Domino Frustrations

[greg mann]

A second, related issue is one that I haven't seen mentioned in the Forum previously. I created a jig to allow me to quickly make the double-wide mortises. Basically, it consists of two parallel blocks that serve as stops for the sides of the machine, spaced to provide the correct mortise width. Others have posted similar jigs. The success of this design assumes two critical design characteristics: 1) that the cutter is centered horizontally in the machine; 2) that the base of the machine is square (i.e., that the sides are perpendicular to the face). I'm not sure if the cutter on my machine is centered, because the base is so far out of square that I can't cut a reliable test mortise to check for center. When I set the face of the machine against a work piece, placed in the jig and set perpendicular to the side blocks, the machine doesn't rest square in the jig. I checked the base with a square and found that it is a couple of degrees off. The only way I can think of to compensate for this is to make my jig intentionally out of square the same amount. I'm working on that, but it seems like a pretty crude design flaw for such an expensive piece of equipment.
Sorry for the lengthy dissertation. Thanks for allowing me to vent.

You are assuming the sides are machined square to the bottom and face. They are not. They are not even machined. The reasonl you see this as a design flaw is because you want to use the sides for location and the engineers did not anticipate this type of use. How do I know they are not square? Because I bought Rick's accessory fence and there are little plates designed to permanently capture the location of the plate by bearing against the sides. When I pushed them in place I saw they were not even. When I looked closer I relized these surfaces were left as cast. This does not cause a problem in the manner of their use with Rick's accessory because you can make the plates conform. I had even considered taking the base to work and cutting the sides square but have not done so. And, since they are not square, there is no way the path of the cutter can be exactly in the center of the sides. To use the tool in the manner it was designed to be used it is not necessary to have the sides square and the cutter path centered. If you want to use the sides to register the tool I suggest you start by making sure you are bearing against the face of your work with the face of the tool and pick a single point for registration on either side of the tool somewhere within the area where the shallow dovetails for the outriggers are machined. I believe your accuracy will improve dramatically.

The squareness of the fence is easy to adjust. I have not detected a sagging problem but gravity is not your friend Perhaps a few ounces of lift while plunging may help but I think I would be doubly sure I have the fence adjusted first. Parallelism of the fence to the cutter path and slipping of the fence can be fixed by skuffing up (slightly) the mating surfaces that need to grab each other and/or repositioning the lever to get a bit more travel. I also use a finger and my thumb and treat the lever more like I would a wing nut. this will help keep you from biasing the fence. HTH

 

[vlahtein]

That said the Domino is a very precise tool, even a small user error can cause a problem with alignment and this is most of the problem.

Most of my "user errors" have been in preparing of the pieces to be joined. You really have to have nice clean flat surfaces to reference from, if you you want excellent joints. Domino machine seem to have a tendency to "amplify" all kind of errors in: use (referencing, plunging, holding...), work piece (flatness, squareness and straightness) and even its own (squareness of the fence ...). I mean that minor errors seem to cause surprisingly bad joint quality. The problems are also dependent on each other, for example work piece errors makes it difficult to align the machine.   

By the way, last summer I used the biggest (sipo) dominoes in an outdoor project. Joining two-by-fours that are far from flat and straight in any direction really made me wonder from where to reference. There are some (hidden;-) unused mortises, but in general the result was nice and strong and did not take much time to make.   

 

[Shutterstile]

First, let me say thanks to everyone who offered advice. You've given me some good ideas to try.

kfitzsimons, while you should certainly consider all of this valuable information before making a purchase, please be aware that my experience involves an atypical use of the tool. As others have pointed out, it does take a bit of practice to get it right. And there are some fairly sensitive adjustments. But as long as you intend to use the Festool Dominos in the recommended manner, most of the issues I've been talking about won't affect you. It's a good tool and the hands-down fastest way I've found to make mortise and tenon joints.

greg mann, I realize the sides aren't machined; and that I'm using the tool in a way that was not intended by the manufacturer. But still. If you were going to go to the trouble of making a mold for any piece of a high end product (assuming you don't work for Steel City) wouldn't you take the time to make it square? When Levi's makes a pair of pants with a wavy stitch, they sell it at a fraction of the cost as blemished. They still function perfectly well, and most people would never notice the difference. But it's a matter of pride.

vlahtein, I think you've really hit on the heart of the matter. I've made thousands of mortise and tenon joints using all kinds of methods over the years. I've never had another one as bad as the very first Domino joint I attempted. After a few tries, I thought about returning the tool. But then I started making my own, oversized tenons and experimenting with some of the adjustment tricks that have been discussed here. I really feel like the problems can be overcome with a combination of experimentation and creative workarounds. If you haven't tried it, I encourage you to create your own 10mm tenons and cut a double-wide mortise in a piece of 5/4 stock. You won't believe how substantial the joint is compared to the largest Dominos.

 

[greg mann]

greg mann, I realize the sides aren't machined; and that I'm using the tool in a way that was not intended by the manufacturer. But still. If you were going to go to the trouble of making a mold for any piece of a high end product (assuming you don't work for Steel City) wouldn't you take the time to make it square? When Levi's makes a pair of pants with a wavy stitch, they sell it at a fraction of the cost as blemished. They still function perfectly well, and most people would never notice the difference. But it's a matter of pride.

I understand your point of view. I even wrote that I have considered machining the sides myself, and will certainly do that if I perceive it adding value to the tool. (And while I am at it, I will try to make sure I do so in a manner that will center the tool path, something I would probably not have thought about without your input. Thank You.) Where we differ is whether it is a lack of quality  to have left it unmachined. Quality is ultimately decided by the customer. AFAIK, you are the only person who has expressed dissatisfaction with the fact the side were not machined square and symmetrical to the cutter path and, AFAIK, I am the only person who has considered machining them. I just don't see it as a quality issue because they have no impact on design intent.

I think an appropriate analogy would be where someone modifies a car to do something the manufacturer had not intended it for, such as road rallying or drag racing. It may be perfectly okay to do that; heaven knows it happens all the time, but no one thinks the OEM should make every sedan capable of 8 second quarter miles (well almost no one  :)

The issues of joint alignment quality also are magnified by the size of the joint relative to the size of the reference surfaces. I applaud you for the creative uses you are putting the tool to. You are finding some of its limitations and in the process of doing so you may make the tool better than it is right now.

 

[Rick Christopherson]

greg mann, I realize the sides aren't machined; and that I'm using the tool in a way that was not intended by the manufacturer. But still. If you were going to go to the trouble of making a mold for any piece of a high end product (assuming you don't work for Steel City) wouldn't you take the time to make it square?

Without being a manufacturing engineer, I can understand you thinking this, but if you were a manufacturing engineer, you would know that the casting process is very imprecise, especially depending on the type of casting. No aspect of a cast component is considered correct unless it has been machined in a separate operation. That is why my jig uses adjustable centering plates, because as an engineer, I knew from first glance that these unmachined surfaces will vary from machine to machine solely due to the casting process. These surfaces were never intended to be reference edges. Those aspects of the casting that are registration surfaces, including the bottom stainless steel plate mount, are machined surfaces.

If all surfaces of a component needed to be registration surfaces, then you would not go through the huge expense of developing the tooling necessary to make a casting, but would instead mill the entire component from a single billet. In reality, only some surfaces and features are registration features, and that is why it is a cast component with machined features.