See:

https://www.mscdirect.co.uk/interstate-er25-x-1in-straight-shank-extension-eri-48370b

MSCdirect, having a US parent, is one of the few UK sources for imperial stuff.

Try finding an imperial shank edge finder here…

Outside chance is Gloster Tooling as they sometimes have imperial stuff.

Can’t you stick a standard one in a capstan sleeve?

EDIT – RDG and Chronos both occasionally have Imperial ‘oddities’ kicking around, might be worth calling esp. RDG

On 14 September 2025 at 18:28 Martin Connelly Said:

…put the new shank over it may be an option, but may be less rigid.

That raises the question of ‘how much less rigid?’.

Let us say we had a 25mm solid shaft; we can calculate the second moment of area.

Now assume that shaft is made from a 16mm solid bar with a 4.5mm wall tube shrink fitted over it. Where would we find the maths to determine its I value?

What about sleeving a 16mm or 20mm dia shank ER25 chuck? Plenty of cheap ones on eBay.

On 15 September 2025 at 17:26 ianj Said:

…from CTC tools

…who are not in the UK, which we must at least acknowledge was a specification of the original post.

I say this as a satisfied customer of CTC.

—

On further reflection of the lower rigidity of a sleeved item, if either the sleeve or the inner item were of a stiffer (higher E-value) material than the solid original, the bending stiffness could be increased over that of a homogonous solid item.

The crux of the matter is the behaviour of the connection between the two, which is still a mystery.

On 16 September 2025 at 07:00 DC31k Said:

[…] The crux of the matter is the behaviour of the connection between the two, which is still a mystery.

Unless they are truly locked-together at a molecular level, the safe assumption is that there will be slippage … hence my suggestion of simple addition of their stiffnesses.

MichaelG.

On 15 September 2025 at 08:39 Michael Gilligan Said:

On 15 September 2025 at 07:40 DC31k Said:

[…] Where would we find the maths to determine its I value?

Start by calculating the stiffness of the tube

Then add the [much lower] stiffness of the shaft

[…]

As everything else is constant … we only have to juggle with the fourth powers of the numbers 25.4 and16.0

To a first reasonable approximation, however, the stiffness of the tube would probably suffice.

416231.4256 – 65536 = 350695.4256

Q.E.D.

.

.

MichaelG.

DC31K suggestion of significantly higher youngs modulus would work if you could find such a material. Sounds like unobtainium.

Even if there were slippage between a sleeve and a shank, you can just add their I values. In fact if the sleeve was shrunk or loctited on I doubt you’d get slippage under the light loads from grinding and so could just treat it as a solid shaft. A more expensive solution would be to get a 25mm shank plated and then ground to 1″. Probably cheaper to import from USA

should have said only one is er 25 with a 1″shank the one in the grinding head is a bit smaller