Sunday, April 25, 2010

welding cart

The welding cart was built to overcome the issue of always working on the ground. For some tasks, the cart is not suitable, and the welder is removed from the cart, and taken to the job, or the cart is simply left near the job, but the earth lead is disconnected from the cart, and clamped to the job.
The welding cart offers another advantage - one of a "large earth"... All my welding experience up until I built the cart was based on attaching the "earth clamp" to the piece being welded. Sounds good, but sometimes it's easier said than done. I had seen other people clamp to a large sheet of steel, then drop delicate work on the sheet, and use it's contact with the sheet as the return path. The entire cart is like that sheet of steel. The return clamp is attached to the cart (in my case by the clamp being attached to a tab on the underside of the table) so anything I place on the top of the table can become part of the current path, simply by it's electrical contact. This simplifies any delicate work considerably, and allows repositioning without fighting with the return lead.

I'll talk more about the welder itself in another page, but it has been considerably modified to make it more usable for the kind of things I want to do with it.

The cart was made from salvaged materials. Most of the sheet metal was cut from a discarded instrumentation cabinet. the steel is all 1.5mm (about 1/16") thick, and was powder coated/enamelled. The cabinet was basically cut so the top and bottom portions became the top and bottom of the cart, but the sides were replaced with other material.
The main structural components (frame, uprights, etc) were made from a rolled shape which I got from the tip. The cross-section resembles a squared up letter C, and it came in lengths of 1200mm (4') with grey paint on it. I believe it was some kind of packing material for shipping motorcycles, but I really can't be sure. The steel is 2mm thick, and the C shape is basically 30-35mm wide, and 19mm (3/4") deep. The slot on the open side of the C is 10mm (3/8"), and a 3/4" square tube will ride inside the C section if one corner is protruding through the slot (I used this exact concept to make the leaf folding mechanism)

Construction was basically determining the finished height, and then making up the side frames to that height with the top member equal to the width of the cabinet top.
The frames were welded to the top and bottom pieces, and some cross pieces were cut and welded in to form a "shelf" in the middle.

The middle shelf does not extend across the entire width of the table, since I determined it would be prudent to have the full depth of the table available on one side for hanging cables. Additional cross beams were cut and welded in to form the sidewall of the middle shelf, and some hooks were welded in on these beams for hanging cables.

The original build on this cart had four wheels, one at each corner, but within a very short time, I determined was troublesome - firstly for the issue of uneven ground, but mostly since the cart would move under the forces of grinding, or other metal abuse activities. The front wheels were cut off, and some 3/8" nuts were welded into the front pillars. Some 4" long cup-head bolts were screwed into these nuts, the heads of the bolts forming the feet for the front of the cart. A telescoping handle was added into the shelf beams, to assist in lifting and moving the front of the loaded cart. The telescoping handle is nothing more than a piece of the C section steel tubing, with another piece of 3/4" square tubing inside it, some stops welded in, and a "handle" to make it easy to pull out.

The telescoping handle can be seen just above the top PVC tube, extended out approximately 6"

The top of the bare cabinet was about 400mmW x 500mmD, and adding the widths of the two support frames either side only added another 70mm to the overall width - not nearly enough room for any serious fabrication. A means of making the table top larger was required.
One of the cut away sides was stiffened up by welding a piece of "C" tubing at each end, the original folded edges were sufficient for the sides since the folds were 3/8" deep, and 3/8" wide, 3 sides of a perfect square.
Some hinges were padded out, and screwed in place for the drop leaf, and the salvaged rear axle of a dumped lawn mower was used for the hinge of the brace. The ends of the axle were trapped in some short pieces of 3/4" square tubing which was tacked under the sheet metal leaf.

Photo taken from underneath the raised leaf, showing the brace, vertical track, and it's joints.

The other end of the brace is bolted to a "shuttle" which runs in a vertical track. The shuttle is nothing more than a piece of square tubing running in another piece of C tubing, with a tab welded to it for the brace to bolt onto.
When the leaf is dropped, the shuttle is in the bottom of the c section track, but when the leaf is lifted into position, the shuttle moves upward, and trips a weighted pawl which prevents the shuttle returning past it. This pawl keeps the lifted leaf in the "up" position, level with the permanent table top. The pawl is released via a lever at ground level which can be activated by the operator's foot.

The locking pawl as viewed from under the shelf. The release mechanism, and counterweight is operated through the 3/8" rod which acts as an axle for the pawl. All joints are simple clearance holes through scrap steel, nothing fancy.
Top photo - leaf lowered

Photo of leaf raised

The welding cart has evolved a little over time, the middle shelf had some lengths of PVC pipe added for providing storage for welding rods (2.5mm and 3.2mm), and a block of wood with some holes drilled through it was added for holding the "live" electrode (handpiece) in an insulated holder so I could put the handpiece down during a job, and not worry about current flowing (the lesson on that effect was most uncomfortable).

The 3/8" cup head bolts failed recently (see Hose suspenders page) when I wheeled the cart out in the street so I had enough room to turn a 4m (12') length of 3/8" square rod through a jig clamped atop the welding cart. It was during the repairs that these photos were taken. The 3/8" bolts, and nuts were removed, and replaced with some 20mm (~3/4") anchors and nuts. I don't know what the anchors were for (part of a toolbox full of junk which I found on the side of the road - it's amazing what falls off trucks around here), but it's nice to use some of them up.

That's about it - I know I took better photos during the construction of the cart, but I don't seem to be able to find them. I know the cart looks rough, and I'm really not in the mindset to go nuts painting things like this when all they do is get dragged between the shed, and the job. I paint things which will spend more time "sitting" than working, unless painting is needed to protect the "thing" - given this cart is my biggest workhorse, I don't see the point painting it. If fact, I have to periodically run the grinder over the top every month or two to remove any rust, or paint which would stop the current flowing through the top and whatever workpiece is on it.

A lot of what was built when I first set up here was built from scrap I collected from friends at work, and the local tip (Salvage). I'd just moved to start this job, and disposed of all my building materials for the move. You will find a lot of what I describe and show in these pages will be made from salvage/ surplus materials. Some if it is my desire to save money, most of it my desire to reuse materials, and find uses for "junk". I read shop notes books from the 1900's for fun, and do not subscribe to the throw away mindset that many others have.

1 comment:

  1. Yes, the welding cart is indispensible in the workshop. That being said, it can be a good project if you’re a beginner welder. Welding carts are very symmetrical, so you won’t have much trouble building them. Also, creating something that you really need is very fulfilling, which can boost your desire to take on more projects.

    Jeanette West