AfriCart – a handcart for Africa

ED302 – design & technology

02.3 Research – Joints

Once I had decided to use wood to construct the cart I then needed to decide on a method of joining it together. Gluing would not be appropriate and neither would using nails or nuts and bolts and so traditional joinery was the solution I decided on.

Practising Mortice & Tenon Joints and Drawboring

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Tenon is shown flush with the face of the board (Mortice)

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Tenon is shown through the face of the board (Mortice)

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Hole drilled through both mortice and tenon – slightly offset in the tenon.

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Pin is ready to be driven through mortice and tenon to give a permanent joint

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Siting pins in preparation for “driving” through.

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Pins were originally externally pinned – this was not a neat solution and the pins could be easily damaged.

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Pining from the inside is neater and they are less liable to damage, note the clamps that allow the pins to be driven in before the tension is released.

Most of this following information is verbatim from online resources and is reproduced here for reference purposes:

Mortice & Tenon Joints

Rules for Dimension

The thickness of the tenon should be around one third of the thickness of the stile, but should be set finally to match the width of the nearest available size of chisel. The width of the tenon should not exceed five times its own thickness, which in turn will determine whether a single or double tenon is used. But if the joint is positioned at the top of the stile, it is usual to divide the tenon width into three parts two for the tenon and one- for the haunch (fig. A). Where the frame of which the joint is a part is to take a panel of some sort and is grooved, the haunch forms part of this. Otherwise, it is customary to make a groove to match a secret haunch (fig. 13 below).

180px-mt_klA: This more complicated haunched stub joint is at the top of the stile. If you get confused when marking out, shade in the waste areas in pencil.

b180px-mt_jl1B: A marked out plain through mortise and tenon joint ready to be cut. The lines marking the mortise and corresponding tenon width are made with a mortise gauge.

c180px-mt_ilC: Initial marking out on both the stiles and rails is best done with the relevant pieces of timber cramped together. Mark the waste first, then the rail width.

Where the rail is wide (over about 75 mm) it is usual to employ a double tenon. In this case, you can either divide the rail width by four and take each tenon width as one quarter (fig. G) or divide it by three and make the distance between tenon centres one third of the rail width.

gmtg_doublehaunchedsG

If you are making a stub tenon joint, the depth of the mortise should exceed the length of the tenon by 2 mm.

The gap allows for excess glue that might otherwise force the joint apart as soon as it has been assembled. When you are cutting the mortise for a stub tenon, make sure that there is at least 4.5 mm of wood between it and the outer edge of the stile.

When marking and cutting a mortise at the end of a stile, it is customary to leave excess waste material known as a horn between 25 mm and 35 mm is usual on a standard sized door frame.

The horn helps stop the stile from splitting as the mortise is cut and also protects the frame in transit to its final position, where the waste is trimmed off.

Marking Up a Simple Frame

If you are making a framework that incorporates joints at the ends of stiles, do not forget to allow for the extra length taken up by the horns when you compile your cutting list. Rail lengths for a framework are normally taken as the overall width of the frame, allowing you plenty of waste material. But if you are using through mortise and tenon joints, add on 12 mm to the overall frame width, this gives you 6 mm waste on each end to be removed when the joint is finally ‘cleaned up’.

With your timber to hand, test each piece for true and mark on face sides and face edges (see measuring & marking). Lay the pieces out as they will appear in the finished frame, face edges inner­most and face sides uppermost. Designate and mark the stiles ‘left’ and ‘right’, and the rails ‘top’ and ‘bottom’. You can also mark the joints A-A, B-B and so on, though the marks should be on waste wood that will be removed later.

Next, place the stiles side by side on the bench, face sides uppermost and face edges outwards, and cramp them together with a small G cramp. Remember to place off cuts between the jaws of the cramp and the work piece to protect the latter from becoming bruised (fig. C). With a try square, marking knife and rule, mark off one waste end or horn, whichever is appropriate on both pieces. Follow by marking the finished lengths of the stiles. The material left represents either waste or another horn.

