Monday
Oct192009

Designing a Backbox

I've put some careful thought into the design of my backbox recently. I even went as far as modelling my design in 3D to see if it would work. Application of a design is another thing entirely though so here's hoping my novice woodworking skills can pay off.

(I'll be releasing detailed plans once the cab is finished. To help those who need it.)

Design Requirements

On a real backbox the translite glass and speaker grill are removed from the front. A lock on the top (front) of the backbox holds it all in place. I don't like gaps or seams, and I don't really like the look of the lock on the front either. So I set about making a design that allows me to slide the speaker grill in from the top. Maybe this is overkill, but hey, it's all part and fun of a custom project.

So, what am I looking for in a design? First it needs to look clean and not clumped together. Secondly and where possible I don't want any seams and especally no gaps.

The backbox needs to be easily serviced in the case I ever need to get back in there.  It also needs to cater for a translite glass, backlighting and a single monitor setup.

The Design...

I really liked the 90's style Williams / Bally backbox with the over hang up top. So in terms of looks, my decision was easy. If you end up using the design and don't like this, it is easily modified to reduce the over hang.

Some key features of this design are:

  • The use of a 22inch 16:10 Display.
  • 4 inch car audio speakers.
  • Sliding top and lock to remove glass / translite.
  • 90's look and feel.
  • No gaps around the glass or speaker grill.

Similar to a 90's Williams / Bally design in size.

Sliding Top / Glass Removal

So from the following pictures you'll be able to see the basic function of the design. A lock on the back holds a sliding panel in place. Routed groves prevent the piece from being removed upwards and the design of the groove covers the inner slot where the glass and speaker grill slides down. The speaker grill is 12mm thick and a small edge is routed on the top of it where the bottom of the glass rests on it.

For simplicity I'm using two sheets of 4mm thick Glass and will wedge the translite image between them. The inner glass slot on the box is approximately 9mm wide. The speaker grill edges are routed down from 12mm to a 9mm edge so that it can also slide down this slot and then push into place below.

It remains to be seen if this is going to work in practice. Manipulating small grooves into MDF can be tricky so I may have to modify things as I actually build it. I'll post what I learn when it's complete.

Top panel closed and locked.Glass slides in and out when panel open and unlocked.Disassembled for service.

Screen Size

The backbox screen serves two purposes. Displaying the backbox image of the table being played and the DMD below that. The (DMD - Dot Matrix Display is what hosts the score and play information on a real pin).

A lot of people are going for full sized 30inch screens on the back box and even a second monitor for the DMD. For me I really liked the opportunity to create some custom artwork around the screen as per the original Ultrapin design. I really liked what I saw of others in the community too. I'm not saying it's a better option, but something about custom artwork really appeals to me.

22inch 16:10 LCD monitors are still pretty common and do the job nicely. If you can get a bigger 4:3 monitor then great, but 22inch were the most affordable right now (which meets one of my earlier requirements to keep cost down) and still gives a simulated DMD of approximately 12 inches wide when the monitor is placed vertically. (appox 13 inches on a real DMD so not far off).

Speakers

I'm using 4 inch car audio speakers (2 in 1 tweeter/mid model) for the speaker grill. This is basically a copy of what BadBoyBill did on his design. You can use the cover as a good routing guide to make perfect sized holes which I'll explain in a future post.

 

« Backbox Build Begins! | Main | Artwork & Theme »