Cutting perfectly round holes

[FORDification]

OK, here's a dumb question, FWIW.

I know that you can use a hole saw to cut a perfectly round hole in sheetmetal. The holesaw normally comes with a built-in drill-bit to get it started and to keep it centered.

However....what if you already have a hole, and you need to enlarge it, but still keep it perfectly centered and perfectly round? What can be done? Any ideas? I suppose one could just spend a LOT of time with a Dremel...I was just wondering if some ingenious inventor has come up with a better idea.

[cobraF100]

I'd make a Pattern of the size I wanted it to be and then Trace it, after you center it, then use a Jigsaw to cut it out.....

Just My 2 cents

[FORDification]

I could do that, but I seriously doubt I could get the hole perfectly round with a jigsaw! I guess I COULD do the rough cut with a jigsaw and then spend a lot of time with the Dremel.

Hmmm....OK, here's a thought: Why couldn't I set up a holesaw with 2 blades...an inner and an outer? The inner blade would be the size of the current hole and would sit a tad lower than the outer blade. The smaller inner blade would stay centered in the existing hole while allowing the larger outer blade to cut.

I believe that's do-able! I might have to give that a try this weekend.

[dutchtreat]

I used a steel plate larger than the existing hole and tack welded it in place over the hole...make sure you have center lines marked beyond the existing hole and on the new plate so that they will line up. This will give you a starting point for the drill bit in the hole saw........Dt.

[FORDification]

Well, the only project that comes to mind at the moment is modifying an F600 instrument panel for larger gauges. Granted, when doing this one I could use a Dremel (or die grinder) since the gauge lip would hide any minor imperfections...but there's been other times I've needed to enlarge an existing hole and keep it perfectly centered and round...I wish I could remember what I was doing at the time. I guess this was more of a general question, for future reference.

....and a drill press is next on the list of shop equipment to buy. That, and a hydraulic press!

[Rockcrusher]

It's a piece of cake if you have a drill press.

1. Lightly clamp the workpiece to the drill press table with the existing hole roughly centered on the chuck. Make sure the workpiece is is at a right angle to the chuck centerline.

2. chuck an edge finder into the drill press and rotate the spindle by hand. While you're rotating the spindle, adjust the position of the workpiece so that the edge finder is equidistant around the existing hole.

3. After the workpiece is centered, clamp it and the table down tight. Replace the edge finder with your favorite flavor of hole saw and press on.

But wait . . . You don't have an edge finder. You can make one out of a piece of round stock that's slightly larger than the smallest capacity of your chuck. Chuck the stock into the drill press and bend the free end until it makes a circle roughly the diameter of the existing hole in your workpiece as you rotate the spindle.

I've used this method a number of times and it's always served me well. It should get you within 0.010" to 0.050" of center depending on how much patience you have.

[67highboy]

I use these for perfect holes you can get them in almost any size...
Electricians use them for conduit in electrical pannels

Check it out

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 21983&rd=1]

[Tim P.]

Well guys I'm a carpenter by trade and i do a lot of remodeling work in older homes, and some of the doors are to be reused with new locksets. However the old setups have a smaller hole or slightly offset. What we do is clamp a piece of wood on one side of door and set our hole saw to the position desired with a longer pilot bit, making sure you're centered, and cut. This can be applied to metal using wood too and it wont mar up your piece unless you're dangerous with a saw and drill.

[heep70]

I was going to use a carbide bit and a high speed drill motor to cut out wider holes in my F600 panel. I figured they didn't need to look perfect being the lip of the new guages were going to cover over the cuts.

[Faithful Old Road Dog]

If you don't have a drill press, I'd do what Tim P. suggested. In the case of drilling out the hole in that cluster, you might get a 2x6 board and a hole saw the desired diameter and bore a hole through it. Now that 2x6 is your template. Center and clamp it over the smaller hole on the cluster and start your cut slow. What's nice is that the template has an 1 1/2" guide which minimizes a lot of wobble. I've used this method for boring holes in studs, joists and floors. Doors as well.

[morganater]

I cut some perfectly good door panels up with a zawzall to fit some speakers. IT worked, but looked ABSOLUTELY terrible. IT almost made me cry the next day thinking of what I did in the big rush to get them in. Luckily i Have an extra set of panels. Anyone have a guess as to how much about a 6" hole cutter costs

[FORDification]

You used WHAT??

Wow, that's like using a sledgehammer to put a thumbtack into the wall.

I think maybe a jigsaw would have been a better choice, since that's something that most people have around anyhow...though you might need to buy a metal-cutting blade for it, if you've only cut wood in the past. Any minor cutting imperfections would then be hidden by the speaker grille.

[jreb333]

would cost you about 15 bucks to take it to a machine shop and get it stamped out.

[jbyrd]

Rockcrushers suggestion with the drill press is your best bet if it can be clamped to the work surface. A Mill would preferable for thicker items, and using an edgefinder and then a boring head. If it was for a panel on the vehicle (and can conduct electricity) I would mark it and then have it cut out with a small plasma cutter (Would take about 2 minutes) and you would have a nice edge.