After getting the 4th axis up and functional, I thought I might as well try a project utilizing it. My concept was to create a dining table using the rotary as well as some old barn wood we had left over from building our house. Here's the CAD version of the idea. The original concept had this with two legs. After calculating how much aluminum that would take and how long it would take to machine, I scaled it back to a single leg.
I had wanted to use the rotary as a true 4th axis (simultaneous movement in all axis), but ran into trouble creating the gcode. My skills in NX 7.5 just weren't up to the task. So I back-pedaled and went with more of an indexer mode - basically turn 90 degrees between each operation. Although it's not what I started out wanting - it still allowed me to machine all four sides without removing it from the fixture.
Which brings me to the fixture. I've never really put much time into setups as I usually just want to get the part done. This time, I realized the number of parts I wanted to make plus using the 4th axis required one. I'd also never used dowel pins for location devices, so thought that would be fun too! Although it's a bit cumbersome to mount and dismount the part, it worked as designed. When I originally made the fixture, I was a bit careless about maintaining parallelism between the top and bottom. I realized this at about the 3rd part when I was having trouble with things matching up when the rotary went all the way around. Once I fixed that - it turned out to work very well.
Once I got that sorted, the first operation was to cut a chunk off the raw 5"x2.5" stock.
Next up was to add a set of holes - 3 threaded and 2 reamed (for the dowel pins to locate) on both sides to use for mounting in the fixture.
Then I sawed this at a 30 degree angle to make 2 blanks. Here it is mounted up on the fixture in the rotary about to do the first position.
I had never used dowel pins to align a jig and got to use over/under reamers to make it work. It was actually pretty easy and it really made things very predictable and repeatable.
To complete 1 part took around 55 minutes of machine time. Most of this was trying to get a very fine finish on the contoured areas which took a lot of passes.
I was originally planning to do enough for 2 legs, which would have required 48 sections. At an hour each, that really added up.
Once I had the buttress pieces done, I moved on to the leg. I mounted the lumber in my lathe and turned the ends. What a mess! Turning wood in a metal lathe gets sawdust everywhere!
After turning that down, I slipped on some aluminum collars to each end and put together what I had for a bit of a mockup.
Now that I had the leg mostly there - I started in on the top. I had wanted to make it up out of a bunch of strips and glue/screw them together. I really ran into issues with warped and twisted strips. I ended up wrestling it around to something I considered acceptable, but it was a lot harder than I thought it would be. It ended up being 48x36".
One feature I attempted was to use 5 threaded rods to hold the top together. Although I got it done, it was probably the worst part of this whole job. I really underestimated how much trouble it would be to drill straight holes though 3 feet of 3/4" strips of wood of varying species! I thought it would be fun to make a set of custom nuts to hold it together. I wanted to recess them into the side of the top. I based the design off the 12 lobed base.
You may be wondering how I got those nuts tightened up. Well you make a tool of course!
I wanted to have a plate mounted on the underside of the top to use to attach the leg and also to help stabilize the wood. I found a galvanized round cover of sort make out of diamond plate. I was going to expose the diamond plate, but ended up liking the other side more.
Next was the base. I found a 20" diameter metal plate that was apparently used as a pipe cap. It probably weighs about 80 lbs and was a bear getting into the mill by myself! I milled a pocket in the top for the leg and on the underside I added pockets for 6 feet, plus thread milled the outer holes to accept an adapter I needed for the feet.
I realized I needed a way to securely mount the aluminum collar on the ends of the leg so they wouldn't spin. I decided to glue it on, but then added a wedge - just to make sure!
And here's the final result!
Some additional notes:
I think the overall design was OK, but in looking at the finished product I think it didn't come together as well as it could have. Not bad for my first attempt at furniture, but there's room for improvement. My brother pointed out there should be some metal form from the base/leg coming up through the top. I think he's right as that aspect is sort of the point of the whole thing. My wife thinks there are too many materials involved and it doesn't really come together - she's right too. Additionally I think proportions of the top to the base are off, I probably should have gone with a circular top. Although I largely managed to solve it, there is tendency for the top to be able to spin on the base as the compression collars just don't provide enough force to resist that.