Part one is done!

More in the next days.

Designing my CNC mill - sneak peek

 The last 12 months i spent developing a concept for a small vertical machining center. As it is with any design process, errors were made on the way. Yet, finally most challenges are solved and i am pleased with the results. Very recently, the first real parts have been finished. More about that later. But first, lets have a short look at the machine concept.

The design is a classical column mill with traversing table and BT30 spindel with automatic pneumatic-hydraulic tool changer (the spindle itself is still very much in progress, so expect some posts on this in the following months).

So let´s get into the basic mechanics. Gross weight will be around 300kg. The machine can be easily broken down into parts light enough to be comfortably carried by two average persons. All moving parts are supported by pre-loaded high accuracy 25 mm linear rails. Axes movement will be driven by 20mm ball screws with attached stepper motors (might be swapped with servo drives as needed once budget is available). No use of linear encoders planned. Once completed, however, the machine will be evaluated to see whether encoders are needed for positional accuracy. Possible speeds with steppers are up to 6m/min. Resolution is 1.5 micron, accuracy will be in the range of 0.01 mm.

The main structure is made out of polymer concrete (Rampf systems EPUMENT) with S235Jr steel inlays. The inlays have undergone stress-relief annealing after drilling all holes for lamination anchors. Linear rails and bearing blocks require a perfectly flat and well-defined surface. To create this surface, all functional areas will be machined on a large machining centre in the coming months, then measured. If the surface after machining is good enough, linear components can be mounted and the machine be used. 

However, if anything goes wrong, i will either 

a) let someone grind the surface (expensive)

b)scrape in all surfaces (extremely time consuming)

Wish me luck!

After one more night of solidworks, this is going where i want it to be.

Getting closer, not quite there yet.

Just playing around with some knife designs. Starting with the carson design M21-12G. Nice pic of a knife a good friend showed me last weekend. Just couldn´t get it to flip properly though.

designing my new cnc mill

Alright, so the goal here was to build a small, compact cnc mill which can be handled and transported by a single person. The machine has to be rigid enough to work with titanium and (somewhat) hardened steel. Aluminum and plastics are on the list as well. The ultimate goad is to have a stout machine for small production runs.

In order to get a feeling for the dimensions of "real" machines, i started with modeling a few known models in CATIAV5. Here you can see (from left to the right):

-EMS P2
-Alpine VFZ
- Thundermill
-minibeast
-FS4MG/FS3MG

Etching my first PCBs this year

Last weekend I started etching my own PCBs. Actually, I started etching in 2012, using the “Toner-Transfer-Method” where the etching mask is transferred to the board using an electric iron. However, the achievable resolution with this method is limited and removing the paper which carries the toner is quite a hassle. Waiting minutes for the paper to dissolve in water, only to see the toner did not properly melt onto the board (i.e. do it all over again) just sucks. So I finally bit the bullet and bought a professional UV-exposure box for using PCBs with photosensitive coating.

Etching machine in use, filled with almot two litres of etching solution at 45°C

My very first try. The rectangles are drawn with 12, 10, 8 and 6 mil traces.

close-up of 10 and 8-mil traces. The white stuff left on the blank pcb is probably some residual photo coating.

One more close-up of the 8-mil traces. The ruler on the right is divided in 1mm-steps.

Tests were conducted using original bungard PCBs coated with 70 micrometers of copper. The photo mask was a design recently posted by another hobbyist from mikrocontroller.net containing traces of 12,10,8 and 6 mil width and printed on transparency film with my old brother-2030 office laser printer. Exposed to ultraviolet light for 90 seconds, the developed in NAOH at room temperature for one minute and etched in Na2S2O8 at 45°C, the board comes out nicely. 

Pretty good for my very first test using this equipment, and by far sufficient for soldering an Invensense MPU-6050 (4x4x0.9 mm QFN footprint) which requires solder pads of about 10 mil width. As you can see, the six mil traces on the test PCB still retain some copper in between, efficiently shorting them out, same with the very top row of the 12 mil traces. Obviously, the board would have needed some more time in the etching bath.