[This is part of my ARCHWAY-101 series.]

I used these few simple layout techniques to find the exact spot where the Flex Trim needs to end. This allowed me to drop the keystone right in place after the I installed the Flex Trim.

But first, here’s a list of the materials I used to make the keystone.


Keystone Materials Inventory

You can use scrap material left over from making the arch pilasters to make the keystones, so I won’t bother calculating the costs.

1. Abacus MDF-100  The top of this keystone is viewed from the upstairs landing, so I made this abacus (that acts as a cap) routered a very small ovolo profile on the outside edge of this piece of 1/4″ thick mdf and t

I normally don’t router anything, but this was the best way to get a delicate detail on such a thin piece of flat-stock.

More about MDF-100 here >>

2. Bed Molding  CM-001  Look closely at the image above, and you can see that I wrapped this bed molding around a block of MDF-300, Item 3 in the picture.

More about CM-001 here >>

3. Fascia  MDF-300  This is made from a small block of 3/4″ mdf.

4. Keystone Foundation  MDF-300  Cut two identical pieces of mdf and glue them together. Sand the edges. That’s all there is to it.

More about MDF-300 here >>

5. Panel Molding  PM-001  I dressed up the edges of my keystone with this little panel molding. It is not a design necessity, just a little extra detail.

If you make your keystone without this panel molding, then reduce the size of the lower fascia by about 1/8″.

More about PM-001 here >>

Cartouche Ornament  This delicate applique I ordered from Decorators Supply. You should know that Decorators Supply has strict minimum order requirements, and so you can’t order just one or two at a time.

There are however lots of other companies that sell architectural ornaments, a quick search will turn up plenty.


How to Layout the Keystones

The following pictures do a better job of describing the process than if I were to blather on. So I’ll just stop right here and let the pictures do the talking.

how to install moldings

archway molding

diy archway


diy moldings

moldings & millwork




flex trim

How to Build ARCHWAY-101 Series

1. How to Build ARCHWAY-101 Part 1: Gallery

2. How to Build ARCHWAY-101 Part 2: Materials Inventory

3. How to Build ARCHWAY-101 Part 3: How to Make the Pilaster Core

4. How to Build ARCHWAY-101 Part 4: Keystone Materials and Layout

5. How to Build ARCHWAY-101 Part 5: Installing the Flex Trim Legs

6. How to Build ARCHWAY-101 Part 6: Installing the Arched Casing

7. How to Build ARCHWAY-101 Part 7: Flex Trim Backband & Keystone

8. How to Build ARCHWAY-101 Part 8: Prep & Paint