Sharpening broad point bits



Brad point bits are designed specifically to cut clean, accurate holes in wood. Like any other cutting tool, they work best when properly sharpened. Although the “business” end of a brad point bit may look a little complicated, it’s easy to sharpen once you know how it works.

COMBINATION BIT Basically, a brad point bit combines the best features of three different drill bits. It’s like a hybrid of a spade bit, a Forstner bit, and a twist bit, see box below.

POINT. Like a spade bit, there’s a sharp, tapered point for centering the bit on the workpiece. This prevents the bit from “wandering" off the centerpoint as you start the hole.

LIFTERS. After the point enters the Wood, two cutting edges or “lifters” take over. Like the cutting edges on a Forstner bit, the lifters act like a pair of revolving chisels that shear off and lift out thin wood shavings.

SPURS. In addition to the lifters, some brad point bits also have two knife-edged “spurs.” To produce a cleaner hole, these spurs score the wood fibers around the perimeter of the hole.

FLUTES. As the hole is drilled, spiral flutes in the bit pull up and eject the chips from the hole like an auger. The basic idea is the same as a twist bit. Only the flutes are ground at a steeper angle so they eject the chips faster.



SHARPENING

There’s really nothing mysterious about sharpening a brad point bit. In fact, you can restore a sharp edge in less time than it takes to drill a hole with a dull bit. All it takes is a few strokes from a file.

CLAMPING JIG. The first step is to provide a way to hold the bit securely in place while you’re sharpening it. To do this, I use a simple clamping jig. This is just a scrap block of wood (I used a 2x4)

SHARPEN LIFTERS. With the bit extending about 1" above the block, the next step is to sharpen the litters (cutting edges). The secret is to create a clean, sharp line along the edge. This requires filing the angled “flat” on the end of the bit, see Fig.1.



FILING ANGLE. To determine the correct filing angle, just rest the face of the file on the flat.
Once you’ve “found” the angle, push the file across the flat in a continuous motion. The trick is to file the flat without nicking the brad point or the spur.
To keep from rounding over the lifter, raise the file off the bit at the end of each stroke. Then find the angle again and repeat the filing process until the surface is shiny and flat.

The important thing is not to get carried away. The idea is to hone the cutting edge. Not reshape the bit. I usually keep track of the number of strokes I make on each lifter. This ensures that an equal amount of material is removed off each edge and that both lifters end up doing the same amount of work.

SPURS. If you have a brad point bit with spurs, the next step is to “dress” the inside of the spurs, see Fig.2. Here again, find the angle with the file. Only this time, tilt the file so the face is against the inside of the spur.
Now take one or two strokes until the surface is shiny and flat. A light touch here keeps from damaging the lifters that you’ve just sharpened. Note: Don’t file the outside of the spurs or you’ll reduce the cutting diameter of the bit.



 POINT. At this point, you may be tempted to sharpen the point. But it's easy to remove more from one side than the other. Since this throws the bit off center, I leave the Point alone.



Tips for cutting tenons


A tenon has two essential parts - the cheeks and the shoulders, see Fig.1.

CHEERS. The purpose of the cheeks is to provide a gluing surface against the sides of a mortise (a square hole or slot cut in the adjoining piece to accept the tenon).
When you cut the cheeks, you also define the thickness of the tenon. This is the critical dimension for a strong glue joint — the tenon must be thick enough to fit snugly into the mortise. But not so tight that it squeezes the glue out of the joint.

SHOULDERS. The other important parts of a tenon are the shoulders. The shoulders are designed to do a couple of things.
First, they cover up any small gaps around the mortise. And they contribute to the mechanical strength of the joint.
In its simplest form a tenon has two long shoulders which are cut on the faces of the workpiece, see Fig.1.
These shoulders define the length of the tenon and determine how deep the tenon slides into the mortise.
In addition, many woodworkers also cut short shoulders on the edge of the workpiece, see Fig.1. These short shoulders create resistance to any up and down movement of the tenoned piece.

CUTTING A TENON. There are two basic methods for cutting a tenon on the table saw — the single-pass method and the multiple-pass method, see Fig.2 and Fig.3.

SINGLE-PASS. With the single pass method, the workpiece is held vertically in a jig and passes through the saw blade to cut one cheek at a time, refer to Fig.2.
Then the workpiece is taken out of the jig to make the shoulder cuts.
By cutting tenons like this, it’s easy to produce a very smooth cheek — which makes an excellent gluing surface.

MULTIPLE-PASS. When you use the multiple-pass method on the other hand, the workpiece is laid flat on the table saw, see Fig.3. The tenon is then cut by making a series of passes over a saw blade (or dado blade).
Since the first cut is made at the shoulder line, both the shoulder and the thickness of the tenon are established with one cut.
This method requires very little set-up time and is a quick way to cut tenons, especially if you’re cutting just a few. The only problem is it can leave a rough glue surface on the cheeks.

Preparation and lay out
Even before you lay out the nine of the tenon there are a couple of things you an do to ensure a good fit.

STOCK PREPARATION. First, square up the ends and edges of all the pieces. This will prevent gaps around the shoulders of adjoining pieces.
Second. if you are cutting tenons of the same size on several pieces, make sure all the pieces are identical in thickness otherwise the thickness of the tenons will vary according to the thickness of each piece.

LAY OUT. After the stock is prepared, the next step is to lay out the tenons. 
Note: 1 always cut the mortise first, then size the tenon to fit. This way I can use the mortise as a template, see step-by-Step drawings.
ShopTip: I like to use a knife to transfer dimension because the sharp lines are more precise than a pencil line.

