The Best Joint?

[riot_nrrd]

Hi everyone - I have a joinery question. I am making a workbench/lumber storage rack. I am basing it on a cross between two plans from Woodworkers Journal, and adding some of my own embellishments. I am basically mounting a table top onto a shoprter version of this rack:

https://store.woodworkersjournal.com/Me ... /wj115.jpg


However, I am trying to make this look somewhat more traditional, so I am trying to avoid using lag screws and such if I can help it.

It is going to be made from clear pine stock. The top will be connected to a "ladder" frame. The ladder frame will sit in pinned saddle joints on 8 supports made up of three boards each (e.g., the saddle will be glued up, rather than cut). Those same three members will also be glued up to form a tenon, which will fit into glued up mortises that are perpendicular to the table top.

Make sense so far?

Now - I want to attach a set of board parallel to the table top to whcih I am going to attach a set of retractable casters. This is going to be based on the design you see on rolling ladders at places like HD and Lowes. So I am planning on attaching them to the perpendicular supports.

In the picture above, this is the section that the wheels are attached to - basically an apron. However, I want that apron to suppot the load (in the picture, most of the load is supported on the perpendicular pieces where the wheels are mounted). The retractable casters are going to be attached to that apron and pivot on an axle, so I need them to be fairly strong.

My plan is to make those out of two glued up 2X6s (nominal). But I don't want to attache the 2X6s to the cross pieces with lag screws.

So I am thinking to cut mortises (maybe 1 X 3) in the long 2X6s, and then essentiall have each cross piece be cut to serve as "double tenons." So 4 cross pieces X 2 tenons each = 8 mortise and tenon joints. I think gravity would hold them for the most part, but obviously I'll glue them up too.

So here is the question(s):

1.) Does this sound like ti will result in a strong frame?
2.) These motrise and tenon joints are going to be end-to-face joints. The only points that will really work well would seem to be the tops and bottoms of the tenons (edge grain) to the tops and bottoms of the mortises (edge grain). All the other sides are going to involve end-grain to face-grain. Is this going to be a problem?
3.) Should I considere pinning the tneons with a dowel or something similar?

If this doesn't make sense, let me know, and I'll try to draw a picture.

Riot Nrrd

[wood4fun]

Riot Nrrd,
One of your great sketches would help a lot to get everyone on the same page. Not sure I'm envisioning the same design you're describing. I can't remember how the HD retractable casters retract...they don't have something similar to the Shopsmith 3-way cam do they?
-w4f

[riot_nrrd]

W4F,

Here is a scale design drawing. I only included the front and top views, becasue my primary focus has been making the retracting casters work. Basically it is a lever pinned to the bench with a steel rod, and the caster acts as a fulcrum. I'm going to lock it in place with hitch pins unless I (or someone else) can think of someting cooler.

But my question is about the red circled areas. Right now, they just show a butt joint. But I need that to be a strong joint, because it needs to hold up the bench and any wood I have stored in it. On the right side, I've drawn what I am thinking is the best option - I'm calling that a mortise and tenon, but it may be more accurate to call it a blind tongue and dado.

So the question is - any other ideas? I can see pinning the tenon with a dowel (shown in orange), making it a through-tenon and pinning it with a dowel, putting the dowels through the face of the base into the tenon and splining them, making it a through tenon and splining the tenons, etc...

As you can see (hopefully?) from the top view, each side can have eight tenons. I could make them BIG tenons and do four, but I think that will weaken the base more than I want. Or I could make them small tenons and do four, but I think that would weaken the crosspieces more than I want.

Any thoughts?

Riot Nrrd

[wood4fun]

Riot Nrrd,

Thanks for the sketch. It helped a lot. I was imagining some quite differrent configs. I like your design. It looks to be a very hand table to own/use.

