AW Extra 7/3/14 – Perfect Edge Joints

Perfect Edge Joints

A 6-step tune-up sets your jointer straight.

By Dave Munkittrick


Jointers are simple machines with few moving parts, but the two beds, the fence and the cutterhead all have to be in alignment for a jointer to function properly. Few things are more frustrating or more common than problems with jointers. This is especially true when you’re trying to get straight, square edges on your boards. I’ve come up with a six-step tune-up that should set your jointer straight. It’s easy to do and will only take an hour or two, depending on how many problems you unearth.

Jointers are supposed to cut straight, square edges, but all too often, they leave a sniped or a bowed edge (see “Common Problems,” page 2). Snipe results whenever the top of the outfeed table dips below the knife’s top cutting arc. A bow cut results whenever the outfeed table rises above the cutting arc. A cutterhead that’s not parallel to the outfeed table, or tables that are not parallel to each other, will make it impossible to get the table height set just right for all fence settings.


Common Problems

Our tune-up will help you identify and correct four common jointer problems:

Problem #1: A table surface that’s not flat.

Problem #2: Tables that are not parallel to each other across their widths.

Problem #3: Tables that are not parallel to each other along their lengths.

Problem #4: A cutterhead that’s not set parallel to the tables.

Click any image to view a larger version.

Common jointer problems result in a sniped or bowed edge. Adjusting the outfeed table height usually cures the problem. However, if both tables and the cutterhead are not in perfect alignment, the problem will return when you move the fence. This tune-up procedure takes care of all the possible misalignments that can cause jointer problems.



The Right Stuff

You will need a few tools to perform this tune-up: A good straightedge, a set of feeler gauges and machinist’s metal shims are must-haves for this job. For some steps, a dial indicator is easier to use than a straightedge.

The straightedge, shims and feeler gauge run about $105 total. The optional dial indicator with a magnetic base and extension arms adds another $40 and is well worth the cost. All these tools can also be used to set and tune-up other shop equipment and to check your own work for flatness (see Sources, below).


A precision straightedge is essential. You can perform all the tune-up steps using this 50" precision straightedge that costs $79. Unlike inexpensive straightedges, this one has a precisionground edge with a tolerance of .003" along its entire length. Such a good straightedge is not cheap, but it’s a good investment for your shop.


A dial indicator with magnetic base and arm can’t be beat for tool setups. A number of these six tune-up procedures are best done using a dial indicator. Like the straightedge, this tool is also useful for other machine setups.


A feeler gauge set is used in tandem with a straightedge to measure very small gaps. If the straightedge reveals a gap, you can measure that gap by finding the feeler gauge that fits under the straightedge.


Metal shims align jointer parts. Variety packs are convenient and easy to use. A strip of aluminum cut from a soda can is a quick substitute for a .005" shim. That coupled with some .001" shim stock should cover all your tune-up needs. Shims can be stacked to create any desired thickness.



Fine Tuning Your Jointer

Step 1: Check For Flat Tables and Fence

Check each table and the fence for flatness (Photo 1). The accuracy of later measurements depends on flat tables. Measure for dips or a droop using the straightedge held parallel to the table bed. Then, hold the straightedge diagonally across the table to check for twist. The good news is that finding twist or dips in the table is highly unlikely. The bad news is that if you do find things out of whack, you can’t do much about it. In extreme cases, a messed-up fence or table may be reground at a machine shop. You’ll have to weigh the cost in time and money against simply buying a new jointer. If your jointer is under warranty, talk to the manufacturer.

Step 2: Align Tables

It’s not unusual for the two tables to be out of parallel across their widths (Photo 2). It’s easiest to check the tables for parallelism with a dial indicator (Photo 3). You can also do the check with a straightedge. Hold the straightedge down on the middle of the infeed table so it extends over the outfeed table. Set the infeed table to the exact same height as the outfeed table. Slide the straightedge over to the fence side of the table and use feeler gauges to check for gaps. Repeat with the straightedge on the user side of the table.

Align your tables by shimming the outfeed table. Loosen the outfeed table’s gib nuts and lift the table so you can insert metal shims on the side of the table that’s low (Photo 4). Shim the outfeed table only because it is moved very little and the shims are less likely to shift during table adjustments.

Recheck the tables and make any necessary shim adjustments until the tables measure in exact alignment.

