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LMI Plate Joining Jig

Jointing plates - whether it is a decorative top for a solidbody or the soundboard/back for an acoustic - are essential jobs in a guitar workshop. Up until now I have tackled these jobs by clamping a beam to my table top, laying the plate halves on the bench, placing a small baton under the joint and clamping a second beam to snug things up, then apply glue, remove the baton and thus creating enough clamping pressure. This is tedious and time consuming. Enter the LMI plate jointing jig!

The jig comes unassembled and is made out of sturdy plywood. The parts have a snug fit although there are some parts that don't align 100%, whist the two ”flat beds” aren't completely flat if a straightedge is used to check them. There were also minor issues with the wedges being a bit rough and getting stuck when inserted between the rope and the plate. Nothing that a bit of sanding couldn't fix, but for this price it shouldn't be required. Will this affect the performance of the jig? Let's see later on. It is useful to note that the wedges have an "up" and a "down" side. The edge of the wedge is slightly bevelled to ease the insertion, something I didn't notice at first. Maybe that is mentioned in on the accompanying DVD. I write ”maybe” as the DVD is of the DVD-R type with a printed label; the label is so thick I cannot insert it in the disc slot of my Mac! After that part failing I didn't dare insert it in the home entertainment system's BluRay player, so I actually have no idea what’s on the DVD.

On contacting LMI about the DVD issue I received a very nice letter from the Sales Manager stating that I was the first customer complaining about this issue, however they would look into it to see if there is a better solution. That is how a customer feedback should be handled!

The DVD issue aside, the jig is pretty self-explanatory. If you have a look at the online videos at www.lmii.com you should be fine if you happen to have issues with the DVD. I also had a problem with one of the screws getting jammed in the nut. After a bit of effort to get it out, I lightly filed the faulty thread away and started over. No biggie, but again something to watch out for.


In Use

After you have assembled the jig, usage is pretty straightforward. Place the bottom part of the jig on you bench, apply glue on the jointed board's edges and lay them on the jig. Place the top part on the top and make a repeated figure eight around the top/bottom part of the jig's ”legs” and lock them firmly in the quick-lock fixture. Inserting the wedges applies additional pressure to clamp the joint shut, whilst also aligning the plates laterally. If needed, the wedges can be given a light tap with a hammer to adjust pressure on the joint. Note the holes in the wedges were made by myself as I was afraid I needed them to help retract the wedges. Something that I discovered was totally unnecessary when I did my tests.



The use of the tool is really a no-brainer. If my explaining it in written form leaves you slightly puzzled, this video at LMI's webpage demonstrates it perfectly so you should be fine:


Talking about no-brainer, this is the bevel on the wedges that I didn't notice. Inserting then the right way up makes things a bit smoother!



An added benefit with this jig - compared to my old method - is that as soon as the plates are in the jig, the entire jig can be picked up and put aside, thus freeing up room on the bench.



The Result

The result of the joint is of cause totally dependent on the efforts you put into jointing the plate edges beforehand. No jig can make up for sloppy craftsmanship there! Or can it? I decided to put the jig to some serious testing....I intentionally left a slight gap between the plates in one of my tests. The edges were perfectly squared off, the ends met each other perfectly but at the middle I had something like a ¼ mm gap. This particular plate was a maple top with plenty of extra width that I could be cut up and started over should the experiment not turn out well.

I glued up the plate with that gap still there to see if the jig had enough clamping power to close the gap, and it did. I had to tap the wedges somewhat with a hammer to see a nice glue squeezeout in the middle but the gap was indeed closed. The result was confirmed after the glue dried and I had the glue squeeze out scraped away. Really impressive. The lateral alignment of the plates was close too, but not entirely perfect. I'd say it was on par with my old method. So it handles hard wood tops very well. Lets see how it handles soft wood tops like an acoustic soundboard. Or wait! Let's make up a really rough test. In one of my wood shipments the supplier had used a cracked spruce top as packing material. So I had an un-jointed piece of wood (OK, with the original crack on both sides...), missing a few fibres here and there and its all quite soft. Could I use the jig to glue those scrap pieces together without even jointing them? Well, yes and no. The joint is slightly sub standard with tiny gaps were some fibres were missing but that’s not really the point. I could get away with using it for something simple of for someone having his or her first go at an acoustic guitar. But the main point is that was able to force the plates together hard enough to close almost all gaps from the missing fibres, and crush a few still attached but misaligned fibres to conform to the rest of the wood, thereby making it possible to get a half-decent joint strong enough to hold up to generous bending, twisting and pulling from yours truly, today's product tester. One of my main reasons for doing this peculiar test is to see how the ropes pushing the plates together would affect the outside edges of the top when applying high pressure on a sub-standard joint in softwood. There were some marks from the ropes but really not too bad. On the contrary; it was totally acceptable when bearing in mind the rough time I gave the top!



The jig passed both my tests with flying colours. Since then I have used it on a few more tops, among them the birch top in the pictures. In use it is simple and almost foolproof. The result is impressive, especially with the maple top that got clamped together in spite of the slight gap. The delivered item however, leaves a few things to wish for:

  • General fit and finish. For the price of this jig, the cut surfaces of the plywood should really be kissed with a little sandpaper before shipping.
  • The faulty screw that jammed in the nut. Really? It would be more favourable to increase the price of the jig by a dollar or two purely to include consistent hardware.
  • The DVD issue. Simple on-body printing is a relatively accessible option and better than thick/heavy labels.
  • The alignment of the parts could be a tad better, however I'm being a little picky. The jig works exactly as intended despite any of this.

So in the end it is a pricey but very well-functioning tool with maybe a few quirks that really shouldn't be there. If LMI had those issued sorted out (and maybe the price reduced to, say 99$) it would get my 100% recommendation. If I had to rate it, I'd say 3.5 out of 5 “stars”. For the price of the jig, it should be perfect out of the box.

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User Feedback



Can't understand for the life of me why would someone pay more than... say... 30 bucks for this.

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It depends on what the jig provides as a return. If you're making a living producing guitars, jigs like this are a quick-fire solution. Even though it is simple enough for an experienced woodworker to produce themselves, buying a ready-made jig is usually quicker and cheaper than making it yourself. A home gamer or weekend enthusiast wouldn't see the financial return, making it look like an overly-expensive jig to buy.

Thirty dollars is a bit of a stretch of the imagination Nicholas; 3/4" plywood doesn't come cheaply. I could maybe build this for about that by using scrap plywood from my workplace, however most people would have to buy a part sheet which immediately hits that budget. I hope this helps illustrate the value a bit better, and when it might or might not be a good purchase for different people.

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