Upgrade Opinions


View Poll Results: What will give me the most bang for the buck?

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  • Replace 60" 1/2"-10 2 start (bent) with 1/2"-10 5 start ($0 - have to do something)

    4 57.14%
  • Replace 1.6A/ph steppers with 2.5A/ph Xylotex ($0)

    2 28.57%
  • Replace Xylotex driver with Gecko G540 ($300)

    4 57.14%
  • Replace Xylotex ps with 7.3A ps ($50)

    1 14.29%
  • Replace Xylotex 2.5A/ph steppers with 3.5A/ph steppers (from CNCRP - $170)

    2 28.57%
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  1. #1
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    Hi there - I have been lurking on this forum for the last few months as I planned to build a CNC. Just as I sat down to order the parts I got an email from a friend with a craigslist ad for a router nearby. The price was right, so I bought it. Not shockingly, it needs a few things fixed.

    I have really enjoyed the knowledge and creativity of this group so I thought I would ask for people's opinions on what I might upgrade first.

    Here are some details about the machine: it appears to be a Maxym - not a lot of information about them. It has a cutting volume of 4' x 5' x 6", a Perske 5hp spindle and THK SR25 bearings and rails on all 3 axes. Hopefully the picture shows that it is a cantilever design, open on 3 sides. The axes are driven by 1/2"-10 acme 2-start lead screws and steppers.

    My experience so far has been positive - the spindle works well, the machine seems tight and rigid.

    Here are the issues:
    1) The long axis (60") lead screw is bent - it has a pretty good kink in it. That limits the feed in that direction to 35ipm. I can get a reliable 70ipm on the other two axes.

    2) The previous owner replaced the electronics with a xylotex 4-axis driver and powersupply, and replaced the long axis (bent) stepper with a xylotex (and gave me the other 2 xylotex steppers). This board has no ability to control the spindle speed - something I would like.

    3) Jogging the 48" axis at 200ipm causes pretty good whip. The stepper cannot handle that speed reliably - why? the driver? the motor? the whip? the paint on the lead screw (mostly scraped off now)? ...? The mechanical structure - linear rails, big cantilever - seemed totally fine going that fast - no noticeable shakes or shudders.

    Questions:
    1) I clearly need to replace the long axis screw, should I switch to a 1/2-10 5 start? This would allow higher rapids without as much whip. What would I be giving up?

    2) Should I replace the original motors (1.6A/ph?) with the xylotex (2.5a/ph) motors?

    3) Should I replace the driver with a Gecko G540? I was jogging at 200ipm along the 48" axis but the steppers would stall - not during acceleration, but in the middle of the pass. Would this be helped with a different driver? The G540 would allow me to control the spindle.

    If I did get a G540 it seems like there are 3 options:
    a) just replace the driver, keep the powersuppy and steppers ($300) - and should I use the original or xylotex steppers?
    b) replace the driver and powersupply, keep the steppers ($350 for 7.3A ps from CNCRouterParts)
    c) replace driver, ps, and motors ($520 from CNCRP)

    Obviously I would like to go for option (c) - but money is tight. So what is the bang/buck ratio for each of these options?

    Here are some pictures - the machine (sans table, I am upgrading the vacuum table that came with it), and the stepper labels.

    Thanks so much

    Bart

    bart niswonger furniture

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    interesting machine. Seems to be designed for easy access for laying down sheet material. I'd be inclined to salvage the linear motion parts and made a traditional gantry to save space but that's just me. That leadscrew has got to go. 1/2-10 5 start is the way to go. Maybe even a bigger diameter to cut down on whip. Could you just use a product like super pid for spindle control? I have the g540 kit and it's great but you could try the super pid and if you need to upgrade to the g540 the super pid is still useful.

    leadscrew for sure.



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    Interesting machine! I love Craigslist. I would guess the the limit on the 48" axis is -- in fact -- the whip, but I'm not an expert. As for the upgrades, I'd be tempted to replace the bent lead screw and then use the machine a bit. Figure out what you're going to do with it, discover its limitations and then base your upgrades on what you really need. When it comes to lead screws, I've been told that the power curve of stepper motors falls off fairly rapidly at higher speeds. So, increasing the number of starts resolves two issues; you can increase IPM with less whip (as you've already figured out), and you're working within a better power curve range for the motors.

    As soon as I saw the picture of your new machine, I wanted to walk up, grab the outboard end of that cantilevered gantry and try to wiggle it. Please post results when you start cutting stuff!



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    Quote Originally Posted by robedney View Post
    Interesting machine! I love Craigslist. I would guess the the limit on the 48" axis is -- in fact -- the whip, but I'm not an expert. As for the upgrades, I'd be tempted to replace the bent lead screw and then use the machine a bit. Figure out what you're going to do with it, discover its limitations and then base your upgrades on what you really need. When it comes to lead screws, I've been told that the power curve of stepper motors falls off fairly rapidly at higher speeds. So, increasing the number of starts resolves two issues; you can increase IPM with less whip (as you've already figured out), and you're working within a better power curve range for the motors.

