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Thread: Epoxy Granite Portal Machine

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    Default Epoxy Granite Portal Machine

    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

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    Default Re: Epoxy Granite Portal Machine



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    Default Re: Epoxy Granite Portal Machine

    If you want a 1 micron tolerance and this is your first build I don't think it's going to happen, not being negative but take a look at KERN, they build some of the most accurate machines in the world and they have a 2 micron tolerance, they can achieve this by using a polymer concrete base which is epoxy granite and they have those bases constantly monitored so when the temperature fluctuates and the base expands or contracts then the computer compensates for that in the gcode on the fly.

    A granite surface plate is a good start but even at grade00 which is usually top end, it will still only be 3-5 micron so your already behind. I more reasonable goal would be 0.01mm for a first build if done very carefully

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    Default Re: Epoxy Granite Portal Machine

    All good info but I'd wager he meant 0.001 inches (not mm) which is around 25 micron and should be doable (though challenging). Working on my on granite machine too....

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    Default Re: Epoxy Granite Portal Machine

    Quite possibly meant inches, I just assumed he meant MM when everything else was in metric. But 25micron is a lot more achievable

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    Default Re: Epoxy Granite Portal Machine

    0.001" tolerance with a 2kW ROUTER?
    With cheap little router bearings?
    An interesting concept.

    Cheers
    Roger



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    Default Re: Epoxy Granite Portal Machine

    0.001" tolerance with a 2kW ROUTER?
    With cheap little router bearings?
    Sure! You could do that! Lets see... a little bit of pixie dust here, a miracle installed in there, and POOF! Perfect tolerances!

    Kidding aside - in principal, it would be possible if you were cutting something really lightweight (some of those fine-grain modeling foams come to mind); or perhaps with a control that scanned the part to less than 0.0001" and adjusted the toolpath accordingly. Where to get such a control, I have no idea...

    Practically, I'd just get a better spindle.

    Overall, I think it's a great hobby project; but I do want to caution the original poster about a few things:

    • Be realistic with your expectations. Ask yourself "How much power/accuracy/size/etc do I really need to make the parts that I want to make?". Investigate commercial machines that do what you want to do; learn how they accomplish that; and scale your ambitions accordingly.
    • Expect to spend a ton of money, time and effort on the project; with nothing functional to show for it until you are almost done. Sometimes family members can be problematic - you should be prepared to deal with someone saying "It doesn't work, you've been messing with it for ages, it's greasy and cluttered, it'll never work, you can't do this, I want it OUT OF HERE!" This person is wrong, of course - with enough perseverance, mountains can be moved with a teaspoon; and you're not alone - you've got all of us!
    • Expect to learn a lot about mechanical systems, rigidity, resonance, chemistry, electronics, computers, and control systems before you're done. Do the research to know what you are doing before you do it - it'll save you frustration & money in the long run.
    • Expect to wind up with a bunch of seemingly unrelated tools - a scale that can handle the weight of the ingredients for the epoxy-granite; a small polymer-drum cement mixer; an oscilloscope & a good digital multi-meter are some of the things that come to mind.
    • Don't forget to allow for acquiring or borrowing some precision reference tools - granite or cast iron squares and straight-edges will be needed to do the alignment of the linear rail mounting points.
    • Get some indicators (dial, digital, and/or "dial test" indicators) that read to at least 5x better than the precision you are shooting for. 10x is better, though. Also, get some indicator holders of various sorts to go with them.
    • Expect this machine to need to live in a climate-controlled space. A garage that is open to the outside by those mesh grates that lets engine exhaust & fumes out won't do. Also, watch out for water heaters... they fail occasionally, and you can come home to a room full of steam and rusty steel. (That one's one I have personal experience with, sadly...)






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    Default Re: Epoxy Granite Portal Machine

    Dear me, so negative. So utterly . . .
    .
    .
    .
    .
    .
    .
    realistic.

    Cheers
    Roger
    PS: I agree with the 10x accuracy bit.



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    Default Re: Epoxy Granite Portal Machine

    Quote Originally Posted by RCaffin View Post
    Dear me, so negative. So utterly . . .
    .
    .
    .
    .
    .
    .
    realistic.

