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  1. #1
    Join Date
    Mar 2008
    Posts
    56

    Knee mill conversion

    Need some advice on my knee mill conversion.

    To fix up the poor repeatabilty issue by base flex im going to mount the lead screw and ball nut assembly onto the column.

    However to take the weight of the table I need to add pneumatic setup to it.

    Ive purchased a Grex100 BOB, I was just wondering what parts do I need to control the cylinders up and down movement.

    Also what kind of cylinder do I need....Magnetic, Double action??? What electronics do I need...something Like a solenoid im gathering and what kind of solenoid. Ive read into some of the options like NC and NO....Any advice anyone can give would be fantastic.

  2. #2
    Join Date
    Mar 2008
    Posts
    56
    Just a thought???? Is it as simple as putting a cylinder in place and a pressure regulator to counter act the weight of the table.??

  3. #3
    Join Date
    Jun 2006
    Posts
    475
    evo4wrx,
    Yes sure is! Just make sure your regulator is a vented type. This means it will maintain a constant line pressure. As the cylinder is compressed by the lead screw going down for instance, the air pressure will rise. A vented regulator will exhaust this excess and maintain constant cylinder pressure and force therefore giving you a weightless knee. The servo and lead screw will have a much easier time positioning the knee.
    You could also run a counterweight like a lot of cnc mill's also do.

    Hope this help's
    Chich

  4. #4
    Join Date
    Dec 2003
    Posts
    24216
    My Excello's have an air cylinder either side of the knee, they also use a air balancing constant pressure system, as mentioned in the previous post.
    This is motorised for initial positioning only by using a ball screw jack, the driving motor has a DC brake fitted.
    The cylinders are single acting and no solenoid is required with this setup.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  5. #5
    Join Date
    Mar 2008
    Posts
    56
    Okay just making sure I have this clear....
    Air from compressor--> control valve --> controller---> some kind of pressure transducer--->(load, being cylinder). Sorry my back ground is electronics.....So gotta have magical smoke or it just doesnt feel right.

  6. #6
    Join Date
    Dec 2003
    Posts
    24216
    Line air in > Manual Pressure reducer > Automatic Pneumatic Constant pressure Unit> Cylinders.
    The standard manual pressure reducer is used to set the required balance pressure, this is set so the raise device has the same load in both up and down direction.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  7. #7
    Join Date
    Mar 2008
    Posts
    56
    Wouldnt happen to have an example part number or link to the products....
    Just been checking out the cost of the electronics path and its about $1800 which is about half the price that I paid for the mill. ....Kind of seems a waste. So back to the manual method.
    Just picked up a Norgren Double action , Magnetic , 100mm bore , 350mm stroke.
    Im fairly sure I dont need the double action. So I just leave one of the ports open????

    Whats the point of the magnetic piston????

  8. #8
    Join Date
    Dec 2003
    Posts
    24216
    I will see if I can round up the part numbers, the magnetic piston is to use external magnet sensor to indicate the piston position.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  9. #9
    Join Date
    Mar 2008
    Posts
    56
    Cheers thanks for your help.
    Looking around for Pulleys and belts now....
    Im thinking 4:1 ratio for X,y,z...im not after super fast speeds and this mill is a bit heavier. My motors are 4600 Rpm Constant torque of 1.2Nm 90Vdc.

    The gecko 80vdc will bring that back to about 4200 RPM. The screws have 4 turns to 1/4 inch. So that should give me plenty of resolution with the 1000 CPR encoders. I did actualy work that out somewhere exact a long time ago. Ims ure its more accurate then the chinese machine could ever hope to repeat.

    The question is how big do I make the pulleys and what pitch. Try as I may I cant find load ratings anywhere for the different kind of timing belts.

    Ill begin the build pictures Tuesday next week when everything turns up.

    Anyone have any supplier suggestions for pulleys....already seen PIES and RS Australia.

