25
Chapter 4Frame Mortise & Tenon Jig User Guide
4-21
If the joint is too loose, turn the guide pin down
➀
. If
the joint is too tight, turn the guide pin up
➁
. For how much,
see 4-22. Rout a complete new joint. Note: It’s possible to adjust the
guide pin and rout only one new mortise or tenon part and get a good fit,
but on a project this would mean routing each part at different settings.
Establish ideal pin height for both mortise and tenon at one pin setting.
21
4-22 How much adjustment is required? One eighth of a
turn of the guidepin knob will change the joint glue-line fit by
0.001"[0,025mm]
➀
, i.e. turn one-eighth up; the bit will reduce
the tenon thickness by 0.001"[0,025mm] (half of that per side
➁
)
and increase the mortise width by the same amount
➂
.
Dimensions and angles shown here are exaggerated.
1
1
2
3
4-23 The FMT Pro can provide this accuracy for settings but
remember, you’re working with wood and a hand-held router,
with lots of movement tolerances; it’s not a computer-controlled
milling machine. Nevertheless, the FMT Pro will allow you to do
very precise and consistent work.
4-24 If you have a dial or digital calliper (every shop should have
one) you can literally measure the tenon and mortise and adjust
accordingly.
Every 0.002"[0,05mm] of difference in mortise to tenon size (that’s
.001"[0,025mm] on the glue line) should require one eighth of a
turn; down to tighten, up to loosen.
4-25 Generally we have found the best fit differential to be
0.005"[0,13mm] “loose”. Basically, the dry joint should “push”
together fairly easily, but not fall apart under its own weight. If a
mallet is needed, it’s too tight.
1
4-26 Once you have established the guide pin setting for a specific
bit/guide combination, record the setting.
For example:
5
⁄16"x1
1
⁄2"[8x35mm] “up 1
3
⁄4 turns”. Using the same
bit and guide next time, use the recorded setting for a good fit
first time. Note: As with all joinery, different wood species do not
necessarily rout precisely to the same fit.
■
MORTISE & TENON ROUTING PROCEDURES
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