    Cheers
    Roger
    PS: I agree with the 10x accuracy bit.
    Negative or realistic?

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    Default Re: Epoxy Granite Portal Machine

    I agree with all of Britt's comments, including that calibration equipment has to be 10x better than your routine gear.

    Cheers



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    Default Re: Epoxy Granite Portal Machine

    Sir Ando - Its an ambitious project. Reality will temper some of the expectations but keep working at it. My advice is to get the machine into CAD and do not buy anything until you have fully resolved the design and the suppliers and costs to your satisfaction. This forum is full of machines that hit hurdles because they changed something and this creates unexpected outcomes. Better to hit these in CAD then in reality.

    So if you can't use CAD get fusion or Freecad and start learning. The rest will follow as time and effort is expended as the Crusade wades through the epoxy dross and the Holy Grail of tolerances are chased. Keep making... Peter

    https://www.adambender.info/post/201...e-frame-how-to



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    Default Re: Epoxy Granite Portal Machine

    Thank you all for the responses. Yes, I mean 0.001 inches. I apologize for the uncertainty. I am very comfortable with CAD, and have already designed several models of the machine. I am not able to finish the design becasue I am unsure about the spindle and the motors. I have requested Precision Machine Design by Alexander Slocum from my university library. (Hopefully I can get it soon.)

    Does anybody know anything about the jainken atc spindles? Are they suitable for steel? Or should I use something like this?

    https://www.aliexpress.com/item/3239...ceBeautifyAB=0

    Is 0.001" achievable with steppers, g540 and an ESS? Do steppers and servos have the same mounting in case I wanted to swap later on? (I honestly cant seem to find conclusive data.)

    - - - Updated - - -

    Thank you all for the responses. Yes, I mean 0.001 inches. I apologize for the uncertainty. I am very comfortable with CAD, and have already designed several models of the machine. I am not able to finish the design becasue I am unsure about the spindle and the motors. I have requested Precision Machine Design by Alexander Slocum from my university library. (Hopefully I can get it soon.)

    Does anybody know anything about the jainken atc spindles? Are they suitable for steel? Or should I use something like this?

    https://www.aliexpress.com/item/3239...ceBeautifyAB=0

    Is 0.001" achievable with steppers, g540 and an ESS? Do steppers and servos have the same mounting in case I wanted to swap later on? (I honestly cant seem to find conclusive data.)



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    Default Re: Epoxy Granite Portal Machine

    Steppers and servos both are capable of 0.001“ and way finer but first off, you're trading speed for resolution in some cases (the pitch of your ballscrews). Second, that won't be the problem in my opinion. It'll be backlash and slop and flex in the entire system which probably can't total more than like 0.0005 for you to hit your goal. So not only do the bearings and ball nuts and mounts all have to have less than that amount of backlash, but your system, across the largest spanned member, has to also flex less than that under load.
    I'm taking some liberties in the math here but just trying to make the point that the motors are probably the easiest part to get "accurate".
    That said, you're making this because you want to and many people have made great machines on their own! Just be realistic about what it'll do.

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    Default Re: Epoxy Granite Portal Machine

    I'm taking some liberties in the math here but just trying to make the point that the motors are probably the easiest part to get "accurate".
    Yup. In theory, steppers - when under no load to speak of - can be just a hair more accurate than servos of equal resolution, because servos have following error. However, in practice; a) you wouldn't have a servo with equal resolution; you'd have an encoder on it with finer resolution than the stepper; b) following error can be as little as +/- one encoder count with a well tuned servo; and c) in any case we are talking about errors on the same order as the quantization error of the control system - so it's not something to really worry about.

    Where servos and closed loop stepper systems have an advantage is dealing with momentary mechanical overload - open loop steppers can get knocked from one step detent to the next; thus "loosing a step"; and throwing off any moves that come afterwords. Closed loop systems will detect this and make a correction - you might loose a little bit of surface finish (although, that might be a non-issue, if as is likely, the overload was during a roughing operation) but you won't ruin the part.

