lock miter vs lapped miter plywood - Woodworking Talk - Woodworkers Forum
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post #1 of 10 Old 09-18-2020, 02:49 PM Thread Starter
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lock miter vs lapped miter plywood

Hi Guys,
was asked by a friend to make some game room cabinets. planning to use Plywood for the carcass, and wondering if the lock miter bit will work in plywood, or if i need to get the lapped miter set? I have a tongue and groove kit for cabinets, but there will always be end grain with this option, sadly. Im not sure how much they want to spend on the materials, I'm hoping to use Baltic Birch ply.

Lock miter in BB plywood, or lapped miter?
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post #2 of 10 Old 09-18-2020, 05:43 PM
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I use a lap joint .....

It's almost impossible to get a perfect miter/bevel on long edges in my experience at least, so I like to use a lap/rabbet joint with a thin exposed edge on the visible side. It works OK in many instances and you need to look closely to see it. A drawer lock joint can also be used for this as shown at about 4:00 in:


This video show how precise you must adjust the bit for a lock miter bit. This would drive me nuts .......

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 09-18-2020 at 06:13 PM.
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post #3 of 10 Old 09-19-2020, 02:46 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
It's almost impossible to get a perfect miter/bevel on long edges in my experience at least, so I like to use a lap/rabbet joint with a thin exposed edge on the visible side. It works OK in many instances and you need to look closely to see it. A drawer lock joint can also be used for this as shown at about 4:00 in:
Making a Drawer Lock Joint - YouTube


This video show how precise you must adjust the bit for a lock miter bit. This would drive me nuts .......
Lock Mitre Router Bits - YouTube

my issue with the lock miter, is that it always seems to blow apart the plywood. thats why I was leaning towards the lapped miter.
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post #4 of 10 Old 09-20-2020, 08:26 AM
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How about biscuits for the carcass?
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post #5 of 10 Old 09-20-2020, 08:35 AM
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Lock miter bits can be tricky to set up, personally I despise them, but I’m sure it’s me.

Standard cab construction like this usually involves either face frame edge banding. Edge banding can be either iron on veneer banding or applied solid wood strips.

How you construct the boxes depends somewhat on visible end panels. If there are no visible sides, then butt joint and screws from the sides are pretty standard.

Visible sides or end panels can be addressed various ways, one I prefer is to apply a panel that looks like the doors, screwed from the inside.

If you’re doing face frames a “screwless” option is tongue and groove the sides into the ff (tongue sides, groove ff)

A drawing of the cab layout would help.

Robert
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post #6 of 10 Old 09-20-2020, 09:32 AM
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Lock Miter bits do not like plywood. You will get a lot of tear-out. I have tried many ways including cutting them in multiple passes at increasing depths.

Biscuits do work, if you build a little jig to keep the biscuit cuter in repeatable positions when cutting the slots. It's best to cut the slots very close to the inside of the corners to prevent them from blowing out through the outer surface.

In most cases, I have just cut full length spline slots in the mitered ends on the table saw, and then used my tenon jig on the table saw to cut cross grained splines from solid hardwood, 2 splines from each end of a board. The resulting cuts are very accurate and fit together well. I cut the splines free of the hardwood board ends using my miter saw and a stop to get splines that fit the miter slots (slot 1 depth + slot 2 depth = spline cut-off dimension). I then repeat the process if more splines are needed. The hardwood grain of the splines must run across the joint and not with the joint or there will be little to no gain in joint strength. You can place many cross grain splines end to end to assemble a long joint, so the donor board does not have to be as wide as the spline slots. When the joint is assembled and glued, the only place that you can see the spline is in the joint ends. If cut the thickness of the blade kerf that cut the spline slots is the same thickness of the cross grained splines, the assembled joint will not slip during glue-up and will be very strong when glued.

Charley
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post #7 of 10 Old 09-20-2020, 07:58 PM
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If the case will be plywood without wood frames then I would rabbit the edges and leave 1/8" . Another words if your stock is 3/4" thick I would rabbit 5/8" deep. Glue up , nail or clamp sides to top, bottom etc. You will only see 1/8" of the plies.
With Baltic Birch I think you will see 1 or 2 plies in 1/8".
Also you can use veneer tape or make thin strips of hardwood. I usually use face frames so the cabinet joinery is not important since it will not be seen.
mike
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post #8 of 10 Old 09-20-2020, 10:35 PM
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OK, I'm convinced after this .....

Quote:
Originally Posted by Rhaugle View Post
Hi Guys,
was asked by a friend to make some game room cabinets. planning to use Plywood for the carcass, and wondering if the lock miter bit will work in plywood, or if i need to get the lapped miter set? I have a tongue and groove kit for cabinets, but there will always be end grain with this option, sadly. Im not sure how much they want to spend on the materials, I'm hoping to use Baltic Birch ply.

Lock miter in BB plywood, or lapped miter?

I really wasn't familar with a lapped miter joint, so I had to watch it being formed. I am now convinced it would be better than the lock miter joint which is tedious to set up and it's self squaring under clamping pressure:



The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #9 of 10 Old 09-28-2020, 08:47 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
I really wasn't familar with a lapped miter joint, so I had to watch it being formed. I am now convinced it would be better than the lock miter joint which is tedious to set up and it's self squaring under clamping pressure:


Infinity Cutting Tools - Lapped Miter Router Bit Set - YouTube
i ordered this yesterday. the cabinet will be completely stand alone, so end grain would have been visable from both sides. needed a strong miter joint.
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post #10 of 10 Old 09-29-2020, 11:42 AM
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Plywood and crosscut router bits don't play well together.

Set a marking gauge and pre-scribe a line will eliminate tear out.

A good option for mitered plywood is a spline.

Robert
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