hardened throughout? So if this is the case then breaking the hard surface with a diamond, carbide or whatever and then finishing with any drill should work right?

[deltaenterprizes]

Correct. New masonry drills work for that also, better if angles are honed with a diamond hone.

[dragonrider]

Brownells has 3 flute carbide drills in sizes for tapping with the most popular sizes for scope mounting, I have a couple and they cut just great. Like drilling soft steel. Anyway even after you got the hole drilled you still need to tap it. I center a 1/4" x 20 tpi nut on top of the hole and I then direct a small hot flame from my oxy/acetylene torch to heat the hole red. Then let it cool and then tapping becomes a piece of cake. Essentially you are just annealing the hole. The nut keeps the flame from spreading out and ruining the bluing so there is only a small spot. This method worked for me on several receivers that I could not drill easily.

[missionary5155]

You can tape these up to the correct diameter for use in a Dremal or put in a pin vese and chuck it up in a drill press.

Good morning
Most any store that sells the Dremel acesories also sells the Shaft Adaptor Kit that contains 4 inserts for the very smallest shaft up to the largest shaft a Dremel can safely use. I use hair thickness drill bits and shafts on pocket watch repairs and with the shaft adapters the Dremel can do it all. And you can place the adapters in a regular drill chuck for drill those small holes with a big drill BUT realise the Dremel adapters are some what soft and a 1/2" chuck can really put the squeeze to the front end.

[Buckshot]

............Since drilling on surface or case hardened gun related stuff generally is farily thin in cross section, IMHO the best tool for the job is a single straight flute carbide drill bit. It's very rigid and the single flute cuts a very clean nice round hole. A double straight flute is almost as good. A #29 bit for a number 8 hole is about $20 At MSC:

Hi-Roc™ Solid Carbide 2 Flute 135° Split Point Straight Flute Screw Machine Drills Size: 0.1360 In., Wire #29 Material: Solid Carbide Flute Length: 5/8 Overall Length: 2

.............Buckshot

[Willbird]

I've drilled out many grade 8 bolts with standard HSS drills. I prefer left hand twist and cobalt for the job, but HSS works just fine if you use it right.

Case hardened rifle receiver? Carbide....

BTW, diamond isn't generally used on steel because the heat breaks the bonding down on the wheel/bit, and because the carbon in steel doesn't agree well with the diamonds.

BUT from first hand information from a guy I used to buy a lot of diamond tooling from, that deal all takes place at high speed, more or less grinding wheels. You can use a PCD (poly crystalline diamond) tool at lower sfm and it never gets hot enough for the carbon-carbon interaction you mention to ever happen.

SOME hi-roc drills, the ones you can drill a hole in a file with for example actually have a dull point that heats and anneals the metal before scraping it out.

Bill

[andremajic]

I also read in brownells kinks that you can use crazy glue to attach a small diameter washer over the place you want to drill to keep it from skipping around. The super glue cleans off easily when you're done.

Or you could drill through a penny with the same diameter drill bit and then glue and center it over the spot to drill.

Let me know how it works, as I read this an have not tried it out yet.