I asked this question and this the reply I got from a very helpful member on here. Hope it helps.
Cheers Pete
Tricky wrote:
Yes, I can help you out, it will be a pleasure.
Firstly, draw a line parallel with the existing arch lip, 20mm wide along the front guard. This line will become your datum. I used a 20mm wide ruler for this and just ran around the lip with a felt pen. This will be your bend line.
Now, draw another line 10mm inside the existing lip just like the 20mm line. So now you have a 10mm line and a 20mm line. The 10mm line will be your cut line.
Cut the arch off at the 10mm line and discard. Now get some vice grips and bend the newly cut lip up at the 20mm line to make a new lip, 10mm wide. Use a hammer and dolly to get the lip square and even and looking nice.
What you now have achieved is to take 20mm off the original arch, 10mm as a cut and 10mm as a new lip.
Hope this makes sense.
Cheers,
Tricky
