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PM932 CNC Build

Discussion in 'MACHINE BUILD LOGS' started by jbolt, Mar 11, 2014.

  1. TomS

    TomS Active User H-M Supporter-Premium

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    jbolt - nice build! My 932 is scheduled to arrive tomorrow. Mind If I pick your brain while I go through my conversion? Once the mill gets here the first step will be a thorough inspection, cleaning and break in followed by installation of a one-shot lube system. After that it's the installation of the ball screws and motors. What length ball screws did you use for the X, Y and Z? I'm planning on using 1605's on the X and Y and a 2005 on the Z.

    Thanks in advance for any advice you can share.

    Tom S
     
  2. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Hey Tom,

    Congrats on the new mill.

    No problem answering questions. Later tonight when I get home I can send you the ball screw sizes. I used 2005 all around. I used pulleys on the X,Y due to space so the driven ends of the shafts may be different length if you direct drive.

    Jay
     
  3. drs23

    drs23 Active User Active Member

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    Have seen this thread prior but didn't read it as I dunno squat about CNC machining or much even about manual but I just read the entire thing. That's a most impressive job Jay. Very, very impressive. Congratulations on such a fine job and finished product.
     
  4. TomS

    TomS Active User H-M Supporter-Premium

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    Jay,

    Thanks for your help. I'm going to direct drive my ball screws so I'll take into consideration that yours are belt driven. I wouldn't expect there to be much difference though as a pulley is about the same width as a coupling half. Or am I off base with that statement?

    Did you have to do any machining on the bottom of the saddle or table to get the 2005's to fit? I've heard and read that fitting a 2005 ball screw and nut to ZX45's requires metal removal.

    BTW - I started a thread about a week ago on the PM forum. It's titled "Taking the CNC Plunge". Has a little background on my approach.

    Thanks again. Can't wait to get started.

    Tom S


    Edit - just saw that you are from Mountain View. My wife and I are central California coast natives (Watsonville). My mom and stepdad still live there. My grandparents lived in Mountain View for years so I somewhat know the area.
     
  5. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Thanks drs23, It has been a fun project and learning experience.

    Jay
     
  6. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    No need to make the screws any longer than necessary so just double check the required engagement on the coupler with a little extra for adjustment.

    On the saddle I only machined the bottom on either side of the boss that the lead screw nut attaches to for the new ball nut mount to tighten flat against. Also squares up the boss. Everything I did would not prevent the original lead screws to be re-installed. The 2005 screw and nut does fit without major modifications to the saddle but it takes careful planning.

    IMG_0735.JPG

    Jay

    IMG_0735.JPG
     
  7. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Here is the ball nut mount being relieved to clear the table. I had to add another angle to what you see to clear the casting at each end of the table where the reservoirs are.

    IMG_0748.JPG

    IMG_0748.JPG
     
  8. TomS

    TomS Active User H-M Supporter-Premium

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    Jay - thanks for the clarification. Sorry for not responding sooner but I'm neck deep into a kitchen remodel. Hopefully will be done in a couple of weeks so I can focus on the CNC build. Unfortunately my mill didn't get delivered yesterday. Roadrunner Transportation says it will get here Monday. We'll see!

    Tom S
     
  9. TomS

    TomS Active User H-M Supporter-Premium

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    Hi Jay. Been working on my PM-932 CNC conversion for a few months and am getting close on finishing the mechanical portion of the project. I have a couple of questions about your proximity switches. How did they work out? Are they reliable and repetitive? I assume they are normally closed switches. Is that correct?

    Once I get the mechanical part done I'll post pictures.

    Thanks and Happy Thanksgiving.


    Tom S
     
  10. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Hi Tom,

    Glad to hear your project is coming along. The proximity switches are okay. At first they were very repeatable but over time have become less so. I have not spent the time to figure out why yet so the jury's still out.

    Yes they are normally closed.

    I'm currently working with a couple of friends building a CNC router for cutting aluminum sheet metal. We will be using hall effect sensors and I want to see how they perform before digging into the proximity switches.

    Please post some pictures of your progress.

    Jay
     
  11. TomS

    TomS Active User H-M Supporter-Premium

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    Thanks Jay. Couple more questions. If I were to leave about 1/8" to 1/4" of over-travel when setting the proximity switches would they be repeatable enough to prevent a crash? If you had to do it over again would you still use proximity switches or go with standard type limit switches? Just wanted to get your opinion because I'm at a point in my project where I need to start thinking about limit/home switch type and placement.

    Tom S
     
  12. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    The proximity switches work fine as limit switches and will always trigger. The repeatability issue I am having is with homing to within 0.001". My Z homes to within 0.003", the Y within 0.004" and the X within 0.007".

    I like the proximity switches for their ease of installation and setup. If the hall effect sensors we are going to use on the router work better I may change to those but they will require enclosures to keep ferrous metal chips away since they use magnets.

