Domino XL skew, or how I learned to stop worrying and love the tool

[jimpudar]

The Fear

I have had my Domino XL for a little over a month now, and have used it on a couple projects. It definitely has a learning curve, so I wasn't too worried when I wasn't getting perfect results.

However, I noticed there was a fairly reproducible skew (i.e. crooked, not level, not parallel) to my mortises so I started doing a little research here on the forum.

After finding the following threads, I started to worry that this might be a widespread problem:

• https://www.festoolownersgroup.com/festool-tool-problems/tolerances-for-domino-xl-skew/
• https://www.festoolownersgroup.com/festool-tool-problems/new-domino-xl-alignment-issue/
• https://www.festoolownersgroup.com/festool-tool-problems/domino-xl-700-mortise-not-cutting-parallel-to-fence/
• https://www.festoolownersgroup.com/festool-tool-problems/domino-xl-mortise-not-level/

Based on the recommendations in those threads, I decided to start troubleshooting.

Initial Troubleshooting

Lots of people suggested first setting the fence height in the storage position, then once the height is locked down tilting it down to 90 degrees. I tried this, but was still getting the same (fairly) consistently skewed mortises.

The next thing to try seemed to be taking the fence out of the equation and registering directly against the base of the Domino. This is when I started taking some pictures. Here you can see the slight skew to the mortise in this piece of curly maple: the left side is pretty bang on 10mm from the bottom edge of the piece, but the right side is a bit lower at around 9.7mm. It's bad enough that you can easily see it by eye in person.

View attachment 1

When creating this mortise, I had the maple clamped down to my workbench and was putting pressure down and forward on the Domino the entire time. I also made sure to plunge relatively slowly. I was using the 10mm XL cutter with a plunge depth of 25mm.

I started wondering if I could still be the problem somehow. Is my bench not perfectly flat? Was I not putting enough downward pressure on the Domino? Plunging too slowly?

I decided to perform the "mother of all tests" to finally determine once and for all whether my motor was really misaligned to the domino base.

The Mother of All Tests

Here is my test setup. I have my homemade MFT top (created with the excellent Parf system) securely clamped to my 500 lbs workbench using Veritas holdfasts. I can't move the MFT top with a deadblow hammer. On top of the MFT top is a precision granite surface plate, flat to .000025".

View attachment 2

I milled up two pieces of red oak perfectly flat and square.

View attachment 3

I then marked a perpendicular line using my best square and thinnest pencil.

View attachment 4

I then clamped the first board to the granite block using two Festool cam clamps. I verified that I couldn't budge the board.

View attachment 5

Next, I cleaned the bottom of the Domino and registered it against the wood and the granite.

View attachment 6

Finally, I took the plunge. I did so slightly more quickly than I had been doing in my previous tests after reading in the supplementary manual that too slow a plunge could cause mortise skew (although how it could cause this I have absolutely no idea). I also made sure to hold the Domino down against the granite with nearly my entire body weight. The resulting mortise looked very clean and to my eye parallel.

View attachment 7

I repeated the procedure for the other board, and found myself with another perfect looking mortise.

View attachment 8

However, the true test would be to join the boards together and see if they showed the symptoms of skew. I carefully inserted a 10x50mm tenon into the mortises and was amazed to see the boards were joined absolutely perfectly!

View attachment 9

Conclusions

Until I did these tests, I was convinced by my seemingly consistently skewed mortises and by the numerous forum posts that there was something wrong with my Domino and that I would need to send it in for re-alignment. I was especially worried that I, like others in the forum, would have Festool send it right back telling me "nothing is wrong".

Given the consistency of the skew I was seeing and that others have experienced, I have to believe that there is some issue with our plunging technique. I will continue to work on my technique and see if I can get these perfect mortises outside of "laboratory" conditions - I'm sure it's possible now.

Hopefully this post will be useful to somebody. I would appreciate any ideas on how my plunging technique can be improved, and would be happy to run additional tests if they can help somebody out.

 

[Birdhunter]

I hope some smart person can explain why a slow plunge produces a skewed mortise while a fast one does not. I can understand how the large bits on the 700 can produce heavy torque that could cause the mortise to be skewed, but not why plunge speed changes anything. Weird.

I had skewed mortises on my 500, sent to Festool, and it came back perfect. This skewing developed over time and hundreds of mortises.

Thanks for doing the testing.

 

[Bugsysiegals]

I’m one of the ones who’s had trouble with my 700 since day one and thus have only used it to show the skew here on the forum.  I tried to use it on an actual project and it made the pieces misaligned so I’ve not used it since.  I was considering to sell it off and get a 500 but it seems I should test again.

 

[CeeJay]

I hope some smart person can explain why a slow plunge produces a skewed mortise while a fast one does not. I can understand how the large bits on the 700 can produce heavy torque that could cause the mortise to be skewed, but not why plunge speed changes anything. Weird.

I had skewed mortises on my 500, sent to Festool, and it came back perfect. This skewing developed over time and hundreds of mortises.

Thanks for doing the testing.

I guess the rotation speed of the bit is constant. Therefore if you plunge slower, there are more bit rotations occurring during the plunge, hence more total torque applied for any given plunge eg torque/mm plunge? Hence the larger the bit, the slower the plunge, the greater the likelihood of skew?

Sent from my iPhone using Tapatalk

 

[ChuckM]

Not an owner, but I've used the DF700 two times, so not being knowledgeable enough about the skew thing. But proper feeding means not too fast and not too low, which applies to DF500 as well, a machine I constantly use. With the DF500, I find having the best control when the plunging speed is steady and not too fast. If you hear the chatter sound, the feeding is too fast.

We lower the speed when using a large cutter on the drill press, and I don't see why we should increase the plunge speed when using the DF700, compared to the DF500.

 

[jimpudar]

We lower the speed when using a large cutter on the drill press, and I don't see why we should increase the plunge speed when using the DF700, compared to the DF500.

I certainly don't want to give the impression I plunged very quickly - I would guess the whole plunge took three to four seconds on the non-skewed cuts. My previous attempts were more like eight to ten seconds, which I am starting to think is far too slow.

Perhaps my next set of tests will be cutting mortises at different plunge speeds with a timer to see if I can get any kind of consistent differences...

 

[ChuckM]

Got it. 3 - 4 secs makes better sense.

 

[Svar]

If traction produced by the cutter is at play, I think the mortice would be skewed the other way from what shown on the picture. It rotates clockwise, doesn't it? Cutter swings to the right - climbs up, swings to the left - climbs down.

What else matters is how the entire gearbox and pendulum flex when gears meet resistance. That behavior could be complex.