Bench Apron Dovetails

Re: Bench Apron Dovetails

ThomD

>I have an upstairs in my shop, so I do run the long segments up between the floor. There is also my rear deck in good weather. But typically I would do this on hoeses, like ripping a board, just bend over it. Or do the cuts with outboard support on a bandsaw. Doubtless many forests could be leveled to make many jigs.

I had a maple base all planed for my last bench, but I got both of my legs broken real bad, after finishing the top, and couldn't stand for long for years. I really like the LV cast iron stuff so I bought their bench legs. I found them flexible, and so I have replaced them with a tresle base.

Like you I used a longer stretcher. It was a big stick. The way I handled it was I made a jig in the drill press out of 6/4 that was drilled with 13 mm holes the correct spacing. This was screwed to the end of the stretcher, bits were inserted to transfer center marks the end of the beam. The jig was removed. a 3/4" spade bit was used to drill in 3 or four inches into the endgrain. The spade was my last choice, but the only tool that would make the cut in my 3/8" drill. These holes aren't hyper critical for accuracy.

Next you place the beam vertical, and as nearly fil the holes as you believe is required to receive a 1/2" threaded stud (cut from rods that come with the legs). put tape on the bottom of the jig, and just enoguht tape on the stud so it holds in the 13mm holes. wax the taped bits. Now rescrew the jig to the beam end. The result after the glue dried is two "hardware bonded" studs. This is pretty much the strongest way of attaching hardware to wood, is used in racing boat applications and such. It's fast, and accuracy is established in lay-out and at the drill press on the jig, otherwise it is a no brainer.

Any small amount of epoxy overflow when you dunk the studs can be spread over the endgrain.

I used this technique instead of clunky captured nuts everywhere, makes assembly and disassembly much easier.

Re: Bench Apron Dovetails

Clay C in Miami

>Thom, thanks for this, it sounds great. But, I am struggling to understand the last full paragraph of it, involving the tape (and wax). I'm not clear on what the tape is doing, or where it is placed.

I assume that the jig is re-placed at the end of the process, so that that it maintains the hardware at square to the end of the stretcher. Would you be so kind as to take another pass at getting this concept through my thick skull? Got a drawing?

TIA,

Clay

Re: Bench Apron Dovetails

Joe Rogers, Northern Virginia

>I bet the tape is to prevent the jig from becoming part of the stretcher. If the tape sticks to the epoxy the jig won't. Also the tape helps the studs center into the hole some. This sounds like a very suitable process. Epoxy is stronger than the wood so it should hold up nicely.JR

Re: Bench Apron Dovetails

ThomD

>nailed it in one, Joe.

I used a scrap of 2x2 nominal for my jig. I centermarked the hole locations, and put small holes top and bottom for drywall screws. So this whole unit gets temporarily attached to the end of the beam, and it is during the insertion of this jig with the studs mounted in it that you find out how accurately you estimated the amount of epoxy required. Usualy a little spils out that would adhere the jig to the end of the beam, and the studs to the jig. The beauty is the protruding (protruding from the beam seated in the jig) segment of the studs is wraped in masking tape. This keeps the threads clean, and holds them in the jig, and the fit is tight enough the epoxy can hardly rise into the holes, and you can wax the outside of the tape. The other piece of tape goes on the contact surface of the jig, this can also be lightly waxed since none of this surface will contaminate the work. I reused the jig several times. I don't mask the end of the beam because epoxy there, evenly over the end, as long any accumulation is whiped off, stabilizes the beam for moisture absorbtion. You do need to think what would happen if the epoxy driped over the beam, you need to pre-finish the beam or wrap it's end with tape, preferably both. It would be a bad idea to only partialy coat the beam end since it might cause diff moisture absorbtion. The holes should be filled to the surface, you can add more epoxy after the first bunch dries, though you need to do it right after it is dried to maintian a chemical bond. Some of the epoxy will sink into endgrain so I usually try to saturate that first just pour some in and wait half a minute. There is a powder you can mix with the epoxy to improve structural properties, but it is total overkill for this process.

I mounted studs in my table top ends this way also. I sacred the end, did the jigging, and subsequently cut the tenon that goes into the ends. If you use this for other projects with BIG loads you need an egineer but it is a omonly used process amoung boatbuilders and well proven. NASA contracted wooden windmill blades (the really long thin one one sees in the desert and everywhere else these days.) The biggest of these were 165 feet across, so 2 80'+ props. All that held these on the hubs were a bunch of hardware bonded studs, very strong process.

Epoxy has thousands of pounds shear per square inch. I'm talking boat building grade stuff, like WEST, not five minute. If one really wanted maximum strength one would make the holes much larger, but 4 x 3/4 inch holes have about 9 square inches of surface each, so you are looking at probably 9-20 thousand pounds to pull each out. That's the beauty, they spread the loads over more of the "fragile" wood. If you taped holes for the studs and glued them in you would have much higher point loads and nothing like the strength, plus this approach buffers heat and humindy changes as far as the fastener interface is concerned. They should never cause splits or. And it is a bit of a performance to do compared to just bolting stuff together, but far less trouble than capltured nuts, and stronger also.

Re: Bench Apron Dovetails

Frank Mutchler in Colorado Springs

>Thom, you say you found the LV legs flexible. LV states that the cast iron legs used for workbench bases are more rigid than any of the commonly available European style benches. What type of flex are you talking about?

Re: Bench Apron Dovetails

ThomD

>Flexible when planing in line with the front of the bench, either in the vise or in the dogs. My bench is 8+ feet long, has a 4 inch top, and the base was substantial. It is far too heavy to move across the floor. So when I would push a plane down some wood, the legs bent with that force, and recovered after the stroke. It was never generally loose, just flexible.

There are other problems, it really helps when making a bench if the leg tops are flat, you need to move parts back and forth across the base while making them, and there isn't a level surface to slide things on. You have to build your bench around the 4 contact points, and they aren't all that comvenient. The underside of most benches is not level, so there are some challenges. I found the cast iron pads were too wide for the normal dog spacing (not a biggie). The bench middle is not supported as it is on tresles. you are dialed in on height and width, which is not a good thing.

As mentioned elswhere in this thread, my design was longer than theirs, and my method of attaching studs was better, but who knows, could have been a problem. Though I still believe it was the legs and not the attachment that was giving. I used to do these seminars for LV, and they provided the benches. Unfortunately the benches they provided were with the wooden bases, so I couldn't tell how they work with their benches.

I did think of either building a truss that would ornament the stretcher beam, and triangulate the base, or just add a nearly invisible strand of 1/16" cable or spectra to take the bounce out. What I did was make a new base, and put a double thickness plywood top on the LV base as an auxiliary table.