Cut 30” circle from 3/16” steel plate using portable bandsaw

Question

I have a 31” x 31” x 3/16” mild steel plate. I want to cut a 30” circle from the the plate.

Purpose: The plate/disc will be the base of a custom charcoal barbecue/raised fire pit.

I’ve seen various videos of people using angle grinders to cut circles from steel plates. But those methods seem cumbersome and laborious to me. I’m wondering if there might be an easier way to do it using basic garage tools.

I don’t have ideal tools like a plasma cutter or an oxyacetylene torch. But I do have a portable bandsaw (not yet used): DEWALT Portable Band Saw, Deep Cut, 10 Amp, 5-Inch (DWM120K).

Is there a way to cut out the disc using a portable bandsaw? I’m willing to drill a hole in the middle of the plate if needed for spinning or jigging. I don’t have a table apparatus for the portable bandsaw, but I can make one or put the saw in a vise.

Answer 1

A quick maths check says to cut a circle into that square, your bandsaw would need to be able to cut a depth of:

(31"  x  sqrt(2)  -  30") / 2 = 6.9"

The instructions for the bandsaw you have say a max depth of 5".

So the only way you could use that saw to acheive your desired cut would be to round off a couple of inches from the outside corners of the square so that it is at most 40" across. But that may not be acceptable to you.

---

Ok, so based on the changes to the question, you are trying to cut out a circle from the square, rather than cutting out a circular hole.

In this case you should be fine using the bandsaw to cut out the circle. Again as the cut depth of the bandsaw is too small (see equation above), you will have to make two cuts, the first to remove excess material from the corners, and then a second pass to form the shape you want.

I would cut the circle slightly oversize - e.g. 31 1/16" - and then use a file and sandpaper to get the final shape. Remember to file in the opposite curve to the circle to avoid forming flat spots:

Answer 2

Since you're cutting away the square parts of the plate to make it circular (not cutting a round hole in a square plate, as originally asked), you can use any tool you'd like, including sandpaper (if you're a masochist).

Draw your circle on the plate, fire up the band saw, bring the blade to the edge of the plate and start cutting!

When you get to the point where the saw doesn't have enough depth to reach from the edge to your line, just cut straight to the nearest edge to cut the excess away so now your edge is much closer to the line. Once that extra material is out of the way, go back to cutting the line.

You may find that your band saw cut is a bit on the ragged side, especially if this is the first time you've used the tool, so cut a bit outside the line so that when you're done, you can use an angle grinder, file, sandpaper, whatever to neatly get right to the line. How careful and thorough you are in this step, of course, depends on exactly how smooth you want your disk of steel to be.