Hello, my friend.
Sit down, please, and listen to my story... Once upon a time (and it was the cold siberian winter) one my friend (and she had her own sewing workshop) asked me to help to design a table for cutting fabric (and it should have all advantages of cutting tables, and it shouldn't have any of disadvantages of cutting tables). Then I (and my friend, who was able to weld) made two tables for her (and every tailor on the planet considered them as the best of their kind).
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Step 1: Origins
Whoof, It was dramatic.
The basic idea of cutting table is that it's a wide plane your unable to snag with needle or pin, about 90 cm up from the floor (with possibility to regulate the height slightly). It's also good to have another plane below to use it as a shelf for lightweight stuff (fabric, books, templates and all this weird sewing things). It's also good for this planes to be rigid and solid, excluding wobbling and flexing. Everything else is bad. I mean, ideally there should not be frames, legs and other stuff you will stumble while sweeping left and right doing your cutting things.
So the typical 'hey_lets_weld_the_rectangular_frame' approach is not wellcome.
After several iterations, the design was.. designed (see pictures).
Also there was some calculations. I've used USSR GOST (State Standart) for furniture and choosed 4'th (from 5 possible) level of usage intensity (sutable for education institutions) so even 100 kg student can jump on the edge of the countertop and it will be OK. Maybe it's not very economically efficient to make such tables for only 45 kg tailor girl, but working with really rigid worktop is a great pleasure.
The dimension of desktop is 2140x900 mm, so two tables give 2.14 x 1.8 m of flat surface.
NB: this instructable is for one who familiar with making steel frame constructions!
Step 2: Blueprints (and a Movie)
The table is all about the frame. Tabletop surface and shelf surface are just rectangles made of some sheet material (I used 14mm wood particle board). It shouldn't be very thick, because it is not supporting structure and doesn't carry load. The size of tabletop is 2140x900 mm and the size of shelf is about 1950x800 mm.
The frame consist of four parts: two legs, tabletop and shelf. All parts made of steel square tubes. 25x25x2, 50x25x2 and 50x50x3 tubes are used. There also 4 M12 nuts and 6 M12 long nuts, 4 M12x15 bolts (inner hexagon), 4 M12x30 bolts (inner hexagon), 4 M10x85 furniture bolts and 4 M10 capped nuts. Only those M10 bolts and nuts are visible, so they should be good-looking (I've painted them white). Also you'll need 4 M12 legs (or leg-bolts, I don't know, the things you screw into nuts at the buttom of table legs to ajust it's height and level, and actually the table stays on them).
Step 3: Step 1: Legs
Each leg consist of 3 pieces of 50x50x3 mm square tube (see first blueprint). There also small piece of 25x25x2 mm tube. Don't forget to file and sand sharp parts of metal after cutting.
If you not sure, don't drill holes on this step. Only you can do is to drill 14 mm holes in horizontal section of the leg and weld M12 nuts inside (or, if you have only M10 leg-bolts, drill 12 mm hole and weld M10 nuts inside, It should also be enough).
Other holes a concentric with appropriative holes on tabletop frame part, so it's better to drill them together later.
To weld all legs flat and uniform it's better to use some kind of tooling (we used flat WPB + wood). The best case if you can weld everything with one tooling assembly (you can cut holes in WPB for this).
Step 4: Step 2: Tabletop Frame
Second blueprint is for tabletop. The outer frame made of 50x25x2 rectangle tubes. The inner lattice made of 25x25x2 square tubes. First you should weld outer frame, then weld inner lattice. Everything should be flat and rectangular (don't forget to check diagonals). Then attach legs to the frame using clamps, accurately set all assembly (i.e. make legs to be vertical and parallel to each other, make them be the same length and so on).
Step 5: Step 3: Tabletop Leg Bracket
Make parts for leg brackets (using 25x25x2 square tube). Clamp brackets to legs and weld them to tabletop frame (first fix and weld side part of brackets, then attach diagonal bracings). After everything is done, table stays assembled with clamps. (There are photos with shelf frame already made, but the experience says that it's better to fully assemble tabletop+legs, then to measure an actual distance between legs and then make shelve).
Step 6: Step 4. Attaching Legs to Tabletop
It's time to drill holes. Each leg attached by 4 bolts: 2 M12x30 (to the outer tabletop frame) and 2 M10x85 (to the bracket). Leg-to-frame attachment is hidden, so first you need to use 25mm core drill bit to drill holes for boltheads in inner side of outer tabletop frame. You'll get 4-6mm hole in outer side of the frame and in inner side of the leg also, use 13mm drill bit to expand it. Then bolt the outer frame to the leg using M12x30 bolts and long M12 nuts. Weld nuts to the leg in this position.
Then accurately drill 11mm holes through legs and brackets. Bolt legs to brackets using M10x85 bolts and M10 cupped nuts. If you use furniture bolts with square necks, use file to square the hole in leg.
Now the table is assembled! Remove clamps, It's time to make shelf.
Step 7: Step 5. Making Shelf
Measure the actual distance between legs at the level where the shelf should be. Make the shelf frame with size actual_measurement minus 5 mm, because you need to be able to install the shelf somehow :) Take 2 long M12 nuts and cut them into halves. Clamp and set shelf frame properly. Using the frame as reference plane, weld nuts to legs.
Using drill and bandsaw make 4 attachement elements of 4 mm steel plate.Then clamp shelf frame to legs and weld attachment elements to the frame such that you could bolt the frame using them.
Bolt the frame. (using them).
Step 8: Finishing
Now the frame is ready. Mark the parts that you could assemble them the same way after painting. Disassemble evrything and paint any color you like. It is also time to obtain tabletop surface and shelf surface. You can measure the actual size of shelf (don't forget to substract 5 mm to be able to install it between legs). I've just ordered rectangles of appropriative size in a shop.
Then screw tabletop surface to tabletop frame using steel corners from furniture shop. Also you can drill some holes in tabletop frame lattice and use them to screw the surface also. Then assembly the table. Put shelf surface on the shelf frame. As practice shown, there is no need to attach shelf surface to shelf frame.
Screw leg-bolts and ajust table level as you need.
Use plastic plugs to cover open ends of metal tubes.
Thank you for your patience :)