Category Archives: Laser engraving

One degree out: update

As it turns out, there was more at hand than a single degree error, now rectified. Thankfully, the method I mentioned in my last post was a success! However, I am now a couple of segments short. The laser power was now fluctuating to the point it could no longer penetrate the perspex I was using. Very strange. Marginally changing the power settings had no effect (I was using settings recommended to me by the laser’s owner). A test cut in my material of a small, 8mm diameter circle was a success. I set up the laser to cut a single segment. The image was perfectly transcribed into the plastic; but not through the plastic. Looking at the cut it became apparent that the laser power was decreasing with the length of the cut; the start of the cut penetrated the 3mm perspex with no problems, but after 30mm or so the beam no longer penetrated. I’m not sure how deep the cut was at the end, but I couldn’t press the shape out nor free it with a Stanley knife.

After a couple of weeks, other users’ experiences of the laser came to light and the alignment issue seems to have reappeared in addition to the power issues. As I type, new parts (a tube and mirrors) are being shipped from abroad in an attempt to fix the issues. Lets hope so, as I may be struggling to find another laser cutter if not!

Advertisements

One degree out

Table update: another small section complete! Or at least, almost. I made a small error.

IMG_2684

Spot the error

The alethiometer table has many sections (I’ll get round to posting the designs eventually!), one of which is a ring around the compass rose, inside the ring of symbols, with the full 360 degrees marked. This will be a slight variation on the wax inlay technique, as I’ll be using a gold gilting product called Rub ‘n’ Buff (Gold leaf) in place of the wax. A quick test before I ordered some expensive nearly-black perspex demonstrated that, with the addition of a little ethanol, the excess gold can be wiped off. The added bonus is that the ethanol also clears off the smoky residue left through the cutting process, without visibly scratching the mirror-like surface.

After a disastrous afternoon cutting the sections out on the laser I managed to cut the twelve sections of the ring. After a short chat with the chap who owns the laser cutter and a few minutes playing around with the settings, we identified the problem. The power dial had been replaced the previous evening, so I had completely the wrong settings. This meant that as the laser was cutting through the material the plastic became so hot it was melting behind the laser and sealing the cut. This cost me a full sheet of perspex and a couple of hours of my time, but I learnt an important lesson; perform a practise cut beforehand. At least then I’ll know I have the right settings!

Did you see it? The top three pieces are missing the last degree mark (on the right hand side). How I managed to miss this when I directed the laser to cut I’ll never know. I can’t leave them like that; I’ll have to fix it. Cutting another sheet of perspex is not an option. So I have to accurately place each segment onto the laser bed in order to engrave a single, 5mm line in exactly the right place at exactly the right angle. Now, what I could do is cut the full shape out of a piece of scrap perspex or ply, drop each incorrect segment into the hole and engrave the missing line. This way I can almost exactly place each section and merely direct the laser to engrave the missing line.

I’ll let you know how it goes.

Marquetry Workshop

When talking about my hobby, one thing people ask me is “How did you get into this?” – “this” being my main project, the table.

There are a number of things which contributed to this, really. The most influential of these was my introduction to Nottingham Hackspace. To be honest, I would never have had the idea, let alone thought it possible, had I not had access to the wonderful community and workshop facilities. Occasionally members run “workshops” where they bring a specific skill or task to an evening or weekend and demonstrate or teach anyone who is interested. It was one such workshop, run by a chap called Martin Raynsford (msraynsford.blogspot.co.uk), which introduced me to the art of marquetry.

Marquetry, for the unknowing, is a process by which pieces of veneer (thin slices of wood, usually of different colours or a particularly exotic species) are inlaid into an object, usually wood and glued into place. Martin had been using a laser cutter in order to precisely cut the veneer and inlay it into engraved pieces of wood, to great effect.

The workshop involved making a simple wooden coaster and inlaying pieces of veneer cut on the laser cutter, to form an image and your name. Needless to say, the act of arranging the pieces and glueing them into place was fiddly! In the end two methods emerged – glueing a few small pieces at a time and allowing the glue to dry before continuing, or assuming the design was less complicated, arranging the pieces next to the coaster, filling the inlay with glue then quickly transferring the veneer into place. A quick dab with a piece of paper towel and pressing a clean, scrap piece of ply over the top and weighing it down was essential. This was because the veneer has a tendency to curl upwards as the water-based glue was absorbed by the dry wood. Once dry, the coaster could be sanded smooth then oiled, stained or varnished to a variety of finishes.

The whole workshop took a couple of hours and my first coaster was a success, given to a friend as a house-warming present (I had personalised it with her name). I was not satisfied with making just one coaster, so a few days later I began trawling the internet for a design I liked to make a set of my own. This was where I first began to learn how to use Inkscape. The image I chose was similar to a Celtic knot-like pattern (I have no idea if that is the correct term!). The image was imported into Inkscape. The tool “Trace bitmap” provided me with a template, albeit a complicated one, so I simplified the drawing slightly by removing lots of small sections, whilst trying to keep at least an abstract form of the original pattern.

