work bench woes

Board stretcher? Coupla thoughts...

Jim Reed @ Tallahassee

>That is a tough problem because the ends get pounded on. My Ulmia has breadboard ends that add about 4" to each end. They are dovetailed on and work well. I would think about adding something like that, or splice something in the center, or learn to live with a short bench. Good luck.

Direct support

Wiley Horne--Glendora, CA

>Les,

I ain't been there before, but experience says that this will never work without direct underneath support. Splines, etc, will do for alignment, but a cantilevered member will not be solid.

IMO, of course.

Wiley

Re: Direct support

les winter

>Thanks, Wiley.

I figure if the top is stiched with steel, it cannot deflect downwards.

You think?

les

Re: work bench woes

ThomD

>The epoxied rods will work. Those are rocking strong connectors. You want to keep them as close to the surface as flattening the top and such will allow. I would want them within 3/8, or a 1/4" of the top after final flattening. The effect on stiffness is to the cube of the distance from the neutral axis. This is why your useful spline has had little effect on stiffness. So for instance, you have 2 inches of displacement from the neutral axis to deal with. If you could get it at 2" vs. the 1" you are contemplating, the stiffening effect would be 8 times greater. So the higher the better. Obviously 2" would have it on the surface, but it demonstrates the stakes.

My preference would be for 3-4 splines of rebar or threaded rod. These are easier for the epoxy to grab onto, longer is better like 16 inches. I assume you will be using some good quality epoxy, as for boatbuilding. You probably need a few splines on the bottom so that when you move it, it doesn't just go "bang" on you some day.

Rely on the glue, for these joints. Do not do something like screwing the flat bar to the bottom of the mortises and them cover them with epoxy. Use some metal the epoxy can interlock with and depend on the epoxy. Also you need the bar to be awash in epoxy with a 1/4" or more all around it or the process is much less effective. So like a 1/2" rebar in a 1" x 1" minimum slot. A 1" bar in a 1" slot will quite likely split away from the wood.

Another option if you have epoxy is to saw across the top at the joint, to a depth of 3/4'-1". then taper this slot out to either side. You need an 8-1 ratio to each side, so 12" overall for a 3/4" cut. You then fabricate a matching piece of wood, the width of your bench, and the length of your scarph, with the grain running across the joint. This is not going to be a really easy pieces to cut, but if you have the means... make the splice a little thicker than the receiving trough. glue in with epoxy. you will now have the equivalent of the top 3/4-1" being continuous wood, and since the top surface is the part that maters relative to stiffness, you will have recovered most of the stiffness of your bench. It is unlikely that you could deflect the top enough to know the difference in actual use. The unfortunate part about this splice is that even if neatly done, there will be a fairly wide and possibly slightly jagged glue line across the surface where the scarph feathers terminate. even after you have everything planed up it will be smooth, but the picture will be possibly a little jagged. You will need to repeat this underneath also.

Fabrication wise it might be easier to have two kerfs plowed out, rather than the single saw cut mentioned above, so that that there is an even depth segment right at the joint. This would give you something to clamp the splice by when you are manufacturing it.

Re: work bench woes

les winter

>How about 3/16" threaded rod in a 1/4" wide slot 1/2" deep?

Les

Deflect downwards

Wiley Horne--Glendora, CA

>Les,

Yeah, I think if you do what Thom says, it'll be hell for stout, and won't deflect.

But what I was referring to is when you want to achieve a feel of depth, or zero spring--a dead feel and a dead sound when you hit it with a hammer. To get that, I think (and I haven't exhausted my credit limit of being wrong this year)--but I think you would need a third pair of legs under the attached part. These legs are all flush on a Roubo, right? Maybe a third pair would add some functionality.

So I agree you can stop deflection by reinforcing it, but to make it dead will require the hammer blow be carried straight to ground, and that will need direct support IMO.

