RF31 clone to CNC - component selection help needed


Results 1 to 7 of 7

Thread: RF31 clone to CNC - component selection help needed

  1. #1
    Registered
    Join Date
    Sep 2008
    Location
    ZA
    Posts
    4
    Downloads
    0
    Uploads
    0

    Post RF31 clone to CNC - component selection help needed

    Hi,

    I have a RF31/clone and I want to convert to CNC. Unfortunately it's the round column version but I read that Mitch? did a conversion to square column and sounds like he did what I thought of doing. I can't seem to find that thread now but when I did look, I could not get the pictures to load/links to work. So I'm only guesing from what I've read that it was indeed a success.

    Anyways, my main questions are what size motors/ball screws and slides/rails to use.

    I seem to recall he used 20mm wide rails for te new Z, is it really needed or will say 2x MGN15 also work?

    From reading it seems 5/8" by 0.2": or 16mm by 5mm pitch ballscrews is what most use. Is this the right size or can/should one go bigger? What about the Z axis?

    Motors I have read anywhere from 450oz/in to over 1600oz/in. I was originally looking at a 1600oz stepper kit on ebay but from experience I know steppers have their drawbacks. I have also found some closed loop 2 or 3phase steppers which should be an improvement but looking at the motor specs, the torque falls off quite rapidly as you increase the speed.

    Here is the link of the closed loop steppers: http://stores.ebay.com/cntop201301/C...ub=10987359015

    The other option I have considered was either Brushless DC or AC servo controls from Omron/Yaskawa or others but came across this: https://store.dmm-tech.com/collections/all

    It is a bit pricey but when you look at the specs, you get 1.27Nm (~180oz/in) continuous or 3.1Nm (~450oz/in) peak, the continuous rating is constant from 0-3000RPM so this speed can easily be reduced and then the torque multiplied. I'm thinking 1:3 so with a 5mm pitch screw you will end up at 540oz/in (1350oz/in peak) and get 196ipm which is probably good enough?

    Anyone use these servo drives before and can comment on the torque specs/life/comparable price?

    Has anyone done all the proper calculations to see how much torque is really needed for these little machines? I would hate to re invent the wheel but I also don't want to buy twice, rather do it right the first time. Excel spreadheet anyone?

    My purpose for the conversion is to make small injection moulds for parts I want to make, mostly aluminum molds but the machine might also see some steel (maybe even proper mould steel).

    There is also a company in town that is handing out CNC work to subs so it will be nice if I can also stand in the queue to get some work for it. Obviously the machine will have limited capacity but it would be nice if it can also earn me some money. I have a big knee mill that will be used to make parts but currently I don't have the time or energy to stand in front of it for it to make me some money so the CNC is a nice alternative option. I'm not really considering converting it as it will cost alot more and as far as I can tell the nut will be a problem as the XY is very close together, its a Lagun FTV-1.

    Comments/advice/warnings welcome!

    Similar Threads:


  2. #2
    Member
    Join Date
    Jan 2005
    Location
    USA
    Posts
    1943
    Downloads
    2
    Uploads
    0

    Default Re: RF31 clone to CNC - component selection help needed

    I converted a harbor freight round column mil a while ago and would recommend not doing it. Mine was RF 25 size though. Yes it can be converted to a square column mil but that will require a while bunch of changes that all take time and money. The mil head will need tip be changed out as well as the column. Unless you already have a cheap source for a column, vertical slide, and head, i would say just sell the rf31 and buy a new mil. The roundcolumn works, but the limited z quill travel is a real pain since you lose x y position when you raise the head. Also, the quill is really meant to be locked for killing operations, so the little bit of play in the quill is not ideal

    I switched to a G0704 square column mil and am much happier, but wish i would have gone larger like a RF45.

    Having said that, steppers work fine, but the new crop of closed loop steppers and the servos available now are really appealing. Three cosy of them had really come down. Mine use 570 oz in open loop nema 23 steppers and work fine. If you are planning to go with linear rails and slides then you won't need a much. My mills use the dovetails and i can get 180 IPM rapids and frequently cut aluminum at 50 IPM. it really depends what performance you desire.