TRANSFER DIMENSIONS. To transfer the dimensions of the mortise to the workpiece. Start by marking the thickness of the tenon, see Step1. Then mark the width of the tenon. see Step 2.
Finally, mark the length of the tenon on the workpiece and check the depth of the mortise to make sure it will fit see step 3 and step 4.






Test fit
The secret to getting a tenon to fit snugly in a mortise is to make trial cuts on a test piece. (Note: The test
piece must be exactly the same thickness as the workpiece.)

SINGLE-PASS. To do this with the single-pass method, make the cheek cuts. Then, since the waste isn’t removed until the shoulders are cut, saw off a comer of each waste piece to check the fit, see Fig.1.

 MULTIPLE PASS. If you’re using the multiple-pass method, take a few passes to create a "mini" tenon at the end, see Fig.2.


Shoulder cuts
If the workpieces have tenons on both ends (such as the rails for a frame), the distance between the shoulders is critical. If they’re not the same on every workpiece, the frame won’t be square.

STOP BLOCK. One way to cut accurate shoulders is to add a long fence to the miter gauge and use a stop block, see Fig.1. The stop positions the workpiece precisely for every cut. The fence prevents chip-out, and reduces kickback.

DONG WORKPIECE. If the Workpiece is long, clamp a stop block to the rip fence, see Fig.2. Then, butt the workpiece against the stop block and clamp it in place before making the cut.

Duplicate tenons
Here’s a quick tip when you need to cut several identical pieces with tenons on the ends (such as rails for a set of frames).

WIDE BLANK. Instead of cutting the pieces individually, start with a wide blank and cut tenons on the whole width of the blank, see drawing.

RIP STRIPS. Now just rip the blank into strips to produce pieces with identical tenons.
Stepped shoulders

A common problem when cutting tenons is that the shoulders come out uneven, see photo. This is usually caused by a rip fence that isn't 90° to the table, see Fig.1.


 As you cut the long shoulders, the piece contacts the fence at the bottom, see Fig.1. But when you flip the piece on edge to cut the short shoulders, it contacts the fence higher up, see Fig.2. This pushes the piece away from the blade creating a "stepped" shoulder.

SOLUTIONS. The best way to solve this is to adjust the rip fence on your saw.
Another Way is to clamp a block to the fence, see Fig.3. This doesn't eliminate the problem, but it does minimize it.

Undercutting

The saw blade often leaves a "ridge" between the cheek and shoulder, see photo. This prevents the shoulder from fitting tight against the mating workpiece.

UNDERCUT TENON. One way to get around this is to undercut the tenon. I do this by making the shoulder cuts slightly deeper (1/32") than the cheek cuts, see Fig.1.


SHOULDERS. Another Way is to undercut the inside corner of the shoulders with a chisel, see Fig.2. Just pare away a small amount of end grain leaving a 1/16" wide border.

To do this, start by pushing the chisel straight down alongside the tenon, see Fig.2. Do this all the way around.
Then, tip the chisel at an angle to remove the waste around the shoulder of the tenon, see Fig.3.

CHAMFER ENDS. Finally, pare a slight chamfer on the ends of your tenons, see Fig.3.

Using The Tenoning Jig



Step 1: Adjust Blade Height.
First, lay out the tenon on the workpiece. Then butt the workpiece up against the back stop and clamp it in place with the ho/d-down bar. Next, adjust the height of the blade for desired depth of cut (length of tenon).


Step 2: Adjust Back Stop.
Now you can adjust the back stop. To do this, slide the tenoning jig so the back stop is over the blade. Then lower the back stop until it just touches the saw blade at its highest point.


Step 3: Se! Stop for Inside Cut.
To set the out for the inside cheek, slide the platform so the blade aligns with the inside layout line. Then thread the left coupling nut against stop block and tighten the wing nut.




Step 4: Setstop tor Outside Cut.
Now, move the platform so the blade aligns with the layout line for the other cheek. Then adjust the right coupling nut, tighten the wing nut, and make a test cut. To complete the tenon, remove the workpiece and make the shoulder cuts.




Using The Drill Press table

It only takes a few minutes to attach the tilting table to the drill press. But before you do, you need to align the table.
The idea here is to orient the table to an “imaginary” center-line on your drill press, see Step1 and Step3.
After the table is aligned, a corresponding centerline is drawn down the middle of the insert, see Step4. This makes it easy to reposition after raising or lowering the height of the table.
Now all that’s required is to set the table to the desired angle and square the fence to the edge of the top, see Step5.

Step 1: After loosening the table clamp, center the hole in the table on a bit chucked in the drill press. Then retighten the clamp. 


Step 2: Next, set the tilting table on the drill press table and attach it loosely with carriage bolts, washers, and T-knobs.

Step 3: Now gently twist the tilting table until the insert is centered on the column of the drill press.
Then tighten the knobs.

Step 4: After adjusting the height of the metal drill press table, simply line the bit up with a centerline drawn on the insert.

Step 5: To avoid drilling compound angle ho/es, square the fence to the edge ofthe table before tightening the clamps.

Locking the fence on the top of the table helps hold the workpiece in place when drilling angled holes.

 When drilling long pieces, the table can be turned 90°.
To prevent the workpiece from sliding, clamp it to the fence.

When the insert gets chewed up after drilling many holes, just remove the old insert and screw on a new one.

TILTING DRILL PRESS TABLE

Shop-Build Clamps


 
No matter how many clamps you have, there’s always a project that requires a few more. But rather than buy more clamps, I decided to build my own.
One is a fast-action clamp for light jobs, see top photo. The other is a bar clamp designed for gluing up wide panels, see bottom photo.