Wiley

Re: Deflect downwards--PS

Wiley Horne--Glendora, CA

>You could also deaden the extension by trussing it from the nearby legs, with heavy stock (4X). However, doing that truss isn't nearly as easy as it looks, and the legs have the virtue of directness, which is the hallmark of a Roubo bench,

Wiley

rebuild it?

ydb1md

>Are you going to be happy with a patch-job in the long run or would it be easier and more satisfying, in the long run, to rebuild the top?

Re: work bench woes

ThomD

>That will be touching the side and bottom of the slot? You want it floating in a sea of epoxy. You would need to put a few shavings in at the ends, or a nut on each end, to hold the rod centered. 3/16 is getting down to a root of 1/8". And the threads are a stress riser. I'd feel better if the piece were a little beefier like 3/8-1/2". The more the merrier. I like to see at least 1/4" around the fasterner.

If you add a tiny amount of graphite powder, just enough to make the epoxy a black colour, you won't have to add caps to the slots, the balck epoxy will look like ebony. I use epoxy died with graphite to fill pitch an knot holes. Too much graphite makes the epoxy a little more flexible which is not a good thing.

Re: rebuild it?

les winter

>You hit it right on the head. I'm not going to spend the next 10 years looking at something I don't really like.

First I cut it too short. Then I spliced on a piece. It was solid, but I didn't like it. Cut it off and spliced on a piece. It was solid but I didn't like it. Cut it off and spliced on another piece. I like it but it needs to be a little stiffer. If it doesn't come out perfect: it's history. I'll live with a shorter bench and/or a different vise. As far as starting all over again, I've got 300+ pounds of glued up maple in this bad boy. I'm going to save it one way or another.

thanks

les

Re: rebuild it?

ThomD

>I wondered. Maple isn't the cheapo wood it once was. Certainly wortha little epoxy.

Re: rebuild it?

Pam Niedermayer - Austin, TX

>So why not weave in a new section, sort of how brick is laid. You should be able to cut out different lengths and insert and glue the same pattern extended. Should be just as strong as the rest of your bench.

Pam

Re: rebuild it?

les winter

>You mean cut a box joint into this 4" thick top? That would be a nice solution. How would you do it?

thanks

Les

Re: rebuild it?

Pam Niedermayer - Austin, TX

>Yes, thanks for the word rescue, a big box joint is what I'd do in this situation. I'd rip the lengths, probably aiming for glue lines, then I'd use a coping saw for the cross cuts, then clean up with a big paring chisel, probably a slick would do. I'd make up the extension with the corresponding box joint built in, no extra sawing involved. Glue it all up and flatten, Bob's your uncle.

Pam

Re: rebuild it?

ThomD

>I want to see you coping the 4" maple! If you have that much time just scarph it, box joints are weak, though in this size of material it would probably be fine.

Re: rebuild it?

les winter

>Thankyou, Pam.

Do you mean take a rip saw and cut and pare 4" deep fingers and match them with the extension? What a job that would be. Maybe you have an easier way?

thanks

les

Chainsaw?

Steve Kubien

>

Re: rebuild it?

Pam Niedermayer - Austin, TX

>My easier way would have been to do it correctly in the first place. That aside, you need an extension that is an integral part of the bench. I think a box joint would do that. Maybe dovetails would work, too, but I'd probably cut them on the underside and add a stretcher underneath.

Pam

Re: Board stretcher? Coupla thoughts...

les winter

>Thanks for all the input. I decided to go with two 1/4 wide x 1" deep x 16" long grooves with a 3/4" deep x 1/8" thick steel strap in each. Plenty of West System epoxy and a 1/4" inlay in the top. The epoxy is setting now. Wish me luck

regards

les

Re: done deal; like a rock

les winter

>Well the epoxy set up, and the two steel traps are permanently part of the bench. No more flex. It's solid and done.

On to the vises.

thanks, all for your input.

Les

Re: rebuild it?

ThomD

>"but I'd probably cut them on the underside and add a stretcher underneath."

You have lost me on that.

Re: rebuild it?

Pam Niedermayer - Austin, TX

>Not to worry, it's all over but the shouting. :) I was thinking that half lap dovetails, or goose necks, or some of those Japanese joints would do the job. It was essentially a carpentry problem.

Pam