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View Zod's profile

Recommendation on accurately cutting molding

by Zod
posted 12-14-2017 08:24 PM


4 replies so far

View JBrow's profile

JBrow

1366 posts in 1066 days


#1 posted 12-18-2017 03:24 PM

Zod,

A 45 degree drafting triangle or perhaps even a speed square could be used to set the mitre saw to 45 degrees. However, I prefer a jig that cuts complementary angles since the jig allows for cuts with minimal set-up time.

Trimming a box with moulding requires mitered angles that when added together equal 90 degrees and each length must be a perfect length and moulding that is of equal thickness. My method for achieving these results is to use a jig at the radial arm saw where the blade remains unadjusted and perpendicular to the fence. This approach could also be used at the mitre saw. It requires moulding that has a portion of the profile that will register flat against the edge of the jig.

The jig is a right triangle where one angle is a true 90 degrees and the other two angles are 45 degrees. It can be made from plywood or MDF screwed together until its thickness is at least 1-1/2” to 2”. One corner must be 90 degrees. A 45 degree diagonal is then cut into the jig (as close to 45 degrees as possible).

The jig is held firmly against the saw’s fence on the left side of the blade. The work piece is held firmly against the jig and the angle is cut on the left side of the blade. While the jig remains flat on the table, it is rotated and positioned to the right side of the blade to cut the opposite end of the moulding. That is the same face of the jig is up whether positioned on the left or right side of the blade. Thus the 45 degree angle of the jig that was away from the fence when on the left side of the blade is now at the fence on the right side of the blade. The second cut is made on the right side of the blade.

If the 45 degree cut of the jig is not a true 45 degree angle, these two angles will produce mitre cuts in the two mating work pieces that add to 90 degrees resulting in a tight fitting mitred joint.

I use short set-up pieces cut from the same moulding stock as that is used on the project. Each set-up piece is cut to a 45 degree mitre using the jig, one cut on the right side of the blade and the other on the left side of the blade. Each set-up piece should be shorter than the smallest dimension of the box.

The first work piece cut is a mitre on one end of the front piece of moulding, leaving the moulding extra-long. The work piece is held on the front of the project and the complementary set-up piece is held on the side of the project and is used to close the mitre joint with the front piece of moulding. The set-up piece on the side of the project is clamped (spring clamp or masking tape) to the project. The front piece of moulding is clamped in place and the opposite end is marked using the second set-up piece. A mitre is cut at the opposite end of the front piece of moulding, but the moulding is cut long. Then it is a matter of positioning the front moulding against the set-up piece clamp on the side of the project and re-cutting the opposite mitre until a tight joint is achieved using the second set-up piece.

Once the front moulding is cut to proper length, it is clamped in place and a similar process is used to cut the remaining pieces of moulding. I prefer to affix the moulding to project at the one time; rather than as I complete the cuts on each piece. This makes it easier to fine tune any pieces that are not quite right.

Milling some extra moulding is my standard practice. I always manage to measure wrong or cut a mitre in the wrong direction no matter how careful I try to be.

View waho6o9's profile

waho6o9

8423 posts in 2723 days


#2 posted 12-18-2017 03:29 PM

Practice on scrap

View Zod's profile

Zod

24 posts in 325 days


#3 posted 12-18-2017 03:32 PM

Thank you for such a detailed response! There is A LOT more involved to successfully doing this than I could have imagined. I try to learn something new with each project and an going to try to work more with molding. I had no system in place and couldn’t get accurate lengths. But following a process has got to be a big help. Thanks!

View rwe2156's profile

rwe2156

3092 posts in 1627 days


#4 posted 12-18-2017 08:20 PM

On small mouldings like this I prefer to cut the miters with a hand saw and miter box.

Cut them a bit long and sneak up on the perfect fit using a hand plane and shooting board.

Use scrap test pieces to fit each corner so you know what to do.

-- Everything is a prototype thats why its one of a kind!!

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