    As soon as I saw the picture of your new machine, I wanted to walk up, grab the outboard end of that cantilevered gantry and try to wiggle it. Please post results when you start cutting stuff!
    This is all good advice. I don't see why you would want the SuperPID if you have a working spindle system. I too wanted to see how the arm would bend. If it is flexing, you may have to run at slower speeds to keep it straight, so high-end ipm's may not be available anyway. I have heard that the round style of steppers loose their magnetic strength much more rapidly than the modern square frames, so replace this along with the screw.

    Finding a user-group or a forum member familiar with this machine's capabilities would be a big, big plus.

    Good find!

    Paul Rowntree
    Vectric Gadgets, WarpDriver, StandingWave and Topo available at PaulRowntree.weebly.com


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    I voted for the Gecko G540. I've got one and it works. Nice to know that what ever problems you may have with the electronics, it is not a problem with the driver. Send Marris at Gecko an email and ask him how these steppers would work with the 540. He has always responded promptly to my emails and he really knows his stuff (I spoke to him on the phone once and got quite the education).

    I would definitely go for larger dia screws (20mm for sure, and that maybe a bit smallish). I'm sure those with more experience can give some insight. I think replacing the existing screws with the same size would be a waste of money. Just my $0.02.

    Good luck.

    Rick



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    It looks like a good find.

    Roton has an excellent set of graphs and application information on screws for motion. From the "critical speed" charts, the upper limit for those screws will be in the 3 - 400 rpm range. As a practical matter, 200 rpm is the upper useful limit of most stepper motor setups unless special care has been taken to go higher. (which is not the case on that machine) The useful point is to pick a screw pitch which gives you the resolution you want at low rpm and the max jog speed you want at 200 rpm. For many people, this is about 1/3 to 1 inch of linear movement per rotation.

    Application Engineering

    I have some of those old vextra round motors as well. They were a good choice a long time ago, but now are obsolete and most likely have lost a good portion of their magnetic field strength. I suggest starting out by buying a good quality nema 23 stepper motor such as the gecko G723-280-4 motors. While this model is slightly lower in holding torque than the -400 oz version, it is highly linear and has good torque even as the rpm s increase. At $ 59 / each, they are an excellent choice and might be as much as 5 X the actual torque of your existing motors. Of course, call or write to Gecko and double check for a professional opinion.

    G723-280-4 Stepper Motor

    I agree that their are significant benefits from replacing the driver, but that is being mostly hidden with those yellow vextra dampers (I have the same ones) The really big boost in linear speed will come when you move to 72 volts and individual G203V drives for each motor, but that is an expensive step. It makes sense to do the motors and screws first, IMHO. I like the idea and price point of the G540, but I have not been able to resist the added potential power of the G203Vs.



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    Bart, you should chime in here and tell us -- if you know at this point -- what you want to do with the machine. Or, do you just want to optimize it because it's a cool machine (and that would be perfectly understandable). As an example, if you've always wanted to do intricate carving in hardwoods, maxing out the speed is not as much of an issue. You can only push around a 1/8" ball nose bit so fast. On the other hand, if you want to do a production run of cabinets cut from plywood, you may well want all the speed it can deliver.

    I would really recommend that you just get it running (replace the bent screw) and do some cutting. Find out specifically what the limitations are compared to what you want to do. Find out if the cantilevered gantry arm can hold decent tolerances at speed. You get the idea. Get to know the beast first, then pour money into her



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    Roton has an excellent set of graphs and application information on screws for motion. From the "critical speed" charts, the upper limit for those screws will be in the 3 - 400 rpm range.
    While whipping can occur above the 300-400rpm range, I run my 60" long 1/2-8 2 start screws at 600rpm (150ipm) with 100% reliability. They even have some minor bends in them, but I played around with bending them until I got acceptable performance out of them. At 600rpm, they whip quite a bit when the machine is at either end of travel, but don't whip much at all once the nut is about 18" from either end.


    As a practical matter, 200 rpm is the upper useful limit of most stepper motor setups unless special care has been taken to go higher.
    This is just not an accurate statement. I'd be willing to bet that almost all Nema 23 steppers used by members here are spinning much faster.
    I use a Xylotex, which is a rather low end drive, and can run my Y axis (40" screw) at 800rpm all day long with no trouble. My X axis ,limited to 600rpmby screw whip.

    Particular setups can give varying results, but most G540 users have no trouble getting a reliable 1000rpm and higher from Nema 23 steppers.