Step 3: Fix Sagging Tables

Tables can also be out of alignment along their lengths (Photo 5). Use the straightedge to see whether the table end dips below the infeed table (Photo 6). Correct a dip by adding shims to the top or bottom of both gib ways on the outfeed table (Photo 7). Retighten the gib nuts and check the tables again. Make any necessary adjustments until the tables lie in the exact same plane.

Step 4: Level the Cutterhead with the Tables

Now that the tables are parallel to each other along their lengths and widths, it’s time to make sure the cutterhead is parallel to the tables. If the cutterhead is not level with the tables, your cut will be heavier on one side of the table than on the other. Jackscrew cutterheads allow you to set the knives to compensate for this; spring-loaded knives or a segmented carbide insert cutterhead do not. The fix for this problem is so simple that I recommend leveling your cutterhead no matter what type of knife holder you have.

Use a dial indicator or straightedge to check cutterhead alignment (Photo 8). If the cutterhead is off, measure the exact amount on the low side. This equals the size of shim you’ll need to raise the cutterhead (Photos 9 and 10).


Step 5: Set Proper Knife Height

To minimize kickback hazards, jointer knives should not project more than .020" from the cutterhead. (Owners of spring-loaded cutterheads have a knife-setting gauge that automatically sets the proper knife projection.) A potential hazard exists with knives set parallel to the outfeed table: It’s easy to unintentionally set the knives so they project too far.

A dial indicator is the best instrument for checking knife projection (Photo 11), but you can make do with a straightedge and feeler gauge.

Step 6: Set Proper Outfeed Table Height

Your knives should be set so that the very top of the cutting arc, also referred to as top dead center, is the same height as your outfeed table. We used the straightedge to accomplish this task (Photo 12), but a dial indicator is another option. To do this, set the dial indicator on the outfeed table and zero it. Then set the plunger over the cutterhead with the body of the indicator on the outfeed table. Rock the cutterhead back and forth; the indicator should hit zero as its highest mark. Check this at several points along the width of the table. Repeat for all three sets of knives. straightedge no gaps outfeed table knife at top dead center

Edge-joint a couple of boards to test your jointer (Photos 13 and 14). In practice, it often takes a little tweaking of the outfeed table height to get it just right. Often the table ends up set .001 or .002" below the cutterhead. Now your jointer is ready to go and should create perfect edge joints every time.

1. To start your tune-up, check each table for flatness. Lay the straightedge on a table and use the feeler gauge to check for gaps. A gap of .003" or less is acceptable.

2. Infeed and outfeed tables that are not in the same plane across their widths need to be made coplanar. (With any luck, your tables aren’t this bad.)

3. Check the tables for parallelism across their widths. Bridge the dial indicator from the center of the infeed table to the center of the outfeed table and zero it. Slide the indicator across the width of the table to measure any difference in height.

4. Bring the tables into alignment by inserting metal shims on the low side of the outfeed table. Choose a shim thickness equal to the amount your table was off. Loosen the gib nuts and lift the table while you insert the shim or shims. Then retighten the gib nuts.

5. Tables can be out of parallel along their lengths. Typically, the tables sag on the ends. This is especially true on older jointers that have worn gib ways.

6. Check for table sag by holding a straightedge tight against the infeed table. Set the infeed table height so the straightedge just contacts the outfeed table. Then use a feeler gauge to determine the amount of dip or rise in your outfeed table.

7. Correct a sagging table by shimming the bottom end of the two dovetailed gib ways on the outfeed table. A table that dips toward the cutterhead would be shimmed at the top end of the gib ways.


8. Check that the cutterhead is parallel with the tables. Rotate the cutterhead so the knives are below the table. Clamp a guide board parallel to the cutterhead. Set the dial indicator against the guide board so the plunger contacts the cutterhead. Zero your dial indicator; then slide it back and forth.

9. I removed the cutterhead here to illustrate how it is mounted. Two threaded rods attached to pillow blocks run through holes in the base and are held in place by a nut and a washer. Place shims between the pillow block and the jointer bed casting.

10. The cutterhead is easy to shim. Remove the drive belt and loosen the bolts that hold the cutterhead in place. Lift the low end of the cutterhead and insert shims under the pillow block. Then retighten the bolts.

