T-Track, T-Slot or Micro Jig dovetail

[Matt Schroeder]

What I like about the microjig handscrew clamps in most cases is the sandwich effect of the dovetail portion going under the work and the hold down pushing down against it. This is different than most t-track hold downs where the stress on the track (or the routed t-slot) is offset from the work. On narrow pieces this benefit is limited and there are probably other times that I am forgetting where it was worse rather than better, but most of the time I am comfortable turning the handscrew as much as I feel I need to to hold the work without worrying that I am going to pull out t-track or blow out a t-slot. Also, if a routed dovetail slot is slightly damaged in one area the longer arm of the microjig clamp averages that out--given my luck, that damaged portion is going to be EXACTLY where I need the head of a bolt on a routed t-slot!

One downside I have found is it does seem a little harder to slide the longer dovetail arm of a microjig handscrew clamp in its slot than a smaller bolt head in a t-track or slot. Takes a bit of getting used to, how to hold the clamp to slide it easily. On balance, I prefer the microjig system overall.

Matt

[al ladd]

The dovetail clamps have a large surface area vs. the T Nuts

Interesting--so the advantage is the pressure is spread over the entire sloped surface of the dovetailed edges, rather than being concentrated on the single intersection of the 90 degree surfaces, as in the t-slot? I'd always thought you could get a strong router t-slot in wood by simply burying the bit deeper, but is the dovetail just inherently stronger anyway? The dovetail would be the stronger of this pair?
t-track vsdovetail copy.jpg

[Will Blick]

some great input...

Yes, the sandwich effect is of GREAT benefit, and prob. a key ingredient into MJ premise. That is made obvious by the youtube video provided previously, where the guy finds the breaking point of the MJ clamps... to accomplish this, he must avoid the sandwich effect by creating a gap between the workpiece and the table top....which is unrealistic in the real world in nearly any scenario I can think of. But it demonstrates the need for the sandwich effect, specially with MDF tops.

I have a LOT of 20mm dog hole clamps, mostly Bessey, and they do NOT benefit from the sandwich effect. On my initial MFT tops of 3/4" under heavy pressure, the top would buckle up, not ideal. I later moved to 1" thick MFT tops, by sandwiching two 1/2" tops, then when I ruined the upper top, I would flip em, and use the bottom one on top, held together with a few screws at the ends, to assure perfect hole alignment. The dog holes are drilled with a PARF system while the two tops are secured together to assure perfect hole alignment. I also have Maple supports every 18" running under the tops, to prevent sagging, as the top is large, so not a traditional MFT table.

As for the T Track slot being routed deeper for more meat... I am sure this is helpful, but the T Nut, still only makes contact in a small area, vs. the long dovetail clamps. I would think if the material is hard like Baltic Birch, it wold still suffice considering the clamping pressures to hold a workpiece stable is not that significant in most applications. But the T system does not benefit from the sandwich effect in most cases.

The few dovetail groves I tried, require waxed slots and waxed clamps, to prevent the clamps from binding up when sliding about. I love the dovetail grooves for the side of a work table, to act as vises....better than the side dog holes, which are in fixed positions. The dovetail table shown on the MJ website looks very useful and quite creative! It combines the benefits of the dog holes and the dovetail system. If I were to create a new work holding table today, I would surely build one of these.

https://youtu.be/6J2lygYQFD8?t=28

[Johnny Barr]

I've tried all 3, T Track, T slot and dovetail for years and have never had a problem with strength (damage) from any of them other than T-track lifting if not secured properly particularly with Kreg auto adjust clamps. So some epoxy and screws and there isn't a problem. I don't think strength is an issue at all with any of them.