"Drilling" a 2 1/2" Hole ???

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Can anyone recommend a reasonable - efficient - cheap ways to create a few holes?

2 1/4" or 2 1/2" holes in 1/4" to 1/2" steel ?

Round would be nice, but not required.


Methods under consideration.

Step drill - I haven't found one that big & am afraid of the $ if I do.
This would be my favourite option - clean and chatter free cutting.

Twist drill - to thin for that without the "helicopter of death".

Indexable tooling carbide insert spade drill - $$$

Bimetal hole saw - seems like the best option so far but will they cut steel ?
I've had bad experiences with some that wouldn't cut metals.

Diamond grit hole saw - seems like a good option but will they cut steel ?
seems like they are made for brick and masonary.

Torching the hole as best I can and filing it out.
labour intensive- but maybe

Drilling a circle of small holes and filing it out.
labour intensive. - but maybe

Milling machine with rotary table - maybe in a year or two, but not today.

Lathe faceplate and boring out - workpiece is too big for the swing of my lathe


Waterjet or torch cut by outside service - prohibitive setup costs for a one off project

Boring head in a drill press - - possible but I might need 2 heads to go from a small hole to finished size because of a limited adjustment range for each.

I'm considering trepanning & making this sort of thing but bigger and with lathe HSS bits - but I don't want to work that hard for a few holes.
http://www.holesaws.com.cn/products/holesaws/adjustable/pic/11001002.jpg



What am I missing ?
Simple and cheap are more important than production speed.
 
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In order of preference:

1) Torching the hole as best I can and filing it out.
labour intensive- but maybe

2) Drilling a circle of small holes and filing it out.
labour intensive. - but maybe

Forget filing, use a rotary tool to clean it up. Make a nice round template out of plex or something easy to cut with a hole saw, and use with a "router" attachment for the rotary tool. They're like $10 for a Dremel or Craftsman tool.
 
I've cut 2" holes in 1/4" plate with a hole saw in the drill press. You have to keep in mind for feeds/speeds that cutting a hole like this is more like cutting something on the bandsaw than it is drilling.

I can cut a pretty darn clean hole with a torch... an extremely clean one with a circle jig. Oh no, not a jig, that's cheating!!! The only good holes are cut freehand!!! :eek: :foot: :p :)

If I am making something critical I usually knock the bulk out with the torch, buzz the HAZ with a die grinder and then use the boring head to dial it in to tight tolerances. The most time intensive part of that is getting the torch fired up and the boring head in the mill.
 
I drilled a 2" hole in my forge body with a bimetal hole saw. Just use plenty of fluid and keep it slow. I did it with a hand drill, and it went just fine for me. Much better than I expected
Jason
 
NickWheeler said:
I can cut a pretty darn clean hole with a torch... an extremely clean one with a circle jig. Oh no, not a jig, that's cheating!!! The only good holes are cut freehand!!! :eek: :foot: :p :)
Click to expand...

Giotto would be proud, Nick!

I'd think a jig and plasma cutter would be easiest. Someone with a plasma and decent experience using it could probably do it in a couple minutes. I recently cut a couple 2 1/8" circles in some 1/8" aluminum. Took about 10 minutes each, noisy as hell, very messy. I think it would take much longer in 1/2" steel, be even noisier, messier.
 
A hole saw , they even make carbide tipped if your in a hurry ! They come in large sizes too much bigger than 2.5" .
 
Twist drill or spade drill would be madness.

Trepanning would be cool. You'd need to be very careful if you elect to trepan the hole. That can be a dangerous process. You'd definitely get cool points though. Very old school.

I always lean towards tools I already have. I would suggest a hole saw if you have one. Otherwise, torching it out and boreing it to size is a very correct approach.

If it were me I might cut it out with plasma and chase the hole with a 2 1/2" facemill. You heard that right, I'd clear out the center and plunge it with a facemill. On a relatively heavy mill. And I'd probably wreck $60 in inserts trying it.

The advent of circular interpolation has taken a lot of the drama out of cutting big holes. Where's the fun in that...
 
Adjustable hole cutters are your friend.
sing-blde-univ-hole-ctr.jpg

http://www.icscuttingtools.com/catalog/page_167C.pdf

Jason
 
Please keep in mind that most hole saws are designed to cut steel 1/8" thick or less. The hole cutter pictured above would be my first choice.
Del
 
Drill 1/8" on one side, then turn the piece over and drill another 1/8".
 
I had to 2" cut a hole in a safe once. It was a smaller one but still had 1" thick walls. Used an HSS hole saw using the back gear on the mill about 100 rpm, and lots of cutting fluid. Took about 1/2 an hour but it got through just fine. Plasma cutter on a jig would work great too if you do not need machined edges. Then you also have the CNC option or waterjet or laser, they are more expensive unless you already have one.
 
Just buy a good hole saw and use that. You can cut from both sides and you will get a cleaner hole. Run slow RPM's, use lube, and you will be fine. Starret and Lennox make good hole saws for steel.
 
Starret, or similar holesaw in the drill press at your lowest speed, securely fixture your work, use a lot of oil, cut 5 seconds, back the blade out to clear chips, cut 5 seconds etc. it will take you a while but I have cut half inch plate this way. I prefer to use a 7/8 inch twist drill to start holes then use my boring head now, but unless you have a milling machine use the holesaw

-Page
 
I had to make a 50mm hole in the body of my forge. Its round (obviously) and 12mm thichness. I scribed the line. Punched a heap of marking spots around it. Then went to town with an electric drill and a 4mm Colbalt bit. Punched the middle out with a cold chisel, then cleaned it up with a half round. Took me a lot less time than I though. Maybe 30 mins

Matt
 
You will be surprised at what you can do cutting with a quality bimetal hole saw.

I cut a couple of 2 1/4" holes with a bimetal hole saw in 3/8" steel. I burnt the teeth of two hole saws in the process.

I went to the store and bought one more and using cutting fluid along with making the cut I cut the next 14 holes with the same hole saw. I was drilling them with an old 1/2" drill and it only ran at one speed. I kept a clear condiment bottle

plastic_bottle.jpg


full of cutting fluid sitting within reach and every few seconds would give the slot the hole saw was creating another squirt of cutting fluid!

I was surprised that I was able to cut that many holes without damaging the hole saw, as long as I kept the cutting fluid to it.!

I have used that same process to cut a couple of holes in 3/4" steel since then with a bimetal hole saw! It sounds rough but the cutting fluid helps keep the heat down and it helps fluch away the debris from the cut!
 
I also say hole saw, unless a slightly rough hole works, then a torch. If the work is flat, use cutting fluid. This is my trick. I take plumbers putty and build a fluid dam around the hole to keep the cutting fluid contained and cut away. I have to cut holes in ss counters in commercial kitchens and use carbide holesaws when possible. The ss counters a a PITA because they tend to work harden if you cut too fast, but I digress....I recently cut a 2" hole in a piece of 1/4"mild steel using the method above. The putty gets gooey if you get too much heat. I usually use the Lenox hole saws...
 
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