11. Proper knife projection increases jointer safety by limiting the cut’s aggressiveness. Use a dial indicator set to zero on the cutterhead. With your hand on the pulley, rotate the cutterhead backward. As the knife rides under the dial indicator, it should read no more than .020".

12. To set the outfeed table height, place a straightedge on the outfeed table so it projects over the cutterhead. Rotate the cutterhead backward and raise or lower the table until the knife barely kisses the straightedge when it’s at top dead center.

13. Fine-tune the outfeed table height by edge-jointing a couple of boards that are narrower than the fence height and no longer than the infeed table.

14. Put the newly jointed edges together and hold the joint up to a light source. No light leaks indicate a jointer that’s perfectly tuned. If you are getting a snipe at the end of your cut, raise the outfeed table a bit. If the jointer puts a concave edge on your board, lower the table. Repeat the process with the fence set at the far edges of the table. The results should be the same, and that should put a smile on your face.







Note: Product availability and prices are subject to change.

Lee Valley Tools,, 800-871-8158, 50" aluminum straightedge, #05N63.05; Dial indicator and magnetic base and arm, 88N31.20; Feeler gauges, #86K99.01; Brass sampler, 6-1/2" x 6", .001 to .010 thickness, #27K07.50.

This story originally appeared in American Woodworker August 2006, issue #123.

Purchase this back issue.



Loose Tenon Joinery

Loose Tenon Joinery

Rout 4 variations of these super-strong joints with a versatile shop made jig.

By Bill Hylton

I've used a number of different methods to create mortise and tenon joints, but I keep coming back to loose tenons, because they're easy, strong and versatile. Instead of cutting a tenon on one part and a mortise in the other, I rout identical mortises in both parts, and connect them with a fitted strip of wood—a loose tenon. Loose tenon joinery is perfect for casework, tables and doors of all sizes.

The only tools you need to start making loose tenon joints are a plunge router equipped with an edge guide, straight bits designed for plunge cutting and a mortising block—a shopmade jig I've designed that you can make in a day.The mortising block minimizes layout work and allows routing both edge and end mortises from the same router setup.

You can use off-the-shelf bits and just about any plunge router, but a precision edge guide is a must. I use the Micro-Fence edge guide, which I think is the best available (see Sources, below).


The mortising block

This jig holds the workpiece, supports the router and controls its movement (Fig. A, below).The jig consists of the mortising block itself, a top extension, an L-bracket and a clamp board for bench mounting.

The face of the block has dadoes and mounting-bolt holes for the two work holders—horizontal for edge mortising and vertical for end mortising. The router sits on top of the block and overhangs the workpiece.The router's edge guide is housed in a track formed by the L-bracket (Photo, opposite). Adjustable stop blocks set the mortise length.


How the jig works

• The jig's registration line locates the workpiece.

• The jig's L-bracket tracks the router and keeps the mortise aligned with the edges of the workpiece.

• The mortise's width is determined by the bit's diameter.To create mortises wider than the bit, you reposition the fence and make a second pass.

• The mortise's depth is controlled by the router's plunge mechanism.

• The mortise's length is governed by the jig's adjustable stop blocks.

• The mortise's lateral (side-to-side) positioning is controlled by the router's edge guide.


Build the jig

1.Mill stock for the main parts and cut the pieces to final dimensions (Fig. B, below).The mortise block's body and the horizontal work holder must be exactly the same length, because you reference from the ends to rout the vertical keyways.

2. Rout 1/4" deep vertical keyways in the mortising block and the horizontal work holder.

3. Rout single 1/4" deep horizontal keyways in the mortising block and the vertical work holder.The block’s keyhole is stopped.

4. Rout mounting-bolt slots in each work holder, using a plunge router and an edge guide.

5. Plane 1/2" thick stock to fit the work holder keyways. Cut pieces to length to create the keys. Attach them.

6. Clamp the horizontal work holder to the mortising block.Tap a 1/2" brad point drill at both ends of each slot to transfer its location to the block. Remove the work holder and scribe vertical lines on the block through the four points you marked. Clamp on the vertical work holder, mark the slots and scribe a pair of horizontal lines.

