I have a month between semesters at Austin Community College. Time to work on the last project in a series!

As usual, more photos at Flickr. https://www.flickr.com/photos/aneel/albums/72177720315236826/ and https://www.flickr.com/photos/aneel/albums/72177720326943829/

When we remodeled our bathroom, we bought a slab of pretty quartzite for the counter. The counter only needed part of it, but you have to buy the whole slab and we didn’t want it to go to waste. We had the counter folks cut the remainder into useful sizes and I’ve been slowly making steel table bases for them.

A long, low table with thick tubing (3" x 1")A square table with an X structureA square table with an airier X structure and a gray tabby cat sitting on it looking very pleased

As my fabrication skills have improved, the bases have gotten more complex.

The base has two trapezoidal ends, and long bars between themThis base has four vertical legs, joined by two X crossesThis base has four vertical legs, but only one X cross at the bottom and a square at the top

For the last of the table tops, I decided on a design with four X shapes around the outside. All of the angles in the two similarly-sized tables were either 45° or 90°. The same is true for the angles on these sides… if you hold the pieces at a 45° angle while cutting them. That’s a bit tricky on a conventional saw.

A CAD model of a table composed of 4 vertical X shapesCAD view of the end of one of the tubes showing the complex angles

No problem! I just spent 6 months in a machinist apprentice program. I can do this on the mill! How hard could it be?

Cutting the corners actually wasn’t too bad, though I did learn some (expensive) lessons about how endmills react to the sudden pressure changes and vibrations involved in milling tube (by shattering). But I did some test corners and they fit together well on the fixture table. On to the welding!

A CNC mill where the entire table is covered with coolant frothTwo pieces of tube cut at the correct angle and clamped to a block on a fixture table

Wait, what do you meant the joint that I want to weld is exactly where that fixture block is. No, of course I can’t weld the exposed angle. That’s the one everyone is going to see and filing it back to that crisp edge after welding it would take forever. Surely I can make a jig that lets me clamp that joint from the other side. Let me just 3D print up a model…

This picture looks like a space ship or some abstract art. Two steel tubes meet at a corner with a black plastic form holding them in place and clamps surrounding themThe same from a different angle

I can’t weld against a plastic jig, of course, so I just need to make that in metal… Hmm. But getting end mills in at those angles is exactly the “you need to hold it at 45°” problem. Let’s figure out how to do this flat… Hmm. Going to need to order some new shapes of endmill… And for clamping, we might as well just use a two-sided jig with bolts instead of trying to get F clamps in at those angles…

(Weeks of messing with tool paths later) Yessss, that should do the trick.

A block of aluminum in the vise of a CNC mill with a V-groove cut in itSteel tubes in the V-grooveThe steel tubes are sandwiched between two aluminum blocks connected with wingnutsThe back side of the jig, showing the joint to be welded

We’re ready to prep all of the parts. Hmm. these parts are longer than the travel of the CNC mill. No problem, we’ll just figure out some creative fixturing and do it one end at a time.

Tubing is held in two vises on the fixture table......one end is butted up against a 123 block that is clamped to the mill's casting well beyond the fixture plate......the other is butted up against a custom fixture blockTwo short and one long pieces of tube are held in the aluminum jigs

Finally welding time! First let’s make the X parts. Just the kind of thing a fixture table is for… Tube on the fixture table with an excessive number of clampsFour stacked X shapes made of tubeTwo of the X shapes held together in the custom jigs

And the tricky part: welding using the custom jigs. It went well for three of the four sides. The fourth needed some “encouragement” from some ratchet straps to come together. It didn’t take too much filing to bring the interior 90° corners up to the necessary level of finish. Much easier than filing at 54.7 degrees!

Two X shapes are fixtured to the table using conventional fixtures and the corners where they join are in the custom jigsAn orange ratchet strap is wrapped around the tubes of the table to get the last couple corners to meet up nicely.After using an angle grinder to do the rough cleanup, files help give a crisp edgeThe shape is complete and all of the parts are shiny

One tricky thing is that the 1” tubing leveling feet that I have don’t fit into the corners of these. So let’s model up some custom ones and 3D print them. All that’s left is a few coats of flat black paint, leveling feet, and the final quartzite tabletop. Finished! Or almost.

A gray plastic two-part device with fins for holding the inside of a square tubeThe bottom part is more visible with the two pieces separate. It is knurled and has an M5 screw sticking up out of itThe frame is painted blackAnd here it has a quartzite top on it

Final quality assurance check? Passed! #cat

A gray tabby cat stands on the table top and sniffs at itThe cat is curled up in a circle on the tabletop