Your next job is to mark the positions of the mortises and, if you are making a wedged joint, the ‘wedge room’ on either side of them. Again, use the try square, marking knife and rule, but score deeply only those areas that are to be cut. Mark very fine lines on the rest of the timber. If you are making a through tenon joint, separate the stiles and mark around them individually. Start at the face edge and work around the timber so as to end up, at the edge below it. Make fine lines at each edge of the work piece to enable you to continue around it without having to score across the whole surface. When you have finished marking the stiles, cramp the rails in the same way and mark off the overall lengths. Do not forget to add an extra 12 mm waste if you are making through mortise and tenon joints. This will be planed off when the joint is assembled.

Mark the lengths of the tenons as described above, together with the haunches where necessary (figs C and A above). Finally, separate the rails and continue the lines right around each work piece.

Marking The Mortises

1180px-mt_1l1. To mark out a tenon, the mortise gauge must be set to the nearest convenient chisel size. Adjust the pin spacing as necessary.

2180px-mt_2l2. To find the middle of a piece of timber with a mortise gauge, try it from both sides until you get the pin marks to match up.

3180px-mt_3l3. After you have marked the tenon on the rail and mortise on the stile, reset the gauge and mark out the tenon width.

4180px-mt_4l4. Use a conventional gauge to mark out where the haunch will be cut. Make sure that you have set it to the correct width.

At this stage, you are ready to mark the widths of the mortises on each stile. By far the easiest way of doing this is with a mortise gauge (fig. 1), a tool similar to a marking gauge but with an adjustable scribing pin in addition to the standard fixed one. You are well advised to go to the trouble of buying or borrowing a mortise gauge, rather than trying to ‘make do’ with existing tools.

Start by releasing the set screw on the stock and adjusting the distance between the pins to match the width of the chisel you are using to cut the mortise out. Next, you must adjust the stock so that the distance between it and the moveable pin allows you to centre the pins on the timber.

To check this, place the stem of the gauge flat on the work piece with the stock face to the face side, then roll the gauge until the pins make indentations in the surface. Repeat the operation from the side opposite the face side. If the two sets of marks co­incide, the pins are centred and you can tighten the stock. If they do not, adjust the stock until they do.

With the pins centred and the stock back against the face side, roll the gauge away from you to mark the mortise widths on the stiles (fig. 2). Keeping the gauge on the same setting, mark around the rail ends to give you the necessary width of the tenons.

If shoulders or haunches are in­cluded in the joints, reset the gauge to the appropriate dimensions and mark them out with the stock against the face edge (fig. 3). Use an ordinary marking gauge to mark the depth of the haunch to be cut across the end of the stile (fig. 4).

If you must use an ordinary marking gauge instead of a mortise gauge, always work from the same face side and edge resetting the gauge for each mark you make.

Cutting The Mortises

Briefly, the procedure for chiselling out a simple mortise (fig. H) is as follows:

h180px-mt_hlH

  • Cramp the work piece securely to a solid part of the bench.
  • Drive the chisel into the marked out mortise to dislodge a deep wedge of waste. Use three separate strokes of the chisel.
  • Work in a series of small chops from the centre of the mortise to one end, removing waste as you go.
  • Turn the chisel around and work back to the other end in the same way.
  • For a stub (blind) mortise, wrap a piece of tape around the chisel blade to give you the required depth. Continue removing waste in the same way then trim all sides.
  • For a through mortise, continue chiselling until you get half way through the wood then turn the work­ piece over and restart the mortise from the other side.

5180px-mt_5l5. The saw cuts for the haunch groove are best made with a dovetail saw, but if you do not have one, use an ordinary tenon saw.

6180px-mt_6l6. After you have made the saw cuts, chisel out the waste wood in the groove with an appropriately sized bevel edged chisel.

