Make straight relief cuts from the outside of the plastic to the curves.
How to shape abs plastic sheet.
This will help prevent the plastic from warping.
A common and safe method of reshaping abs plastic is to use boiling water which reduces risks involved with accidentally overheating abs.
Then mark the cutting line with a highlighter.
Secure it with a clamp to prevent the material from moving.
This will act as a guideline and will help you achieve the shape you are.
Dipping the abs into a bath of cool water will help quickly lower its temperature so it will hold its new shape.
Use a plastic cutting knife to cut the sheet down to the general overall size.
Make several scores along the guideline.
Depending on how deformed your part was originally you may need to repeat the process two or three times slowly bringing the abs back into its proper shape a little more each time.
Measure the size of the of the overall piece you need.
Make sure the sheet is just big enough for the form.
Water boils at 212 degrees fahrenheit at which point abs becomes soft and rubbery but will not burn.