    I need to do some research on the resolution of the proximity switches I have to see if they are capable of what I am expecting. They may not have the sensitivity I need or my triggers need refining.

    I have never used mechanical switches but it is my understanding they don't have the repeatability I am looking for. They would work fine for just limit switches.

    Jay
     
  13. JimDawson

    JimDawson Global Moderator Staff Member Director

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    A flag type photo eye may be a better choice for home switches. Mechanical limit switches are very repeatable if you use the correct switch. A snap action switch is not the correct switch. What is needed is a slow acting switch, much more repeatable and no dead band. Snap action switches work OK for travel limits.

    The other problem I have run into is the speed of the homing routine. It should be a 3 step process Move to the switch at moderate speed, very slowly move off of the switch, very slowly move back to the switch. This normally gives a pretty accurate position. The only reason you really need to set the home position is to set the software limits.

    The real question is why would you need home a mill at all. Normally you would zero off of the work and use that as the reference. If I need to park my table after an operation, I pick a convenient location and tell the table to go there after the operation is complete. There are other machines that do need to have a fixed home position, like a dispensing machine where the stations are fixed to the table and never change.
     
  14. John Hasler

    John Hasler United States Active User H-M Supporter-Premium

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    This could be a software problem. If the processor is polling the switches rather than being interrupted by them repeatability will depend on how busy it is and how fast the table is moving. Even if the switches generate interrupts you could still have a repeatability problem if the interrupts are low priority. This is where real-time design becomes important.
     
  15. TomS

    TomS Active User H-M Supporter-Premium

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    Thanks Jay, John and Jim for your input. You've clarified my questions so I will order proximity switches for my conversion. My plan is to reference off of the Y and Z axis ball nut mounts so I can place the switches inside the base and column thus protecting them from coolant, swarf, etc. The X axis is a bit more trouble to mount under the table so I may mount it on the front of the table.

    Tom S
     
  16. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    I've run a few projects multiple fixtures and work coordinates setup at the same time. G54, G55, G56 etc. Havng a repeatable home position allows me to simply reference "all home" at the beginning of a session without having to set the offsets each time.

    My vises and tooling plates are also indexed to the table with pins. The vise edges and tooling plate index pins are a known offset from home position so with a good repeatable home position it is simple to switch between the vises and tooling plates.

    On complex parts that require many hours of machining I will reference the home position between parts just to verify there have been no missed steps.

    Jay
     
  17. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    How would I determine if it is a software problem?
     
  18. John Hasler

    John Hasler United States Active User H-M Supporter-Premium

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    Do I understand correctly that the software that monitors the switches and controls the motors is running under Windows XP? If so make it do something challenging while it tries to home and see if the error increases.

    To fix it the best you can do is try to minimize the number of processes running while the switches are being read. Uninstall or shut down everything you possibly can. XP was designed for the desktop, not for control.
     
  19. JimDawson

    JimDawson Global Moderator Staff Member Director

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    If you can hang loose for a couple of days, I'm getting ready to fire up Mach3 on a 4 axis machine I just put together. It will be running on a clean install of XP Pro, SP3. I am also using snap action switches for the travel limits and they also double as the home switches. Normally I would not use snap action switches, but they were cheap and good enough for my application.

    I'll post my findings and all of the setup information for both XP and Mach3 when I get it going. I don't need extreme accuracy for this machine, but I will check the repeatability of the limits and see what I can do to get them to at least 0.001.
     
  20. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    John - Yes it is on XP. It was a clean install of XP pro. The PC only runs Mach3 and is not connected to a network, no anti virus etc. I have disabled as many unneeded processes as possible but there could be some I missed. Not sure what I could do to challenge the software while homing.

    Jim- no hurry, I'm too busy with other things to tackle this right now. Next spring I plan on doing a partial tear down to make sure everything is still tight and true. Plus the machine needs a good cleaning. One of the downside of flood coolant.
     
  21. John Hasler

    John Hasler United States Active User H-M Supporter-Premium

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    Copy a large file.
     
  22. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Thanks, I will give it a try.
     
  23. JimDawson

    JimDawson Global Moderator Staff Member Director

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    OK, I checked the repeatability of my limits. As close as I can tell they are dead on 100% of the time using a 0.001 reading indicator. I'm using about 20% speed when I'm homing. My motor speeds are set at max 70 IPM, so 20% speed = 14 IPM. I'm using about 15 degree cams to actuate the switches.
     
  24. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Project Update:

    I had a mishap with the mill where during a 2" deep contour run a piece of material that should have fallen away got sucked into the cutter (3/4" end mill). The 1/2 thick piece of aluminum jammed between the part and the cutter stalling the spindle. Running at 20 ipm it moved off the part before I could e-stop. The spindle is fine, the x-axis (the moving axis at the time) is fine but the Y-axis, which was not moving now has a dead spot in the motor. The drive also makes the motor very noisy. At low rpm the motor hesitates as it goes through the dead spot, at moderate speed it vibrates like crazy and at full power it runs like normal. I swapped the X & Y drives and the Y drive makes the X motor sound noisy. The Y motor on the X drive is less noisy but still has the dead spot. I'm not really sure what was damaged but for now I just plan on replacing the motor and drive.