    A major G540 reseller posted last week on the Mach3 Yahoo group that he reliably runs small steppers at over 2500rpm on small mills with high tpi screws.

    Gerry

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  9. #9
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    For the OP, choosing which components to upgrade is a very tricky question. The truth is, everything should be upgraded.

    Screws. 5 years ago, 1/2-10 5 start screws were the #1 option for people building machines with up to 60" screw lengths. But they whip. Enough that today, the vast majority of builders choose rack and pinion over acme.
    The 1/2-10 5 start may give you more speed, with less whipping, but you'll probably need more power to spin them. Your motors are on the small side.

    Motors. I'd upgrade the motors to utilize all 2.5 amps that the Xylotex can deliver. Something in the 250-280oz range, with the lowest inductance you can find. Double shaft would be preferred. Many machines with Xylotex drives suffer from resonance, which can greatly reduce performance. Adding dampers to the rear shafts can make a huge difference in some cases (but not all).

    Personally, I think upgrading the motors and screws is the best, least expensive option. You might also consider 1610 ballscrews from Ebay, which are far more efficient, and will whip less due to their larger diameter.

    The G540 is a far superior drive, which will let you spin the motors much faster. Which will cause your screws to whip badly. The long screws are the limiting factor here. To really take advantage of the G540, You'd also want even bigger motors, and even bigger screw, like 2010 ballscrews.

    As far as speed control, you can add a PCI parallel port and get a speed control card to control your VFD.

    Gerry

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  10. #10
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    First off - thank you all for your responses! It will take me some time to digest the content!

    As for what I want to do with it - I build furniture, mostly from wood although I use some aluminum and would like to be able to cut it. My furniture tends to have surface texture. Up until now I used a table saw and bridgeport to cut the textures, my hope is to use the cnc. Both the tablesaw and the bridgeport leave a surface that needs only a slight sanding - I am not sure I can reproduce that with a cnc, or at least one within my price range, but I am interested in finding out. I expect to trade time for quality of finish - I like the idea of the machine running while I do other things in the shop. But 35ipm is a bit slow - 200ipm rapids would be great.

    As for the big cantilevered "proboscis" - I had exactly the same response - grab a-hold and push. When I first saw it, the mount to the nut on the x axis was loose, so you could move the whole thing. Closer inspection revealed that while it moved, it did not rack. Now that I have tightened the nut mount down I cannot move it at all by hand. I am not sure what tolerances it can hold - I want very much to find out! But my only other experience is with a Techno 4x8, and I could see the gantry "wobble" while cutting, and I could see the result in the surface of the cut. I have not seen or felt any of that in this machine. Of course, that machine would not stall cutting at 150ipm, mine won't really break 50.

    One thing I did not put on the list is switching to a fixed screw, rotating nut model. There is enough space on both the x and y that I think I could make something work, and as I understand it, that would solve the whip issues.



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    I completely agree about getting it running before pouring in the money. I got it going and cut a sample surface to compare to a sample I cut on a Techno cnc. It took longer (lower feed rates) but the quality was at least as good. It showed me that the z axis does not hold well, and from what people have said, I think I need to replace the old vertex steppers with the xylotex I have.

    I have been pondering the question of how to test the tolerances. I am sure there are good ways to do it. Does anyone have recommendations of patterns to cut or other ways to determine accuracy & precision?

    Thanks

    Bart



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    Quote Originally Posted by ger21 View Post
    While whipping can occur above the 300-400rpm range, I run my 60" long 1/2-8 2 start screws at 600rpm (150ipm) with 100% reliability. They even have some minor bends in them, but I played around with bending them until I got acceptable performance out of them. At 600rpm, they whip quite a bit when the machine is at either end of travel, but don't whip much at all once the nut is about 18" from either end.




    This is just not an accurate statement. I'd be willing to bet that almost all Nema 23 steppers used by members here are spinning much faster.
    I use a Xylotex, which is a rather low end drive, and can run my Y axis (40" screw) at 800rpm all day long with no trouble. My X axis ,limited to 600rpmby screw whip.

    Particular setups can give varying results, but most G540 users have no trouble getting a reliable 1000rpm and higher from Nema 23 steppers.

    A major G540 reseller posted last week on the Mach3 Yahoo group that he reliably runs small steppers at over 2500rpm on small mills with high tpi screws.
    Hi Gerry, ok, maybe in more detail, what I refer to as a special setup:
    - 72 volt power supply
    - Gecko G203v
    - Low inductance motors with a relatively flat torque profile (compared to the low end stuff)
    - nema 23s

    This is a very specific setup compared to what he has now, but maybe not for this forum. His motors might spin up at 700 rpm, but how much torque is left with the existing setup, especially with those old round vextra motors ? The motor charts would indicate nearly nothing, so loosing steps is very possible.

