This is just a simple idea I was thinking about regarding non-structural hidden connections. Overall the connections seem relatively stout as the screw head has a reasonable amount of plastic locked below it inside the track but the PLA they were made with is too slick and the joint has a tendency to slide no matter how tight the fit is. As soon as I get a heated bed working I will make another attempt in ABS. Sketchup file attached below.
Great job Rick, these are cool! The idea of making a simple connection like this of course has always been a want, and would be great for making quick builds but the hardest part is going to be coming up with a way to be able to lock them or tighten this kind of connection once it's in place. This may be an idea to present to the Openbuilds community of engineering minds here to see what we can come up with
There are commercial fitting available that attach extrusions in the same fashion. The key to tightening the fittings after installation is drilling clearance holes to access the bolts after assembly. In the example above, the holes would be drilled horizontally, through the center of the extrusion on the left. If you locate the holes precisely, they only needs to be large enough for your tool, which should leave plenty of metal to maintain structural integrity. This is obviously easiest when only drilling through a single thickness of extrusion, but I guess two or more is theoretically possible with a little patience and right drill press setup.
@Buckethead, there's really no need for commercial fasteners. An M5 screw with a precision shim fitted into the slot will do the trick. This procedure is shown numerous times throughout the forum. The problem comes from the length of that access hole when you are working with 60 and 80mm wide sections. Avoiding drilling that hole was what I was hoping to resolve here. As a side note, I haven't yet resolved the slippage problem but I have found a way to put it to good advantage. It makes for a nifty glide system on an adjustable router template. And it can be built for a small fraction of the $360 that Festool wants for a similar system. I will post the build as soon as I can get the clamps worked out.
I wasn't saying to use commercial fittings, just using them as an example of how you might tighten your fittings after assembly. It seems to me that the only way to solve your slippage problem for the original fitting above is to drill access holes and tighten the fittings after the fact. It's just simple physics... if the fittings are loose enough to insert in the first place, then they will be loose enough to move around. You could stop the slippage by expanding your idea, and making the fitting longer so you can add a locking screw that would be accessible once the rails are joined. A recess for the screw head, and a short screw should allow everything to be contained within the t-track for a flush installation. This solution works best for rails joined in a T, like your router jig, because you could lock both sides. It might not be as effective for an L because you can only lock the inside. Still, it would probably work well enough for assemblies without a lot of load on the connection.
80/20 have a fastening system that goes into the slot of it's extrusions. IIRC, you tighten it up using a standard Allen key in the slot. Kind of limited movements, but all you need is 1/6th of a turn. Problem is, it requires you to drill a large hole in the slot of one of the pieces for the round cam head of the fastener. MG
Yeah, what he said... Much easier than drilling a hole all the way through the extrusion, but you would almost have to have a milling machine to do the counterbore. MG
Yeah, I was thinking about that too. Problem is, hole saws are very inaccurate, and you would have the pilot hole going into the extrusion. You might be able to do it with a Forstner bit if you could clamp the extrusion in a drill press vice or something... Anyway, these are only available for 80/20 extrusions, and would not be compatible with V-Slot. This was just a suggestion to show what's out there. Hmmm. there are also Bed Bolts, I wonder if they could be adapted... MG
