Keep chugging along

Steppers ordered
While dealing with my Discrete math class (scored 100% on the midterm wooo), and keeping my airsoft business alive (shipping product); I managed to select and order some 425 oz-in stepper motors for all 3 axis on our CNC machine. All together with shipping it was 163.17$, We could have gone with a ~300 oz-in motor for 30$ less, but the price/performance difference was warranted an increase in power. We wanted to be sure we could meet our torque requirement. We are happy with rapid speeds of around 70 IPM, but we are confident with appropriate gearing/microstepping we can hit whatever targets speeds we need. Other than the previous research and calculations that were conducted a few days/weeks ago (with that program I wrote), I did additional research on cnczone. The interesting reads I found were:

http://www.cnczone.com/forums/forumdisplay.php?f=193&order=desc&page=17
http://www.cnczone.com/forums/showthread.php?t=27527&page=2
http://www.cnczone.com/forums/showthread.php?t=80245
http://www.cnczone.com/forums/showthread.php?t=75192&page=2
http://www.designworldonline.com/articles/3807/21/Improving-High-Speed-Performance-of-Hybrid-Stepper-Motors.aspx?utm_source=mcnl&utm_medium=newsletter&utm_content=feature&utm_campaign=MCNEWSLETTER
http://www.homeshopcnc.com/StepperMotorFAQ2.html

Also while inspecting specs on keling's website I needed to convert 2.15N-M to oz-in, a quick google solution was found at:

http://www.unitconversion.org/torque/newton-meters-to-ounce-force-inchs-conversion.html

It looks like our machine will be severaly limited on the Rapid speeds based on the controller board, with a max voltage of 36V. So we can't overdrive the steppers much. They run 6V stock. So we will only be able to run them about 2x their rated voltage even though we could go up to 20x their rated voltage. With the stepper order aside, I continued my frame research for our machine.
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Frame Research
For awhile we were seriously considering making the whole frame out of epoxy/granite composite. But after eyeing the costs, the difficulty in manufacturing and the time frame we are on, Troy and I decided it would be wise to follow the KISS principle. I had found several instances of aluminum Bosch framing for homebuilt CNC machines. Given the repeated success I had found, I pushed for what we know works, and with ease. Given our constraints on the project Troy, agreed heartily. Although, we both conceded it would be very cool to incorporate some E/G aspects into the project later to enhance rigidity and vibration absorption.

A simple way to do that would be to fill the cavities of the aluminum framing with E/G. Also we also conceded it would be very nice to have a solid head, so we may make that solid later. At the moment I am toiling with fasteners. I measured one of the THK rails we obtained from ebay. They appear to have 7mm holes for SHCS (Socket Head Cap Screws.) and 9mm countersunk holes. A quick google search is not promising for 7MM SHCS.

http://www.roymech.co.uk/Useful_Tables/Screws/cap_screws.htm

Shows some typical metric SHCS sizes. M7 is not on the list. I wonder if they are specialty screws for the rails, or if they simply use M6 screws.

In my research I began to learn that these so called aluminum frames, are sometimes nicknamed "80-20" extrusions. Which I guess is some sort of industry standard. Apparently there is even a whole section on cnczone dedicated to 80-20 frames. (i'll have to read into it more before making final design decisions.)

From an inspection of Bosch's website and manuals it looks like a 45x45H extrusion section should meet our demands for the X/Y tables. I am a little concerned because milling flat that extrusion will be a hastle on the bridgeport mill that hasn't been opened up yet at our shop. Not to mention we don't even know if the bridgeport's ways are true. Any error in that machine will be amplified in our own base if they are off. And from my research it is not uncommon for these extrusions to have about .008" of variability across a single piece. I also read some individuals using T-slot inserts that are premachined and have SHCS holes in it. I hope i can find more on this.

Some websites concerning 80-20 framing:
80-20 surplus
80-20-T-Slot-Aluminum-Extrusion-45-S-45-4545-
Bosch 3D models
Bosch Website
http://www.3dpublisher.net/SWDownloads1/2044316659-857082/Machining.PDF

I know I will be ordering some Mic6 precision ground plate for bolting some of these frame parts together, just don't know the physical dimensions yet. So that's on hold. I want to model the whole thing in solidworks first.

So to review:
I need to:

• M7 screws- do they exist for the THK rails?
• Precision ground t-slot rails for 80-20 t-slots to bolt the THK rails to - do they exist/where?
• 80-20 End machining options at bosch are confusing, figure it out!
  
• Model it!
  

The truth about building a CNC machine
Gosh everything about this project is Read, Read, Read, process, learn, discover how very little you actually know, rinse and repeat. And somewhere in there you feel confident enough that you aren't going to make a disastorously horrible mistake, and that it is about time to learn by doing.