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Finished the sandblast cabinet

Since last time I’ve posted, I’ve finished the sandblast cabinet. Here’s how it looks when it’s done.

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How I got here from my last post was once I built the basic shell, I lifted the hopper inside the cabinet and attached it.

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Before moving on to cutting out the openings for the glass and holes for my arms.

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I made some tabs on the door sides which would give the door clamps something to pull against.

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After this came some metal prep

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and getting a coat of primer before winter set in and shut me down.

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While I couldn’t paint during winter, I was able to make some progress. Using a hole punch, I created the openings for the electrical boxes for the lights.

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That’s it for the sandblast cabinet. I’m off to my next tool, a Coldsaw Station because I’m tired of cutting steel on the floor.

Here’s a rough idea of what it’ll look like.

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How to make the hopper

A visitor asked how I made the hopper. I was going to reply as a comment, but figured I’d write a full post to show how I made it.

The easy way is to use SketchUp. I’ll use the dimensions Tom is asking about for his hopper. 40″ x 24″.

First, draw a rectangle in SketchUp that is 40″ wide by 24″ deep.

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Next, use the Push/Pull Tool to give it some height. This is what we don’t know yet, so let’s just use 24″.

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Pan to the underside of our newly created 40″ x 24″ x 24″ box, since the trap door is on the bottom.

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Next, use the Tape Measure tool to draw some guide lines. Make sure it’s in Guide mode by having the + sign in the cursor. Use the Ctrl key to toggle the tool mode. Now, click on the green axis line and let’s place a guideline at 20″, half the width of the box. Draw a horizontal guide using the red axis and place it at 12″. You can use one of the edges and let the tool select the midpoint of the line.

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There may be an easier way to do this, but this works for me.

Using the Tape Tool, create horizontal guidelines that are offset from the horizontal mid-line by 2″, and 1.5″ offset for the depth mid-line. It should look like this.

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Put the model in Wireframe mode, and draw lines from the 3 x 4 rectangle to the 40 x 24 rectangle at the top. In my picture I drew two of the lines to the wrong corners. It’s easy to see this mistake when you start deleting lines. Just undo in SketchUp to correct any mistakes you make.

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Using the Eraser Tool, erase the 40 x 24 rectangle on the bottom. Be sure to take it out of Wireframe mode when you’re done.

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OK, this gives us our plenum, but how tall should it be. If we imagine a right triangle that starts at the center point of the 40″ side, travels along the top face of the plenum, and stops at 10″ back, which is 1/2 the depth of the plenum, less 1/2 the depth of the bottom face. Then the triangle takes a right angle and travels vertically down, it will arrive at the midpoint of the front edge of the bottom face. The hypotenuse of this triangle would be the height of the 40 x 3 trapezoid shape. In case my explanation doesn’t make sense, I’ve drawn it out.

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Now that we’ve drawn this triangle, we can ask SketchUp to give us the height of this 40 x 3 trapezoid shape. Comes out to 26″. But how do we know this is enough or not? TP Tools also sells a pickup tube, or you can make your own. In my case, I measured the length of their pickup tube, added some extra for good measure to arrive at the length. I don’t remember how long I made mine, but let’s say in this example, that we want this hypotenuse to be 30″.

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Using a2 + b2 = c2 (a squared + b squared = c squared), we know the hypotenuse we want, 30″, we know one side, which is 10″. So how tall would this plenum be to make this work out. Solving for B gives us b2 = c2 – a2, or b2 = (30 * 30) – (10 * 10), or b2 = 900 – 100, or b2 = 800. Taking the square root of 800, gives us 28.28″.

Knowing this, we can now solve for the side. The triangles top edge is (40 / 2) – (3 / 2), or 20 – 1.5 or 18.5″. The height will still be the same, 28.8, so now we know a and b, this gives us a2 + b2 = c2, or (18.5 * 18.5) + (28.8 * 28.8) = c2, 342 + 829.44 = c2, or 34.22″.

Now that I have my dimensions, I can draw them in SketchUp. Select the face that is 40 x 3, right click and choose Select -> Bounding Edges. We’ll make a copy of this face using the Move tool in Add mode (Ctrl key) and drag it to the Origin.

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Using the Rotate Tool, rotate this face to lie flat on the earth plane. We need to rotate around the red axis, so make sure the Rotate tool is in the right orientation.

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Once rotated, it should be lying on the earth plane. This is the starting shape of the front side of the hopper. But we need to make it easy to mount inside the cabinet, and we need an way to mount the trap door and we need to have the sides edges line up with the other pieces. So let’s create some flanges (not sure if that’s the right word).

I’ll use a 1.5″ flange on top, a 1″ flange on the sides, and a 1″ flange on the bottom which we’ll mount the trap door to.

After drawing some guidelines and drawing some lines, this is what you end up with.

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If we bent this shape using a sheet metal brake, this is how the shape would look.

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After all this, it might be easier to take your steel to a local HVAC company and tell them you want a plenum that is 40 x 24 that reduces to 3 x 4, has a 1.5″ flange on top, a 1″ flange on bottom with the 40″ side having a length of 28.8″, or round up to 29″.

