I would like to build some stretcher frames for painting. They use a complex miter joint at the corners. It looks like the joint would require a combination of bandsaw cutting and table saw cutting to high precision. It can best be described as a 45 degree section on the two top and bottom parts with two center parts making a lap joint.
This is typically done on pine with a thickness of 1" to 1.5".
Can anyone give me advice on the effective way to cut the joint?
Dick
Richard Cline wrote in news:dcline- snipped-for-privacy@news.silcom.com:
Did you mean stock thickness or stock width? 1.5" is about the thickness of a modern tubafor, and would make for a sturdy, but heavy stretcher frame.
Is there a particular reason you couldn't use a lap or bridle joint, and then reinforce the back with a triangular plate of 1/4" ply?
The reason for the lap miter is to make it somewhat self aligning, I believe. More complexity than you likely want or need.
Patriarch
You would be better off stretching/restretching the canvas with the proper pliers.
Miter sled/tenoning jig for the tablesaw will do 'em, but IIRC it's six passes.
Big sliding MDF jig on the tablesaw. It's a pain to make, but once you have it you can bang out frames at great speed.
So are you looking at stretchers like these?
Dick,
If I'm imagining the joint correctly, it sounds like a mitered-corner lap joint and is desciribed in detail in Yeung Chan's book, "Classic Joints with Power Tools" on page 96. He says it is commonly used in frames and, though it looks complex, it is fairly simple to do on the table saw if you follow the right sequence (which he shows you).
I was just looking at this book for ideas about how to approach a miterd slip joint I need to do. He describes one on page 116 that uses two through tenons. I'm going to vary it a little and use one tenon but I think his approach will work just as well. Hope this helps.
The plan would be to have a 1/4 inch tennon on a 1x3 inch slat/rail. Mark the outside face of each rail. Start with a 1/4 inch dado blade. Using a tennonning jig cut a slot with one side of the blade alligned with the center of the rail. Test by turning the rail around in the jig and making another pass. Adjust the jig until a very thin shaving in the center is removed on the second pass. this will allow for a left and right miter joint. cut all the lefts on one end and rights on the other by facing the outside face to the left on one end and to the right on the other. trim the 1/4 shoulder at a 45 degree on all pieces. trim the 1/2 inch shoulder to 1/4 inch thickness at a 45 degrees to match the already trimmed shoulder. The thickness of the triangular tab will determine the tightness of the joint. I call these mortice and tennon miter joints, not sure if its the right name. Jack
That's done with a lock miter bit for your router or shaper.
Actually, I'd better clarify that last bit. I was looking at an ad in Wood that was offering a bit called a lock miter, and it had a profile almost identical to what you are describing. You'd have to use something sort of like a tenoning jig to hold the board upright as you cut, but it would be quicker than messing around with any kind of saw, IMO.
Yes, that appears to be the type of stretcher I want. Unfortunately, the photograph has the interesting joint at the far edge of the photo so the detail is not visible. This is claimed to have a couple desirable features. It is self aligning. If the canvas sags, it is possible to install small wedges in the joint to tighten the canvas.
Dick
No "if" about it - those wedges are an essential part of assembling the frame. Note also that the frame won't stay assembled unless it has canvas on it - there's nothing stopping the bars from falling outwards.
The frame bar joints can be thought of as four parallel "sections". The outer two are a plain miter. The inner two are complementary halves of a half lap joint. However the inner edge isn't cut square across the bar, they're cut at an angle (about 1 in 8, or maybe 1 in 6 for cheap canvas) and some way back from where they'd touch the other bar. The gap is filled up by the wedges. Wedges are 1/4 the thickness of the bars, and you always put them in in pairs.
I use two tablesaw jigs to make stretchers. Both are MDF "cradles", sliding in the table's slots. They have a flat base, a sloping face at right angles to the sawblade, some buttresses beneath and some stops and guides.
Stock is prepared to a standard thickness of 3/4". Your jigs care about the thickness, and the blade height cares about the width. You really need a sawblade that cuts a kerf accurately 1/4 of the stock thickness, which might be hard to find.
First step is to crosscut to length, using my everyday crosscut sled.
Second step is to cut the half-laps. Because these are handed, you only need one jig. Make sure you cut the inside edge (always against the face of the sled) on the same side at both ends! This jig has the sloping face at the wedge angle, about 1 in 8 short of vertical (83°). Two vertical (sic) rails form the lateral guides. The bottom of these rails has a lengthwise stop across them (this gets sawn in two on the first use). Side to side positioning is such that the kerf goes through the second quarter of the stock. If your sawblade kerf is too narrow, space the rails apart (by the difference between 1/4 stock thickness and the actual kerf) and use a couple of passes, with the stock resting against each rail in turn.
Third step is to cut the mitres, in two passes. This uses a similar sled, but with a 45° face and a pair of stop rails that are spaced far enough apart to allow two positions for the stock - each cuts one side. The end stop is the same as before.
For safety, put some toggle clamps onto the sleds. You're going to be waving some long timber around and it's only supported at one end. It's also useful to make a dedicated setting block for the sawblade height. To keep the stock as low as possible for all passes, I saw at two different blade heights.
Wedges are made from beech, bandsawn to thickness and quickly hand planed to smooth them a little (optional). I saw them into a wedge shape with a sliding jig on the bandsaw table, then stack them into a pile and trim the ends by hand, eye and bandsaw.
Insert wedges with a hammer, not a mallet. You get better feedback as to the sound changing if something bottoms. I like a square-headed Japanese hammer for this job.
Thanks for the detailed information. It looks like I need to fashion a couple jigs and get serious.
Dick
Unfortunately, with the 1/2 laps, one part you might need to adjust is covered by canvas, and a devil to adjust with wedges. This joint takes a tenon jig and miter jig to do well, but adjusts a lot easier. Still, the big stretcher pliers and a stapler do a credible job, though not necessarily on the first attempt, unfortunately
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