Cutting Holes In Sheetmatal

[EdK]

Thanks for all of the suggestions. My drill press' low speed is way too fast and doesn't have a VFD. I'm going to go ahead and use the hole saw, it's a new Milwaukee bi-metal one. I'm going to hook up the VFD to the mill temporarily like I did when I first got the mill to make sure it functioned prior to disassembly. That will allow me to get the speed down to where I'll need it.

Ed

[rleete]

A hand drill will actually be better than the drill press. That circular rocking motion is key to getting a clean hole without destroying the teeth on the saw.

Use a good lube. I'd either use a thread cutting oil or a synthetic automotive oil, such as Mobil 1. Steady pressure, but don't force it.

And slow, slow, slow. You should be just about able to count the teeth as it rotates. If the oil is smoking, you need to back off.

[Mayhem]

Can you get a hole saw to suit a brace Ed?  That would be plenty slow enough

I frequently use hole saws in sheet metal and agree with what everyone else has said about using them.  I've had good results with my drill press but you have to ensure everything is locked down tight, as they can want to wander.  I've posted this before but this is the setup I used when making the burner tube for my furnace (that I haven't made yet).

   

[Roadracer_Al]

C'mon Ed, just make your own Greenlee punch. It'll only take an afternoon.

Since we're talking about hole saws, I have a few hints & kinks I'll share. I use them all the time in my mill.

First off, the rattly ill-fitting arbors which they sell with hole saws are wretched, the work of the devil, IMHO, and contribute to the saw jamming in the cut.

I made some 3/4" arbors for hole saws.  They look a little like a slitting saw arbor.  I went to my friendly local fastener distributor and bough 2 sticks of all-thread which are the sizes for large and small hole saws. 5/8-18 and 1/2-20. I tapped the arbor for a chunk of all-thread, and slit the end of the all-thread so I could remove it with a screwdriver if it ever gets buggered up. I started with a 1 1/4" bar, and left the mating surface as large as possible after a light clean up on the outer diameter. This arbor is sufficiently stiff to run without a center drill, and to take a half-circle out of tubing (try *that* hand-held!) The plan is to make a fistful of them so I don't have to switch saws on the arbors. (maybe I'll make some R8 arbors!)

I run hole saws very slow, about 80-120 RPM, depending on size. I use heavy sulfured cutting oil, very liberally from a cleaning supply spray bottle.

Here are three great tips regarding the actual hole saws.

1) the mating face between the arbor and the saw is rarely true. This results in cutting only on one tooth which gets dull quickly, then just drags and makes heat. If you chuck the saw up in a 3-jaw chuck you can put a light facing cut on the mating surface and the saw will run significantly truer.

2) the sheet metal saw body is often too thin, and becomes thinner after facing which can allow the saw to bend or strip the thread. The solution is to cut a 1/4" thick disk and weld or braze it to the back of the saw. The key technology is to put the teeth in a shallow pan of water to keep from damaging the hardness when you weld. Also, the paint is NASTY - you'd do well to use paint stripper to remove the paint from the back and inside of the saw prior to welding. Once the disk is affixed, chuck it up in the lathe again and face the surface, and re-cut the threads.

3) If you want a precision hole, and the hole saw is cutting oversize, you can clamp a belt sander on the mill table and adjust the size by sanding the OD off.

[PixMan]

I've done up to 4" holes in (somewhat thinner) sheet metal just the way DaveH describes. The orbital motion makes a slightly bigger hole but solves the biggest problem: Too many teeth in the cut at once stalls the drill motor or breaks your wrist. I use high quality Lenox Bi-Metal (HSS teeth) saws as my Metabo 1/2" drill doesn't go quite slow enough for a cheap high carbon steel one.

[dallen]

grab some scrap and do a couple practice holes to start with so you don't trash the box.

[PixMan]

Me, I wouldn't bother with test pieces. This isn't rocket surgery and it would be really hard to bugger it up so badly that it was junk.

[pepi]

(05-18-2016, 09:29 AM)Mayhem Wrote: Can you get a hole saw to suit a brace Ed?  That would be plenty slow enough

I frequently use hole saws in sheet metal and agree with what everyone else has said about using them.  I've had good results with my drill press but you have to ensure everything is locked down tight, as they can want to wander.  I've posted this before but this is the setup I used when making the burner tube for my furnace (that I haven't made yet).

Wounder if a longer bit in the saw would steady things up, long enough to be thru the material before the hole saw starts to cut. Hand drill and hole saw sounds a bit Flintstones. Cannot envision that as something I would do, fore see it adding another variable to the mix.

I did this cluster using a battery powered hand drill, 2.25 holes, exhaust pipe sliced up for the spacer rings.

[the penguin]

I have found in sheet metal, I drill the pilot hole and have a 1/4" smooth shaft in the holesaw arbor, it helps with the wandering, as the drill bit will cut with any kind of side pressure.

About 95% of my holesaw use is with a cordless drill, usually, where I have to drill, is rarely able to put into a drill press. Just last week, I drilled 4, 6" holes, through 3/16" steel, with a hole saw in the stack assembly of some boilers, so I could weld stack sampling adapter into the stack. A 6" holesaw and a hand drill is a fun time, especially 10 feet in the air, on a step ladder,

[EdK]

These holes are for a fan at the bottom of the VFD enclosure and a filter at the top. No precision needed at all.

Ed