7.Drill holes for the work holder mounting bolts at the four points where the horizontal and vertical lines intersect.To secure the 3/8" bolts, I cut threads in the wood itself.To do this, drill the four holes with a 5/16" bit and use a 3/8"-16 tpi tap to cut the threads (see Sources).No cutting fluid is needed; just turn the tap into the hole, then back it out. Alternatively, you can use Tnuts or drive threaded inserts into the body to secure the bolts.

8.Glue and clamp the top extension to the mortising block. Clean off any dried glue after removing the clamps. Then joint the assembly to ensure that its top surface is square to the face.

9. Attach a 3/8" thick wood fence to your router's edge guide.Then size the L-bracket parts to create a groove that will house the fence.The fit should be snug, so the fence slides without any wobble.Glue the L-bracket parts together and install them.

10.Make both stop blocks from one long piece of 5/8" by 2-3/4" stock. Rout the 1/4" deep keyway and two mounting bolt slots. Cut the stops to final length.Make keys and attach them.

11. Rout matching keyways in the top of the mortising block.

12. Set the stops in place on the block and mark locations for mounting bolt holes.Drill and tap the holes for 1/4"-20 tpi bolts.

13. Install toggle clamps on the work holders (see Sources). I installed longer threaded spindles on all the clamps and used a 500-lb.size on the vertical work holder. Be sure to mount the clamps so they don't interfere with the router.

14.Draw a registration line centered on the face and top of the mortising block.

15.Glue on the clamp block.


Create the basic loose tenon joint

1. Lay out an edge mortise (Photo 1). It doesn't have to be elaborate, just lines marking the mortise ends and centerline. Only one line is essential: a centerline across the mortise. This mark aligns with the jig's registration line.

2.Position a test piece on the jig, using the horizontal work holder (Photo 2).

3.Adjust the work holder so the edge of the workpiece is flush with the jig's top. Line up the workpiece centerline with the block's registration line (Photo 3).Adjust the toggle clamps to hold the work securely.

4. Install a bit designed for mortising in the router.Up-spiral bits are popular these plunge cuts, but they're not essential.

5. Install the router on the jig and test-slide the edge guide's wood fence in the L-bracket groove. Apply wax, if necessary.

6. Bottom the bit onto the workpiece. Then move the router to center the bit on the mortise centerline (Photo 4). Lock down the edge guide and set the plunge depth.

7. Install the stop blocks to establish the length of the mortise (Photo 5).

8. Rout the mortise (Photo 6). That's all it takes. As long as the faces of the workpieces are oriented the same way on the jig, all the edge mortises routed with this setup will be the same, regardless of where they fall on the workpiece. Just scribe a centerline across each mortise, and align it with the registration line on the block (Photo 7). If all of the mortises are located in the same place on each workpiece, you don’t even have to mark them. Instead, just fasten a stop on the jig against the end of your test piece and use it to register the workpieces.

9.The only change you have to make to rout the matching end mortises is to switch work holders (Photos 8 and 9).

10.Mill loose tenon stock to complete the joint. First, plane a length of stock to fit the mortises. It should slip in without wiggling or binding. Rip the blank to width, slightly less than the mortises’ length.Next, round the blank’s edges to match the mortises. Then cut individual loose tenons from the blank.


Reinforce a cope and stick joint

Routed cope and stick joints look great, but their stub tenon construction may not be suitable for large cabinet doors. Adding loose tenons strengthens these joints.

Rout the mortises before you rout the cope and stick profiles, so you don't have to work around stub tenons on the ends of the rails. (The mortises won't interfere when you rout the profiles.) Center the mortises across the thickness of the workpiece.They probably won’t align with the stub tenons produced by the cope cuts, but that doesn’t matter, because everything will be hidden in the assembled joint.

Start with the end mortises.Offset them away from the rails' inner edges, so the panel groove won't cut into the mortises (Photos 12, 13 and 14). Locate the edge mortises in the stiles according to the rails' offset end mortises.

Be mindful of the rails' offset mortises when you rout the profile and panel grooves. It's all too easy to rout the wrong edge.


Twin mortise joints

In post-and-rail constructions made using thick stock, you can make stronger joints by doubling the loose tenons.The inside mortises on the posts of these corner joints will intersect, so they must be shorter; their tenons are mitered.The outside post mortises are deeper, so their tenons can be longer.The rail mortises can all be the same depth.

