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  1. #1

    Red face LMS 3990 conversion to CNC

    Hi All, have found and read a tonne of great info from this forum since I've recently joined, looking for info on others who have converted this LMS 3990 to cnc, unfortunately most of the links are now dead or do not exist anymore? Companies have closed, or the owners have passed away
    Bought a LMS 3990 several years back and love it. Does what I need it too with the exception of the automation.
    Have scowered around for nearly 1 year looking for an upgrade kit, most had issues with ball-screw length's, custom drilling/machining to get the parts to fit, Companies stating their X2 design will fit fine? leading to their disappearance.
    Working with a company now who does show interest in making this work for me, in return will be available for all in the end. Some design changes are being printed through me for fit and design, when all is 100%...final parts will be sent to me for the actual conversion.

    I hope there is some interest here for this? Will catalogue the conversion step by step for others, list planned electronics, and ask for advice during this on what others think will work best????

    Fusion will be the cad/cam/cnc foundation, looking to use 425oz stepper's with DM525T drivers, Mach3 software, and undecided on the control board(s) at this time, would love some input on something that just flows together and plain works with fusion
    Do want some sort of control at the machine for setup/zeroing/manual adjustments if required??????

    Hope to see some input from your thoughts
    Cheers
    Randy

  2. #2
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    Re: LMS 3990 conversion to CNC

    From a bit of experience. I personally think that converting a sieg X2 design machine is like flogging a dead horse. The Z design is a let down, X axis is no better, and the gib setup isn't good. It can be a money pit trying to get it right without getting the end results. That's mostly why the kits are all but done with.

    Most will agree (or have moved onto) the G0704/PM25 size platform, is the way to go.
    It has better travels, twice the weight, stronger spindle, for not a huge amount more money.
    You can also fit double nut screws in them for more accuracy.

    Nema23 motors work best with at least 48vdc, and if they're inductance is 3mh or more. Then 60vdc overcomes it and gives brilliant performace.

    If you plan on a lot of use and saleable parts then my advice is......
    Save your money for a PM25 or bigger. Machine parts for the PM (X,Y) manually on the Sieg.
    Use new PM x,y to then machine the Z parts for it. Then go back and refine the x,y parts on the PM you machined on the Sieg.
    (because the Sieg parts are rarely level).

    That's what I did (my sieg was converted though and I basically got fed up with its design issues). I have still yet to refine my X axis on my PM25 clone. The table has lift on traverse, ball nut housings off the Sieg not were level enough.

    Going from the X2 to the PM was an eye-opener!!.

  3. #3

    Re: LMS 3990 conversion to CNC

    theres still lots of room for someone who wants to put out a decent kit for x2 mills .
    Any converted bench top mill/drill is a turd in the big scheme of things but they work and can get the job done if a guy works within their limits and knows how to make them work . The x2 beats the crap out of using a sherline or the other small brands . The key thing is they are mill/drills and they were never designed for heavy mill work
    I had 1 for a hobby machine which was a drill press made butcher job conversion but it worked and it was a cheap conversion , within no time it turned into 4 plus a g0704 . I've since upgraded and they all sit in the corner of my garage , except I'll be setting at least 2 of them back up for prototyping , and the original one will be going into a trophy like show case in my shop . Them little mills can produce some very fine detailed work but they have to be maintained and adjusted every few hundred hours of machining , it's a small price to pay for what a guy can get out of them

  4. #4
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    Quote Originally Posted by metalmayhem View Post
    theres still lots of room for someone who wants to put out a decent kit for x2 mills .
    Any converted bench top mill/drill is a turd in the big scheme of things but they work and can get the job done if a guy works within their limits and knows how to make them work . The x2 beats the crap out of using a sherline or the other small brands . The key thing is they are mill/drills and they were never designed for heavy mill work
    I had 1 for a hobby machine which was a drill press made butcher job conversion but it worked and it was a cheap conversion , within no time it turned into 4 plus a g0704 . I've since upgraded and they all sit in the corner of my garage , except I'll be setting at least 2 of them back up for prototyping , and the original one will be going into a trophy like show case in my shop . Them little mills can produce some very fine detailed work but they have to be maintained and adjusted every few hundred hours of machining , it's a small price to pay for what a guy can get out of them
    True on the sherline lol.
    I found that shallowish cuts with 8mm was X2 bearable but it wasn't very quick. Did a fair bit of slotting though.
    The drawback I found was that if you used thrust bearings on Chinese C7 screws you could get a wobbly screw due to how it sat.
    The table would pick up on it, leave marks and wear the gib prematurely.
    My STRONG advice is to make your own X axis end bearing plates and Y axis front bearing mount to take 28/12/8 (7001) Angular contact bearings in there. (That's if you use 1605 ballscrews).
    They are mint to use and make a massive difference. (fit them back to back, I think).

    Design could be with a bearing in either side of the mount pressing onto a 3 to 4mm thick central ridge meaning 19-20mn bearing set, then +0.5mm either side for clearance making part 21mm in total.
    Make sure ballscrew shaft machined end to seat the bearing load on is no more than 19mm long to the threads though.
    If you use 1204 ballscrews you can use 10/26/8 (7000) AC but the screws aren't as strong as 1605.

    I use the 12/32/10 (7201) with 1605DFU on the PM clone.

    I think you should roughly get my meaning with this.

  5. #5

    Re: LMS 3990 conversion to CNC

    an improperly machined ballscrew will bounce the table , and most chinese off the shelf are poorly machined . I didn't add end supports on the 3 I converted , and I see it as being fairly unnecessary for such short screws . Even my pcnc440's don't have end supports
    The only one I had a bounce on was the 4th that I added a fusion kit to , and I really wasn't impressed . They used good ballscrews it's just too bad they couldn't machine them properly . It more or less left ballscrew marks on the facing op which a few rubs on 400 grit removed , it was very slight but annoying , otherwise it machined well . It wasn't long after I bought that one that I decided to upgrade , so I didn't have a chance to get that issue resolved .

    I had the belt drive kits on all of mine which put the spindles around 4500rpm , and with a 3/8 end mill I ran aluminum at .035" depth at 35ipm while ramping profiles , it was reasonable and the finishes were decent . There's no hogging with them , thats for sure , but they can get the job done

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