Thread: Cutting Tri Quad

I'm not sure what your 'Tri Quad' is but if is similar to what we call 'Crown Moulding', the key is to cut it as though it is on the wall.

When I did the crown molding for the house, I made a right angle sled for the SCMS. I would position the molding on the sled and cut. The sled looks like a letter "L" when viewed from the end and had a small forward fence to hold the molding against the back fence. The sled was held with the molding against the existing fence on the SCMS.

All cuts were made with the SCMS radial angle at 90°. When I got to a corner the saw was tilted either left or right to 45° but still on the 90° radial. Only when going around a corner was the SCMS adjusted to 45° either left or right as needed.

Once I got my head screwed on straight, the project was simple. If you are going back to the wall and not around the corner, your good piece is the off fall. Cut your 45° side first and then a straight 90° cut with the molding flat on the SCMS. Make your 90° cut so that the bottom of the molding on the 45° side meets the cut exactly. (Maybe +½mm)

One other tip. When measuring the length of a piece to fit, you're measuring on the bottom and transfer the mark to the back side of the molding. Then us a 45° adjustable square to bring the mark around to the front of the molding.

It is so much easier when cutting as if the molding is on the wall. It is easy to visualize your finished product that way.

Originally Posted by John James

I can not get my head around the following. I need to position tri-quad timber under a cornice but for the life of me I can't work out the angles to cut in the miter box. Easy enough with square lengths like skirting but this has me stumped. Can someone explain it to me like a four year old.

Hi John

Firstly welcome to the forums. Please don't be a one question run-and-hide poster. Hang around, comment or contribute to discussions. Make a friend or three.


your question
I'm not sure that a four year old understands the concept of spring angle -- but that is what you are dealing with and need to understand.
The simple way is with an L-shaped support jig as mentioned by Rich.

Post a photo or sketch of the molding and corners and the collective wisdom will see what they can do.

When you place tri quad moulding in the mitre box, it has to be positioned in the position that it is going to be attached.
The picture below shows it positioned as it would be if going between the wall and the ceiling.

E6A670FE-7196-4DA6-BCBD-64981FC93F72.png

So, to cut it at an angle. I would place it, as shown, with the bottom narrow edge against the bottom if the mitre box and the rear flat surface against back of the mitre box. The other flat surface would be uppermost and the sloping down diagonal face, towards you.
Hope that makes sense