Holes Needed in Thick Steel

[bosco]

I need some suggestions on the best method on how to cut a 3" (80mm) diameter hole in a 1.5 inch (40mm) thick steel plate. Here's a little history. The company I work for purchased a piece of equipment that is mounted on a 4 ft square by 1.5 in steel plate. This plate is provided by the equipment manufacturer and has several holes already cut in it. After the equipment and the plate had shipped, we find out that we need 2 additional holes cut in this plate. The additional holes are required so that armored electrical cable can pass through the plate. The manufacturer was contacted and they have no ploblem with our construction crew cutting these additional holes, but they didn't recommend a method. Issues that need to be considered are that the new holes need be smooth so that the insulation on the cables will not be comprimised. Also, heat is an issue when cutting these holes because it could alter the integrity of the steel. Of course the new holes will need to be cut at the job site and we have already given construction a "heads up" and ask them what method they intend to use (but have not heard back from them). Any suggestions ...? Oh, just to let you know ... the equipment is a loading arm that pumps LPG onto a ship.

All suggestions appreciated.

[mcinfantry]

water jet.
plasma as a LAST resort.
no way on oxy/acetylenet....

just my .02.

well, i reread it.

oxy/acet may be your best bet.

[pieter]

3" O.D. Might be too big for a Magnetic Drill.
Quick look on ebay shows bit in the 2" range.

One of your crew may have a mag drill with bits.
Or you might make a call to some strucutral steel fabrication/erection
outfits that might make the 2 holes for you with their mag drill.

Oxy/acteylene can give you clean cuts which are smooth and won't
hurt steel that thick (warpage). But you state that is not your first method.
especially with whatever gases are nearby...

Pieter

[Gordon Maney]

At the last place I worked the machine shop occasionally used what they called core drills. They were not core drills in the geological sense, meaning hollow drills. They were large, three and four flute drills, and were more aggressive in heavy plate. We had some that were approaching 2 in. in diameter, but the diameter you are describing is awfully big.

We had some retro-fit applications where we ran these core drills in a magnetically attached drill. They had to grind the morse taper to straight shank to run in the chuck of the mag drill.

Is this place presenting enough flat surface that you could put a mag drill on it?

Is this just HRS, is it mild carbon steel? Another possibility is that you might do it with a hole saw run by a mag drill.

The alternative being that you disassemble this device and send just the plate to a local machine shop and have them machine it. Maybe that is easier, all things considered.

Pieter was posting his response while I was writing mine, I discover...

[JimmieD]

I used to have to fab some heavy steel from time to time, up to 4" plate. It can be testy, and thank God for electro magnet boom cranes!

If it were me, for an expeditious field fabrication, I'd drill a hole through the plate with a 3/8" jobber's bit, the long aircraft type bits. Use this as your starter hole for oxy-acetylene, and cut your hole from the drilled portion around the inner circumference of your 3" hole. With so much mass in the plate the heating should not be an issue unless it's heat treated steel, which is unlikely. Letting it air cool in atmosphere with no quenching will maintain the temper of the steel. Don't let anybody pour water or oil on it.

You don't have to cut the entire hole all at once either. Cut a portion, let it cool, cut another portion etc. Some like to run water over the plate while cutting to help carry away the heat, but you don't want to cut the hole and then cool with water because of possible warpage and changes in metallurgy.

Once you've cut to your approximate size bush the hole with 3" EMT electrical conduit. Flare one end of the conduit, drive it into the hole, peen flatten first flare and peen/flare the other end over so that EMT acts as a bushing. Possible to make up a bushing of any material in the chosen O.D to fit in your hole so that I.D of bush fits specs., whether EMT, copper, DOM tubing if it has to be precise, or PVC/ABS. You can even prefab a DOM tubing bushing with flat steel flange on one end, drive in place, and weld a flange on the other side, then grind to flush.

If you look at it as a problem of fitting a spec sized bushing in the hole instead of cutting an extremely precise hole to tolerance it's an easier job that can be done by any decent wrench on the crew.

[Gordon Maney]

I really like your bushing idea.

What do you mean by peen flatten?

[Gordon Maney]

Continuing with your bushing idea, you could make it from a mild steel tubing, TIG weld around both ends, then grind and polish it to look as if there were no welds.

Put a chamfer around the outside diameter of the ends of the piece of tubing, on a lathe, to give a little more room for weld bead.

You could grind a bit of a chamfer in the hole in the plate to provide more room for your weld bead.

[JimmieD]

I speak of peening it over with a hammer and dolley as needed, flattening it into place tightly, as if to flange it with a hammer. Other option is to drive in a bushing that is oversized in length and then cut/grind to flush.

[JimmieD]

This reminds me of one I really must share. I had to join two pieces of 4" plate, each about 4' X 8' to make one 8' X 8' sheet. It was a tough weld but it came out allright. Afterwards I was in the shop with old Hal, a tall soft spoken southerner. Another guy came in and asked for the 1/2" Dayton drill. I gave it to him and he chucked up a long 1" drill bit into it. Then he proceeded to thread a leverage handle into the drill body, a piece of 3/4" galvanized pipe about 4 feet long.