Two copies of the drawing had to be made – the shapes of each section in order to cut the veneer and block-filled sections to engrave the coaster. The latter was “mirrored” and inset, to allow for the diameter of the engraving laser beam, whilst the former was outset. This changes the drawing minutely by shrinking or expanding it half the width of the laser beam, approximately 0.15mm. If I had not done so, there would have been a gap the width of the laser beam around each piece of inlaid veneer!

A couple of hours of cutting later and I was ready to begin inlaying the coaster. In the end I opted for a variety of colours of veneer – my partner had purchased a mixed pack of coloured veneers for a similar project (http://fowkc.wordpress.com/2012/09/19/fluxx-box/) and I merely “helped myself” to the leftovers. Of which there was quite a lot. This produced a variety of pleasing combinations and I now have a selection of unique coasters scattered around my living room and desk, coated with a clear varnish to protect from inevitable cup-rings. In fact, I was so pleased, I engraved my name into the back!

IMG_2145

Completion of symbol tiles

Image

Thirty-six newly finished tiles!

One section is complete – the production of the symbols! This is probably my favourite part, despite the pitfalls of the process. 36 individual, unique, wax-inlaid perspex tiles, each featuring one of the symbols from the alethiometer.

So how did I do it?

Step one was obviously to find an image of the symbols. There are dozens of images of alethiometers on the internet, but only two were useful. One of them is below (apologies to the person who posted this on the internet – I’ve lost the original link)

Image

Stock image of the alethiometer symbols

So I separated each symbol and saved them as individual .png files, using Paint. They were then imported into Inkscape and rotated until they were upright and exported as a bitmap (.png again, but if these had just been saved as they were the page background would have been saved as well and I didn’t want that).

Meanwhile, in DraftSight, I created a CAD design of the tiles. Overkill, possibly, but Inkscape wasn’t accurate enough to keep me happy. Using Draftsight I could draw two circles centered on the origin, direct the program to draw a line dissecting both circles, then use Pattern>Circular pattern to replicate the line every 10 degrees around the circles. these could then be cut into individual tiles. One tile was then saved as a .dxf (R13 ASCII).

In the meantime, I ordered some perspex from http://www.plasticstockist.com. Specifically, 3mm thick Silk Opal 040 (51% light transmission). This is a partially transparent, slightly off-white perspex with a matt side. Given that the symbols in the alethiometer illuminate (admittedly only in the film, but it looks awesome!), I want to mount LEDs underneath the perspex in order to create that golden glow. This cost me something in the region of £7, excluding postage.

I had originally sized, aligned and saved the complete tiles in Inkscape and attempted to import both the tile outlines and symbol images as a complete file into the laser software NewlyDraw, but it was having none of it. Using DraftSight, I replicated the tile drawing until I had 36 copies and arranged them as economically as possible. The laser cutter I would be using has a maximum bed size of 200 x 300mm, which restricted me to a maximum of thirteen tiles per cut, in two rows of five (alternating between upright and upside-down) and one row of three, rotated through 90 degrees. Obviously the third cut would only produce ten tiles – this allowed for a practice cut to be made, to ensure that the settings were correct for both cutting and engraving the perspex – I wanted an engrave depth of around 1mm.

Image

Newly lasered tiles

The practice cut was successful, so I went on to cut the first sheet of thirteen tiles. Not much to look at originally, but that would soon be fixed. Approximately a month before the idea emerged, someone I knew posted this link (http://www.redtorope.com/2011/02/laser-engraved-wax-filled-high-contrast-panels-for-electronics-projects/). Essentially this involves filling the engraved plastic with a contrasting wax. Crayola wax crayons were mentioned, but I didn’t fancy shelling out for an entire pack just for one crayon, and I would probably need three or four to fill all the tiles. A couple of hours scouting around the internet and I came across some furniture repairer’s filling wax, in “Ebony black”, priced at £3.50 for a single stick. Marginally softer than crayola crayons, but ultimately cheaper and without the wasted crayons.

Image

Melting the wax into the engraved channels using a heat gun 

Image

Removing the excess wax

Image

The remaining wax is easily cleaned off using ethanol

The method I eventually settled on (which worked better in a warmer room, given that the workshop was pretty much the same as the outside temperature – somewhere around zero degrees centigrade!) Involved heating the perspex tile with a hand-held heat gun and warming the wax until it was soft, but not runny, then vigorously rubbing over the engraving. Once I was satisfied with the amount of wax laid down, a quick blast with the gun to melt the wax and fill the cracks. Obviously, I had applied an excess, so this was carefully scraped off using the practice tile. Any remaining wax could then be easily cleaned off using a little ethanol and some paper towel.

Image

The three stages of wax-filling

And that’s it! This job was a little more time-consuming than I originally imagined, as I originally had quite a few problems getting decent images, accurate drawings and persuading Inkscape and the laser-cutter software NewlyDraw to do what I wanted them to do, but the end result is worth it.