How I mounted the trap door, was once I had the 3 x 4 opening with a 1″ flange, it fit inside the plastic part from TP Tools. I then drilled some holes through the plastic and steel and use cap screws or rivets to attach the trap door to the steel hopper.

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Building the sand blast cabinet

Once the hopper was done (I can’t say that without thinking of the Dish Network commercial) I moved on to building the sand blast cabinet.

The cabinet will measure 5′ wide x 6′ high x 30″ deep. Back in February I picked up 16ga sheet that I cut out the panels from. I struggled with how I was going to build the cabinet until I came across the idea of building some scaffolding. It’s not an original idea, it’s just how I chose to put it together.

It started with building a wooden framework that I could clamp the 16ga panels to. In this photo I’ve placed the door frames against the scaffolding to make sure I had the dimensions correct.

Then I began to hang the sheets of metal. There are the rear panel, top, window, front panel, two side panels and two legs. Here’s a picture showing everything but the side panels and the legs tacked together.

I created another framework to support the hopper while I moved it into position inside the cabinet.

Next step was to build the legs. If I was to do this all over again I would make the legs and the front panel from a single piece and cut out the front opening. It started with laying out the 16ga sheet, using a straight edge and the plasma cutter and cutting out a piece.

Then once I have a piece that is the correct overall dimensions, I need to reduce it down by cutting the angle for the legs. The legs are about 2′ tall with a taper from 20″ at the top to around 8″ at the floor. This is around a 60 degree angle. So using a straight edge and the plasma cutter

I end up with this shape

and using a set of butt joint clamps, I can clamp it to the rest of the cabinet.

The side panels were cut out and drilled that I’ll use to weld the leg panels to the inside of the door frame.

In this picture I’ve clamped the side panels to the door frame prior to welding.

Here’s it’s all roughly welded together before inserting the hopper.

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Sand blast cabinet – hopper

I didn’t get any pictures, or if I did, I can’t find them, but after building the work support out of 1.5″ x 1.5″ x 11ga angle iron that measures 58″ x 34″  this will give me plenty of space to clean a fender and possibly a bumper.

I started with cutting out the hopper out of 18ga sheet which I then clamped to the work support frame.

I was going to use a spring loaded trap door at the bottom of the hopper to allow me to drain it and replace the media when necessary. The trap door I’m using came from TP Tools, so I made a spacer out of some steel I had laying around and clamped it in the hopper. 

I kept cutting out the 18ga sheet to make the other two sides and ended up with a decent funnel shape. When I was in high school I worked at a HVAC company where I made plenums. I sure wish I had the sheet metal brake and spot welder that I used in that shop. I then proceeded to tack weld it together.

After everything was together I moved on to fully welding the joint and grinding it smooth.

I double-checked that the trap door would fit the hopper.

When this was done, I turned it over and added seam filler to the joints. The idea is to make a box that is air tight enough that the vacuum will draw air through the inlet and not all over the place. I don’t want it leaking like a sieve. It’s not a good picture but it’s all I have from this step.

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Shop air

After getting the cutting torch and drill press I was in the mood to solve another problem I was having at the shop. Not enough air.

I have a 30 gallon Craftsman compressor that I bought a few years ago for the house. When I moved into the shop I took the compressor with me with the idea that I would eventually replace it with a larger compressor.

When my dad and I had our shop we had a 5 HP 60 gallon compressor and a media blast cabinet. It was great but the compressor wasn’t a true 5 HP and it would struggle to keep up with the compressor, or keep a dual-action sander running. So I was looking for a real 5 HP or larger.

I wanted a Champion compressor, but those things are really expensive and buying new would really cut into my truck budget. But since Karen turned me on to Craigslist, I thought I’d look for a slightly used one.

Boy did I luck out. Not long after I started looking, a used Champion came up for sale on Craigslist. It was in Garland and was just refurbished by an air compressor company and looked to be in great shape. I took an hour off for lunch with the idea of driving over there and making what I thought was an obscene offer. Well they took my offer and now I had to get my new compressor over to the shop in Fort Worth.

When I got to the shop I was able to locate a neighbor who had a fork lift and they were kind enough to unload it for me in the shop.

Compressor

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Cutting torch & drill press

Last week I had finished prepping the sides to the frame rails and was ready to lay down the 2” x 1/8” flat-bar that would serve as the top and bottom of each frame rail. After trying to bend the flat-bar I realized I would need some heat to make the job easier and to keep the flat-bar in shape while I tack welded it together.

After pricing what a new oxy/acetylene torch was going to run, Karen started looking for me on Craigslist. She found a guy in Cresson, TX who was selling one. He also had a 18” Delta Drill press for sale which I also needed. I only had this small 10” drill press at the shop and while it was functional, it just didn’t have enough oomph to do what I needed it to do.

Since Monday I was off for Marlin Luther King Day, we drove out to Cresson to pick up the new tools.

He told me he was near the “old Pate Museum” and I asked why he used “old”. He told me that the family has shut down the museum at the end of 2010. A couple of months back I was thinking about going out to visit the Pate Museum. I remember going to Pate with my family when they used to have the Pate Swap Meet held out there. I must have spent a lot of summers in my childhood going to Pate. It was always my favorite swap meet and it must have been my dad’s because I remember us going numerous times.

We picked up the tools and dropped them off at the shop before heading home.

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