  10. #10
    Join Date
    Mar 2008
    Posts
    56
    For the next person trying to find power ratings of belts YAY.
    http://docs-asia.electrocomponents.c...6b803c5d9d.pdf

  11. #11
    Join Date
    Dec 2003
    Posts
    24216
    For charts and sizing see the Sdp-si web site.
    Also for availability, Misumi of Japan are world wide and have an excellent selection of hardware, the free catalogue is worth it alone.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  12. #12
    Join Date
    Jun 2006
    Posts
    475
    evo4wrz,
    On my mill I used XL series belts and pulleys 4:1 from Associated World Bearings (AWB) http://www.awbbearings.com.au/ They are pretty much straight out of the Gates catalogue and overnight delivery.
    The vented regulator I used is from SMC and the part No is IR2020-02 it has 1/4" port's and works very well. My cylinder is a 4" double acting tie rod aluminium cylinder. I leave the top port open to atmosphere and connect the precision regulator to the bottom port with 1/2" copper pipe. You will not need a magnetic switch for the cyilinder in this application as all the cylinder is doing is constantly taking weight of the knee so the servo and screw can moove the knee without having the weight of the knee to contend with. Think of it a bit like the power steering in your car - You are still making the wheel turn, the system is just assisting you.

    Chich

  13. #13
    Join Date
    Mar 2008
    Posts
    56

    Yay toys turned up.

    Had a few things turn up today

    PBDX 135 8020 x 2
    Gecko 340 x 7
    g100 x 2

    4 meters of leed screw
    12 x ball screws
    UPS 2000va as I plan to run the gecko 340's close to 80vdc and a surge or spike will trip the fuse.

    My entire electrical setup will go into a 40RU rack mount cage. Im going to use slide based 4RU server cases in the cage for ease of access.

    Still waiting on the DC-03 Digispeed , VFD , united dgital Enocders. Transformers, air jack, regulator (thanks for the product code chich).

    And im with Chich on the comment of united digital and their rip off attitute of using UPS. The freight was $290.00 for something that weighs next to nothing. You guys if you are reading this pull your act together. Also get a tracking systems automated like Gecko theirs is brillant.

    I setup the G100, got it talking to the PC wasnt too hard.
    I will start milling up the leed screw mounts this weekend for the mill. Have had the bearings there for ages so may as well use them before they go rusty.
    Im going to convert the mill to 4 axis, and use both the horizontal spindle and the vertical. Both are 2.2Kw 3phase.

    The servo motors are 90vdc 7.2amp 4800rpm. I got 10 of these from china about 7 weeks ago. I wont need 10 but just incase I blow one I have a hot spare. Im also planning on using an encoder and axis to drive the chuck on the lathe....no idea how yet as far as software setup but im sure there is a way.

    The other idea I thought of for the lathe was to use a 3 phase 2.2kw motor and an encoder based servo motor and engage the servo motor at the beginning and end of chuck movements to ensure finite control. Again no ideas on details....but first things first...MILL.
    Attached Thumbnails Attached Thumbnails P9160010small.jpg   P9160007small.jpg  

  14. #14
    Join Date
    May 2007
    Posts
    72
    Quote Originally Posted by evo4wrx View Post
    And im with Chich on the comment of united digital and their rip off attitute of using UPS. The freight was $290.00 for something that weighs next to nothing. You guys if you are reading this pull your act together.
    US Digital encoders?

    If you're getting things from the states try Woody.

    He'll consolidate, repackage and resend stuff. Top bloke. Charges a very reasonable per package fee (~$15).

    Repacked my 10 US Digital encoders + cables and put them in an US Postal Service US$11 envelope for me.

    Saved me a bundle.

  15. #15
    Join Date
    Jan 2007
    Posts
    219
    Do you have a link for the motors? I just finished retrofitting my knee mill and am unhappy with 1 of the motors that I used. How much were they? -Adma
    www.adambrunette.com - Converting My Harbor Freight X2 And My Jet Jvm-830 Knee Mill, As well as many other projects.

  16. #16
    Join Date
    Mar 2008
    Posts
    56
    I wouldnt recommend the DC motor supplier I used to anyone. They took over a month to get the motors to me, I had to hound them, that still didnt work and I ended up getting a mate of mine who could speak native to them.

  17. #17
    Join Date
    Mar 2008
    Posts
    56
    id give give Keling inc a go if I were you motors seem very well priced.

    Failing that get on Alibaba and you will find a lot of cool stuff.

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