Gunsmithing Best way to drill large holes in steel

[Pester]

I know.....this is not exactly a gun smithing question but I could use some help from the experts here. I frequently drill holes up to 1 1/4" and find that if I step up in drill size that the holes drift from the original starting point.

If I use a hole saw there is a lot of clean up in the cut and they get hot. Admittedly I am using Home Depot quality hole saws.

Most of the steel is cold rolled mild steel but occasionally I get a request for something like a 4130 cro moly.

Is there a better solution I am missing or is this pretty much it?

Thanks...........

 

[diverdon]

How thick, how deep, how many, and for what use?

 

[diverdon]

1" plate or less then lasers can do a very nice job.

https://videos.thefabricator.com/Trumpf-Highspeed-Eco-9-28-17.mp4

 

[Waorani]

Rotabroach or similar cutters. Traditional hole saws are primarily for wood. Really need to use in a mill or heavy duty magnetic drill though.

 

[MotorOilMcCall]

Plasma or a Torch can get you pretty decent holes, but if you're worried about positional accuracy, you'll need a CNC machine like a laser or plasma table...

Beyond that, you'd be amazed what quality hole saws/fly cutters can do...

 

[skinnj1]

Laser, Waterjet and plasma are all options if you are sub'ing out work but assuming manual machines annular cutters, mentioned above, are pretty effective, if thickness and accuracy are not extreme / an "iron worker" with punches may get it done reasonably fast, if holes are big/deep enough a carbide insert drill bit may be the answer if you have enough HP at the spindle

 

[cornhusker86]

Inserted drill in a mill or lathe.

 

[B y r o n]

My question would be what type of accuracy are you trying to hold?

 

[Ledzep]

Maybe not at your disposal, but using a CNC mill and CAM software to mill out pockets gives super clean results. Spiral ramp feed in with a 1/2" or 3/4" endmill then a clean up/spring pass.

 

[Pester]

Yep, this is why the Hide is great.

I should have mentioned that I am making bits(the kind that go in a horses mouth). I cant afford a bunch of new equipment but do have one of those combo mill/drills. I could do each shank one at a time, one hole at the top and one hole at the bottom, but if I pair them up to drill the hold and tack the steel together then I have good alignment between the two sides. And thats where the hole saw is a challenge because its so rough I have to do a ton of clean up. It does not have to be super precise but clean would be good. If I double them up I never use more than 1/4" so that would be 1/2" if I did them together.

It does not look like the the RotaBroach items are horribly expensive so I will give those a shot. Is there a recommended brand for low tech work?

 

[skinnj1]

Yep, this is why the Hide is great.

I should have mentioned that I am making bits(the kind that go in a horses mouth). I cant afford a bunch of new equipment but do have one of those combo mill/drills. I could do each shank one at a time, one hole at the top and one hole at the bottom, but if I pair them up to drill the hold and tack the steel together then I have good alignment between the two sides. And thats where the hole saw is a challenge because its so rough I have to do a ton of clean up. It does not have to be super precise but clean would be good. If I double them up I never use more than 1/4" so that would be 1/2" if I did them together.

It does not look like the the RotaBroach items are horribly expensive so I will give those a shot. Is there a recommended brand for low tech work?

The industry term is "annular cutter" some cheap Asian ones are worthless 1 and done cutters some cheap Asian cutters are actually OK, decent ones (US and Euro) are considerably more exspensive. Annular cutters can be resharpend by the same type of cutting tool reconditioners that resharpen / regrind endmills. Locating one as local as possible is recommended.

 

[Snuby642]

Step drilling steel is not good.

Slow and lots of lube/coolant will give a clean cut.

 

[Pester]

Thanks folks. Not sure how I went so long before hearing about them but I will get some ordered after my next check. From the you tube video's it looks like these will work really well and the clean up time alone should make it worth it.

I will start looking around for local people that resharpen.....great suggestion.

 

[Waorani]

https://www.mcmaster.com/annular-cutters

Can you chuck 3/4" in your mill/drill? Or possibly use one of MT 2/3 adapters?

 

[Bradu]

The annular cutters work great and will last a long time if ran at the correct speed and you use a cutting oil. I used them with a low profile mag drill to drill holes in truck frames, I would guess we drilled several hundred 3/4" holes running them dry before they wouldn't cut well.

 

[earthtrekker1775]

I always liked using .50 BMG APIT.

 

[...]

get yourself a Trepanning cutter and chuck it in your drill press.

https://www.mscdirect.com/product/details/95604039

 

[Sieg]

I use Blair Rotabroach cutters with cutting oil. Clean, accurate dimensions, and fast cutting. They exploit how bad traditional hole saws really are.

