Z Touch off repeatability test

Bevore making chips, you need to know where your tool stands relative to your workpiece. Naturally,  setting Z is most critical when changing tools. Whenever you put a new tool into the spindle, you will want it to have exactly the right offset.

The simplest and cheapest way to do it is using a touchplate. Just connect one wire to your spindle, the other one to a piece of PCB on top of your workpiece. Using a simple script (use the pre-installed button script „auto tool zero“ in Mach 3), the z-axis is moved down until your tool touches the pcb. This position ist then defined as… no, not as zero, but as e.g. “2mm“, or whateve the thickness of your touchplate happens to be. The spindle then retracts to a given height (5 mm above zero, in my case). This way of touching off basically costs nothing at all (well, two cables and a small piece of scrap pcb you got laying around).  My machine´s resolution is 0,0025 mm. But, how precise is the touchoff process itself?

Well, let´s find out!

First, i did a short repeatability test, touching off again and again 50 times in a row. This is, touch off, note down machine coordinates, touch off again, etc. Then i paused for 5 minutes, then did another 50 touch-off´s. Inbetween the touchoffs, the touch plate was not moved nor touched with my fingers.

After the first 100 measurements, i did a row of 25 further measurements. Onty this time, the touch-plate was picked up with my fingers and then placed back on top of the material.

 Let´s have a look at the results (y axis scaling is in mm):

As you can see, the first 50 measurements are pretty accurate, only changing aound +0/-0,025, which is exactly the machine´s accuracy. This means, touching the plate is detected within one microstep of the stepper. Pretty impressive!

The next 50 measurements done after the break are more scattered, but accurate well within 1/100 mm. Not too bad, apart from those three outliers!

Now, on the last 25 measurements. I picked up the tough plate after every measurement, which is how you would do it normally. The results are varying greatly, scattered over 5/100mm. I can only guess all the errors that are adding up here: Varying touchplate thickness, uneven workpiece surface, touchplate not lying exactly flat on workpiece surface etc. In real life, there might be a chip or two stuck on top of your workpiece, even making everything worse.

 So, seems like my touch-off process can be improved. What do you think?

AGBs und anderes

Wenn ich in einem Onlineshop bestelle, lese ich ja nur selten die AGBs. Gestern habe ich es doch mal getan.

Nur ein Wort:

Chapeau!

"Was für eine Welt könnten wir bauen, wenn wir die Kräfte, die ein Krieg entfesselt, für den Aufbau einsetzten. Ein Zehntel der Energien, die die kriegführenden Nationen im Weltkrieg verbraucht, ein Bruchteil des Geldes, das sie mit Handgranaten und Giftgasen verpulvert haben, wäre hinreichend, um Menschen aller Länder zu einem menschenwürdigen Leben zu verhelfen sowie die Katastrophe der Arbeitslosigkeit in der Welt zu verhindern. Wir müssen bereit sein, für die Sache des Friedens die gleichen Opfer zu bringen, die wir widerstandslos für die Sache des Krieges gebracht haben. Es gibt nichts, das mir wichtiger ist und mir mehr am Herzen liegt. Was ich sonst mache oder sage, kann die Struktur des Universums nicht ändern. Aber vielleicht kann meine Stimme der größten Sache dienen: Eintracht unter den Menschen und Friede auf Erden." (A.Einstein)

Drones again in solidworks

Once again, i got bitten hard by the drone bug.

Started with the model of a brushless outrunner which i had designed in autodesk inventor back in the day:

Lets do it all again in solidworks (1 hour of work):

Luckily, i still had all the decals in my archives. Ordnung rockt:-)

Watch out for more to come!

If you want to have the models, just shoot me a mail.

Looking forward, looking back, or: lessons learned

Today, drones have become mainstream. The drone boom is at it´s peak, or maybe beyond.

More than ten years ago, on the way into our summer holidays in bavaria, we stopped at a gasoline station. My dad bought me an issue oft he P.M. magazine, featuring an article on small unmanned airplanes. I still remember that day like yesterday. I was hooked.

I simply knew MAVs, as outlined in that article, were possible. I imagined the endless possibilities for a small, portable „eye in the sky“. In the coming years, i was daydreaming of drones literally for days on end. The more technology evolved, the more my imagination grew. I read DARPA´s „Towards a new dimension in flight“ on my dad´s old mac. This is one oft he first „scientific“ papers i ever printed out (in color!), and one oft he first papers i read. I knew this technology would shape the future. It was the future.

Yet, the technology i imagined was vastly different from what it turned out to be. I was inspired by the agility of nature, fooled by the promises of modern bionics (or should i say biomimicry?). I expected drones to have their final breakthrough only when artificial muscle became cheap and reliable. Eletro-chemical (or purely electrical) muscle like in Michelson´s entomopter  The MFI (micromechanical flying insect)-project became my holy grail. But again, i was fooled. Different technologies became standard, quadrocopters became the kick-starters of civil unmanned flight innovation. Different terms were coined. Ten years later, it is not MAVs, UAVs or MFIs. It is drones.

  But even more than this, i was passive. I dreamed.

I had not yet learned how to educate myself. Different people my age started (and, very recently, sold) companies which became world leaders in UAV innovation.

 It does not count what you think or imagine. Thoughts do not change the world.

Only actions do.

Lesson learned.

Some progress

Last weekend, the mill base and the column were given away for milling and drilling. If all goes according to plan, i will finish the mill in a week or two. Yesterday, i finished the configuration of Mach3 on the cross-slide (y-axis). Mach 3 can really be a bit messy when it comes to setup, but now everything is running fine. The x-axis can now reference itself by a switch, soft limits are working, coordinate system is implemented. Axis scaling is configured correctly. Transporting the polymer concrete subassemblies was done with two steel bars attached to mounting/anchor screws on each part. All easy. I am happy to say that my weight calculation in CATIA was spot-on. Both parts are massive and heavy, but good to carry with two persons.

Meanwhile, enclosure planning is making progress. Stay tuned:-)

 Agenda for today: write test code for x axis repeatability test.

solidworks render - asctec hummingbird

Apart from some welding, i have been using last weekend to sort through my old files lately, deleting everything i do not need anymore. I am not even halfway through with cleaning up, then i found this. About two years ago, i was busy improving my skills in solidworks. Being pretty much into drones back then, i went for an ascending technologies hummingbird as a small personal design challenge over one weekend.

Not much text today. I have been in the shop WIG welding the whole morning and early afternoon. The underframe for the mill is nearly finished. Will be all done tomorrow. I could not take any photos in the shop as i was only a guest there, so here are a few shots of the mill out of the CAD from this afternoon. Ah, and i finished cutting the threads in the crossslide of the mill, where the linear rails will be mounted (see last picture). All those little things amount to a lot of work, yet not much visual progress. I know i am heading in the right direction, so this is fine with me. One step at a time!

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