25mm > 35mm hole in cast iron

[bigegg]

I need to enlarge a through hole in a piece of 25mm thick cast iron.
The hole is currently 25mm diameter and I need to open it up to 34-35mm.
It needs to be reasonably concentric and perpendicular to the face of the plate.
Easiest way would be to bore out on a lathe, but what if no lathe available?
Will a 35mm step drill follow the existing hole?
Other ideas?

It's for a hand wheel - I want to put a m20 nut in the hole.
It will take an m16 nut at the moment, so I suppose the alternative is to drill+tap the nut to m20.

 

[atomant48]

I've used a step drill to open up holes in RHS with no problems but the difference is it fully penetrates before jumping to the next bigger step etc. With your plate at 25mm thick it will be working quite hard as it will be cutting on all steps simultaneously if you get what I mean. Your idea of opening up then nut sounds good as long as there's enough meat left.

 

[brightspark]

step drills no good at that thickness and its cast iron if u have a pedestal drill and can fasten the metal down u can use a hole saw and steady away slow speed I've drilled 20mm thick steel with one before

 

[bigegg]

Should have bought m16 all thread, instead of the clearance m20 at screwfix

 

[Fazerruss]

How big is the hand wheel?

 

[bigegg]

How big is the hand wheel?

About 6" diameter

 

[Fazerruss]

If you get stuck I may be able to fit it in my lathe as long as it's got 3 spokes.

 

[Onoff]

Would a Starrett Oops not help? Stick a 25mm on as the pilot (guided by the existing hole) with a 35mm for the hole you want.

 

[Toleman]

On site I with holesaws in wood I would clamp something behind it. Pilot the centre then use a 35mm hole saw. You may need a longer centre bit for the arbour

 

[bigegg]

If you get stuck I may be able to fit it in my lathe as long as it's got 3 spokes.

Thanks for the offer!
Unfortunately, it's a solid wheel, so won't go in a 3-jaw.

 

[bigegg]

Would a Starrett Oops not help? Stick a 25mm on as the pilot (guided by the existing hole) with a 35mm for the hole you want.

Think we have a winner!
Bonus points awarded for giving me an excuse for me to buy a new tool.



Just ordered this one

 

[Onoff]

Think we have a winner!
Bonus points awarded for giving me an excuse for me to buy a new tool.



Just ordered this one

And when you get a minute make up these homebrew adapters either side then you can mix & match big/small Starretts to your heart's content: