Spot welder from scrap, part 2
So I had the transformer assembled, aluminum wires terminated and copper clamps machined. And in case this doesn’t ring a bell, the story began here in the spot welding from scrap part 1. Next I’ve machined a pair of copper rods to a sliding fit for the bores in the clamps. Clamps, meanwhile, were bolted to the aluminum terminals and from the next photo you can already get a rough idea of the overall geometry of the electrode assembly.
The clamps now have to be mechanically secured to some kind of chassis. The upper clamp, with the electrode, must be movable, while the lower one must sit firmly on the frame. I decided to make the frame from steel profiles and therefore at least one of the clamps had to be isolated from the frame. It was easier to isolate the lower one exactly because it does not have to be movable.
As an insulator I’ve prepared a block of composite material and mounted it between a pair of 20x30 tubes. In the center of the block there is an opening into which a steel bushing is pressed into.
The bushing sticks out somewhat below the isolator and this additional length together with precise central bore serves as a guide for the copper electrode and ensures its vertical alignment.
A pair of rests are located on the other end of those tubes to serve as a mounting bed for the transformer.
For the upper electrode assembly analogous bushing was precisely fitted to a reamed bore in a cast iron block, through which it smoothly slides:
And with a second pair of frame tubes it could be now assembled with the transformer in place:
At this stage the device lacked a mechanism that would apply pressure to the electrodes (and a workpiece between them). I have struggled a bit with its design and settled on somewhat elaborate kind of lever transmission. It starts from a collar that is fixed onto the upper bushing and has a pair of protruding pins.
The pins are meant to slide in channels of a very specific shape in a pair of side plates.
In order to layout the channel’s shape and their alignment with the main axis I had to resort to a precise scaled graphical construction that ensured that the normal to the channel’s surface at the contact spot is directed downwards throughout the lever movement range. This condition allows the pressure to be transferred to the electrode assembly without undesired side-to-side wobbling action.
The plates were then placed onto axis and mounted on the upper frame.
For the lever’s handle I took a round still tube, but for purely aesthetic purposes I decided to skim it on the lathe.
And pushing a threaded header into the tube was an easy job for my shop-made hydraulic press (the same one, used for crimping of the cable terminals in the part 1).
The design of electrodes incorporated interchangeable tips and for that the threads were turned onto the copper rods.
And with the tips and lever in place it already has the most of the functional components to operate.
Of course, it still needs finishing touches, so read on Spot welder from scrap, part 3.
