cutting a large-radius circular band out of steel sheet

[Florin Andrei]

Material is steel sheet (either mild or stainless), perhaps 0.065" thick.

I need to cut a half-circle band, like a large letter C. Outside diameter around 17", inside 15", so the width of the piece is 1". Same question for a full circular band, like the letter O, same diameters, just a full circle instead of half. I guess the technique should be pretty similar.

The edges must look pretty good, warping or notches are not acceptable. The whole piece should remain as flat as the original sheet.

I've done this before with plywood, using a router and a jig. How should I do this when the material is steel? I have some ideas, but I'm pretty new to working with metal, so I'd like to hear first from people more experienced than me.

I have access to a mini-lathe and mini-mill, drill press, and a random assortment of usual simple tools.

 

[chip_slinger]

Make a simple circle jig that can support an angle grinder. Put a cutoff disc in the angle grinder and go to town. Cut the larger radius first, then change your jig to the smaller radius and you will end up with a donut. Cut it in half for the "C", leave it whole for the "O".

 

[chip_slinger]

Or, get it burned out or plasma cut at your local steel supplier or higher-end welding shop.

 

[f350ca]

I'd cut it with a fine blade in the jigsaw and use a flap disk on the angle grinder to smooth out any imperfections. Or zip it out on the plasma table in 1/4 the time.

Greg

 

[JimDawson]

Given the tools you have available, the best and least cost simple solution I can come up with, using common hand and power tools is to use an Air Nibbler. These are available from Harbor Freight for about $25. I have used mine for 20Ga stainless, and 16Ga (0.063) mild steel. You need a new tool anyway.:whistle:




Make a simple plywood jig as you have done in the past for router projects, and use this tool just like a router. They leave a pretty clean cut so a lot of finishing is not required. Don't forget to oil the cutter and the air line.

If you need a bunch of these parts, then having them laser cut is the least cost CNC type method.

 

[Holescreek]

I would be very tempted to try it with a carbide cutter in a router. If you could use a speed control to drop the RPMs to about half of what you would run in wood it should be easy. The finish would be better than any reciprocating cutter and more controllable than a disc.

 

[JimDawson]

I would be very tempted to try it with a carbide cutter in a router. If you could use a speed control to drop the RPMs to about half of what you would run in wood it should be easy. The finish would be better than any reciprocating cutter and more controllable than a disc.

I have actually tried that, with a speed control. The result was less than satisfactory. I was using a 1/4 inch, carbide window cutout bit in 16Ga mild steel. It chipped the bit pretty quickly, then just started trying to burn through the metal.

I use carbide bits on aluminum all the time, in both my mill and my hand router with speed control. When using the router proper personal protection is absolutely required. Full face shield, hot chips fly all over.

 

[Round in circles]

I cut a sheet of 1/10 inch thick mild steel up to make lids for 45 gallon oil drums I was going to use as rat proof feed bins once they'd been hot water & soap power washed out.


I had a simple cheap Bosch hand held electric jigsaw ,there is provision at the base plate to slide a trammel bar in it.

So for me it was simply a case of going to the local big box store and buying a bit of flat bat that could be ground down to fit the trammel slot . I measured the radius , drilled a 1/8 hole in both the bar and the centre of the circle, then firmly pulled the two to gether with an extra long pop rivet .
I used a BOSCH steel cutting grade fine jigsaw blade on mid speed with the blade inclined back one stop ( if memory serves me correct) to cut it out. It only needed a flap disc to clean up a few rough bits

 

[fixit]

Drill the material & mount it on the end of your MILL table from the "PIVOT POINT" run the table the require distance, Plunge the end mill through the plate & rotate the material as needed. raise end mill relocate table repeat at new radius. after radius cuts are complete, clamp material to table make end cut by moving table, raise end mill rotate 90 deg repeat. Sound easy ?

fixit