Assembly Table questions

[Graham Hutchinson]

I'm planning an assembly table and after some research I've come up with the following design.

Approximately 34"x68"
5/8" MDF core and skins
core members 2.75" high, so total thickness 4"
8" center to center core grid
Halved joints at each core grid intersection (cut with dado blade on table saw)
3/4" x 4" trim around the outside
4 legs with leveling casters (I have an uneven basement floor)

Any comments on the above design?

I read on one site where the MDF with the half joint cuts had expanded when the glue was applied, and the joint could no longer be made. Has anyone else experienced this?

Not sure whether to add a hardboard top. What are the pros and cons?

Also considering some 3/4" holes for bench dogs and clamps but I have not seen any assembly tables with them. Has anyone found them useful on an assembly table? I would reinforce the cell on the inside that contained the hole.

thanks in advance for your input

Graham

[Chris Fournier]

I've made alot of torsion boxes over the years, given your application I would not bother with the lap joints - there is simply no need.

279542

This is my current assembly table and the top is a torsion box like you propose and the core is simply butt jointed (glue and stapled), it is like granite and extremely flat. I welded up the base and took great care to keep it square and flat then I built the top on the base (3/4" MDF faces and 13/16" particle board core with laminate on all external surfaces). This table is worth every moment and $ that it took to build and I know that you will feel the same way about your assembly table too. Make your table as large as you can for your work space, you won't regret it.

Show us your table when you're done!

[tom coleman]

i made a 65 inch table, top was 3 layers of mdf topped w hardboard then banded w hardwood. I mounted a vise on one end and drilled a series of dog holes in line with with vise. Served me well. Next step is to add auxilliary top with Kreg Track for pocket hole jpoindery

[Sam Babbage]

I agree with Chris, glued butt joints are fine. Space them far enough apart to get your brad gun (and hose) in between. Lap joints are massive overkill and can even lead to problems, as you mention.

[Kevin Jenness]

The scantlings are fine, but the top will be heavy. If you want to move it around by yourself, make the top of thinner material and use thinner core stock spaced more closely. I work on a 4x8 p-lam clad assembly table made with 5/16" basswood core strips about 3 1/2" o.c. with 1/4" lauan skins. It's 25 years old and still going strong. I am 25 years older and can still pick it up and slide it around easily.

I have built quite a few torsion boxes, and I find the half lap method faster and easier than butt-jointing myriad small pieces and keeping them aligned for glueup. I gang the full length strips together and cut the half laps with a dado head on a sliding table saw, then the frame practically assembles itself.

[Kevin Jenness]

Looking back at the original question I see that some have had trouble assembling glue-swollen half lap joints. There is no need to glue these joints- they add nothing to the box's strength which comes from the glued joints between the core and skins Whether half lapped or stapled, the core joints are merely a way of holding the core strips in position for gluing the skins on.

I also note that the description of my table left out it's depth, which is 4". I think that is about right for a 4'x8' table with minimal base framing.. I have a 3 1/2'x8' x2 1/2" torsion box that I use as an auxiliary table. It is plenty strong in bending, but I have to take care in setting it up to avoid twist if I need it perfectly flat. The 4" thick box takes a lot of force to twist out of plane.

My top sits on two 20"x28"x42" hollow boxes made with 3/4"x4" pine frames on 4 sides and 1/4" lauan skins on the last two faces. Normally they rest on the 20"x42" faces on the floor, giving a net table height of 32". For assembling and working on deeper cabinets,I slide the torsion box aside and rotate the supports onto their wider faces, giving a net height of 24". I find this makes hanging drawers and doors a lot easier. The lightness of the parts makes this an easy process, and they can be readily moved right out of the way to give unobstructed floor space, always at a premium in a small shop.

Be sure to put solid blocking anywhere you intend to mount a vise or other hardware.

[Graham Hutchinson]

Thanks everyone, good suggestions. Weight is an issue for me. If I every want to get it out of the basement, the table will have to be carried out on its edge.

[Chris Fournier]

Weight is always your friend until you have to move it. The top I posted takes two guys to move. If you intend to bash about on your table then heavy is good. Personally I wouldn't consider a 1/4" face and I would dispense with any solid wood components and use sheet goods for stabilities sake. I pound on my table like mad and it sucks it up.

[Loren DeShon]

<<Also considering some 3/4" holes for bench dogs and clamps but I have not seen any assembly tables with them. Has anyone found them useful on an assembly table?>>

I put Rockler T-Track in the top of my assembly table and I don't know how I ever did without it. I'm going to add it to the tops of my workbenches that don't yet have it.