    I pulled the table off to inspect the ball screws and everything there is good. I did discover that coolant was getting into places I didn't think it could. I use Rustlick ws-505o at about 7.5:1. It's just amazing where this stuff will work itself into let alone its ability to remove paint and adhesive.

    While I have the machine apart I extended the notch for the Y-axis in the base to pickup 2 more inches of Y travel and also machined some reliefs in the bottom of the table to gain 3 more inches of X travel. The 20 mm ball nuts are too tall to fit under the thickened casting under the end wells on the table. I was able to safely remove enough material to get the extra travel I had originally lost. It seems you can never have enough travel.

    Other thing I discovered is that the Z-ball nuts were not getting oil through the one-shot oiler. Once primed the system drains back through the X and Y ball nuts. To fix this (hopefully) I have installed in-line check valves on all the supply lines to the ball nuts and ways.

    One of the sheet metal sponsors for the high school robotics team I help mentor is making me a new one piece splash shield with drain gutter to fit around the front and sides of the table. In addition to that I will be replacing the factory way covers which have not held up well to the flood coolant, with a single sheet of 1/8" rubber. One end will be attached to the cross slide and the other to the Z dovetail plate. I'm going to start with an 18" wide piece to see how it works. My only concern is how it will bunch when the Table and Z are at their closest to each other. The rubber sheet is cheap compared to high quality way covers so its worth a try.

    Also in the mix is:

    Changing out the Chinese BOB and UC100 USB controller for a PMDX-126 BOB, Eithernet SmoothStepper.
    Upgrading the spindle bearings.
    Changing to a belt drive and VFD.
    Adding a no-mist system
    Re-doing the control box that houses the motor drive, power supplies and BOB so the components can be removed/replaced without having to completely dismantle the box. (poor original planning)
    Trying out some mechanical slow acting switches for my Home/limits to see if the work better than the proximity sensors.

    Here are a coupe of photos of the underside of the table being milled on the trusty old Smithy Granite 3-1.

    Jay

    table_mod.gif Table_mod_close.gif
     
    Last edited: Feb 24, 2015
    gt40 likes this.
  25. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Jim, what type of plunger/actuator arm is on your limit switches?

    Jay
     
  26. JimDawson

    JimDawson Global Moderator Staff Member Director

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    They are roller lever type.

    IMG_0435.jpg
     
    Last edited: Feb 24, 2015
  27. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    The mill is once again operational.

    The Y-axis motor and drive have been replaced. The head was knocked out of tram by 0.080" which surprised me.

    I was able to reconfigure my control box that houses the drives , BOB and controller so all the components can be individually removed without having to disassemble half the box.

    I installed a new PMDX-126 BOB, PMDX-107 spinde control card and an Eithernet Smooth Stepper (ESS) in place of the old generic BOB and UC100 controller. This was much more complicated to setup. The PMDX suffers in places from too much information in the manual and a little too cut up for my liking but I managed to fiddle my way through it. The ESS suffers from too little documentation. Hurray for online forums and Google! Anyway I really like how the ESS nests on top of the PMDX-126 as a daughter board. Very tidy setup. I am having an odd issue where if a limit switch is triggered the keyboard jog function no longer works unless the system is power cycled. Additionally, if I plugin the xbox controller the keyboard jog and fly-out jog become inactive? Fortunately the xbox controller works fine which is what I normally use for jogging anyway.

    I installed the new coolant shields. The shield around the table is really slick and does a great job of directing coolant off the table without it getting into everything. The rubber way cover is also working out nicely. One end connects to the cross slide and the other end to the Z dovetail. To keep the rubber sheet from bunching behind the table I added an intermediate support that is suspended from the column. It's a little Rube Goldberg-ish but so far it is working well.

    Next is to machine the motor mount for the belt drive conversion.

    20150310_180346.gif 20150310_180357.gif 20150310_180403.gif
     
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  28. Boswell

    Boswell United States Hobby Machinist since 2010 H-M Supporter-Premium

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    When you hit a limit switch, are you selecting Limit Override in Mach3 before you try to jog back off the limit switch? Wait, are you using Mach3 ?
     
  29. TomS

    TomS Active User H-M Supporter-Premium

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    Jay,

    I like what you are doing, especially the belt drive upgrade and upgraded spindle bearings. Waiting anxiously to see how you do these mods.

    After extending the Y axis notch and removing the bellows how much total travel did you end up with?

    Tom S
     
  30. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Yes and yes!

    Jay
     

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