Archives for posts tagged ‘welding’

55-gallon drum smoker

This past fall I took an evening welding class at a local technical school and got very excited about making things out of metal. I already had an old stick welder that I didn’t really know how to use, and I ended up buying a MIG welder–the Hobart Handler 140 from Northern. After making lots of small assemblages out of scrap metal¬† I managed to build a stool and a couple of plant stands, but I had bigger plans.

There’s something special about creating useful objects. A smoker is a nice combination of supremely useful (preparing sustenance) and slightly frivolous (do you need a smoked pork butt to survive?). There are certainly faster and more efficient ways to cook food, but damn smoked meat is good.

I looked around at commercial smokers and custom hacks and talked to a few connoisseurs, and decided the Weber Smoky Mountain was a good design to start from. It’s simple and effective, and in the end it mostly convinced me that the design need not be complex.

Something appealed to me about using the iconic 55-gallon drum as a building block, so I went out and bought a couple from the local scrap yard. One of them even got immediate use as a beer barrel at Crushtoberfest!

A little sketching on different configurations, and I decided a ‘T’ shape would be simple, stable, and functional, and provide plenty of opportunity to practice the MIG on some thin sheet metal. I laid it out in CAD, which made it easy to generate the intersecting curve between the two barrels.

I printed the curve at full scale and wrapped it onto the barrel, traced the curve, then cut the barrel with a jig saw. The first dry fit was amazingly close (way to go, CAD!) but there was still a lot of grinding here and there to accommodate the ribs in the barrels.

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I measured and marked the door openings on the barrels and cut them out with the jig saw.

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The next step was grinding the paint off. The last thing I wanted was burning paint fumes getting into the food, so every bit of paint needed to go. If I were to do this again I would find another way… sand blasting, chemicals, burning it off, etc… anything but taking it off little by little with an angle grinder. I’ll admit the Gator brand paint & rust remover discs I found at Lowes were very effective (if a bit pricey at 9 bucks a piece). But my shop is now coated with a thin layer of green paint dust, much of which ended up in my nose and likely my lungs.

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On the first day of grinding I wore a respirator and glasses but nothing else. After washing my hair three times in a row to get the paint dust out I learned to don more protection. For the insides of the barrels I also used an LED headlamp.

As the barrels were made of surprisingly thin metal (20 gauge) the door openings needed to be reinforced with some angle and rolled sheet metal strips, which were plug welded from the outside and tacked from the inside.

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The doors also needed reinforcement, in the form of sheet metal ribs tacked onto the undersides.

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I welded small pads onto the barrels and doors for the stainless steel hinges. These pads were ground flat then drilled and tapped.

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After grinding the rest of the paint off I welded the two barrels together. This was a challenge, since the metal was so thin and the fit was far from perfect. To prevent burn-through and warpage I used a “stitching” technique where you put a quick tack weld across the joint, wait a second or less and put another tack next to it, continuing like that for about an inch at a time. Apparently this puts less heat to the metal than a continuous bead, but the end result looks very similar. With a little practice I was even able to bridge relatively large gaps between the barrels with short, controlled beads that build on each other, kind of like ants crossing a stream.

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I shopped around looking for off-the-shelf replacement grates that would work but none of them were big enough for this guy. So I bought about 80 feet of 1/4″ diameter 304 stainless rod (from onlinemetals.com) and cut it to length on the abrasive chop saw. I scored a piece of 1x pine on the table saw at the proper spacing to use as a jig, and clamped the rods down. The MIG would have been perfect for welding the grates, but I would have needed to buy stainless wire and a separate tank of tri-mix gas (65% argon, 33% helium and 2% CO2). The stainless itself was already pushing my budget, so I bought a handful of stainless welding rods and used the arc welder.

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Next I drilled holes for the dampers– two sets of three holes at the top and two sets of four holes the bottom. The top ones were made like typical grill dampers with a round rotating plate. The bottom ones needed to be on a curved surface, so they slide along the surface rather than rotating.

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In both cases the moving damper is retained by screws, so I drilled holes and tacked some steel nuts behind them.

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I then drilled a series of holes to allow the smoke and heat into the top barrel. My step drill bit did an amazing job, but the cordless drill still went through two fully charged batteries getting the job done.

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Next I tacked on some small support tabs for the grates and six small sections of square tube as feet.

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After a thorough deburring, wire-brushing and degreasing with alcohol, I set about applying a high-temperature grill paint. There are several available but Rustoleum High Heat Brush On was a) available at Lowes and b) didn’t require curing at a high temperature like most of the products I found online. Unfortunately it only comes in black, which is actually slightly brownish. They recommend only applying one coat, which I agree with after trying to touch up a few spots after drying, resulting in some weird gloss differences. I then tried the spray can version of the same paint, but found it to be flat finish (vs. the brush-on which is satin). The lesson here is get it right with the first coat because you really can’t go back and hit it again.