Considering each pair of nearby mortise & tenon joints, 8 along each apron rail, we can consider their ability to resist the forces they'll encounter:

• Shear: up/down: resist weight of table, racks, and contents (major standing load): good, because tenons are strong against breaking off, due to their grain orientation.
• Shear: slipping further into joint: ok: tenons and cheeks dead end into rails, plus tenons are pinned
• Shear: slipping out of joint: ok: pinned (the pins supplement the poor gluing contact surfaces you mentioned)
• Shear: sideward force on rail: good, because tenons are strong against breaking off this way, due to grain direction
• Torque: cross-piece sag: resisting the weight of the table, racks & contents (major standing torque): ok: 2x6s(8) should resist sag of considerable weight.
• Torque: parallelogram in top view: e.g., rolling the cart and crashing the front apron corner into a fixed object: hopefully, you won't be doing soap-box derbies with this table:):
  • micro view around joint: moderate due to the limited glue contact surface you mentioned, though the paired pinned tenons give some moment of inertia against this torque, if they can't slide (it looks like you've got them pinned to the uprights, so that would resist sliding relative to one another), but to further resist this torque locally, some simple corner blocks would give lots more face/face glue surface contact area to reinforce the joint.
  • macro view of entire table (top-view ladder parallelogramming): weak, so to reinforce this, diagonals parallel to the floor would create triangles and resist parallelogramming. For example, viewed from top, you could put a diagonal between the 1st and 2nd cross pieces, and another between the 3rd and 4th: in top view of the ladder: [ |\| |/| ]
  
  Again, the joint might not encounter much of this load to resist, but they're 2 easy solutions, one at the micro level, the other more macro.

But that's just my 2cents...others might see strengths/weaknesses I've missed or rate their practical significance differently (I focused on the dead weight applied to the structure. I haven't really considered what woodworking forces you'll apply to this table, other than hammering down on it. Sideways forces, for instance hand planing, seem an order of magnitude less than the weight loads. I'd guess that moving this table around, given all of the mass of its contents, if you're a packrat like me, the biggest non-weight load will be when the corner of the table snags a fixed object like a doorway, cabinet, etc. Hope this helps. Good luck w/the table. Let us see how it turns out.

-w4f

[riot_nrrd]

Can't beleive I didn't think of just blocking those joints. Duh. Sometimes you miss the forest for the trees.

I'm not too worried about the racking of the top ladder, because it will have a large table top holding it in multiple locations - that should keep it square, so long at I place my screws logically (i.e., not just on the rails, but on the cross members).

Thanks for the suggestions! I'll post photos when done.

I have most of the lumber and have built the casters... got the Veritas twin-screw vise and a bunch of t-track in the mail yesterday.... woo hoo!!!!

- Riot Nrrd

[riot_nrrd]

Well, I've been picking at this for several weeks now, and wanted to share:





I have glued up most of the top, and will be planing it next weekend.

The retractable casters work awesome. I was worried that they would be too wimpy, so I totally overbuilt them, and they work like a charm. I will be putting some kind of pedal on the bar so it looks nicer, but right now, it is working great - it feels almost silly how easy it is to raise and lower it. I have loaded up the glued-up top, a bunch of lumber, my chop saw, my mortiser, and a portable router table on top of it all, and it both lifts and rolls easily.

W4F - I ended up using a blocking similar to what you suggested - one 2X6 with slots cut into it glued to another 2X6, then matching cross-members to fit into the slots. It's nice and rigid. There is a little racking (like you thought ther might be) so I'm going to get a sheet of plywood, rip it in half, and then use it to tie the suproting legs together at multiple points.

I'll post more pics when its all done.

RiotNrrd

[wood4fun]

Looks like it's coming along great, RiotNrrd. Should be solid as a tank when it's done. Can't remember ever wishing I'd made a storage/utility unit LESS strong.

Sorry for the delay in responding (my employer occasionally wants me to do some work -- can you imagine?).

Keep the posts & pix coming!

-W4F

[charlese]

Looking real good up to now, Riot!!:) Keep going! Looking forward to seeing more.