Thursday, January 13, 2011

Visualizing the Lathe Bench

So, I got some comments about my lathe workstation idea, saying that people couldn't visualize what I was thinking of.

Well, thanks to the wonderful people at Google, that's easy enough to resolve.

Someone asked for a threeview; but I think reciprocal isometric views, and a face on view (rather than two faces and an isometric) would be more illustrative.

So here's a couple of shots of a quickie sketchup model I did...

first the left iso:

Then the right iso:

And the end face:

Not sure exactly why sketchup added and/or subtracted 1/64th inch to the measurements, because I know they were accurate when I drew them up.

The lighter wood is 4x4 dimensional lumber, milled to 3". The mid tone wood is 3/4" plywood, and the dark wood is tempered hardboard.

I'm not sure whether the center uprights are necessary or not. I'm thinking with the T-Beam for the top, it's probably strong and rigid enough without them. Also, I wouldn't be doing any silly through joinery on the middle shelf. Just a gap around the legs with some edging.... if I even put the legs in at all.

What the drawing doesn't show is the metal top coaming (done with drywall corner probably), shelf edging (probably some premade molding trim strips), bottom framing, or the casters and height adjusting feet.

I left them off for clarity; and because I haven't found exactly what I want to use yet. Same thing for whatever dust and chip collection system I end up rigging (probably one of those big ABS chutes into my shop dust collector).

Also,  I need to reduce the height of the legs based on whatever heavy duty locking casters I find, so that the worktop ends up at 40 inches.

Now that I've clarified with a drawing, let's confuse things again.

I'd probably put in another 3" frame member across the bottom center of the upper shelf (between the center legs), and a triangulating crossmember between the leg uprights, crossbolted into the legs and the shelf member, and screwed into the bottom of the plywood end plates.

The end plate is a full structural gusset, glued and screwed into each individual member, for rigidity.

For the drawing, basically because I didn't feel like taking the time to do it, I just show a simple miter and butt join from the top of the outboard legs, to the bottom of the T-Beam. For the real thing, I haven't decided whether I'll rafter cut it, to give a two face join; or cut a corner block and pocket screw through it (thank god for Kreg jigs).

I'll probably put 3" longmembers and crossmembers across the bottom of the outside legs, and from leg to leg, both on the bottom and the top of the base shelf. Then I'll do inside corner bracing on the bottom frame, with a 3" brace, and a 3/4" ply gusset glued and screwed over it; to bolt the casters and feet to. Finally, I'll run two more 3" longmembers,  from one the inside edge of the corner brace, across the entire bottom to the other inside edge of the corner brace, on each side... or if I decide to keep the center legs, I'll just run the two long members underneath the legs and screw up through them..

All that will edge the base shelf, keep the center of the base rock solid, add mass, AND make for a seriously rigid frame structure.

If I end up dogboning the bottom shelf, I'll leave the end crossmembers, but move the outer long members inboard to say... an 18" wide center section; then triangulate the frame with outside corner bracing (making a 7" right triangle with diagonal members on all four corners, from the end of the outboard legs, to the long members).

However, I don't think I need to dogbone it. Looking at it drawn up, and given the mass of the thing; possibly including a few bags of lead shot, or sand... I think I can reduce the width of the bottom shelf/splay of the legs, down to 28". Given the lathe is 8" wide (the benchtop it's on is 9" wide) and the toolrest is right on the outside edge of that width, that would only leave 9.5" sticking out further than the tool rest, which should let me work just fine without leaning in...

...and frankly, even at 32" wide that's still only an 11.5" reach; and I've personally got a 14" reach from 90 degrees, elbows straight down from the midline of my body to the center of my fist (add another 5" from the center of my fist to the tips of my fingers). In a normal working stance, I don't think the full width bottom shelf would restrict my movement or force a reach at all, especially with 4" or 6" casters on the thing, so I can get my toes under the frame (somehow, I'm not worried about the frame collapsing and falling on my feet).

Of course, I'm taller than most, with longer arms than most.

Oh and yes, I know this is a ridiculously heavy, and overbuilt design.

That's the point.  All up, that's about 96 linear feet of 3" milled 4x4 and most of a sheet of plywood. It should weigh in around 280-300lbs, depending on the total weight of the hardware and fasteners used.

I WANT it to be very heavy to absorb vibration. I want lots of doubled up structure to improve rigidity; but I also want it to be of very slightly elastic elastic wood construction, to better damp out that vibration.

Oh and incidentally, the total cost, including fasteners, would run about $180 if bought from a home despot in my area.

One might also note, that if you took the 32" wide dogbone base I talk about above, graft it to the top T-Beam instead of just the 9" wide benchtop, and run a couple of legs down the outside corners into the base frame; one could make one hell of a rigid, heavy, solid, and ambidextrous shooting bench.