Sewing help needed please! I am confused with correct way to cut lovely material.

[OldCrowMedicineShow]

I have not made anything from a pattern since school many years ago ds has a school ceilidh tomorrow and they need to wear tartan.
I found a beautiful piece of good wool tartan plus have a waistcoat pattern. Everything is ready but before I cut the tartan, there is a correct way and a wrong way to cut. Words like 'bias' 'selvage' and nap lurk around but I don't remember anything about them.
I am also going to attempt making a tie.
The same selvage/bias/nap confusion for some silk type material for the back so it hangs nicely.

Please help!

Selvedge is the neat edge running down the long edges of the fabric, this runs parallel to the grain. Tartan doesn't generally have a nap or a pile, but can have a one way pattern. Also make sure you match the pattern on the seams and cf up

The back will be cut on the bias, which means place the grain at 45 degrees to the selvedge

Thank you!

I pinned then cut the back pieces, the material is a silky polyester with silk slubby bits and it is quite heavy so sits beautifully.
Am gathering up courage to cut the tartan but there is a lot of material for matching up the check. It is nerve wracking, though!

Should I put a little iron interface (lightweight) around the shoulders? It says to interface the entire back but the material is fairly stiff anyway plus doubled (the two parts of the back).

The most important nit to match up is the cF. Make sure you allow for seam allowance.

You could interface the tartan shoulders, neck and fronts. But I wouldn't interface the back if it is all of the silky stuff. Actually, I would, I'd put some around the back neck.

Thank you, Orangeanddemons.

I have hit a huge problem. The new patterns do not include seam allowances and I'm not sure how to get an accurate edge. How do you do this, please? I don't have a stabby wheel and am desparing now
How do you mark exactly what is on the pattern from the pieces which have been cut out?

You will gave to measure the seam allowance. Pin the pieces on and measure1.5 cm out with a tape measure and tailors chalk all the way round.

You do tailor tacks for pattern markings or just poke tailors chalk through the pattern piece to mark markings.

Tie two pencils together with a rubber band and draw around the pattern pieces with them. The outer line is your seam allowance.. Measure what it is and then find the corresponding line on your machine!!

Geniuses!

A bit late to the party and you will have sewn your waistcoat by now but for seam allowances I tape two pencils together and draw around the pattern again (I save the original pattern and trace a new one in tracing paper or greaseproof paper) It gives a nice even seam allowance.

Thank you FuckOffJeffrey

Not late to the party at all, the waistcoat is 'resting' in the sewing pile and I had to wait for a while until a tracing wheel then dressmaking carbon paper arrived then I lost the pattern my nerve. Child will be a fully grown adult by the time this project gets finished.