When I first thought about homebrew cnc I never thought I could do fine detailed line and text work and presumed it would be only good enough for cutting mdf into rough shapes! However, I read on the net about drag engraving where the spindle doesn`t spin and you simply drag a diamond across the top layer and “scratch” the surface. I didn`t have much faith but I found a few simple ideas on the net and thought I`d have a go at making one.
The commerical ones are very expensive and start with the smallest shank of 12mm. My er16 spindle can only take 10mm max and although adapters are available, I read that if your spindle can`t handle 12mm, it is likely the bearings will not be beefy enough to withstand the sideways cutting forces of dragging the tool across the work surface. Sounded sensible to me and with my little home made brushless dc motor spindle, didn`t want to risk it.
No worries anyway, since I`m making it, I`ll just make a massive body – this is actually a massive advantage as my spindle bracket is 43mm, so making a body of 43mm means I can just drop the drag engraver straight in place of the spindle!
I turned the outer body to 43mm, reamed a 12mm bore. Used 12mm silver steel which I reamed 1/4″ to fit the diamond tool (this needs turning a little deeper so less is held out the top). The 12mm silver steel slots in the centre bore…ideally to a shoulder. I didn`t do this and ended up turning a little face cap and holding it on with 3 screws (can be made out in the first photo). A spring sits on top with a little brass spring stopper and then a rear end cap screws on that with an M8 thread and bolt to apply and adjust pressure onto the spring (M8 bolt needs replacing with a nice little thumb screw asap)
I`m very chuffed with the results. Setting the pressure depth and spring took a lot of scrap test efforts but got something I`m happy with.
Here I`ve attempted to fill cut, so the diamond drag engraver sweeps across in many steps to fill the letters. All was going well until my double sided tape gave way!
I really wanted to put it through its paces and so I got in contact with my pal who teaches art and one of his personal interests is line art and computerised line art – or at least I`ve certainly seen his original work being lots of lineart. I sent him an email asking if he had anything already as a computer file and got a reply: “have fun! – attached:BOB.jpg”
So, the truth is, I`m not sure who Bob is or what Bob is for that matter – how very arty, I guess you have to make your own mind up. But anyway, I was chuffed to bits with how it came out. I imported the jpg in Vcarve and copied to a vector – then off we went: