Sunday, July 31, 2016

Moving on with my coffee table project, it was time to weld up the legs.

To get started, I clamped all of my cut pieces into the fixture for tack welding.  This is 18ga 304 stainless steel tubing.

After tack welding everything up, I set up a back purge.  Since these welds will be ground flush, I wanted to make sure I get decent penetration and a strong weld all the way through.  To prevent contamination on the back side, I modified a fitting to thread into the 3/8-16 hole and purge the interior with Argon.

Next step: Welding!  I was moving really fast to keep warping to a minimum, so they aren't the best looking welds.  My goal here is to achieve decent penetration, but they will be ground flush.

I was practicing a few different techniques.  Since these aren't critical welds, I tried a few different travel speeds and amperage settings to try and minimize warping.

After grinding, I had to fill in a couple low spots.  Since these will be metal finished, I don't have the luxury of adding putty or filling imperfections with powder coat.

When adding filler to low spots, I kept the welds as cold as possible.  These were just barely hot enough to stick some filler to the surface without getting full penetration since I am no longer back purging.

And after some grinding, it's all flush!

The next step is the fillet welds.

I did this first one with hand files and sandpaper, but it took forever.

I ordered a few of these Metabo unitized felt abrasive discs.  These are 6" diameter and designed for smoothing fillet welds in stainless steel.

These have a special size 1" arbor and are designed to fit their $800 Fillet Weld Grinder.  I don't have one of those, but I decided to make a nut and try them out on my variable speed polisher.

I fired up the lathe and turned an aluminum nut with a 1" arbor.

The best feature of these is that you can dress a shape into the wheel.  I dressed a sharp point so I can get right into a sharp corner.  I just taped a piece of sandpaper to a block and ran the grinder over it. I found that about 2100rpm worked best for smoothing the stainless and shaping the wheel.

This is the only intermediate photo I snapped.  I started by grinding the weld with a cutting disc, then blended with the Unitized Felt disc, then finished it off with hand files, sandpaper, and my Dynabrade orbital sander.

Both hoops are now finished!

Kage approves.

Tonight I got the cross braces tacked into place, I still have to finish weld and then grind all of those.

A table shaped object emerges!!

Monday, July 18, 2016

In my spare time over the past few months, in between other projects, I decided to build a coffee table for my apartment.  I found a few concrete tables that look cool, but decided to build my own.

Here is the plan.  I ended up making it 18" overall, but the look should be similar.

To make the mold for the concrete top, I used a sheet of melamine.  I am pouring it upside down, so the smooth mold surface will become the table top.

I backed up the melamine walls with 2x4s so they remain perpendicular under the outward pressure of the concrete.

In order to seal the mold and add a radius to the top corners of the table, I ran a bead of silicone caulk around the perimeter.  In order to get a crisp consistent edge, I masked it first. I also made a steel tool, shown here in the foreground, to get a consistent 1/8" radius in the caulking.

Next I prepared to pour the concrete.  I am using Quickrete Countertop Mix, specially formulated for this type of thing.

What a damn mess.  This part of the process reminded me of why I prefer working with metal!

I also added some wire rebar, not shown, and tack welded some 3/8-16 weld-nuts into the structure.  This will allow me to bolt the tabletop to the stainless steel legs.

Speaking of stainless steel, I'm now at the fun part!  I bought a bunch of 18ga 304 stainless steel tubing to use for the legs.

After marking the tubes, I cut everything with a grinder and 4-1/2" cutting disc, then did the final trim to my scribe lines using a belt sander with a ceramic 80 grit belt.

Everything is cut!

I wanted to add threaded inserts to the bottom of the table so I could use it on hard floors.  Right now my apartment is carpeted, so I decided to recess the inserts so the threads don't get caught in the carpeting if I want to slide it around.  I made a dimple die and formed them in a 20-ton press.

After dimpling, I welded a stainless steel nut to the inside.

In order to get both legs exactly the same, I tacked up a steel fixture to keep everything square.  I added some 0.020" stainless steel shims to one side so I can pull the parts out since it's captured on all four sides.

Next steps: welding and finishing!