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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Epoxy Granite Portal Machine
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  1. #21
    Join Date
    Mar 2012
    Posts
    74

    Re: Epoxy Granite Portal Machine

    Quote Originally Posted by ando600 View Post
    Hi all,

    I have been reading cnczone for a long time, finally time to post.

    I am in the process of designing an epoxy granite portal CNC. I will be using it for personal projects and research. (R&D, robotics applications)

    I currently have 2 700mm thk ballscrews with mounts, 1 set of 40mmx900mm linear rails with 4 blocks, one set of 35mmx750mm linear rails and a thk kr46x250mm linear actuator. I also have most of the electronics. (PC, ESS, power supply, g540) I have a bosch 2hp router and a SuperPID controller.

    I have several questions.

    1. I am considering using a granite surface plate as the base for my machine, and then building epoxy granite supports and gantry. Is this wise? What is the best way to construct the gantry? Also, what machine mass would be necessary? I was estimating 400-600lbs.

    2. I am considering using servos instead of steppers. I was thinking of getting the MB3 BOB from cncroom, or the c80 BOB, and then the DMM DYN2 AC 400W Servo Kit. (Or maybe the 750W. I need to do the calculations for my ballscrews.) What is the practical difference between good steppers with a g540, ess and servos? My goal is accurate to 0.001 with decent feeds and speeds.

    3. I realized that my bosch router is not going to be suitable for my workload. I might want to do rigid tapping at some point. I am considering a jianken atc spindle or possibly a bt30 atc belt spindle with a 1.8kw servo drive. Would the lower rpm on the belt/servo drive impact my capabilities? I am planning to machine aluminum, steel and occasionally titanium.

    I have a limited budget. I bought most of these parts a couple of years ago, and I am in no rush to get this done.
    I have access to a machine shop and a waterjet. I have a pretty good feel for manual machining, and I have access to knowledgeable people.

    Any guidance is appreciated! This is my first CNC build.

    Thanks
    Just similar as you, I prepared precision parts for several years which were bought from ebay which include 4 pieces THK KR33 and 1 piece NSK linear actuators with some small size linear rails. No extra ballscrews are needed. Easy servo stepper motors were bought also. Now, my router is under the building and was finished around 60%. The most critical and getting-headache portion is the precision alignments of those precision parts on the metal frame. As well, the required measuring tools like granite parallel and right angle triangular blocks etc are bought.

  2. #22
    Join Date
    Jun 2010
    Posts
    4252

    Re: Epoxy Granite Portal Machine

    If by stepping up gear 4/1 to reach 12000rpm on spindle, with using the timing belt, will there be too much noise?
    That depends on the quality and size of the bearings, their alignment, and the mass of the spindle carriage. There will be some noise imho.

    But if changing to v-belt? will there be slipping problem and rigid tapping not be possible?
    Not a lot of slippage with the right V-belts, but enough that rigid tapping would not be realistic. But trying to do rigid tapping with a 12kRPM spindle is an unlikely prospect anyhow. I suggest that 120 RPM might be fast for rigid tapping, but doubtless someone will claim higher speeds (at very high cost though).

    Cheers
    Roger

  3. #23
    Join Date
    Mar 2012
    Posts
    74

    Re: Epoxy Granite Portal Machine

    what concern is the noise that comes from the hitting of gear tooth of fast rotating small gear with timing belt tooth, ..don't know ..has not yet enough experience?1

  4. #24
    Join Date
    Jun 2010
    Posts
    4252

    Re: Epoxy Granite Portal Machine

    There might be some noise from the toothed belt if you are using one of the original 'timing belt' designs (with backlash), but the modern designs such as GT2 & GT3 are pretty much silent.

    Cheers
    Roger

  5. #25
    Join Date
    Mar 2012
    Posts
    74

    Re: Epoxy Granite Portal Machine

    I have not much experience in using timing belt.. just using a long XL type one for gantry X-axis drive...but only last for 2 years time(broke). Now in my new machine I plan to use much stronger HTD 5M type for the axis drive....But for the spindle which is of 750~1kW servo motor(3000rpm). I firstly suppose to use HTD 5M as well. Now, I hesitate that if it will has the noise problem?! According to your suggestion GT3, it is of thinner in thickness, what type of strain and material it is? will it last long enough and suit for that power rating servo motor?

  6. #26
    Join Date
    Jun 2010
    Posts
    4252

    Re: Epoxy Granite Portal Machine

    The HTD is definitely a modern upgrade over the old trapezoidal (XL) timing belts. The difference is the modern curved tooth shape vs the old angular shape. I suspect that the GT2/3 may be even better, but only by a smaller amount. Don't worry about the thickness of the belt: it does not figure in the strength. It is the cords in the belt which matter, and there is only a single layer in any of them (for reasons of dynamics). Check the vendor specs, but I think even the 5 mm GT2 belt is rated at >10 kW at 3000 RPM. They are STRONG.

    Cheers
    Roger

  7. #27
    Join Date
    Mar 2012
    Posts
    74

    Re: Epoxy Granite Portal Machine

    Thanks for the information. There is a picture of my CNC milling machine that is under building.Attachment 431020

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