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Thread: Clearpath SDSK for mini mill?

  1. #21
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    Default Re: Clearpath SDSK for mini mill?

    You can't "upgrade" a poor machine into a good machine. It has to be a good machine to start with. First, and foremost, it must be RIGID, and that means LOTS of metal, usually cast iron, which means HEAVY. About the biggest "hobby" level machine on the market right now is the Novakon Torus Pro, which is what I have. It is about 1400#, with travels of 25"X, 15"Y, 12"Z, linear rails on Z, with a 1.5HP 3-Phase spindle, and AC servos on X/Y/Z and will do 500 IPM. It is probably good for +/-0.002" on average. The Tormach 1100 is in the same class, with smaller travels, and much slower drives. Either machine will set you back about $15K. If you want better than that, then you're looking at a commercial VMC, like a Haas MiniMill, which starts at about $30K, and is probably good for about +/-0.0005".

    How much do you want to spend? You have to be realistic - quality is expensive, and there are no short-cuts. The X2 is fine for many jobs, and a great learning tool, but it is very limited in many way, and can't really be greatly improved without spending as much as it would cost to get a better machine to begin with. Getting down to even +/-0.001" requires a very rigid machine, very high quality bearings, slides, and high quality ground ballscrews, not Chinese knock-offs. It requires feedback, not just on the motor, but on the axes, to take out thermal effects. It requires dual-closed-loop servo drives. One of those motors, or ballscrews, will cost far more than the entire X2, and probably weigh almost as much as well. The whole machine must be designed as a system, understanding the countless trade-offs that go into every single component choice, and every design decision.

    Regards,
    Ray L.



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    Default Re: Clearpath SDSK for mini mill?

    Thanks, Kenny, for the encouraging words. I know Clearpath motors on a mini mill is like putting lipstick on a pig. But it's what I wanted to do, just to be able to see what they're all about. Due to lack of space, I will never be able to own a machine much bigger than the X2...that's a fact that will not change. So, if that's what I'm stuck with and I can (and am willing) why not outfit it with some nice motors? I wanted a G0704 or something like that but even that would be a stretch to fit in my tiny work room.

    Ray, I know you're right on all accounts but you're going in the wrong direction...I need small. :-) You've provided a wealth of great information but still haven't answered my humble question. Why does Centroid require such high precision encoders for use with their motion controllers when even a large machine like you are describing cannot hold tolerances that would take advantage of that kind of resolution?



  3. #23
    Member Kenny Duval's Avatar
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    Default Re: Clearpath SDSK for mini mill?

    You can't beat the physics. The bigger more precise machines have a couple things going for them.

    1. Mass - The more you have the better off you'll be. Bigger machines have bigger castings, more structure and are just flat out stiffer than the smaller mills. That same mass leads to them being impacted less by temperature swings as it would take longer to change it's temperature. Metal grows and shrinks with temperature and why Ray mentioned the linear scale on those machines that can compensate for the growth or shrinkage of the machine.

    2. Linear Rails - less friction and there for less stiction than a dovetail machine. Add to that the poor surface contact and finish work on dove tails of the smaller mills and you either have excessive slop that leads to error or stiction and friction that lead to error.

    3. Ground Ball screws - Way more accurate over their entire length than a rolled screw. They are also larger on the bigger machines so less likely to twist when the machine is changing direction. Think torsion bar front suspension on the old Ford trucks and Nissan trucks.

    4. Precision spindles - Good ones are expensive and in some the bearings they use would cost more to replace than buying the X2. Less spindle run out leads to less tool holder run out leads to less tool run out and thus less total indicated run out.

    Ray is specifically trying to give you a realistic expectation of the performance of the X2. If cost is no concern and your only limitation is footprint then I say have a good time dropping what ever you want on it. Drop on the Clearpath motors and enjoy.

    In terms of the Centroid control it has been engineered to run on those larger machines and thus wants to maintain a high level of accuracy. They support Rigid Tapping and that requires fairly tight coordinated movements.



  4. #24
    Member CS900's Avatar
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    Default Re: Clearpath SDSK for mini mill?

    I'm going to play devils advocate here if I can.

    I'm not entirely convinced you can't get +/-.001 out of a benchtop mill. Granted not over the entire travel, but if the feature is sufficiently small (maybe under 1"?) I don't see any reason it can't happen. I'd agree that you should have as little backlash as possible for repeat ability, which usually means high quality ballscrews and support bearings, and as much rigidity as you can get; but if you've done a good job tuning your machine (backlash comp, ballscrew mapping, repeatable limit switches, properly adjusted gibs) and your programming is done smart, I don't think +/-.001 is unreasonable at all.



  5. #25
    Community Moderator Jim Dawson's Avatar
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    Default Re: Clearpath SDSK for mini mill?

    If you were running a 0.5 or 1 inch lead, then 8000 count (or more) would be needed to get reasonable resolution. This would also imply insanely fast rapids are achievable if your servos are big enough. Expensive industrial machines do have sub-micron resolution on the encoders, but that is far away from hobby class machines.

    Notice that I said resolution, this is different than accuracy. Modern motion controllers/drives will position the motor to +/- 1 encoder counts or better, but there is no guarantee that the table will actually be where the controller thinks it is, the actual position error could be +/- several microns. The best way to overcome the inherent inaccuracies in the mechanical system is to put linear encoders on the load rather than relying on the motor/leadscrew system for positional accuracy.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Clearpath SDSK for mini mill?

    Quote Originally Posted by Scot808 View Post
    Thanks for the reply, guys. That's about what I figured but then there are those guys with the high res motors, I thought maybe I was overlooking something.

    I hear what you're saying, Ray, but due to lack of time and space, I'll likely never have anything bigger/better than the X2. So, being curious, I figured I'd give them a try just to see. I might be foolish and uninformed but I'm not dumb...I'm well aware of the X2's shortcomings.
    Don't be discouraged, by some posters, you can fit servo's to any type of machine you like, and there will be a benefit, no matter what it is

    If you are looking for a better resolution, you would not find that with a ClearPath package, is you want a better package you would look at Dmm servo's which is a better price and use 16 bit Encoders this is when you start to see a difference, it should never be about what your resolution is, it is more about how smooth your machine will run because of the high resolution

    DMM | AC SERVO DRIVE | AC SERVO MOTOR | ROTARY ENCODER

    Mactec54


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Clearpath SDSK for mini mill?

Clearpath SDSK for mini mill?