Hal looked at me, looked at him, and looked back at me. In his slow drawl he said, "Aw don't think ya wants ta be doin' that there, bowah [boy]." The hotshot replied, "I've done this a bunch of times, Hal, I know what I'm doing!" Hal spit out a long and precise stream of Red Man such that it splashed on the fella's boot toe. "Well, then I reckon you know all about it then, sonny."

The drilling went well for about 1 1/2 - 2 minutes, with lots of oil and gentle pressure at full speed on the drill. Then the impatience caused more pressure on the drill motor and the drill bit caught hard, and the drill's torque spun the handle right around into the guy's fanny and tossed him about 10-15 feet across the shop.

Hal looked at me deadpan with a twinkle in his eyes and said, "Let's go get us a cup of mud, Jimmy, I don't think I'm a wantin' ta watch this anymores. It hurts too much..." and another stream of Red Man put an exclamation point at the end of his sentence. I think I learned more from that man Hal than I learned from my own mother, I think. At least with a whole lot less words. And he still makes me laugh going on 30 years now....

That was in Richland, in case anybody knew old Hal.

[JimmieD]

The nice thing about DOM tubing is the huge range of sizes available. One can get it spec'd for an inside diameter or outside diameter because of the precise method of manufacture. It's [DOM] Draw Over Mandrel for uniform dimension. You can get virtually any wall thickness so by juggling diameters and wall thickness nearly anything is possible, as if you can spec. it in both I.D. and O.D. at the same time. DOM is much cheaper than seamless ChroMo too, while being quite strong, and welds very easily with Ox/Acet, arc, MIG, TIG or other methods.

With Gordon's further tech and better finishing touches you could have a real nice finished product there, Bosco.

[skeely]

no question about it....a mag drill with a 3 " cutter and plenty of cutting fluid will take care of matters in about 15 minutes for a really smooth cut. a journeyman ironworker with a good victor torch and a clean tip can match the time but the cut is slightly rougher, same with the plasma torch. check jancy engineering for cutters

[Steve Pellock]

Use a mag drill as other have posted with an annular cutter bit. Try Fastenal they carry Hougen bits.

[Charles Talbert]

A magnetic drill press & an angular cutter is what we use on heavy plate. Cuts out a plug instead if drilling with a bit. Much faster & cooler not that heat is a big deal on heavy plate like you are working with. Landmesser Tools in Michigan is a great source, huge variety of sizes & tools for any need. They are specialist in BIG stuff.

[bosco]

Some great ideas here guys and I really appreciate the info. I am learning a few things. The site is still in the construction phase, so no hazardous gases are in the area. The equipment has not arrived at the job site yet .. it's on a slow boat from France to Qatar. I'll try and post some pics of existing installations so ya'll can see what we're dealing with here.

Originally posted by mcinfantry
water jet.
plasma as a LAST resort.
no way on oxy/acetylenet....

The water jet method was discussed briefly and not sure if that equipment is available ... but we are checking on it.

Originally posted by pieter
3" O.D. Might be too big for a Magnetic Drill.

I'll admit that i am not familar with the mag drill, but after doing a bit of research I found that there are bits available in the diameter we need.

Originally posted by Gordon Maney
Is this place presenting enough flat surface that you could put a mag drill on it?

I don't believe that would be a problem. Once they off load the equipment and transport it to the laydown yard it would be easy to fairly easy to take the plate to the fab shop.

Originally posted by JimmieD
The nice thing about DOM tubing is the huge range of sizes available. One can get it spec'd for an inside diameter or outside diameter because of the precise method of manufacture. It's [DOM] Draw Over Mandrel for uniform dimension. You can get virtually any wall thickness so by juggling diameters and wall thickness nearly anything is possible, as if you can spec. it in both I.D. and O.D. at the same time. DOM is much cheaper than seamless ChroMo too, while being quite strong, and welds very easily with Ox/Acet, arc, MIG, TIG or other methods.

With Gordon's further tech and better finishing touches you could have a real nice finished product there, Bosco.

I really like that idea, but labor is cheap and schedules need to be met. The quickest and most efficient way is what we are needing. That bushing idea I really like and would like to use that in the future.

Originally posted by Charles Talbert
A magnetic drill press & an angular cutter is what we use on heavy plate. Cuts out a plug instead if drilling with a bit. Much faster & cooler not that heat is a big deal on heavy plate like you are working with. Landmesser Tools in Michigan is a great source, huge variety of sizes & tools for any need. They are specialist in BIG stuff.

I believe the mag drill is the correct choice here, but it is not my call. I can make suggestions to the one in charge, but it his decision only. I just wanted to be educated on what methods are available, since I just deal with electrical issues. But those are my cables going through those holes. Thanks you all for this imformation. I will post pics of the progress soon.

Thanks again....

[pieter]

Landmesser Tools in Michigan is a great source, huge variety of sizes & tools for any need. They are specialist in BIG stuff.

Thats good to know....

Thanks,
Pieter