7180px-mt_7l7. The easiest way to start off large mortises is to drill a series of holes within the confines of the marking outlines on the stile.

8180px-mt_8l8. Afterwards, remove the rest of the waste wood with a mortise chisel, held as shown and used in the correct sequence.

Where necessary, the ‘wedge room’ outside the mortise must also be chiselled.
Line up your chisel on the appropriate line with the bevel point­ing towards the centre of the mortise.
Chop downwards at an angle of about 85° to finish the wedge room 3-5 mm from the end of the mortise.
For a haunch groove, you need to make two saw cuts: one to the waste sides and one to the depth of the groove (fig. 5).
You can use a tenon saw (hacksaw) for these, though if you have one, a dovetail saw is easier to manage.
Once you have made the cuts, remove the waste with a suitably sized bevel edged chisel (fig. 6).
When cutting large (over 12 mm wide) through mortises, you can save yourself a great deal of hard work by drilling a series of overlapping holes before you start chiselling.
The bit should be slightly smaller than the width of the mortise (fig. 7).To avoid splintering the wood, drill through from one side until the tip of the bit just breaks the surface of the other.
At this point turn the work piece over and finish the holes from the reverse side. Use wide and narrow mortise chisels or heavy firmer chisels to remove the rest of the waste.

Cutting the Tenons

The procedure for cutting a simple tenon is the same as that for cutting the pin in a halving joint.

Make the longitudinal cuts first, then the cross cuts, cutting to the waste side of the line at all times (figs 9 to 12). Afterwards, clean up the tenons with a bevel-edged chisel.

Where a rail is too long to place vertically in the vice, arrange it at an angle, parallel to the bench and firmly clamped.

Many craftsmen prefer this set up for all tenon cutting, so it is worth trying in any case.

9180px-mt_9l9. On large section timbers, use a panel saw or crosscut saw to make cuts with the grain. Make sure that the timber is well supported.

10180px-mt_10l10. Crosscutting, such as cutting ‘ away the shoulders around the tenon can be done with a dovetail or tenon saw and a bench hook.

11180px-mt_11l11. Make angled cuts with the work piece once more secured in the vice. Here, the secret haunching above the tenon is being cutaway.

12180px-mt_12l12. Take extra care when you cut out the final pieces of waste. Even at this stage, a slip can still ruin the finished joint.

13180px-mt_13l13. The finished rail, showing the sloped secret haunch that will become invisible when inserted into its matching slot on the stile.

14180px-mt_14l14. When making a double joint, use a coping saw to cut away the waste between tenons. Take care not to stray outside the marked lines.

15180px-mt_15l15. Assembly of all mortise and tenon joints is made easier if you first bevel away the edges of the waste on the tenons with a sharp chisel.

Haunched tenon:

Make the longitu­dinal cuts as normal, but remember that one will be shorter than the other to allow for the haunch itself. After­wards, cut the haunch, the cheeks and finally the shoulders.

Double tenon:

To remove the space between double tenons, first make the longitudinal cuts. Remove the waste with a coping saw (fig. 14), then saw off the cheeks and the shoulders. As with all tenons, clean up the finished cuts with a chisel.

Assembling Non-Wedged Joints

  • When you have cut all the joints, assemble the frame in a dry run (without glue) to check the fit.
  • The joints should require no more than light tapping with a ham­mer and an off cut of timber (to protect the work) to get them to interlock.
  • If greater force is needed, dismantle the frame and make small adjust­ments.
  • While the frame is together, set out whatever cramps are necessary and cramp up the frame without adhesive.
  • Check that it is square by measuring the diagonals, which should be equal in length.
  • Tidy up the inside surfaces of the frame with a finely set plane and glass paper.
  • You can, if you wish, apply a finish to the inside edges of the frame timbers at this stage.
  • But mask off the mating surfaces of the joints first to keep them clean for when you apply the glue.
  • Finally, glue and sash cramp the joints, using off cuts of timber to protect the work pieces.
  • Wipe off any excess adhesive while it is still wet.

