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.