    5/8 or 16mm screws would likely be fine for aRF 31, but i would probably go with 20mm if room is available without too much modification.

    I can't help on rail sizing, but there are plenty of examples of RF45 and g0704 conversions that have added rails to give an example.

    Sent from my RS988 using Tapatalk



  3. #3
    Registered
    Join Date
    Sep 2008
    Location
    ZA
    Posts
    4
    Downloads
    0
    Uploads
    0

    Default

    Just to be clear: I only intended on using the linear rails for the new z axis column.

    Yes a bigger machine will be better but this is what I have and besides I don't have space/money for a bigger machine anyways!

    Im not planing on making a fancy new head as I have a 2hp DC motor + drive I'm planing on using as the spindle motor. Im thinking along the lines of a 30 taper spindle cartridge bolted to an angle bracket/arm mounted to the z axis bearings. Laser cutting and welded steel construction. I have a lathe and big mill, welder and other tools. I think this should be quite doable.

    I see there is another user on here that used the same AC servos I'm looking at for the same type of machine and he seemed very happy with it. Will follow up with him.



  4. #4

    Default Re: RF31 clone to CNC - component selection help needed

    I've seen a couple of videos of guys that have gotten 350 IPM from 570 oz-in steppers.

    16mm screws are usually adequate. Personally, I would go with a 20mm ballscrew on the Z.



  5. #5
    Registered
    Join Date
    Sep 2008
    Location
    ZA
    Posts
    4
    Downloads
    0
    Uploads
    0

    Default Re: RF31 clone to CNC - component selection help needed

    So I found "Application sizing guide" pdf and also Bob's excel spreadsheet and they both give me similar results.

    I don't have the weight of the table etc but worked on 200lbs and another 150lbs for the fixture.
    300IPM for rapids and 150IPM for cutting and the max cutting force of 428lbs

    This seems to yield a required motor (with a 3:1 reduction) of 0.677lb/ft and the DMM 400w motors are 0.936 lb/ft rated, peak is about double that.

    So this looks like it will work. I would still like to hear from anyone using it to find out if they had any problems.



  6. #6
    Registered
    Join Date
    Dec 2011
    Location
    United States
    Posts
    6
    Downloads
    0
    Uploads
    0

    Default Re: RF31 clone to CNC - component selection help needed

    I've sold more than 80 CNC kits for the round column mill. They are fine with the stock lead screw. Ball screws aren't more accurate. The tolerance is the same as for a lead screw. With backlash compensation you can hold .001 to .0015" tolerance.



  7. #7
    Member
    Join Date
    Jun 2011
    Location
    US
    Posts
    692
    Downloads
    0
    Uploads
    0

    Default Re: RF31 clone to CNC - component selection help needed

    I can tell you about what the minimum torque you can run an RF-31 on. I bought a pre-converted one and it uses a max-nc closed loop stepper setup. Couldn't find exact torque ratings but I estimate them around 100 oz-in holding, and they're 5:1 reduced. At the 20 ipm max cutting I use I figure they're around 60 oz-in, so about 300 to the screws (5mm rolled ball-screws with adjustable anti-backlash.)
    Torque that low wouldn't be usable without being closed loop back to the controller.
    I was going to upgrade much the way you're planning on 400w servos with 3:1 pulleys, but have already moved on to another project so can't say how they would work.

    On mine the front half of the head is cut off and replaced with a light linear bearing stage with the original quill (with AC ball bearings in place of the original roller bearings,) and a treadmill motor hanging off the vertical stage. It used 10mm or 12mm linears when I got it, but I immediately upgraded them to 15mm as the originals just looked too tiny. For a larger head (the moving part of the Z of mine probably weighs under 50 lbs altogether,) you would probably want to step up to 20mm.



Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

RF31 clone to CNC - component selection help needed

RF31 clone to CNC - component selection help needed