The Festool KA-UG extensions (left and right hand) will be available in the US shortly, so I thought I'd share how I calibrated the built-in tape measures.
This pictures show calibration of the left-hand extension; the procedure for the right-hand one is pretty much the same, just on the other side of the blade
When I first got my extension, I noticed pretty much straight away that the tapes were slightly out. To be honest it's not that surprising, as it depends to a certain extent on each individual saw:
Firstly, you need to attach the extension to the saw (ensuring the 'V' groove on the saw is free of any debris) and tighten the thumb-turn on the underside to lock it down:
Adjust the leg support screw to get the extension level (obviously if you're using the extension directly onto the floor or a bench, skip this step!):
To check the accuracy of the scale, you need to cut a test piece. For this you can use any material you have lying around (in this case I used a narrow strip of MDF) as long as it is parallel & square, and between about 400 and 1200mm in length.
Step 1: Lay your test piece on the saw and trim the end off to ensure you have a nice clean end cut:
Step 2: Set the end stop to a specific length, just a little shorter than your test piece (in this case, 780mm):
Step 3: Turn your test piece around, and place the cut end against the stop. Clamp the piece down firmly:
Step 4: Cut the piece to length. DO NOT release the clamp!
Step 5: Keeping the test piece clamped down, measure the length of the test piece:
In this case, the actual measurement is 780.5mm, meaning that the UG scale is reading 0.5mm under.
Step 6: Using a 5mm allen key (I used the one from my ETS150 sander) undo the 3 hex-drive machine screws near the thumb-turn:
Don't worry about the steel plate becoming loose at this point - it is held firm by the thumb-turn.
Step 7: Gently
undo the thumb-turn until the aluminium extrusion will 'slide' against the steel piece. Slide it away from the saw approximately 10mm, and re-tighten the thumb-turn:
Step 8: Set the stop to the same measurement you made of the actual length of the test piece (in my case 780.5mm):
Note that to help with setting stops in between the mm marks, you can use the reflections in the polished face of the flag. Here, the reflected mark appears to be equally spaced with the actual marks, meaning that the flag is precisely half-way between the marks:
Step 9: Again, gently undo the thumb-turn, and slide the extrusion back towards the saw, until the stop is against the end of your test piece:
Whilst doing this, ensure that the back edge of the extrusion is up against your test piece by gently squeezing the two together:
Re-tighten the thumb-turn.
Step 10: Use a known straightedge to check that the extrusion is aligned with the fence:
And then re-tighten the three hex screws:
You can now remove your test piece and perform another test-cut (steps 1-5) to double check that the scale is now correctly set!