Introduction: Laser Cut Wheelchair Model.
I am a senior lecturer in making at The Arts University Bournemouth. I am part of the BA (Hons) Modelmaking teathing team. When I am not teaching modelmaking I make and sell lamps and lights at my website, www.willstrange.net.
Welcome to the first in a series written with the experience of teaching students how to make. These will suggest projects that should help my students and others with similar interests.
Laser cutters are fabulously useful for cutting out flat shapes very accurately, or repeatedly. This accuracy makes it possible to fix those 2d parts together to make 3d things too, but all too often I see these assembled with weak, glued, butt joints. For some fine details on delicate architectural models this is fine, but for jigs, mechanisms and prototype development something stronger and easier is needed...
Here's a project to practice basic laser cutting, to produce a simple model that uses 'tab & slot' joints for strength and accuracy.
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Step 1: Design, Preparation & CAD:
The model is designed to be laser cut in acrylic sheet and glued together with a solvent adhesive, using 'tabs & slots' to locate the parts. It is a model that I use as part of my teaching of BA (Hons) Modelmaking at AUB, where I am a senior lecturer. I use this model to illustrate to students how to use the laser cutter and how a fairly detailed 3D model can be assembled from simple 2D parts.
This is 'dolls house scale’, 1:12, as drawn, but can obviously be enlarged or reduced to change this. If you do this remember to either use different thickness of material or alter the drawing, as the 'tabs & slots' will scale with the rest of the drawing.
The slots rely on being the same height as the thickness of the tab. If cut in 2mm material, the slots should be 2mm high. The tabs and the slots should always be the same width.
Download a set of files from my Thingiverse pages here. There are sets of files in different formats, chose the most suitable for the software that you have. The files are labeled as 'black, 'grey' and 'colour'. For the best results cut the 'black' in black material, as these parts will be the tyres and details that look best in black. The 'grey' file will cut the frame and wheels etc, these look best in grey, silver or similar. The 'colour' file will cut the seat and backrest. These can be any colour you like.
Tip: Pinseal finished material can look a lot like leather for these parts. Real leather could look really cool and practice cutting another material (I've not had a chance to try this yet).
Step 2: Ingredients:
- 170mm x 140mm 'Grey' 2mm acrylic sheet.
- 60mm x 110mm 'Black 2mm acrylic sheet.
- 60mm x 80mm 'Colour' 2mm acrylic sheet.
(These sizes allow for 4-5mm space around the parts for positioning in the laser cutter.)
Step 3: Cutting the Parts:
Here at BA (Hons) Modelmaking I have access to Trotec 'Speedy' laser cutters. Any other kind of laser cutter will be fine and, with a little editing, the files will work fine for cutting with a CNC router too. The Adobe Illustrator files are set up to cut, from Adobe Illustrator, with a Trotec laser cutter, using Trotec 'JobControl' software. The outlines are set to a hairline thickness and the colour is pure red (R, G, B = 255, 0, 0).
Note: In the pictures I am assembling my model with 3mm acrylic after first scaling the drawings acordingly (This made it easier to photograph and big enough to use as a teaching 'prop').
The back wheels are added by sliding a round spacer, or hub, onto the 'axles' followed by the pre-assembled wheels. Use a little solvent to fix these, and then support the model so that he wheels do not bear any weight while the glue sets.
Step 4: Assembly:
The model is best fixed together with solvent adhesive. Plastic Weld, Acrylic cement or similar is used to weld the plasic together, making a much stronger joint than any glue that does not weld the plastic together. Follow the exploded diagram for assembly of the pieces...
Start by fixing together the 2 wheels. Place the 'grey' spokes inside the 'black' tyre and tack together in a couple of places. add the 'grey' push-ring. and fix this sub-assembly together. Repeat to make the 2 wheels.
Lay one of the side panels down and fix the seat and back-rest in place. An engineer's square could be used to make sure that the seat and back-rest are perpendicular to the side panel. Add the other side panel and let the model sit for a couple of minutes to allow the solvent to set a little.
Stand the model up again and add the 3 'grey' beams below the seat and between the push-handles. These will give the model plenty of strength, once the solvent is left to set.
Note: One of these beams is long enough to provide an 'axle' for the back wheels. Make sure that this is in the right place.
Step 5: Now the Details...
The front wheels are glued into place so that their centres align with the centre of the 'hubs' that were cut as part of the side panels.
Foot rests have tabs that fit into slots in the side panels. Fix these in place, one side at a time, with the side panels laying down. They might drop out of place if the model is moved too much before the solvent has time to set.
Arm rests fit into rebates in each of the side panels. Fix these in place with the model resting on it's wheels, upright.
Step 6: Notes:
The model is intended to be used to demonstrate the principles of 'tab & slot' construction, how this can enable 3d objects to made from simple 2d parts, and to teach students how to use the laser cutter. It is not meant to be a toy...
Made with acrylic sheet the model will be fairly fragile and is not suited to rough play by small children. If broken, the acrylic parts will have very sharp edges!
For children, cut the parts from softer material. Try soft foam or cardboard?