    That said, you're making this because you want to and many people have made great machines on their own! Just be realistic about what it'll do.
    Yes; if your expectations are reasonable - or straight up low - you can be pleasantly surprised when your creation outperforms them. However, if you have unrealistically high expectations, you are guaranteed to be disappointed when it fails to live to up the "pipe dreams"...

    Do steppers and servos have the same mounting in case I wanted to swap later on? (I honestly cant seem to find conclusive data.)
    Most steppers of the sort that you'd use for a CNC machine are made in NEMA standard frame sizes - 17, 23, 34, or 42, typically. Some servo motors are also available in those frame sizes; however there is much more variety in servo motor frame sizes than there is in steppers.

    However, it's typically not a major problem to make some adapter plates; should one need them.

    I have no personal experience with this company's products, but they have been recommended by other people on this forum... and they do have servos in NEMA frame sizes.
    DMM | AC SERVO DRIVE | AC SERVO MOTOR | ROTARY ENCODER






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    Default Re: Epoxy Granite Portal Machine

    Thank you for your responses.

    Does anybody know of a good spindle servo? (1.8 Kw, 8000 RPM) Is direct drive necessary if I want to do rigid tapping?



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    Default Re: Epoxy Granite Portal Machine

    Thank you for your responses.

    Does anybody know of a good spindle servo? (1.8 Kw, 8000 RPM) Is direct drive necessary for rigid tapping?

    - - - Updated - - -

    Thank you for your responses.

    Does anybody know of a good spindle servo? (1.8 Kw, 8000 RPM) Is direct drive necessary for rigid tapping?

    - - - Updated - - -

    Oops. DIdnt mean to double post. Sorry.



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    Default Re: Epoxy Granite Portal Machine

    Does anybody know of a good spindle servo? (1.8 Kw, 8000 RPM) Is direct drive necessary if I want to do rigid tapping?
    No, it's not required; but it can't be a friction-belt drive (like a V-belt) - they will slip a little; putting a large amount of force on the tap. Gear drive works if the backlash is low enough and you can setup the control to handle it; but timing belt drive works best if it's not directly coupled. It helps if the pulley/gear ratio is an integer multiple; but depending on the control may not be a strict requirement.



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    Default Re: Epoxy Granite Portal Machine

    Quote Originally Posted by Richmaple View Post
    Steppers and servos both are capable of 0.001“ and way finer but first off, you're trading speed for resolution in some cases (the pitch of your ballscrews). Second, that won't be the problem in my opinion. It'll be backlash and slop and flex in the entire system which probably can't total more than like 0.0005 for you to hit your goal. So not only do the bearings and ball nuts and mounts all have to have less than that amount of backlash, but your system, across the largest spanned member, has to also flex less than that under load.
    I'm taking some liberties in the math here but just trying to make the point that the motors are probably the easiest part to get "accurate".
    That said, you're making this because you want to and many people have made great machines on their own! Just be realistic about what it'll do.

    Sent from my SM-G960U using Tapatalk
    Hmmm.
    On a mill I've used some decent AC bearings. Double nuts shimmed as tight as they can go, jaw couplings, a fair bit of work.
    I can't get lower than 0.03mm (0.0012").
    Some expensive linear rails on it then maybe I'll half that but still.



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    Default Re: Epoxy Granite Portal Machine

    Quote Originally Posted by ando600 View Post
    Thank you for your responses.

    Does anybody know of a good spindle servo? (1.8 Kw, 8000 RPM) Is direct drive necessary if I want to do rigid tapping?
    Most I've seen is about 6000rpm (think was Mitsubishi or something). That's like about £1000 plus. Then you need a drive to match.
    Generally ones less than £1000 go to 3000rpm.
    Likely have to overdrive one with a timing belt.



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    Default Re: Epoxy Granite Portal Machine

    Quote Originally Posted by dazp1976 View Post
    Most I've seen is about 6000rpm (think was Mitsubishi or something). That's like about £1000 plus. Then you need a drive to match.
    Generally ones less than £1000 go to 3000rpm.
    Likely have to overdrive one with a timing belt.
    If by stepping up gear 4/1 to reach 12000rpm on spindle, with using the timing belt, will there be too much noise? But if changing to v-belt? will there be slipping problem and rigid tapping not be possible?



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