Installing Trim

[Jon Middleton]

I need advice on the proper techniques for installing trim around the outside of veneered MDF. I'm finishing an equipment cabinet for my home theater, the top of which is mahogany MDF. I cut the trim to 45s, but cannot get seamless corners. Only the front and one side had exposed MDF, so it should have been simple. But, I ended up with a tiny gap. I'd like to be able to wrap all four sides with solid wood trim, and my current approach is not working. I tried a search to no avail. Are there articles on this. I know it can be done, so it's a bit frustrating. My cuts are clean, I just need to be able to apply good clamping pressure and make reliable, accurate cuts.

[frank shic]

check the angle of the corner. it might be close but not exactly 90 degrees and double check your miter saw as well. try mitering a test piece and testing out the fit at that corner.

[Jon Middleton]

The mitered trim fit well before I clamped it up, and the angle was correct. I need advice on how to cut the trim pieces to precise length and clamp them tightly. My gap is about .010", maybe less, but I want a foolproof method of making seamless trim joints.

[Chris Tsutsui]

Trim can be frustrating for me.

I too would double check the angles on the cabinet to make sure they are 45 degrees. Then I might be pursuaded to cut the angles on my trim to a hair less than the angle it measures to ensure that the visible seam is tight. Or I wonder if back beveling the trim will help...

The mitersaw needs a sharp blade and the fence has got to be square to the blade and table. I'm not sure how you are setting up the mitersaw to make those cuts do you have a crown moulding type of stop or are you using compound angles?

[scott vroom]

Without seeing pictures it's difficult to know what the problem is. If everything fit before clamping, then it's possible that the clamping is the problem - maybe it's bending the trim and creating gaps?

One trick I've learned over the years is to cut mitered molding just minutely longer than measured to prevent gaps during installation. The principle behind this is it's always easier to trim off a tiny bit more, but impossible to add more back on. Working with molding is tricky, in part because perfectly cut miters don't always translate to perfect joints at the install. Another trick I've used is to cut the miters just a hair wider than 45 degrees on outside corners.....this helps prevent an open gap at the joint.

Hope this helps

[Bob Lloyd]

You did not state but if the gap is the same at the short and long points of the miter then one or more piece is too short; if it is one or the other then the angle is wrong. I would do as Frank suggests and cut test pieces. I would use two short test pieces either end of the first long side to make sure that you have a good length and fit at both ends and then install it. Work your way round the edge off of the installed piece. Run the next piece long, cut it to fit the angle of the installed piece, mark and cut the other end using a test piece. When you get to the last piece again cut it long but cut both angles to make sure both miters are tight. Then measure the length and cut it. When doing something like this I reverse the last piece away from the work when I mark it, I find that it is more accurate. As Scott stated, it is better to leave it a little long and sneak up on the cut to get a tight fit. I hope that helps.

[frank shic]

for inside corners i usually use a laser measuring device to figure out the right length. for outside corners i usually cut it long and nibble away until i get the right fit. don't forget: caulk hides small gaps really well!

[Prashun Patel]

The quality of my miters (while still not perfect) has improved since I discovered two things:

1) You have to clamp the piece down during the cut so the blade doesn't move it.
2) A brad or pin nailer really makes life easy.

If the pieces are large enough, another trick is to glue waste blocks to provide parallel bearing surfaces for a clamp on the corner.

[Gregory King]

Try under cutting all of the miter cuts a couple of degrees as well, so that the faces touch first.

[Rich Engelhardt]

I get much tighter joints if I miter trim the same way as I do crown - upside down and backwards.

[Jon Middleton]

I'll post up some photos later if I get the chance. I was able to track down the guy who made some cabinets for us 13 years ago, and will pay him a visit. His stuff is perfect.

[Jon Middleton]

My visit was good. First, he recommends cutting miters on the table saw, using a sled. I'll be making my sled with 3/4" MDF, fastening a second piece of MDF cut at 90 degrees as closely as possible to 45 degrees to the blade. Cutting your two pieces on opposite sides of the sled will compensate for any error, as the angles will be complementary.

Clamping is best done by installing one side first, then clamping the off end of the second piece so that there is a slight gap at the joint end between the second trim piece and the MDF. When you then clamp the joint end, it is pulled down into the joint exerting pressure against the first trim piece, which closes the joint tightly. He emphasized the importance of applying glue liberally to the joint, as this helps close it also.

I'll give this method a try and report back.