Orient the workpieces with their outside faces against the mortising block. Set up and rout the outside mortises.You'll have to change work holders when you switch from routing edge to end mortises. Reposition the bit and rout the inside mortises (Photo 15). Reduce the final plunge depth when you rout these mortises in the posts.


Loose tenon table joint

In this construction, the apron usually is inset from the leg faces.My approach is to set up for the mortises in the legs (Photos 16 and 17).To rout the aprons, I use double-faced tape to install a shim equal in thickness to the inset between the apron and the block (Photo 18).Be sure to install the aprons outside-face-in before routing their mortises.


(Note: Product availability and costs are subject to change since original publication date.)

Micro Fence,, 800-480-6427, Micro Fence Edge Guide.

Buy Destaco,, 800-560-9292, De-Sta-Co Horizontal Toggle Clamps, #215U; #225U (500 lb. cap.).

Tap and Die sets are available at hardware stores and home centers.

Fig. A: Loose Tenon Mortising Jig

Despite their name, loose tenon joints fit as precisely as traditional mortise and tenon joints, and are just as strong.

Fig. B: Dimensions

Mortising Block

Stop Block

Horizontal Work Holder

Vertical Work Holder

This story originally appeared in American Woodworker April/May 2009, issue #141.

April/May 2009, issue #141

Purchase this back issue.

Click any image to view a larger version.

Adapt your router to the jig by installing a fence on the edge guide that fits the slot formed by the jig's L-bracket.This keeps the bit aligned as the router slides back and forth. To move the bit laterally, you simply adjust the edge guide.

The Basic Loose Tenon Joint

1. Lay out one edge mortise on a test piece to set up the router and jig.The mortise centerline is used for positioning the workpiece on the mortising block—it's the only layout mark required for every mortise.

2. Set up the jig to rout the edge mortises. Install the horizontal work holder and position the test workpiece so its edge is flush with the top of the jig.Then tighten the bolts.

3. Align the work's mortise centerline with the jig's registration line.Then lock the test piece in position.

4. Install the router and adjust the edge guide to center the bit on the work.Then adjust the router's plunge-depth stop to the desired mortise depth.

5. Install the stop blocks. Move the router to one end of the mortise and align the bit's edge with the layout mark. Slide the stop against the router and tighten the bolt. Set the second stop the same way.

6. Rout the mortise with a series of shallow cuts. Plunge the bit about 1/8", feed quickly to the far stop, retract the bit, return to the starting position and go again.

7. Mark your stocks' outside faces and always orient the same face against the mortising block when you rout. Once all the edge mortises are routed, switch to the vertical work holder to rout the end mortises.

8. To mount the vertical holder, clamp a workpiece with its mortise centerline aligned with the jig's registration line. Slide the holder against the workpiece and tighten the bolts.

9. Install the router and rout the end mortise. The length, width, depth and placement of the mortise don't change when you switch work holders.

10. Size a loose tenon blank. Plane a length of stock to fit the mortises. It should slip in without wiggling or binding. Rip the blank to width, slightly less than the mortises' length.

11. Round the tenon blank's edges to match the mortises.Then use a crosscut sled to cut individual loose tenons from the blank.

Reinforce a Cope and Stick Joint

12. This variation requires offsetting the rail mortises, so they don't interfere with the panel groove. Lay out the offset mortise on a pre-routed rail.Then use this rail to position the vertical work holder.

13. Rout the mortises before you rout the cope and stick profiles.Your initial set-up positions the mortise in only one end of each rail, because both ends of the rail must be routed with the same face against the block.

14. To position the mortise in the other end, install a shim equal to the panel groove's depth between the work stop and the rail.

Twin Mortise Joints

15. Rout twin mortises in two steps. Lay out and rout the first mortises in both the edges and ends. Reposition the bit for the second mortises and go again. Always orient the same face against the fence.

Table Joint


16. With table joints, the aprons are usually inset from the legs.Start by mortising the legs. Clamp the leg with its outside faces against the block and the work-holder.Position the bit, set the stops and rout the mortise.

17. Flip and rotate the leg to rout the second mortise. It doesn't matter that the leg now extends in the opposite direction, because the mortises are centered on the jig's registration line.

18. To inset the aprons from the legs, you offset their mortises by the amount of the inset. Attaching a shim of the desired thickness to the jig automatically offsets the mortise correctly.