Any triple boring guru wisdom?

Are there any general guidelines for boring a triple?

Trying to swap a front end, sans triples. There's no way they will work.
Non race application.
The top triple needs a shim.
But the bottom triple needs to be bored out by 2mm (aluminum). Going to take it to a machine shop.

It seems reasonable that the lower triple encounters more stress. Who has done this before? What is considered a minimum wall thickness for the lower triple? Anyone ever broke a bored triple?

 

I bored a set of SV triples in order to fit a 1st gen R6 front end on my endurance SV while keeping the SV offset. It needed a 2mm total increase in diameter. I don't think you are going to find a "standard wall thickness". It's going to depend on triple material, fork type, bike type, application, and desired feel. I checked that the wall thickness wasn't a huge percentage change before I started. The setup was a little tricky. I had to make a fixture to hold it and a shim of the correct thickness to support the bore. Then, with the shim in place, I tightened everything down and checked the bore position and cylindricity. As with most things, the actual metal cutting was the fast part.

 

Thank you @SLLaffoon . Do you remember what percentage that you took off? I'm pretty sure SV triples are Al, right?

The lower triple in question is thin but it is tall. A full 58mm tall or almost 2-3/8 inches. The wall thickness is 4.75mm. So if I bore 1mm out, giving me a 2mm greater diameter, the amount of material removed is 21% of the pre-bore thickness. Instead of a 4.75mm wall, I will have a 3.75mm wall. That seems like a lot to me, but given how tall the triple is, I don't think that it is too much.

 

Chamfer or radius the edges to reduce the possibility of stress cracks developing.

 

Yes, and it will also make it much easier to slide your forks in and out without scratching or scoring them.

 

The lower triple is steel. I'd have to go back and measure them. They are cast, so it tapers and is not a consistent wall thickness. They are a bit thicker than 5mm though.

 

Thanks @fastfreddie essential info. Thanks again @SLLaffoon .

 

I just added a touch, but I appreciate the thought.
SLLafoon's input was more informative in that it suggests this is not as easy as it may seem, even with a machinist involved. You have three set points along the length of each fork that have to line up when you're done, the top, the lower and the axle spacers. Sounds daunting.