Mitered trim glue-up tips requested

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Forum topic by GregD posted 12-23-2016 01:34 PM 1525 views 0 times favorited 8 replies Add to Favorites Watch
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788 posts in 3612 days

12-23-2016 01:34 PM

Topic tags/keywords: tip question gluing miters

I am looking for tips for gluing on mitered trim pieces.

I want to glue 3/8” thick 2” wide trim onto a plywood rectangle (about 18” square) to get a frame-and-panel (flat panel) look. I want to miter the trim. When I dry-fit the parts the joints are tight, but it takes a lot of adjusting with a square to get everything right. For my first glue-up I clamped the parts into place, removed 1 part, added glue, and put the part back into place and added clamps. I found, however, that this still requires a bit of fussing to get the part back into place precisely. My first attempt wasn’t bad but I’m hoping to do better.

The outer edges of the trim frame hang over the plywood a bit and then are trimmed flush with a flush trim router bit.

So I’m looking for hints. Some ideas I’ve had:

1. Dry fit the parts as before but then draw a pencil line across each joint to show the proper alignment.

2. Glue the mitered corners together first and then glue the assembly of trim pieces to the plywood. I was planning to use masking tape to pull the corner together when gluing.

3. Tape the mitered corners together. Put double sided tape on the top of the trim pieces. Press on top of that a piece of plywood scrap to hold everything together. Then glue the assembly to the plywood.

-- Greg D.

8 replies so far

View 000's profile


2859 posts in 1375 days

#1 posted 12-23-2016 02:20 PM

I would put the frames together first using miter spring clamps, or a band clamp.
Then I would drum sand them, and then apply them.

View gailmo's profile


29 posts in 1514 days

#2 posted 12-23-2016 02:22 PM

I am not an experienced woodworker—but I did this on a buffet I built last year. My technique was one I just kinda fell into. I cut the first piece to length and used pocket screws to mount it. I then fit the next corner to the first piece making sure the cut was good and even. I then carefully measured the length of this second piece and cut it to fit. I usually took “little bites” off of the end until I was comfortable that it would fit both ends. I then pocket screwed the second piece on. Then I worked on the third side using the same technique. The last side took me a bit longer. I probably micro-sliced off the ends 3-4 times until I got it to fit. Pocket screwed it on and totally amazed myself because it worked.

I also put a groove around the piece to set off the edge. I grooved the plywood and was a bit angry with myself because when painting, the open groove sucked in the paint and I never could quite get it to be perfectly filled. It still looks fine -to everyone but me!

View JBrow's profile


1368 posts in 1396 days

#3 posted 12-23-2016 11:16 PM


I like gluing the frame together as a sub-assembly first and then gluing the frame to the plywood.

An alternative idea using tape would be to do the fusing and fitting at one corner and with the mitre joint perfect, clamp the pieces to the plywood. With the trim clamped to the plywood apply masking tape to the outside edges so that the tape bridges the long points of the mitre. The masking tape would thus act as a temporary hinge. I would prefer masking tape to painters tape here since masking tape is a little stickier. This process would be repeated for the remaining four corners, but the last corner gets no masking tape. Once the fit is perfected and the edges taped together, the trim can be un-clamped from the plywood, glue applied, and the trim re-installed, folding it as you go.

A square registration block at the first fitted corner could be fastened to the plywood with two intersecting edges making contact with the inside edges of the trim. This square registration block would thus register the trim during glue-up. A shallow mitred corner of the square block would keep the square block’s corner from contacting the intersection of the inside corner of the trim, making for a tighter mitred joint. Double sided tape or a C clamp could be used to secure the square registration block.

View Cooler's profile


299 posts in 1319 days

#4 posted 12-27-2016 04:13 PM

If you are going to be doing a lot of this type of work a miter vise works great. Standard fare for picture framing shops and now available for under $70.00 (I paid a lot more 30 years ago, but it was made in the USA).

Adjust the pieces until they mate perfectly. Then release on piece and apply glue and replace and cross-pin using a 23 gage pin nailer or pre-drill and drive in brads with a brad pusher.

This is fairly slow, but will result in nearly perfect joints if the miters were cut accurately.

-- This post is a hand-crafted natural product. Slight variations in spelling and grammar should not be viewed as flaws or defects, but rather as an integral characteristic of the creative process.

View MinnesotaSteve's profile


54 posts in 1367 days

#5 posted 12-28-2016 07:28 AM

I’ll just toss this out there… I bought these when I was doing trim work in my house, especially helpful framing in doors and windows. This won’t get you square, but it’ll help hold the miter together as you glue it up.

I looked at other similar tools, they were either thicker or strangely over complicated. The collins ones are really simple, easy to use and work great. And relatively inexpensive, like $30 for a set of 4.

View Carol's profile


62 posts in 989 days

#6 posted 01-02-2017 03:37 AM

if i understand right, what you would end up with is a trim frame attached to a flat panel of plywood?

what i’ve sometimes resorted to to square a project, and works great for frames, is a thin ratchet strap and 4 small right angle brackets. clamp a large square to the work surface so you have a solid right angle. place one corner of your trim rectangle tight against the corner of the square. put the rest of the pieces in place, then place the angle braces/brackets around the corners. run the ratchet strap on the outside of the brackets, and tighten, keeping your frame square by measuring on the diagonal as you go.

maybe glue up the frame, then attach it to the backing?

-- Carol

View GregD's profile


788 posts in 3612 days

#7 posted 01-02-2017 04:46 PM

Been busy with other things since my post.

I did try gluing the mitered corners together first using precision clamping squares at the corners. It went much better but one remaining challenge is that the pieces are not typically uniform width so I can’t use the outside corner for alignment, and I have a roundover on the inside edge so that is not as easy to align. This next one I’m going to dry fit the miters before milling the roundover so I have a clear inside corner to judge alignment. I’ll then draw a pencil line across the joint to indicate proper alignment.

Off to the shop…

-- Greg D.

View diverlloyd's profile


3592 posts in 2333 days

#8 posted 01-02-2017 05:07 PM

Brow is onto something. Using masking tape like that works very well it’s how I glue up mittered boxes and frames.
Woodworking masterclass on YouTube has a couple videos about it. The gentleman is from New Zealand and puts out some good videos.

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