Wedged Joints

16180px-mt_16l16. On a through wedged joint, the wedges are tapped in as far as they will go then the waste on the tenon is trimmed off.

  • Cut wedges for the joints from off cuts of waste wood.
  • Do this as carefully as possible, since you cannot test them in a dry run with the tenon in place.
  • Make adjustments to the widths of the wedges where necessary, then glue and cramp up the assembly.
  • In the case of a through wedged joint, drive the wedges in once the tenon is in place in its mortise (fig. 16).

Finishing

When the joints are thoroughly dry, remove the cramps. Cut off all the waste horns, pieces of wedge, through tenon ends with a fine saw, cutting no closer than 1 mm to the work. Afterwards, use a finely set plane and glass paper on a sanding block to complete the finish.

However, after speaking with a master woodworker, David Taylor of Brighton, I discovered Drawboring:

Drawboring is a technique that greatly strengthens a mortise-and-tenon joint, transforming it from a joint that relies on glue adhesion into a joint that has a permanent and mechanical interlock. In essence, you bore a hole through both walls of your mortise. Then you bore a separate hole through the tenon, but this hole is closer to the shoulder of the tenon. Then you assemble the joint and drive a stout peg through the offset holes. The peg draws the joint tight. Drawboring offers several advantages compared to a standard glued mortise and tenon:

  • The joint will remain tight. A common problem with mortise-and-tenon joints is that the joint can open up and develop an ugly gap at the shoulder. Sometimes this is caused by the wood shrinking as it reaches equilibrium with a new environment (such as your living room with its forced-air heat). Sometimes this gap is caused by simple seasonal expansion and contraction, especially with woods that tend to move a lot, such as fl at-sawn oak. The peg in a drawbored joint keeps the tenon in tension against the mortise during almost any shrinkage.

  • The joint can be assembled without clamps. Drawboring is excellent for unusual clamping situations. Driving the peg through the joint closes it and clamps are generally not needed.  Chairmakers use drawboring to join odd-shaped pieces at odd angles. It’s also an excellent technique when your clamps aren’t long enough. Or when you don’t have enough clamps. Drawboring also allows you to assemble a project one piece at a time if need be.

  • The joint can be assembled without glue. There is good evidence that drawboring allowed early joiners to assemble their wares without any glue. This is handy today when you’re joining resinous woods (such as teak) that resist modern glues or when you’re assembling joints that will be exposed to the weather, which will allow water to get into them and destroy the adhesive.

  • The joint doesn’t have to be perfect. The mechanical interlock of drawboring means that your tenon’s cheeks don’t have to have a piston fit with your mortise’s walls. In fact, you might be surprised at how sloppy the joint can be and still be tight after hundreds of years. Drawboring requires you to be careful only when fitting the tenon’s shoulder against your mortised piece. The other parts of the joint are not as important. And while I never argue against doing a good job, drawboring ensures that every joint (even the less-than-perfect ones) can be tight for many lifetimes. For this reason, I think drawboring is an excellent basic skill for beginning woodworkers.

So why has drawboring become an almost-lost art? It’s a good question, and one that I cannot fully answer. I suspect that modern glues and machine-made joinery made the technique less necessary, particularly for manufactured furniture. Drawboring does require several extra steps, and the benefits of it – particularly the long-term durability of the joint – is not something that is apparent to a customer.

Another reason the technique has fallen out of favor, I suspect, is that manufacturers have stopped making drawbore pins. These tapered steel tools allow you to temporarily assemble the joint to check the fit and to ease the path that the wooden peg will later follow. You can drawbore without drawbore pins by relying on the peg (and luck) alone. But once you use a proper set of drawbore pins, you will wonder why they are not in every tool catalog. Fortunately, you can make your own set of drawbore pins inexpensively.

Drawboring Basics

Joint Details

I have drawbored many joints during the last five years or so and have found the methods described here to be highly effective. My method is based on historical descriptions of the process from the 17th century and my own work.

