Sunday, 3 May 2015

LASER CUTTING TERROR’S BULKHEADS

I have arrived at the stage of my build where I am assembling the bulkheads that will give shape to the ship’s hull. I have already created bulkheads for this model using the traditional method – gluing the plans to plywood and cutting them out using a scroll saw. 

The old bulkheads - cut using a scroll saw (prior to sanding). 

However, I recently decided to change the way I will construct the bow of the model. I had originally modified the forward stations to account for the extra bolsters and planking at the bow, but I've recently decided to try to build these fittings (as a means to determine how Rice actually reinforced Terror against the ice). This necessitated rebuilding the two most forward station bulkheads. 

And this gave me an excuse for a whole new mini-project.

Following a current trend, my local public library recently opened a prototyping studio, which includes design software, 3D printers, and an Epilogue Mini 24 Laser Cutter. The library allows you to book the equipment for several hours each month - for free. I've wanted to experiment with a laser cutter for some time, and since I needed to make new bulkheads anyway, I decided to recut all of them. My hope was that it would result in a more accurate build.

The Epilogue Mini 24 Laser Cutter. The bed capacity is 12" x 24". 

The cutter works very much like a traditional printer and will engrave (raster) or cut (vector) based on the thickness of the lines shown in the image file (I used high resolution PDFs for this). My first attempt, using factory recommended settings, was somewhat of a disaster, resulting in charred and smoldering wood and unusable pieces (plywood is notoriously difficult to cut because of its inconsistent composition).

My first disastrous attempt. Note the burned and charred edges.

For my second attempt, I conducted some tests and determined the proper power settings needed to cut 5mm plywood with the thinnest, most accurate, cuts and a minimum of charring and burning [1].

As a test, I cut a series of discs with different power settings. 

The appearance of the cut edge with the proper settings (no charring). 


I engraved the station markings on each bulkhead.  The machine automatically engraves before cutting.

The bulkheads being cut. 

You can tell the cut was successful if the part drops away from the sheet. 

A finished sheet. 

Each bulkhead fits into slots on the false keel. 

The bulkheads slide snugly into place. 

Test assembly proceeds. This is just a dry -fit. 

The bulkheads dry-fitted in place. They need to be properly aligned, but I'm happy with the run already.
Mini-Crozier allows us to visualize how large Terror actually was (quite small for a Royal Navy vessel).  

A view from the bow.

This view shows the run of the ice channels very nicely. 

A top-side view from the stern. The bulkheads are just dry-fitted here and will need to be
aligned properly before gluing. 

I am very pleased with my experience using the laser cutter. The bulkheads are much more accurate than I could have produced by hand, and the process took about a tenth of the time normally required to cut and sand these parts. I will certainly be using it again when I need to cut more complex shapes and components for my build. 



Footnotes:
[1] For those interested, low speed, power, and PPI settings are a must, and the recommended wood settings for the Epilogue Laser will not work on plywood. Your goal should be a setting that will just barely cut completely through the wood, as this results in the thinnest cuts and edges that are browned, but not charred. My settings for good quality 5mm birch plywood were: Speed = 10, Power = 38, and PPI(Frequency) = 150.

14 comments:

  1. It is fascinating how the state of the art technologies have not only helped to find the Erebus and to scan it but they are also helping you to build a model of the ship ten times faster than usual...at least as for the hull. I guess that the printer couldn´t help you too much with the rigging.

    Excellent work and excellent test! I am eager to see how the planking of the hull evolves.

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  2. Astounding technology and accuracy. How many different types of wood will eventually be involved in the process?

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  3. Thanks you Andrés and Glenn for your comments, they are much appreciated. I plan to use at least three types of wood in the construction of the ship, including Swiss pear for the hull planking, holly for the ice channels and the deck planking, and perhaps another type of wood (to be decided) for the deck fittings.

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