It had escaped me too till I remembered making one as an apprentice. OK in a pillar drill at low RPM but an unbalanced bitch in a hand held black and decker.
It got lost along the way somewhere. I never owned a pillar drill :-(
Stitch drill, then use a file or flap wheel in a drill to smooth out the bumps. Stick a piece of something solid over the hole on the opposite side to the one you're working from and use this to give a centre. Use a Sharpie in a trammel "compass" (piece of wood with a nail and a hole for the sharpie) to draw a 10" diameter circle and a second, concentric, circle that's smaller by the diameter of your drill bit. Alternatively, if your original hole is still a good shape, you could simply make a scribing block to draw the circles the desired distance away from the current hole. Use a centre punch to mark points on the inner circle slightly more than your drill diameter apart. Drill all the points with a smaller drill, then with your final drill, a quick zap with the jig saw to take out the ring, then file or "flap" to desired smoothness. (If the overlap is big enough then make the hole slightly larger and don't worry about the lack of smoothness.)
Only if you haven't got a jigsaw. That's a really sketchy way yo make a round hole.
For this application, he would probably want one with an integral compressor (most need an external supply of compressed air)
That was a plasma cutter, not an oxy torch...
This is an oxy fuel cut:
Although an oxy torch I have used to cut steel.
I would use a oxy-propane cutting torch if I went the gas route. Propane is more affordable.
Do you mean rust? I'd have thought you might discover the tin worm has spread further under the paint like it does in cars. Doing that with a jig saw sounds a bit painful. I'd have thought some company might have a tool and jig for this job, but I guess that might cost a bit. Brian
Maybe he needs to make it a square window, though in a boat, you can introduce stress points and find leaks at the corners, but that might mean doing two anyway, to make the thing look right. Those tool on a rotating spindle are OK for thin steel of about 4 inch dia, but I'd have thought to do it with the size he has would introduce too much stress on the arm for it to be viable. How did they do it in the first place? Some kind of punch when the boat was disassembled.
Brian
Amazon does a 10 inch hole saw. It says it is only for thin metals, but back it off, cool it down and lubricate well and it might manage 5mm steel.
Not possible without a centre ... that's why I proposed stitch drilling
Easy enough to screw a piece of wood over the hole to create a centre
As I suggested elsewhere in the thread, a piece of ply on each side of the hole, with screws holding them together in the existing hole and you have a centre.
I remember my father stitch drilling holes to make rounded corners for windows he was putting in the back of a van (he had to pay £5 tax to convert it). It was a long and laborious job, even in thin steel bodywork.
+1. Stitching is a last resort if you want a clean hole. Almost anything is better than stitching. Id use a jigsaw for a one off, as I said. Most people have a jigsaw. Fly cutters , 10" hole punches, plasma cutters and CNC routers, not so much..
Apologies, I didn't spot that ... but ply isn't going to cope with the side loads caused by jams when going through 5mm. Also, I really wouldn't fancy trying to use a 10" hole saw in a hand drill to go through 5mm steel. A while ago I badly injured my wrist when a 16mm bit jammed when drilling-out a gate hinge - and that was only using a high torque battery drill. If the surface is flat it *might* be possible to use a hired mag drill (Rotabroach?) - I've used them to make holes in an RSJ (for pipes and cables), but not 10" diameter! If 't'were me I'd stitch drill, as I described earlier, with decent sharp drill bits and some oil.
PS The "single tooth cutting bit, mounted on an arm" that you mentioned is called a fly cutter - very useful but it's a brave (foolish?) person that tries to use one hand-held.>
I would hate to have to try that for a 10" circle in 5mm steel. It would take forever. I suspect an oxy-acetylene cutter would be the easiest way to do it.
I couldn't remember the name, until TNP reminded me of it.
Stitch drill is a last ditch method where you don't have a jig-saw. I cannot recommend it. It would take ages, and take longer cleaning the edge up with an angle grinder.
I recommend you look up plasma cutters. Obviously you need a mains power supply as they take quite a bit of power. They are incredibly cheap to run.
Then on down to oxy-propane, oxy-propylene and then oxy-acetylene.
Do you know anyone with a plasma cutter or an oxy-acetylene set?
That's why, when diamond core-drilling 5" holes in my brick walls, I invested in an SDS drill. Hammer turned off, rotation on and the in-built safety clutch protects your wrist ... and the rest of you when you are drilling your hole from the top of a ladder.
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