[Jim Andrew]

I'm also in the process of building an assembly table. Am using a harbor freight motorcycle lift as the base to make it a variable height table. Picked it up a couple days ago on their blowout sale for 299. My plan is to use some oak strips to fill under the 3/4" offset on the edges, and around the outside to make the table wider, then a sheet of 3/4" ply for the table top. Am shopping for some clamp track now, as I would like to add the track to one side and end. Appears that just regular T track is not heavy enough to stand up to the Kreg clamps, looking for a lower cost alternative to the Kreg klamp trak.

[Ruhi Arslan]

Am using a harbor freight motorcycle lift as the base to make it a variable height table. Picked it up a couple days ago on their blowout sale for 299. My plan is to use some oak strips to fill under the 3/4" offset on the edges, and around the outside to make the table wider.
Unless you use auxiliary legs on the perimeters, it will be dangerously unstable. As big as it is, even if when the weight is positioned right in the middle, it is very easy to tip front to back (yes, in the long direction) and very shaky side to side. Like to hear how it works out.

[Chris Fournier]

I'm also in the process of building an assembly table. Am using a harbor freight motorcycle lift as the base to make it a variable height table. Picked it up a couple days ago on their blowout sale for 299. My plan is to use some oak strips to fill under the 3/4" offset on the edges, and around the outside to make the table wider, then a sheet of 3/4" ply for the table top. Am shopping for some clamp track now, as I would like to add the track to one side and end. Appears that just regular T track is not heavy enough to stand up to the Kreg clamps, looking for a lower cost alternative to the Kreg klamp trak.

We had one of these lifts kicking around at work, it was very unstable as has been pointed out. Perhaps you will be able to modify it!

[Michael W. Clark]

Appears that just regular T track is not heavy enough to stand up to the Kreg clamps, looking for a lower cost alternative to the Kreg klamp trak.

I saw some 3/8" T-track at ttrackusa. It looks heavier, but I haven't used any. You could also rout a t-track in hard maple and use lots of screws/bolts to attach.

[Jim Andrew]

You might look at the harbor freight website and see the lift I'm using. It is not the small lift table, it is the large one built to drive a motorcycle onto and lift the entire machine up. The platform is 26 3/4 wide by 86 5/8 long, and the wheels are 21 wide and about 51 length wise. Figure if you can drive a Harley onto it, and it is stable, should be pretty stable for a work table. My big deal is the clamp track, have to wait to get some ordered before I can build the top. On tops I have used for gluing, if they were finished the glue came off easily, unfinished it has to be scraped, so think I will give it a couple coats of finish. The melamine is pretty brittle, just pb with the melamine coating, so think I will go with ply.

[Ruhi Arslan]

This one is instructional and not painful at all like many other amateur "youtube star" instructional videos.
http://www.finewoodworking.com/woodworking-plans/video/build-a-torsion-box-assembly-table.aspx

[Ruhi Arslan]

You might look at the harbor freight website and see the lift I'm using. It is not the small lift table, it is the large one built to drive a motorcycle onto and lift the entire machine up. The platform is 26 3/4 wide by 86 5/8 long, and the wheels are 21 wide and about 51 length wise. Figure if you can drive a Harley onto it, and it is stable, should be pretty stable for a work table.
No, it is not. I have one. I rigged an overhead anchor point to tie the motorcycle from top not to be trapped underneath while working on my motorcyles. If you must insist that it is stable, raise your lift and sit on either end of it but be prepared to run as it tips over you. Good luck.

[Jim Andrew]

I'll try sitting on the ends and see how it works. I have it raised up high as it will go and it seems very solid. A wood top and a few work pieces won't come close to the weight of a large motorcycle, my plan is just to use it as an assembly table. Found some 1.5" x 3/4" T track on ebay, from username 8020 and got it ordered. Said expect it in 4 days.

[Alan Schaffter]

First, I have a lot of experience with torsion boxes and did quite a bit of research on them for the article I wrote for American Woodworker in 2009 (Dec/Jan 2010, issue #145). My two-part article shows how to build the torsion box assembly table top and how to build adjustable legs for it.

First, you may be compromising the strength of the torsion box by attempting make it do double duty as an assembly table and work bench, especially if you cut holes and slots in it. The purpose of using a torsion box for an assembly table is to make a table that is flat, will stay flat, and is strong, and light.

Torsion boxes get their strength from the height of the web, strength of the skins in the horizontal plane, and the bond between the skins and web. You can make a strong 8' long assembly table using just 1/8" - 3/16" thick hard board- I built one and tested it with over 300# of bricks stacked in the center. It was supported at each end only- the total deflection in the middle was only 1/2"!!

