Before commencing with this tutorial, you need to ensure that you are confident in the basic setup and adjustment of your jointer. Each step should be read through thoroughly and the reasoning behind them understood before considering powering up your jointer.
Jointers excel at producing straight planes on wood. To produce cuts at specific angles requires that a workpiece is presented to the cutters at the correct angle whilst simultaneously maintaining stability on the infeed and outfeed tables. Temporarily adding material to one end of the board as a prop presents a problem - as soon as the workpiece meets the cutter, one of these all-important reference surfaces disappears in a cloud of chips. This drops the cut, leaving both a sniped entry, an incorrectly-cut angle and additional cleaning work. Not to mention it can be unsafe!
The key is to produce an angled reference on the workpiece which rides along the jointer and is not removed until the workpiece is stable across the feed tables. This has been adapted from a common technique employed by furniture makers to taper chair legs. It is especially appropriate for guitar makers on the basis that any tolerances in the initial measurements do not express themselves as any significant tolerance in the final cut.
A small amount of trigonometry is involved here! If you have a particular aversion to mathematics of any sort, please seek the help of a trained scientist or other responsible adult!
Firstly, ensure that your workpiece is squared on all sides and both ends and that these are all jointed flat. An engineer's square is a better tool than a carpenter's square....essential equipment if you have a jointer!
Mark on the face of the blank where you want your cut to start and extend that line over to all sides using your combination square. I didn't do this because the combination square was more than two metres from where I was standing. If there was a cup of coffee next to it, things might have been different.
Here is where our trigonometry work comes in useful. We need to calculate the length of the opposite side from the angle within a right angled triangle.
In this example, this is a 1° angle starting 260mm from the end of the blank. This leaves us with the known values being the angle (θ), the side adjacent to the angle (A) and our unknown value the side opposite to the angle (O). Remembering the mnemonic "Some Old Hippie Caught Another Hippie Trippin' On Acid" (SOH-CAH-TOA) we can see that our sides (O and A) require us to use the TOA part, or:
Tangent (θ) = Opposite / Adjacent
Next we re-arrange this formula to put the unknown on its own, giving us:
Opposite = Adjacent x Tangent (θ)
Plugging in our values we get:
Opposite = 260 x Tan (1)
Opposite = 4,538
Awesome. We have calculated that a 1° angle drops 4,5mm over a distance of 260mm. We can now note that on the end of the blank. The mark is not important; only the value. Also mark down the halfway point between the end of the blank and the start of the angle. This mark does need to be fairly accurate. Although the photo notes "260mm" next to my mark, this was because I wasn't thinking about the clarity of what I wrote due to a lack of coffee. Still, the mark was in the correct place which is the most important thing.
Next, set up your jointer's feed tables to be parallel and joint flat one face of a piece of scrap wood. Then dial in a cutting height exactly half of the height of the mark at the rear of the blank. In this case, 2,25mm. Since tolerances to a hundredth of a mm are impractical, anywhere around 2,2mm and 2,3mm is perfectly acceptable.
To illustrate these looseness of this value's tolerance, setting a cutting depth of 2,5mm would leave you with an angle of 1,1°, or 3,0mm an angle of 1,3°.
Dust your table free of debris and test feed your scrap in a short distance and pull it back out. Measure that the cutting depth is acceptable.
This jointer has a digital readout indicating the cutting depth. I do not trust it. As it turns out, it was over half a mm out. Manually setting the cutting depth is far better! If it's wrong, pass your scrap piece all the way through to flatten it and then try this step again.
Now that your jointer is set up, align your neck blank angle and end down as shown:
Run the blank through the jointer until the cutter reaches the halfway mark made earlier (130mm). Hold the workpiece still and turn the jointer off before removing it. We do not want accidents here.
Now reverse the neck blank so that the small cut you have made is now aligned towards the rear end. Apply pressure at the end so that the blank tips up, pivoting on the end of the cut.
There we have it! Two perfectly angled reference surfaces which will continue to guide the workpiece until the cut surface reaches the outfeed table and becomes stable.
All that remains is to run the blank through the jointer once more. It is important to bear in mind the points to apply pressure whilst performing this final cut. As soon as the cutter reaches the leading fulcrum point (the halfway point) and cuts it away, the face on the outfeed table is now ready to have pressure applied for feeding the cut out. A long push hook board is vital for this procedure to be carried out safely however I couldn't find where it had disappeared to....sorry....
The finished cut:
A very marginal discrepancy existed somewhere in my demonstration piece as the leading edge of the cut erred around 2,0mm or so from the original marked location (cut starts second mark along the edge). Given the acute angle used, this is still an extremely accurate and reliable cut. The end of the blank was perfect, with the cut intersecting the pencil mark exactly.
Although the jointer I used in this demonstration is very large, any jointer that has an infeed table long enough for the final cut will work admirably.
Any comments or questions on this article? Post them below!
How To Cut A Neck Angle On A Jointer by Carl Maltby is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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