# How to cut a 12.5 radius in some box steel



## Beau (31 Jul 2018)

Got my first welding project to do and needing to fix some 25mm diameter steel tubing to the end of 20mm box. First plan was just to cut a V in the box and just weld the sides but is there an easy way to create a 12.5mm concave on the end of some box? Tried drilling at 25mm but that was messy and going to kill my drill press. Lots to do so dont fancy filing them concave. Thanks


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## Trevanion (31 Jul 2018)

The best way I've found to do something similar is to jam a piece of wood into the box section and go at it at the slowest speed you possibly can on a drill press with a holesaw. If looks are unimportant as you're probably covering it with weld anyway you could probably get away just hacking at it with a grinder until it's roughly how you want it.


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## sunnybob (31 Jul 2018)

a hole cutter will work if you dont have any oxy acetelyne to burn it out. But you must allow the extra length of box section material to cut a 25 mm hole fully. then slice off the unwanted half of the box section.
Slow and steady wins the race, with oil lubrication often. I recently cut a 42 mm hole in 10 mm thick steel plate with a standard hole cutter. And it still had teeth left.


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## Beau (31 Jul 2018)

Had wondered about trying a holesaw. Got 32 to do and looks dont matter just needs to be strong and consistent. Thanks for the tip re pushing some wood inside.


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## sunnybob (31 Jul 2018)

youre not going to cut 32 with one hole saw #-o #-o 
buy a half dozen =D> =D> =D> 8)


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## Phil Pascoe (31 Jul 2018)

If you haven't a hole saw, stitch drill it. Do e.g. 12 o'clock, 2,4,6,8,10, then 1,7,3,9,5,11 depending on the size of the bit.

Edit - which is a tedious way of doing 32


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## novocaine (31 Jul 2018)

sorry but a decent hole saw will drill that all day long. I've drilled more than that with a starett (the only thing starett I own  )
Clamp 2 lengths in the vice with the seam on the centre line and do 2 at time to cut out the hard work. if you haven't cut the box to length yet then mark it, drill it then cut it with a zip wheel or a reciprocating saw with a metal blade in. 16 holes instead of 32. batch work is a puppy, but with a bit of thought you can make it quicker.
also, oversize it by a mm if you can and use a grinder to nip the edge of to give you a V grove.


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## Beau (31 Jul 2018)

Had a quick go with a holesaw that I had . What it didn't like was going through the sidewall of the box as the diameter required is larger than the box section width. Hope that makes sense


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## novocaine (31 Jul 2018)

Slow speed. 50rpm or lower.


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## --Tom-- (31 Jul 2018)

I’d do it on a linisher with a 25mm contact wheel. If you’re anywhere near Cardiff happy to help out


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## Beau (1 Aug 2018)

novocaine":3azfq1wf said:


> Slow speed. 50rpm or lower.



Not got a great drill press and it was at it's slowest speed  Might try a Starett saw though before looking at other options


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## Beau (1 Aug 2018)

--Tom--":22m7ors2 said:


> I’d do it on a linisher with a 25mm contact wheel. If you’re anywhere near Cardiff happy to help out



Not got a linisher (new to metal work). Presuming it's a bit like a belt sander? Sounds like a good way to do the job though. Had wondered if there was some sort of diamond drum I could put in the drill press sort of like a drum sander for metal.


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