Monday, January 31, 2011

My wife's drafting table

Time for another project post.  You heard about my welding last time with my garden arbor.  Today, we talk about the drafting table I am welding for my wife.

For those of you that don't actually weld, there is a list of welding terms here.  You might want to refer to it eventually. :)

My wife took painting 1 and design 1 at the local community college this passed semester.  Now she wants a drafting table she can do her work on, but doesn't want to pay for it.  Since I'm welding now, we decided I should build her one.  Against her better judgment, we went to the local scrap yard for supplies.  (That's another thing I love about welding.  It's hard to find wood that has been sitting out in the weather for months in a dump and still use it.  But metal, for the most part, is just as good now as it was to start with.)  She didn't want to go, because she didn't think we'd find anything that looked good enough.

Of course, once we got there it was like everything had "Sale" signs on it and she went nuts.  We ended up finding some light-weight angle iron.  I honestly think it is too thin for the size of drafting table.  She wants this table 3ft by 5ft.  And with just a square frame of this, it twists very easily.  I'll fill the top with MDF, so that should stiffen it up quite a bit, but when she is raising and lowering the top, the bottom may twist and get wonky.  So I'll probably have to reinforce sections somewhere, but I'll worry about that later.

These are the two pieces I have completed so far.  The bottom is just a rectangular frame with pipes welded on for legs.  The top is the same thing, inverted.

Original Weld Quality
My welds were very ugly at first.  They're strong enough, and I've ground out some of them on the bottom piece to make sure the two pieces of metal have fused properly, but they're still ugly.  My welder sputters and skips, etc.  I think it is probably that I am moving too fast, or otherwise pulling the wire out of the puddle.  At least, that was one of the issues that caused the same symptoms when I was in the welding class.  Click on the image to the right to see a blown-up version, if you can't see what I mean in this one.  The width of the bead is uneven, it's rough in places, etc.

New, better weld quality
But then, something happened.  The first thing I noticed is that I started seeing a lot of porosity in my weld.  I don't have a picture of that, but for those that don't know, it means the weld starts looking like a sponge.  I checked my gas and everything looked right.  I checked my nozzle, and it had a little spatter on it, but not much and taking it off didn't make any difference.  I turned the gas up a bit to see if that would fix it.  It seemed to help a bit, although not much.  I also started seeing a drop of metal form on the end of the wire before it got to the puddle.  At this point, I was trying to weld up the side of my joint, so gravity wasn't pulling the drop into the puddle.  I decided to stand up and stretch and mess around a bit.  I seemed to recall that the wire melting early like that meant that the voltage was too high.  So I lowered the voltage and tried again.  It still did the same thing.  In MIG welding, your voltage controls your arc length.  Basically, how far away from the metal you can be while welding.  Since I had turned the voltage down, I moved a little closer to the joint.

And suddenly, my welds looked completely different.  Now, they are nice and smooth, no stuttering or skipping or anything like that.  Even the sound of the arc was better, going from a crackle to a hiss.  Sure, there are still flaws, but compared to my other welds, it's perfect.

Weld ground out.  Note the pinholes on the left
I ground out one.  I want to tell you that the vertical pass was actually done with the old settings, not the new, but I can't in all honesty.  I think it was, but I'm not sure.  There are pinholes in the vertical pass, but even then, the percentage area is small.  Sure, it will probably fail a bend test or something, but it will still hold, and my wife isn't going to be jumping up and down on this anyway (or she'd better not).  And the horizontal pass is completely fused, with no defects that I can see.  (Oh, and these were not welded vertical and horizontal, they were both welded flat.)

For anyone wondering, that large hole on the left hand side is the kerf from the grinder as I cut the bottom of the angle iron off.  On the bottom frame of the drafting table, I just overlapped the ends of the angle iron, so the sides are lower than the front and back.  On the top part, I decided to put more effort into the fabrication, so on the short pieces, I cut out a notch.  This allowed the end of the longer piece to fit in and be welded in place.  The image to the right is a view of a corner where I haven't welded the outside yet.  I ran out of wire, and haven't installed the new roll yet.  You can see where I cut out the bottom of the angle and fitted the other piece in.  You can also see that I'm barely leaving any gap and haven't beveled the edges at all.  The reason for notching it instead of overlapping it was to give me a flat surface, and I still can get one on the bottom if I grind my welds out.  But if I had thought about it, I could have beveled the edges and only welded from the outside.  That would have left me a flat surface on the inside as well.  But, I'm only using 1/2 inch or 3/4 inch MDF on the inside anyway, so I'll be welding some sort of riser to the inside to get the MDF above the edge.  That means the MDF will be above the inside welds and it won't cause a problem.

So, that's where I stand on the drafting table.  My next steps will be to make brackets to weld on the front corners, drill a hole, and stick a bolt through to form a hinge.  I still haven't decided how to make the desk raise or lower.  I've actually come up with several methods, and they won't be too hard to raise, but it will take two people to lower.  This is because the desk is too large to allow my wife to reach a support mounted in the middle, and it's also too large and flimsy to allow a support on just one side.  I'll keep you updated on what I decide to do, and how it turns out.

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