Loose M&T

I built an adjustable fixture that allows me to make very accurate loose mortise and tenon joints. I have been using tenons fabricated from hardwood, either Oak or Poplar. Needless to say, it requires some work to achieve the 1/4 inch thickness required for a tight joint. I am now considering using 1/4 inch tempered hardboard. It is stable, strong and has a uniform thickness. Any have experience with this technique??
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hardboard has no strength. It will help with alignment but can easily snap under stress.
If this is something you do a lot you should plane or wide belt or drum sand a bunch of real stock to the proper thickness. The other much more common option is to use plywood. Maybe baltic birch will have consistent enough size or you can adjust the mortise to fit the ply thkns.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Very different physical characteristics there. Much better IMHO to make the tenons from the same wood they will be used to join, so that the tenon expands and contracts at the same rate as the mortises.

"Needless to say"?? Apparently you don't have a thickness planer available to you; with a good thickness planer and a modest amount of practice, achieving any particular thickness is quite easy. You don't even need precision tools to measure very small variations from the desired thickness. If the desired thickness is 1/4", plane four boards to the same thickness, then stack them and measure the combined thickness. If the stack measures 1-1/32", you know each board is 1/128" oversize. If a stack of eight is anywhere between 1-31/32" and 2-1/32" then you know each board is 1/4" +/- about 0.004".

I wouldn't even dream of using hardboard, tempered or otherwise, for floating tenons. The whole point of a mortise-and-tenon joint is its strength, which would be significantly compromised by the substitution of hardboard for solid wood. Additionally, the very fact that it *is* stable is another reason it's unsuitable for this purpose. The wood that you're joining will expand and contract with changing humidity, while the hardboard will not, thus compromising the glue joint. Best practice is to make the loose tenons from the same wood that they are used to join.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Doug Miller wrote:

I think it would depend on what you are building. If you are building heavy furniture or something similar, listen to all of the other posters. If you are making something light like picture frames, then try the hardboard. I have been using the Lee Valley hardboard biscuits for years to make picture frames and have never had a failure.
I also have a very quick system for cutting tenon slots. I use a router with a slot cutting blade, a router table and two fences. The main fence is positioned so the blade is correctly positioned for the joint. The second fence is positioned loosely on the other side of the piece to be cut (this prevents kickback). ie so the piece being cut is sandwiched between the two fence. The left end slot goes into the blade from the right, the right end goes into the blade from the left. Using this system you can accurately cut the eight slots for a picture frame in about a minute.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

You're right, of course, but I have my doubts that the OP is using 1/4" tenons to build picture frames. <g>
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Buy a 6mm bit, then buy these, http://www.festoolusa.com/products/domino-joining-system/tenons/domino-beech-6x20x40mm-494939.html
Then buy this, http://www.festoolusa.com/products/domino-joining-system/domino-df-500-joining-system-574258.html
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Save the hardboard when you need a nice smooth surface, not for M&T.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Biesemeyer fence, featherboards to run the stock straight. Vernier calipers to mike the test thickness, dial indicator with magnetic base to help tap the fence over as needed. I shoot for an easy 0.005" max slack. Most glues have ample shear strength to make the joint indestructible.

Birch veneer ply will be uniform and a heckuvalot stronger.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.