This method is a really easy way to get nice looking 3D extruded profiles.
The sign features interchangeable acrylic plaques with things like "Please wait to be seated" and stuff like that.
Other than the initial laser cutting of the profiles you won't need much in the way of tools to make shapes like this.
A 9" grinder
A 5" grinder with 80 grit sanding discs.
A welder, MIG and TIG
Hammer, Files etc.
3mm Cold rolled mild steel sheet
25x25mm Square Hollow Section
15x15mm Square Hollow Section
6mm Mild steel plate
I made a model in 3D for the laser cutting profiles and to get a cut list for the other parts.
Step 1: The Base
The top was a piece of 6mm steel plate.
The plate was cut about 10mm smaller around to allow for a weld and a bevel
This lets you do a fillet weld around the plate and frame, leaving enough weld to grind flat, leaving a nice
beveled edge. (See Weld detail below)
1. Fillet weld 2. Weld ground down to bevel, leaving sufficient weld to hold.
1. Not enough space for fillet weld. 2. Grinding down leaves little to no weld holding the two together.
I also did a few 50ish mm long fillet welds on the insides first before I fully welded the inside.
Total overkill really but I wanted to make sure this thing sat dead flat. A few tack welds would be enough
The problem with welding on one side only is you're likely to pull the SHS around.
One side gets hot then contracts pulling the SHS, see Detail 2.
1. Welded both sides, SHS stays flat. 2. Welded outside only SHS pulls around on it's corner (exaggerated)
Having said all that we aren't building a spaceship, this thing just sits there, so getting these weld details exactly right isn't necessary.
It's a good thing to keep in mind though when welding/finishing, coming from a boiler/structural apprenticeship
this is just habit now for me to do these thing this way.
Step 2: The Frame
I used some 15x15mm SHS to form a backbone down the star profile.
Then I tacked each of the laser cut profiles to a backbone.
I connect the two together with bits of 15x15 to space the two profiles out the distance I want.
Step 3: The Profiles
Continuing from the previous step I used piece of C Section to align the two halves of the shape.
You can use this technique to align pipes and other round objects
The two fixed points of the C section allow you to align curved/circular objects fairly well.
Once aligned I welded the two halves together.
Step 4: The Sides
using clamps to hold the parts down to the shape.
You want to pay particular attention to the alignment at this stage. If the two edges are to far out of alignment once you go to grind the top of the weld off to produce a bevel it will be uneven along the edges.
You also run the risk of grinding off too much of the weld or the sheet metal creating a weak join.
See welding detail below.
1. Pre ground weld, leave a small gap to allow weld to properly penetrate.
Once you have all the sides on you're ready to weld.
Step 5: Welding
The reason I like using TIG is because it produces a small neat weld.
It doesn't take much grinding to get a nice bevel along the edge.
You can just as easily use the MIG (Metal Inert Gas) process but you'll probably end up doing a lot more finishing work to get the beveled edge nice.
I weld small runs of weld alternating positions along the edge and also between sides.
This keeps the heat to a minimum at any one spot which stops the sheet metal distorting.
It's probably less of an issue with mild steel, aluminium and stainless are a lot worse for distortion.
Referring to the weld detail again 1. You want to try and keep the weld between the two outer edges of the steel.
If you can follow this all the way when you grind the bevel it will be perfect all the way along.
Step 6: Finishing
Then I put on an sanding disc holder with an 80 grit on to finish it off.
You want to start sanding/grinding on the start of the edge, go all the way along in one smooth pass, lift the grinder again then go back to the start. If you just go back and forth you'll end up grinding more of the start and finish of the run and the bevel won't be even.
Going back and forth in small passes with also produce an uneven bevel.
Try and keep the sanding disc on the same angle to or you will end up with a wavy bevel.
I also sanded the side flat too, you'll end up with a few lumps and bumps from the tacks holding the frame on the inside.
After the sanding/grinding with the angle grinder I went over the whole thing again with some 300 grit on an orbital sander.
Step 7: Plaque Holder/Bases
I used 25mm X 50mm RHS and TIG welded some pieces to blank off the ends.
This piece bolts into a notch in the top of the star, the plaque holder is riveted and glued to this.
I used bolts to connect this piece because I didn't want to weld the star. I wanted i to look like
the star was just snugly holding the piece in place.
The plaques holders themselves were made from 3mm aluminium sheet with some aluminium round bar in the corners, screwed in from the back with countersunk screws.
Also had to weld the base to the shape too.
Step 8: Finished
After that was a coat of satin finish clear.