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While the paint was drying (24 hrs… it’s oil-based) I fabricated some handles out of a 1″ maple dowel. I don’t have a wood lathe but the metal lathe did the job. A few coats of Polycrylic and they’re ready to assemble.

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The smoker can be used in one of two different ways– with charcoal in an expanded metal basket or with wood on a traditional fireplace grate. I suppose I could retrofit some gas burners or even electric heating elements, but that’s a project for another day.

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And last, final assembly. I bought a 3″ smoker/grill thermometer online, and used some nickel-plated chain for the lid stays. I also fabricated a sheet metal “drip tray” to cover the holes under the food and deflect some of the heat.

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I figured my brother-in-law Pete would make much better use of this than me, so we gave it to him for Christmas. Here he is opening it…

Pete getting his present

 

controller box mounting arm

I don’t usually build as I go, without detailed planning or at least some sketches. But one Saturday a few weeks ago I had several hours to myself and I was itching to make some physical progress on the CNC conversion, so I took a quick inventory of my metal stock pile and just started building.

custom CNC controller box welded steel The mounting arm for the CNC controller box–that physically attaches the box to the mill–is a very simple part with well-defined parameters. The controller box has four mounting holes on the back side and the column of the mill is a thick iron casting that can be drilled & tapped basically anywhere. I knew approximately where I wanted the box to be, so it was a simple connect-the-dots part design. I had a 2′ length of square steel tube and some angle iron, so I started chopping it up and dry-fit it to the back of the controller box.

MIG welded steel

I MIG welded it together (still practicing that welding… getting better) and cleaned it up, then primed it with some Rustoleum, then did a quick test fit on the mill.

custom CNC controller box mounting arm

custom CNC controller box

A couple of coats of black lacquer and it’s good to go!

custom CNC controller box mounting arm

CNC mill – metal fabrication

With the CAD design more or less complete it’s time to make some parts. I generated some 2D views of the various parts and plotted them at full scale, then spray-mounted them to some sheet metal, most of which I had cut to size beforehand.

fabricating parts for the custom CNC controller box

As a result, most of the fabrication involved simply drilling and tapping the right sized holes in the steel:

fabricating parts for the custom CNC controller box

But some of the more complicated parts required cutting out larger areas of material. I did most of this very slowly with the jig saw and a metal-cutting blade. But some of the rectangular areas allowed me to use the mill!

fabricating parts for the custom CNC controller box

I quickly realized that this machine will be challenged by steel, as even this thin material caused the whole column/head to flex as I cranked on the wheels. I think it will be possible to machine steel, but the feeds will need to be very slow and it will definitely require copious amounts of coolant.

Here’s the “lower cabinet assembly”–the part that will house the motor drivers and their power supply–welded up and primed:

fabricating parts for the custom CNC controller box

The front panel of the controller box required extensive modification, done entirely with the jig saw and drill bits (the large holes were made with a step drill). I couldn’t wait to dry-fit the assembly onto the mounting arm:

fabricating a custom CNC controller box

The front panel also required a fair amount of welded parts on the back side, for mounting the monitor and keyboard. Notice how the thin sheet metal warped after welding:

fabricating a custom CNC controller box

Final fitting before priming and painting:

fabricating a custom CNC controller box

Next step, assembly…

DIY tube-bending tool

My plans for the milling machine oiling system call for some small-diameter bent brass tubing. I looked into the various tools designed for this, but the high end is too expensive and the low end looks pretty cheesy. I also wanted a small bend radius, which is hard to come by in off the shelf tools. It seemed easy enough to design a simple bending tool, and besides there’s nothing I like better than making stuff that makes other stuff.

My tubing has a 3/16″ OD and I was aiming for a 3/8″ bend radius (to the centerline of the tubing). I only anticipate needing 90 degree bends, but it didn’t seem any harder to allow for 180 degree bends. With these parameters I modeled up a simple design in CAD and ordered a few pieces of brass and steel from onlinemetals.

The first step was to grind a lathe tool blank to a 3/16″ diameter half-round shape. With this I turned some 3/4″ brass round rod into a set of rollers that closely fit the 3/16″ tubing.

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I then milled the end of a 4″ length of 9/16″ square brass bar to accept the smaller roller, and drilled it for a tight fit to a 1/4″ dowel pin (1″ long).

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I then drilled two 12″ lengths of 1/8″ x 3/4″ mild steel to accept the two rollers and welded two more shorter lengths of steel to create a rectangular tube handle. Done and done!

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The square brass bar is clamped into the vise, and the tube to be bent is gently clamped to the brass bar with a rubber-jawed clamp. The first test worked perfectly!

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The bends aren’t perfect– there’s a small amount of collapsing, probably from the small bend radius and the imperfect roller profiles. But I sawed through one of the bends at the thinnest part to see how much collapsing there was, and I think it’s acceptable for my needs.

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Here is the collapsed section (top) next to the normal tube section for comparison. Not bad!

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Next step: experiments in brass soldering.