We can engraved curved surfaces as well as flat ones, but it depends on the curve and the material. Here’s an example.
We engraved these beautiful beech coffee tamper handles for Made by Knock for their customer, Machina Espresso. They’re so tactile, and are perfect for engraving if you can work with the curved surface. That was the biggest challenge, along with getting the logo centred on the top. You can easily spot if engravings are out by a millimetre.
It’s all about focus
The principle is that flat surfaces should be engraved. This is because the laser beam is focussed vertically onto a horizontal surface. The distance between the lens and the material surface is crucial for high quality engraving. Lenses have specific focal lengths that should be adhered to for best results. Even a tolerance of plus or minus 1mm can be a problem depending on the material used and the lens selected.
These principles need to be adhered to more for sensitive materials like acrylic and metal where a reduction in engraving quality is very easy to spot. Wood, on the other hand, is much more forgiving.
My secret weapon
My secret weapon is my 100mm lens. It allows me to work with a curve of around 8mm, particularly if the material is forgiving like wood is. I’ve used it to engrave these tamper handles and mini wooden baseball bat muddlers for mixing cocktails. It is still important to keep engravings on relatively flat areas for best results.
Before we went into production, we engraved Machina Espresso’s logo on a few tamper handle seconds to judge the largest size the logo could be engraved to keep the logos on the flattest part of the handles. It was important to know at what size engraving quality would deteriorate, and to make sure that engraving results would be consistently high quality.
Customers request all sorts of weird and wonderful commissions. Customers have lovely ideas to personalise gifts that are only limited by their imaginations, so no two jobs are ever the same.
A customer approached us to ask if we could engrave a pair of matching wooden tankards. He’d commissioned them as gifts for friends for their festival themed wedding or ‘wedfest’. If possible, he wanted to personalise them to make them extra special. Perhaps they would become family heirlooms to be treasured for years to come.
Engraving cylindrical objects
It is possible to engrave cylindrical objects, but this has its challenges. The laser needs a flat surface to focus on for best results. If the laser beam loses focus, engraving quality suffers and becomes fuzzier. The more out of focus the beam becomes, the worse the effect is.
We suggested that for something a little different and to maximise the chances of success, we could engrave the tankards vertically. This tactic would allow the laser to focus on the relatively flat spine of the cylinder. It worked a treat and you can see the results in the photo.
Top tips for engraving cylinders
We used our 100mm focal length lens to compensate for the slight curve on the circumference of the tankards. We performed a nice deep raster engrave to give a 3D effect on them, and the look really suited the chunky tankards. My customer was delighted with the results.
LaserFlair makes fun and funky acrylic jewellery for Jaggedy Thistle in Dunkeld. We laser cut their reindeer brooches in the run up to Christmas along with highland cows and Scottie dogs. This is how it all happens.
We need vector artwork to create items like this. Jaggedy Thistle provide the artwork for their bespoke products, and the acrylic in the colours they require.
Vector cutting detailed shapes
Vector artwork is very simple. It consists of hairline shape outlines, and the laser follows the lines in the artwork to cut out each shape. There is a vector line for each outline cut on a piece. In the case of the reindeer in the picture, we cut the eye shape first. When the body is cut, the whole reindeer can drop out of the acrylic sheet and is then in the wrong position to cut out internal detail. This is why we set the machine’s cutting order so that internal details are cut before outline shapes. We minimise waste by using our laser cutting software to tile shapes which maximises yield from the acrylic available.
Protecting the pieces
Acrylic has a protective film on each side to prevent the surfaces from scratching. We leave it on during production to protect the acrylic surface from the heat of the laser which causes discolouration near the cut edges. After manufacture, it protects the pieces during shipping, keeping each shape in perfect condition as acrylic is easily scratched.
When Jaggedy Thistle receive their delivery, they remove the protective film from each brooch. Then they add the red noses and brooch pins, and mount them on cards for sale. Aren’t they cute!
Perspex branded acrylic is the best quality. Other brands have additives that make the cutting process significantly slower and smellier on the laser. This adds to production time costs and can decrease operator comfort.
We had to complain about some 8mm white acrylic that was not Perspex branded. We had bought it for a project with a designer who was prototyping a product. When we cut it with the laser, the edges went brown when they should have stayed white, and it was all down to the makeup of the acrylic. We also had to run the machine at a slower speed than we’d expected for the thickness of the material which made the process less profitable for us. Thankfully, the supplier gave us a refund for the material as they agreed that it was of inferior quality to branded Perspex.
We learned something that day, and now we never order acrylic that isn’t Perspex because of these problems.
How is acrylic made?
Acrylic, unlike plywood, is less varied in sheet thickness, but there’s more to it than that. There are two kinds of acrylic, cast and extruded, named after their production processes. Cast acrylic is made by pouring the acrylic into a mould to set. Extruded acrylic is rolled to a set thickness during the production process.
So theoretically, extruded acrylic should be closer to the nominal thickness of the sheet. You won’t see the same thickness differences between cast and extruded acrylic that you’d expect between nominal and actual thicknesses of plywood, where you can expect differences of 0.2 to 0.3mm. The errors are far smaller.
But not all acrylics are equal, and this is the important thing to watch out for. It could affect the look, quality and cost of your product.
You’d assume that 3mm plywood is 3mm thick, wouldn’t you?
Wrong! With plywood, thicknesses are nominal, not actual. This is because plywood is made up of different layers glued together. 3mm usually has 3 layers, and the result is an actual thickness of 3.2-3.3mm. 4mm ply has another layer, and is usually 3.8mm thick.
Potential design disasters
This can create a whole worlds of pain for designers and manufacturers if they want to create products made up of pieces that slot into each other and require a good fit.
If you assume a thickness of 3mm and you design 3mm slots in artwork and then try to fit 3.3mm thick wood in the slot, it’s not going to happen. Or if 4mm ply were used, 3.8mm parts would be too loose.
Imagine making 300 reindeer kits for Christmas, sending the artwork to a maker, and getting back parts that don’t fit?
This could have happened to one of our earliest customers, but we made a prototype, realised the problem and fed it back to the customer. They tweaked the artwork before we performed the production run. This simple check saved our customer – and us too – a lot of time, money and heartache.
Always check that your designer and maker are speaking to each other to avoid disasters like this.
I love these wooden rings! But when Waiata Bespoke Jewellery (nga waiata as they were then) first got in touch and asked if I could engrave the backs of their chunky wooden rings with their logo, I wasn’t sure if I could do it.
Engraving on a curve
First of all, rings are cylindrical. Lasers need a flat surface to engrave. This is to maintain the right focal length for the laser beam for best results.
Secondly, the rings have such knobbly stones on them and nga waiata wanted to supply them made up rather than without the stones. How could we support them securely in the laser so they wouldn’t wobble or fall over during engraving? Any of these scenarios would be disastrous for engraving quality.
It’s amazing what you can do with Blu Tac! I use it all the time to support jobs on the machine. A nice big blob on the engraving bed floor held each ring securely, even although the stones are all different shapes.
My secret weapon
Now for the engraving. The text was small and fine and was to be centred in the middle of each ring back. I used my longest focal length lens which helps maintain focus better over curved surfaces. I also slowed the engraving speed down to maximise precision and minimise any wobble from the machine. This ensured crisply engraved letters, with a nice depth of engraving to give good visual impact in the chunky wood.