Thursday, 7 April 2016

Never: Laser cutting a pinball playfield

Some of these different sections are excepts edited from my weekly progress posts during my six weeks of holidays in February -> March.

Translate to cutter file I'm retheming a Bally Supersonic, retaining the most part of the layout and making alterations to the inserts for LEDs. The slow careful process of measuring the parts on the Supersonic playfield and mapping them out in Illustrator.

Why lasercut? A pinball playfield is usually CNC routed, with a router you are able to control the depth of a cut, so you can make a small lip at a precise depth into the plywood for plastics to be glued into. I've designed my own plastic inserts, with a more detailed shape than standard pinball plastic parts. So to do this I need the intricacy of lasercutting, and unlike the router, lasercutting cannot cut a certain depth into a material.

The 'sandwich' method After some advice from Justin in woodwork, I decided to make a sandwich of plywood using two outer sheets (top & bottom) of 3mm and an inner core of 6mm ply. Although I could have used only two sheets, I'm told this sandwiching method will give extra strength to the playfield, which is something I was worried about when glueing together plywood sheets face to face.

Test Cuts Tested the sandwich concept of using sheets glued together, while creating a lip for plastic inserts to be glued into place.

Paper plan I made a quick paper plan of the playfield cutter template I've been working on. I laid this over the playfield and made small alterations - since it was all measured by hand there was bound to be a few bits a little off.
Sourcing materials needed 3mm and 6mm laser ply to make the 12mm playfield, luckily they had just the right amount in stock already at uni, so I snapped it up!
Finish file prep booking the larger lasercutter to cut this size and depth of material costs quite a bit more, so I want to make sure there are absolutely no file issues before hand so not to waste time. The staff in lasercutting are very helpful and let me jump on one of the computers a bit earlier to sort out the ordering of cutting - which can only really be done in the software not in Illustrator.
Cut it out Apart from registration of the material on the lasercutter bed, the process is all in the setup on the software side of things. When cutting, it's a case on monitoring the cut is all going to plan. Some bits on knots in the plywood needed to get a second pass, which is done with great care!
Cutting complete that is the laser cutting done and I now how the three different layers ready to glue together.
Plugs or Pegs From past mistakes in lasercutting and glueing together sheets of material, I knew it would be near impossible to line up the sheets precisely without some guides. I used a registration method using plugs and slightly different sized guide holes cut near the edges of the playfield. I originally found this method via Milwaukee Makerspace blog.
Fancy a sandwich? not lunch time it's glueing together the sheets. I used some diluted wood glue and a brush to quickly slap on the glue - using slightly diluted means the glue doesn't dry as quickly during application. Then it's weight and time. Overnight to dry.

We have a playfield! It's slightly unreal having the physical playfield cut, it's obviously such a crucial part of the final piece, so have put a lot of time into it, although it feels like another big milestone completed, I'm still so far off finishing!
Plastics Next is to laser my plastic inserts into 3mm acrylic, first step is to try out different size tolerances to try to achieve a snug fit in the lasercut wood.

Dial in the right size Testing out the different sizes on the cut playfield, I can tell right away 0 is too loose and +0.2 is too tight. +0.1 is just right so can go for it. I prepped different files for each possible size so i just open up the +0.1 and get cutting again, there's a lot less to do so back to using the smaller lasers.
Glue the inserts are easily glued into place. Doing a bit of reading up there were a few options for glue, although nothing perfect, it seems normal wood glue is sufficient!

What I'd do differently
  • I would glue the plastic inserts into the top layer before glueing together the sheets - it could be done when the bottom two layers are drying.
  • Although I engraved guide marks for drilling, I would try to lasercut these, slightly smaller than the screws, this will save time having to drill later on.

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