A disaster in the making

Some people will have seen the laser etched blocks I produced as my first project with SM1. I was pleased with the results and determined to make a few sets of kids toys with alphabet blocks. I also experimented with colour but it proved more difficult to solve the issues thrown up with non-toxic paint finished for young children. In the end I found a non-toxic poster paint but was not happy with the overall result. The image below might be informative…

The wood is pine and I had not realised just how difficult it would be for the laser to etch the much harder wood of the annular rings. In fact in many cases, the laser did not touch the harder wood even on 100% power for the 1600mW upgraded version.

I had idly wondered whether something in the paint was protecting the wood from the laser beam. It was a newbie’s stupid thought really as the next image is shown with plain blocks. Remembering how successfully I had engraved the first wooden blocks from exactly the same source.

The letter M on the left of the image shows the quality I was getting initially. the blocks inside the red ellipse show what the quality is like on the a few of the batch of 1200 blocks I had purchased. A complete newbie error made because I had no idea how much wood varied in its grain or hardness. If I work on the principle that the batch of blocks I purchased are all going to give me some sort of issue (these blocks were randomly selected from a box of 400 blocks) then a solution needs to be found.

I had thought about coating the blocks in some sort of acrylic paint that would smooth their surfaces while adding little to their overall dimensions. I rejected that on cost and toxicity for kids mouthing the blocks. In the final analysis I decided to try and carve the blocks using the CNC capabilities of SM1.

The major problem to overcome is how to hold the blocks stable and in the correct position for any carving operation to take place. I did not want blocks to shift while being carved nor did I want the cost or the inherent safety issues if the endmill would break at regular intervals. Liking the notion of a jig for the laser etching of the blocks, I decided to try and adapt it.

My idea is to use some form of quick release clamp system that would hold the block for carving and release it quickly for flipping faces and then retighten it to carve another face. It turns out that the sort of clamp system that I think I need to use is available commercially. I do not need to buy the whole system but just want to buy a few bits to enable me to make my own jig.

I am now in the process of assembling the necessary bits to make up a jig for carving the blocks. I will post the resulting images of the jig assembly process and the first carved blocks.

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I would think you could use your existing jig, with a deeper hole. I think if the hole holds over half the block, it should work just fine. Maybe 75% for a bit of extra safety margin.

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I also wonder if a combination of the two might work. Maybe the action of roughing up the surface from the CNC will give you enough texture that the laser can burn it? As a quick test, try sanding one your problem blocks with some 120 grit paper and see if that helps.

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Thanks for the responses Craig. The deeper hole in my current jig is a possibility with one slight concern. The cube size is a nominal 40mm and some are 40.6 while some are 39.8. I understand that working with wood can easily see tolerances of ± 1mm either way. While the square hole in the jig has to accommodate such a variation, it also has to permit the easy placement and removal of every size variation I am likely to deal with.

This reality means the receiving space was machined to around 40.7mm. I have to expect the variation in my wood blocks and account for that. Being slightly oversized has not had any negative effects because the blocks do not really move much once placed and I always favour holding the block forward and to the left in the jig.

The SM1 bed stays stationary while the module head does all of the moving. The concern for me is that with around 1mm of deliberate play when placing blocks into the jig, that a block being carved may move with each direction change of the endmill. Apart from the end result looking poor, it may break mill bits or lift and damage blocks.

I now have a solution but have to wait to implement it because my drill press is away being serviced. Surface clamping provides the options that I need and I have to figure out the way to best apply the clamps. I have some images for you to better understand how I propose to solve the issue of holding blocks rigidly while carving them.

The first image shows how few parts I needed. The system is produced by UJK and is known as a surface cam clamp. It can be purchased as a kit or as separate pieces with longer parf dogs and pairs of wedges as well as the bits you see here. There is an instructive video presentation on this page too. Included is a tool to create a chamfer at the edge of the 20mm hole so that the supplied stainless steel dogs sit in the hole and balance on the chamfered edges correctly.

The description from the tool suppliers is incorrect in stating that the 20mm hole in the clamp is slightly offset. The clamping action is provided by a variable width of clamp material around the centrally placed hole in the clamp. (this is what I understand a cam to be) The width of the cam varies about 2mm around the hole in the clamp and the slope tightens against the workpiece.

The clamps are only 12mm deep and they fit over the chamfer on the short parf dogs. The next two images show the chamfer detail and the clamp sat on the parf dog showing nothing protrudes significantly above the clamp itself.

The final image shows how I intend to apply them to the jig. I have found a nice piece of American walnut that is 40mm deep. My intention is to use its full 200mm length sitting along the ‘Y’ axis rail because there will be very little movement of the actual jig as the carving will be done by the module head moving. The 150mm width will not impinge on the ‘Z’ axis rail because it will sit further to the right in the SM1 enclosure so avoiding the upright rail.

I had considered the use of a single clamp and while it may work, holding the block against the hole side, it strikes me as mechanically not as efficient as holding the block from both sides. More to follow once I have my drill press back and can complete making the jig.

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Yes, a good thought. I had tried that Craig… it made no difference to the ability of the laser beam to burn through the tough wood sections.

Are you using the 200mW or the 1,6W Laser module?

Hi @xchrisd. I am using the 1600mW laser module.

Haven’t done much laser engraving yet (just a few big pictures) but wondering, that you can’t get a burned dot…

Have you taken the really well focus point?
Sorry, no other idea yet.

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It is the material @xchrisd. If you would imagine me trying to burn into steel with such a low powered laser beam. The wood at the annular rings is heavily compressed and very solid. It will blunt a sharp chisel or plane blade in a very short time. For clarity, I have attached one of my images showing the focus of the laser beam while it is etching different wood.