    He is trying to put in just a little money and get maximum benefit. That is why I suggested using a screw with a high lead (which is at least as high of resolution as the 3:1 r/p setups) and a very decent quality stepper motor ( $ 60 ) This gets him running for under $ 200 total so he can see if the machine is worth spending more on or not.

    The real nice setup of course is ball screws rather than rack and pinion, but that can be serious money.



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    I use the same Xylotex drive, at 24V, and get up to 800 usable and reliable rpm. You don't need 72V and a G203 to get decent performance.

    Gerry

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    Quote Originally Posted by ger21 View Post
    I use the same Xylotex drive, at 24V, and get up to 800 usable and reliable rpm. You don't need 72V and a G203 to get decent performance.
    It sounds like your screws are about the same length as mine too. What steppers are you using? Are all your screws 1/2-8 2 start?

    If you are getting 600-800 rpm reliably on 2 start screw, could I expect to get the same on a 5 start, or is the torque required to turn a 5 start screw significantly higher and therefore I would not be able to actually move it?

    I am going to go ahead and swap the old vextra motors on Y and Z for the xylotex 2.5A/ph steppers since I have them. I can reuse the vextra dampers. Then I should be able to see at least what Y is capable of.

    Thanks again!

    Bart



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    My X and Y screws are 1/2-8 2 start, and my motors are Pac Sci 253oz 2.3amp bipolar series.

    It's very difficult to say how the 5 start screws will work. They should require twice the torque to move a given load, but they are more efficient, so the requirements may be slightly less.

    Gerry

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    JointCAM - CNC Dovetails & Box Joints
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    A further update -

    I hooked up the xylotex stepper on the 48" axis - now I can reliably (at least in the time I have tried it) move that axis at 175ipm, which I believe is somewhere over 800rpm (1/2-10 2 start screws advance .2" / rev, right?) The only trouble I have is in the last inch of travel (way out on the proboscis) where there was paint residue. I think I got all the paint, but I wonder if I may have scratched the screw since it still stalls there. But I can live with 48" of Y rather than 48.5".

    I am pretty happy with that - at least for the moment it is fast enough for rapids. Now I want to see how fast I can cut, and how accurately.

    Ger21 - I notice you straightened your lead screws - I think I might try that with the X axis. I figure it can't hurt and I might learn something.

    Thanks again for everyone's input,

    Bart

    Last edited by bartniswonger; 04-25-2013 at 10:20 PM.


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    Default further progress(?)

    Its been quite a while, and I have been pecking away at this machine as I can.

    - I straightened the X axis, trued up the z axis and cut a subtable flat. At that point I was running each axis at 40ipm - this still caused trouble at the very end of the x axis where there is still some paint residue.
    - There were a variety of PC problems causing little pauses periodically, found them, fixed them. Hopefully that will rid me of missed steps - lost about 1/4" over the X axis while surfacing the 4'x5' subtable.
    - The VFD causes a GFCI (separate circuit, the VFD is 3 phase running through a phase converter, the GFCI is on a 120 circuit) to trip - noticeable since my radio is on that circuit. I hope I fixed that today by finding the spindle was tied to a 120 circuit ground, rather than the VFD. I have not yet tested to see if that worked.
    - I thought I had toasted the power supply, bought a new one. Found out that when you toast a xylotex driver it looks like the PS is toast, but no, the driver is toast. Next time test the PS with no load prior to pronouncing dead. Maybe there won't be a next time?

    So - now I need a new driver and I am tempted to go for a Gecko. I think the G540 will meet my needs and am looking at these motors:
    NEMA23 381oz/in 3.5A Dual Shaft Stepper Motor KL23H2100-35-4B | Automation Technology Inc

    But I am wondering about upgrade options again:
    1) Can I simply replace the driver and keep using the same PS and motors?
    2) Should I upgrade the PS now, or when I upgrade the motors?

    3) I think the mechanical structure is beefy enough to move quickly with minimal flex, which would be nice. It is heavy, but the linear ways are pretty rugged and the whole thing moves smoothly when the screws are not installed - and moves smoothly faster than the screws can move it right now (or when last they could). However, I will need to upgrade the screws in order to go much faster. I imagine I will want ballscrews, to take advantage of their increased efficiency and decrease the whip with a larger diameter. The question is then, how fast can a G540 spin a 60" ballscrew (2010?) moving 100-150lbs, and is that enough? Or should I be looking at G203Vs now with the idea of slowly upgrading the motors/ps and screws as I can?

    I like the G540 because it is so self contained - has all the protections and can drive the spindle. But this machine does have a nice enclosure for the electronics and I can add the spindle control in other ways. If it seemed like I was going to want the 203Vs eventually, I think now would be a reasonable time to get them.


    What are your thoughts?

    Thanks so much!

    Bart



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