 

[Bobkittjc]

The annular cutter would be the best bet for single pass hole quality probably, but you're machine will need to be more rigid to run it (I believe, someone correct me if I'm wrong). Drilling undersize with a hole saw and cleaning up with a flycutter or boring head would be easy and make use of what you probably already have. I'm not sure how you've been cleaning your hole-sawed holes before so if this is old news just ignore it. Good luck!

 

[4darkseid]

Vertical Mill, manual or programmable.
Clamp it
Measure it
Drill it
Mill it
Finish it

 

[hermosabeach]

If it is your company
If it is your time, then the right set up should pay for itself.

I am amazed at what old Mills sell for used... That does require much more knowledge than I have to figure out if it is a deal or a dud... what is worn out.

8" x 29" 2 HP Mill/Drill with Stand and Power Feed - Grizzly Industrial

<h1>G0760 8" x 29" 2 HP Mill/Drill with Stand and Power Feed</h1> <h2>A heavy-duty combination machine ready for high production.</h2> <p>The G0760 8" x 29" 2 HP Mill/Drill has a 2 HP motor and enough table space to make quick work of just about any machining job you can throw at it.</p> <p>The...

www.grizzly.com

Does either side of the bridle need to be beveled/ radiused? how smooth is the finish?

-- I can't find the video, but Hans Vang was interviewed about his shop and back boring shotgun barrels. His grandson was in college and has a ton of questions about how he did the machining. Grandson is in college and researched milling techniques and came up with new speeds and ways to cut the barrels to do a cleaner job and to double the life of the cutting tools.


I'm not sure where to point you to find someone in your area who might offer you some hand on time with their equipment so you can determine a great starting point.

 

[308nate]

Here's a video using a indexable drill 1.5" in diameter going through 1.5"steel plate. I would recommend at least 10 hp and a pretty rigid set up for a drill this size, but it sure makes short work of the task.

 

[TxWelder35]

I use those annular cutters on my mag drill all the time. I bought a whole set on Amazon made of HSS for around $120 or so. I have drilled hundreds of holes with each one, usually 1/2 and thicker.

Vibration and heat is what kills those bits. Make sure it's clamped good and use a cutting fluid.

 

[Rubicon Precision]

Here's a video using a indexable drill 1.5" in diameter going through 1.5"steel plate. I would recommend at least 10 hp and a pretty rigid set up for a drill this size, but it sure makes short work of the task.

Seeing that done on a TL tool post makes me feel more confident spending the money on a 1.5” CoroDrill 880 for my turning center.

 

[Pester]

If it is your company
If it is your time, then the right set up should pay for itself.

I am amazed at what old Mills sell for used... That does require much more knowledge than I have to figure out if it is a deal or a dud... what is worn out.

8" x 29" 2 HP Mill/Drill with Stand and Power Feed - Grizzly Industrial

<h1>G0760 8" x 29" 2 HP Mill/Drill with Stand and Power Feed</h1> <h2>A heavy-duty combination machine ready for high production.</h2> <p>The G0760 8" x 29" 2 HP Mill/Drill has a 2 HP motor and enough table space to make quick work of just about any machining job you can throw at it.</p> <p>The...

www.grizzly.com

Does either side of the bridle need to be beveled/ radiused? how smooth is the finish?

-- I can't find the video, but Hans Vang was interviewed about his shop and back boring shotgun barrels. His grandson was in college and has a ton of questions about how he did the machining. Grandson is in college and researched milling techniques and came up with new speeds and ways to cut the barrels to do a cleaner job and to double the life of the cutting tools.


I'm not sure where to point you to find someone in your area who might offer you some hand on time with their equipment so you can determine a great starting point.

I got the mill drill some time ago from an old guy that wanted someone to want his stuff rather than just sell it off. I was lucky to get it but its on the older smaller range of mill drills. I wont go much more than 1 1/8" and if I want to radius anything it would be pretty rare. The rein and bridle loops will get smoothed out and, maybe, a smidge of a radius. There are a lot of bit makers that are true artists but my goals are not that lofty very often.

Thanks to everyone for the help.

 

[chevy_man]

Annular cutters are my go to.

And this stuff is magic for even hole saws. I cut 18 6-3/4" holes in 1/8" with a $25 Morse (garbage) saw and it still cut like new using this lube.

BOELUBE PASTES - The Orelube Corporation

www.orelube.com

I swear by that stuff. All too often people look at the tool, and forget that the heat treatment is adversely affected by the heat you're putting into the tool. While carbide and the like negate lubricants to a point, I've found that even my carbide hole makers last 10x longer using lube.

 

[Decoy]

+1 for trepanning based on your equipment. With a light hp machine you can go slow and add coolant or oil to keep the heat down.

 

[Maxduty]

low speed and lots of cutting fluid.