My daughter has the following homework question regarding vacuum forming:
“Formers need to be smooth and have a rake. Explain below, using a simple diagram, what a rake is and why it is necessary.”

My Google Fu isn’t working. I think this is referring to the draft angle i.e. the angle on the sides to ensure the part releases from the former but I can’t find it referred to anywhere as “rake”.

Any ideas?

I don’t know but the ‘rake’ of a bike fork is another name for the offset.

Never heard it called rake. Must be draft angle. Rake angle is a term in machining

It seems like poor and/or old fashioned language use. Rake angle is used with cutting tools as is relief angle, which is also used in moulding terminology and should give you more hits. Maybe an expert will be along shortly.

Side angle has to be less than 90 degrees (rake). If the sides undercut model then you won’t be able to get the former out once you’re done.

I’m not an expert but did use one at Art College a looong time ago.

Draft applies to castings and forms (including forgings) and usually defined from the natural or imposed parting line, (imagine making a sandcastle the bucket has a taper on all sides to get the bucket off) most often it is planar for simple mechanical things for ease of manufacture but can be curved along a boundary for example a split of halves on a curved phone when used in a mould tool either way the key thing to remember is that draft is allowing you to pull the object without getting it stuck

Rake is applied to cutting tools as said above

Rake is the angle (sometimes referred to as clearance)to the cutting face normally for machine tools. In this instance it is the angle to the base or former for your mould. Imagine a pyramid. The mould would lift off the pyramid once formed because the sides are raked. If they had a negative rake like a diamond, the mould would be unable to be released vertically off the former.

You’ve also got to consider how the material will stretch over a vacuum forming mold. You cant have a large vertical surface even if the other side is very shallow as the material would pull too thin.

Thanks all, good advice as always.