The first detail to tend to is the size and location of the hole through the mortise. I have found that a 1/4″-diameter hole is good for cabinet work. For larger-scale work workbenches, doors and windows for homes) a 3⁄8 “-diameter hole is better because the peg is stouter. In general, place the hole 3⁄8 ” from the opening of the mortise in furniture work and 1 ⁄ 2 ” in larger work. Make the hole as deep as you can. Usually this requires boring it through the entire assembly, though the hole can be stopped in thick stock. The goal is to ensure that the un-tapered part of the peg passes into the other wall of the mortise.

Historically, many of the drawbore pins I’ve encountered are a diameter that’s best suited for a 3 ⁄ 8 “-diameter hole and peg. Entryway doors and large windows are appropriate for this larger hole and peg. I have encountered (and own) a set of old pins that work with a 1⁄ 4 “-diameter hole, however, so this approach is historically accurate.

The next thing to consider is how much to offset the hole in the tenon. The bigger the offset, the sounder the joint, but the bigger the risk that you’ll destroy the tenon or peg during assembly. The traditional joiner was advised to offset the holes by the width of a shilling, according to Joseph Moxon’s “Mechanick Exercises,” a 17thcentury
how-to book on woodworking. I had difficulty locating a shilling from the middle to late 17th century (I did try), but according to one knowledgeable collector of English coins, a 17thcentury shilling would be about 1⁄ 16 ” thick.

An offset of 1⁄16 ” will indeed almost always work and is easy to assemble.  But I’ve found that it’s sometimes not enough to get the job done. Some of the joints I assembled with this small offset were just a bit wiggly.  For furniture-scale work, I prefer a 3⁄32 ” offset.  For big-scale work, I’ll push that offset to almost 1⁄ 8 ” if the parts of the joint are large and the wood is a tough species, such as ash or elm. Experience will be your guide.  Begin with small offsets in a sample joint and gradually increase them. You’ll know when you’ve found the sweet spot.

I sawed apart a completed drawbored joint to show how the oak peg bends through the offset hole.  This was a 3/32″ offset in ash.

Marking the offset on the tenon must be done with a bit of care because small changes can make a significant difference and cause the tenon to split in fragile woods, such as cherry. If you mark the offset with a slightly dull pencil, it can shift your mark by 1⁄ 32 ” or so. I recommend you use a sharp mechanical pencil or (even better) a knife.

The shape of the peg is important, too. I whittle mine so the last 1/2 ” tapers to an 1⁄8 ” tip. In almost all cases, I use straight-grained white oak for my pegs. It must be completely dry; wet pegs will shrink in time and allow the joint to loosen up. Typically I’ll split out my pegs from some dry oak using a pocketknife and mallet. This is called “riving,” and it is a technique used by chairmakers to produce durable chair parts. Wood that is shaped by riving is stronger because it splits along the wood’s grain lines. Sawing cuts across the grain lines, which can create a more fragile peg in some cases.

I then whittle the pegs round or roughly octagonal. Another option is to pound them through a steel plate with the correct-size hole bored in it. When pressed for time, I’ll use dowel stock, which I have found to be satisfactory as long as I choose dowels with straight grain.

When you knock the peg home, you’ll sometimes create a small gap between the hole and the peg as the peg leans heavily into one side of the mortise as it makes its twisty path through your joint. If this gap is unsightly, try a different strategy on your next joint. Whittle your pegs slightly larger in diameter and switch to an octagonal
shape. Again, a bit of practice in a couple sample joints will help you get it right.

Despite everything I know about drawboring, I still glue most of my joints and even coat the peg with glue before driving it in. It cannot hurt. But I do take great satisfaction in knowing that when that modern glue has given up, the peg will still keep everything in place so the joint will be just as tight as the day I made it.

Written by Mr. Elphick

April 10, 2009 at 12:01 am

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