Tuesday
Nov032009

Backbox Build Begins!

Starting The Backbox Build

Ok so I've been floundering on the build and that's because I'm learning as I go. When you don't have a dedicated workshop and while you juggle 2 kids under the age of 3 it's all so fun. My wife has been very supportive of this, so again - thanks luv!

I've also taken a step back and decided I don't want to rush this build. I am only going to do this once so I want to take as much care as I possibly can to get a finish I'll be proud of. Yes, that means the perfectionist in me is going to make it all that more frustrating. Seeing friends on the forums already so far ahead and enjoying their cabs and the latest Visual Pinball tables only makes me want this finished sooner.

Taking my backbox design, I've simplified it a little since the original drawings. I originally had plans to have complicated joins on all the sections but when I came to build it I found that MDF is not the ideal medium to route detail in as it can easily flake off. So now I will just have one slot for the glass and speaker grill and a sliding top section. The rest will be screwed together, patched up and have art work over any seams / gaps anyway.

Without making this a detailed guide here are some steps I followed and some thinking of the progress so far.

Cutting

The backbox is made out of 18mm thick MDF. The first and obvious step is to measure your pieces very accurately. MDF is cheap but time isnt, so as always measure twice, even three times before you cut once! "Yeah yeah" I hear you say, but I'm always surprised how many times I think I've thought it all through perfectly only to find mistakes.

Because I needed extremely accurate measurements for sliding panels it's not a good idea to just lay measurement of all the pieces next to each other (as in share edges) without taking into account the thickness of the saw blade that you will be using to make the cuts. Just a couple of mm out will make gaps appear! So I would make a cut, and then measure the next piece if I was to share that cut on the next piece.

I used a circular saw to cut my straight lines with the help of a quickly made saw board. (A saw board is a guided straight edge that you can run your circular saw along to maintain the accuracy of the cut. Remember though that you need to take into account the blade thickness (usually 1-2mm) when you setup your straight edge or sawboard.

Circular saws are ideal for straight cuts as the blade lends itself to straight cuts. You make sure your blade if fully spinning before you enter the cut, then guide it along the straight edge smoothly. You also want to catch the piece or support it as it comes free.

Table saws are great (wish I had one) but if you want to create non 90 degree cuts (like the front of my back box) then you need more complicated jigs. So I stick with a circular saw for this. A jigsaw can be used when clamping a straight edge is too tricky but you need a very steady hand. Another option is to use a router to tidy up edging but if you follow the circular saw technique carefully you should be fine.

Cutting MDF produces dust, a lot of dust! It's bad for your health to breath it in. Traditionally pinball cabinets are made of high quality plywood so to save on this and use MDF, it comes with another price - dust. Did I mention it produces a lot of dust? Make sure you wear the appropriate safety gear when cutting this stuff you will really notice it that night if you don't, coughing up thick dust for the next day. Not good!

Safety first. I try and wear this most of the time when making cuts

Router Table

With the main pieces cut it was time to add the routing detail. Trying to do this by setting up guides and passing the router over the work piece is a real pain. So, I made a very quick and cheap router table out of a spare piece of MDF and some bolts I had lying about. Check out the guide I added on how to create and use a table quickly. Remember this is really for the novice who want's to save cash. If you have a router table already then great!

To work a router table you set and adjust the bit and fence accordingly then pass the piece through. You can also setup and attach templates to make cuts and straighten edges with the right router bit.

Here is examples of what the router table let's you achieve with a 5mm straight wide bit.

Slot routed in the edge of the sliding top panel.Left side panel. Speaker grill and glass slot and the double slot for receiving the top panel. Using the same 5mm bit and adjusting the fence for multple passes allows for wider slots.

Practice Practice Practice!

It's a good idea to make a practice piece or two while you develop this routing skill. This was my first time using a router table, and making sure I practiced each cut first really helped me not ruin the final pieces. You get to feel the cuts and understand how the depths actually look even when you've measured what you think is right. You also get a feel for the cutting action and pull of the machine. Practice practice practice first!

Back Lock and Air Vents

From what I've seen, traditionally backboxes have 7 holes. As I'm placing a lock in the centre I've made 8 including the lock (6 probably would've been fine). I've recessed the lock so it looks flush. You do this with a slightly larger spade bit to make the recess followed by a smaller one to cut the hole (not the other way around!). When cutting holes like this be sure you place the piece flat onto a spare piece of wood to drill through to. Then you will reduce tear away on the other side. It really will tear ugly if you don't do this, just try it on scrap first if you don't believe me!

Back panel. Centered air holes with lock.

The lock latch rotates upward and will fit into a groove on the top sliding panel. This will prevent it from being able to slide out.

I actually made a mistake when i placed my lock on the back box, I was thinking aesthetics and not function and placed it too low. Easily fixed by making the latch longer but there's an example of not measuring twice or three times before making a cut! Over eagerness can get you into a lot of trouble.

Speaker Grill

In the following pictures you can see the speaker grill. I cut this with a jigsaw and to be honest hated the result. Even with a very steady hand the circles just weren't good enough. It doesn't show in the pictures but there is unevenness in the cuts and it makes it looks poor when you hold up the speaker. I redid the panel with a routing technique and the results are 1000 times better. I'll make a separate post on that and how to go about it.

Putting It Together

With all the slots routed and pieces cut it was time to assemble. First I clamped the box together into the exact shape and then carefully predrilled all my screw holes. MDF can really fracture if you don't do this, so don't skip that step! I also recessed the drill holes slightly so the screw heads would sink in correctly and not be exposed at all. I used particle board woods screws for the job. They actually come with a square head bit and are good because there is a low chance of slippage when power drilling them in.

With the main body in place I was able to then slide in the top panel. It should be a super tight fit which is ok, I had to be careful to apply pressure in an even manner to get it in place. This doesn't need to have the action of a sliding drawer. Once assembled I expect I'll rarely need to open this again but I'll have the option which was the whole point of the design with out losing the gapless appeal. (The only gap being on the top of the box which you can't see.)

Top sliding panel goes in.The speaker grill can slide in and then followed by the eventual translite glass. The speaker grill actually is thicker than the slot but it's edges are routed to that width so it can slide down easily. It should fit nice and snug.

Speaker grill being inserted.

Speaker grill down and top shut.

Mistakes

You can see in the photos that the speaker grill / glass slot is slightly wider at the top of the box. I didn't allow room on the top panel to let this slide in as I changed my original design slightly on the fly. Another good lesson - don't change design on the fly! Typical time pressures and impatience will get you into trouble. I had to chisel the slot wider to get the speaker past the top panel, such a stupid mistake but luckly nothing was done that I can't easily hide. Annoying though! I contemplated redoing the whole thing out of pure frustration but soon realised that would be a complete waste of time. I'll make sure the corrections to my mistakes are included in any future plans I release.

Anyway onward and upwards... patience! I need patience! Lesson learnt.

« Speakers and Grill | Main | Designing a Backbox »

Reader Comments (2)

and if I try a hundred years would not be able to do that

May 1, 2010 | Unregistered Commentergerovital

After reflection on this back box design I can honestly say this level of detail is not necessary. I would still recommend the slot for the glass to fit into but the rest can just be screwed together.

May 23, 2010 | Registered CommenterDan Potter
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