Some thoughts on building & using a DIY Michelson Laser Interferometer

 

-coming soon-

http://www.cncecke.de/forum/showthread.php?101142-Maschinenvermessung-mittels-Laserinterferometer

Lessons learnt

I built my own polymer concrete cnc mill. It turned out to be a quite usable, stout machine, yet mistakes were made along the way. If you want to do the same, here are some things to consider before building

1. If you are serious in building a machine, design the machine in CAD before building. Good CAD programs are (not necessarily in this order) CATIA V5 (unobtainably expensive), Solidworks (cheap in a good way), Fusion 360 (free for hobby use)
2. Think of coolant& chip management. If you want to run your machine for extended periods of time (possibly unattended), this is of utmost importance. Make sure your machine does not leak. Make sure the way covers are coolant-proof and tight enough to not let through any aluminum chips, even if you are working with pressured air or splashing around with coolant. 
3.  Do not underestimate enclosure building
4. Think of safety. If you EVER want to use your machine for commercial purposes (even as a side job), you have to build it compliant to certain standards. If not, you might loose your insurance in case you get injured using the machine (a powerful machine is a dangerous machine!) Research those standards in advance (highly country specific)! 
5. Do not underestimate routing for power and pneumatics. In the design phase, planning the electrical&pneumatic systems will probably take more time then the structure design itself. Plan in advance, do not start building before finishing the routing. Adding a bracket in the cast (mould) is easy, drilling a hole in mineral concrete is not. 
6. No, seriously, do not underestimate routing. Really, i cannot stress this enough.
7. Financial calculation: your machine will get much more expensive then originally planned. Those ‚ main‘ components like linear rails and ballscrews are expensive, but the devil is in the details. Personally, i have ended up spending more money on the rest oft he machine then on what you might consider „central components“. Make sure you have +20% extra budget at hand to allow for short-term purchases (and believe me, those will come).
8. Casting: If you are working with mineral concrete, make sure you pre-condition the mould with release agent. I neglected that (using too little) release agent, making the wooden form stick to the epoxy resin. I spent about three evenings litterally chipping away the wood with hammer and chisel.
9. Do not build your own cnc machine just to save money. Given the same machine quality, even a ‚cheap‘ diy build will hardly save you any money. Only build your machine if
10. a.       You want to learn something, or
    b.      You have a special requirement no machine on the market can satisfy (probably not), or
    c.       You know exactly what to do (professional experience), or
    d.      You have access to free components or
    e.      You see the time building the machine as „free time“ (not assigned to hourly rates
11. You need a cnc machine in order to build a cnc machine (normally).  A precise machine has to be scraped in
12. Think of measuring equipment. To build and adjust your machine (and then measure parts), you will need at least
13.  
    a.       An angle (granite or steel)
    b.      A precise steel ruler as long as your longest linear rail
    c.       A dial test indicator
    d.      A good caliper
    e.      A good micrometer
14.  Those alone will set you back a grant (and thas barely enough to get started). Buy brand (Mitutoyo, Mahr, …) or buy twice. 
15.  Be prepared to invest another 1500€ into a bunch of quality toolholders (like, 15 or 20 of them, at least)
16. Another 1000€ goes into some basic stock (aluminum, steel, titanium) and some toolings (endmills, indexables etc.)
17. Have fun. There´s not so many people around crazy enough to build a proper VMC. If you have made it that far, you are welcome to shoot me a message if you have any specifiy questions.

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.