How do you choose the best domino length?

[smr.111]

I've searched the forum and can't find any relevant information related to this.  I am looking for information on choosing the correct domino length for various applications.  In understand the concept of using a domino thickness that is 1/3 of the material or using multiple dominos in a large joint for increased strength.  I've also read a number of articles on mortise and tenon.  However, the general rule of thumb for length with M&T appears to be simply that the tenon is at least twice as long as it is wide.  We obviously have significantly more options that with the domino system.  What I can't find is any information on when to use a 8mm x 100mm domino vs a 8mm x 40mm domino.  Should I always use the longest domino that will fit in the material?  This would seems unnecessary in many cases, but will this create the greatest strength is solid wood (ie material that is equally as strong as the tenon-not plywood or MDF)?  Any information would be very much appreciated.

 

[Birdhunter]

My thought is that I use the longest tenon I can without it poking out the backside of the piece. I think this spreads any bending, tensile, or torsional loads out over a larger area than a stubby tenon.

 

[clark_fork]

I use Dominos for leg and apron assembly and to maximize the Domino length, I will cut the ends at 45°. I have a jig to cut these safely. Another item to keep in mind is that the mating holes do not have to be the same depth to achieve strength.

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My starting point is this simple guide.

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[wisey]

Hi all, first post I’m not a joiner, just an interested medley who likes to have a go myself, I’m currently making a window sill out of 250x25 MDF the window is a bay window with 2 quite large but joints on a 45 deg angle, I already have a df700 domino and would like some guidance on domino length and size.

Thanks
Andy

 

[JeromeM]

Hi all, first post I’m not a joiner, just an interested medley who likes to have a go myself, I’m currently making a window sill out of 250x25 MDF the window is a bay window with 2 quite large but joints on a 45 deg angle, I already have a df700 domino and would like some guidance on domino length and size.

Thanks
Andy

With MDF I would use a thinner longer domino as the water from the glue will have less chance of telegraphing, also if you are going to sand the surface leave it much longer than you think necessary as otherwise you will find low spots when the glue has completely dried and the paint will show them up.

 

[Birdhunter]

This is a great question.

First rule is to not plow through the backside of the wood. Embarrassing!

Second rule is to leave enough wall above and below the mortise to eliminate blowout when I tap in a glued Domino. Embarrassing!

Third rule...If I’m using a Dominos mainly for alignment as gluing edge grain to edge grain, I’ll use a small Domino (5) and shallow mortise. The shallow mortise saves time and cutter wear. Narrow mortise on one side and wider mortises on the other side allows for minor imperfection in drilling the mortises. I’m a master of imperfection.

Fourth rule... If I’m using a Domino for strength, I’ll use the biggest longest Domino I can without violating the first two rules.

Fifth rule... It’s ok to have different depth mortises on either side as long as the Domino fits.

Sixth rule... It’s ok to trim off a Domino if none of the standard lengths fits.

Last rule....  Always verify the correct plunge depth is set by fully extending the cutter and comparing it to the piece of wood I will be cutting.

Oh yeah, be sure the fence is tightened down before cutting. A staggered row of mortises is embarrassing.

 

[Michael Kellough]

Good job [member=15289]Birdhunter[/member] !

 

[Birdhunter]

Guess how I know all those oops things are embarrassing.

 

[Cheese]

The only thing I'll add to Birdhunter's great list is to also check the cutter width setting before that first plunge. [big grin]

That too is embarrassing.

 

[wisey]

Also may i ask, on the setting of the DF700, you have 2 tolerance settings, basically tight and i think the other setting is supposed to give you a 3 mm of lateral movement, mine with the lateral setting selected the Dominos are that slack they almost fall out ?? am i mistaken or could this be a fault with the machine ?

With the tight setting selected they are nice and tight, but soon as i select the setting that gives a bit of tolerance they are very slack and you can even move the Dominos slightly up and down, this is with both the 12mm bit and the 14mm bit there is no difference !!

Any ideas anybody or is this normal ??

Thanks

Andy.

 

[Birdhunter]

Not normal. There should be lateral play but tight fit up and down. Are you sure you are not letting the machine move during the cut?

 

[wisey]

Hi, thanks for the reply, yes checked that for movement squarnes, I've tried with different size cutters, when on the tight setting its absolutely perfect, just not acceptable, so my supplier is changing the machine, a lady customer service rep at festool told me thats how they should be, you need to use glue she said to get them tight .

thanks

Andy

 

[Michael Kellough]

The lady is wrong. They should be snug between the flat sides. At the narrow setting they should be a little difficult to fit in. Either the Dominos are defective or the machine needs work/replacement.

 

[HarveyWildes]

If you're looking to add strength to the joint, consider making your own wide dominos.  It's not needed for edge jointing applications, but it's a good option for frames and other similar joints.

 

[Birdhunter]

I’m glad for you that you are getting a new machine. I have both the 500 and the 700 and both produce snug tenon fits on any width setting.

I’d love to know why your Domino produced different results on the wide setting.

 

[Cheese]

As both Michael & Birdhunter said, that condition is not normal, there's something awry with your tool.  [smile]

It's also rather disconcerting that the Festool rep said that was normal. [mad]  Was that Festool USA?

 

[wisey]

Hi and thanks for all the replies, like i said in my post im not a joiner but ive messed about with joinery and cabinet making all my life, some people have fast cars i have Festool

The Festool customer service rep was in the UK, she swore blind the Domino's were suppose to be loose on the slacker setting !!

New machine delivered and they are now perfect tight and how they should be, great service by the uk supplier would defo use them again.

Reference to an earlier reply on the thread, is it possible to get none water based wood glue ? if there could be a problem with moisture from the glue affecting the MDF would this not fix the problem ??

thanks

Andy

 

[Kodi Crescent]

Also, make sure your stock is flat and your reference surfaces are the same.  If referencing from the base of the machine, a minor dip in the table or warp in the material can result in the edges not aligning perfectly.

 

[Straightlines]

If you're looking to add strength to the joint, consider making your own wide dominos.  It's not needed for edge jointing applications, but it's a good option for frames and other similar joints.

Actually, and not to be argumentative here, another traditional method is to use multiple tenons (structurally much stronger even with small tenons), and the good news is that the Domino makes this a piece of cake, just offset the cut to the 1/3 line from each face.