However, if you plan on subjecting the top to heavy point loads (hammering or clamping in a small area) you better make the top skin a little thicker and/or reduce the spacing of the web. I used 1/2" MDF for both skins and web- it was convenient to be able to deal with just one thickness, but even that was probably overkill.

Also, I used halved joints on the web- they were easier and quicker to make and assemble and the end result was a perfectly rectangular box with straight sides- no cutting 40 to 50 little pieces and gluing them in place one at a time and also individually fitting and trimming pieces in the last row to ensure the sides of the box were straight- a time-consuming and awkward method used by David Marks and Mark S. I used a simple indexing jig made from a peg inserted into a slot in a 2 X 4 attached to my miter gauge. I set my dado width for just slightly wider than the thickness of the MDF for a slip fit and cut all the lateral and longitudinal web pieces in less than 15 min.

http://www.ncwoodworker.net/pp/data/1421/medium/145_AssemTable_spread1.jpg

Torsion box made with tempered hardboard (and some pegboard) and yellow glue (no brads). No sides either:

http://www.ncwoodworker.net/pp/data/1421/medium/P1040010.JPG

Hardboard torsion box supporting over 300# of bricks:

http://www.ncwoodworker.net/pp/data/1421/medium/P1080028.JPG

Cutting halved joints in the MDF web pieces:

http://www.ncwoodworker.net/pp/data/1421/medium/P10100792.JPG

http://www.ncwoodworker.net/pp/data/1421/medium/P10100705.JPG

Applying glue to the edges of the web before attaching the bottom skin. Corner reinforcing will hold the upper legs:

http://www.ncwoodworker.net/pp/data/1421/medium/P10101181.JPG

I used 18 gauge brads to hold the skins to the webs until the glue dried:

http://www.ncwoodworker.net/pp/data/1421/medium/P10101301.JPG

[Brian W Smith]

A friend bought me one of those HF motorcycle lift tables as payment for some machine work(more like a tip or thankyou,didn't want him to pay me).At the time we were using a big heavy wooden table for M/C(motorcycle)work.....but that isn't the point of post.

The HF table makes a dandy finishing table in our spray booth.It's usefulness as a "bench" would be limited as posted above.But,if you stay within those limits....it'll work just fine.I've used ours several times for case work when assembly got too crowded and needed expedience to keep the show moving.

If we were to use it "full-time".I'd try ratchet strapping it,to itself......huh?Yup,use adj length straps at each corner,as limiters...then give the table a cpl elevation strokes.Its either that or it needs to interface with another bench,preferably one solidly anchored.It would be as a "wing" or adjunct,that's adj in elev.

Still think they work best as part of finishing however.

[Michael Dunn]

<<Also considering some 3/4" holes for bench dogs and clamps but I have not seen any assembly tables with them. Has anyone found them useful on an assembly table?>> I put Rockler T-Track in the top of my assembly table and I don't know how I ever did without it. I'm going to add it to the tops of my workbenches that don't yet have it.

I'd like to see pics of that.

[glenn bradley]

Also would skip the lap joints. No need in my experience. Variable height is a plus even if it is only 16" and 30" or something like that.

[Chris Fournier]

I have made torsion boxes that I cantilivered from walls in residential and commercial settings and I needed them to be light.

If you look at the image I embedded Allan you will see that my assembly table is not intended to be set up used and then torn down, rather it is a permanent fixture in my shop and I will woodwork, metalwork, weld, fix machines on it and it will be beat on. For this reason, the core is robust as are the skins. Heavy is an asset in this application. I have seen torsion boxes where the skins were thinner materials and the core telegraphed through and it ruined an otherwise gorgeous furniture piece.

[Kevin Jenness]

Chris makes a valid point about telegraphing of the core grid through a thin skin. If I were set on using a thin skin under a veneered piece for light weight, I would probably use a commercial honeycomb core. The resin impregnated paper and Plaskore honeycomb products I have used have cells about 1/4" across.

[Curt Harms]

I built an assembly table to do some kitchen counter type work. I needed it movable. I used 3/8" ply top, '1/4" ' Luan bottom skin, 1 X 4 planed to 1/2" thick for the web. I glued 4 stubs in corners of the web structure to attach legs. The legs are attached with 4 bolts, the bolts hold both the leg & cross braces so it only takes a few minutes to disassemble and is flat & pretty light. I can't easily get it out of its current location or I'd take a couple pics.