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  1. #1
    Nema17 motors driving 1204 ballscrews? ...that ok? ...or will I see the CNC police knock on my door?

    Ok, here's my dilemna.

    My first machine I built (a rite of passage I think)...been there done that...my engineering skills suck & therefore my machine sucked - I won't be building anymore.

    My Second (present) machine a modest sabel 2015 (http://www.cnc-sable.nl/images/sable%20text.jpg) ...fairly well constructed, certainly rigid enough for the stuff I cut (pcbs & the odd bit of acrylic)...the problem is insufficient accuracy. This machine uses bog standard M10 threaded rod & drive nuts of uknown parentage/pedigree (but I suspect are in the delrin accuracy scheme of things) ....& I'm now milling quite small SMD PCBs - I need more accuracy (& ideally a bit more speed...I do like a whizzy machine)

    So, I could just upgrade my present machine to a new one ...but I've a penchant for fixed gantry machines (I like how much quieter they are - I've neighbours & a wife to consider as I do this in a spare room) & they're not that common....in fact they seem quite rare - especially those fitted with ballscrews/nuts.

    I've found a Chinese supplier (http://redsail.en.alibaba.com/produc...a_RS_3020.html) ....bottom line is it's gonna cost me the guts of a grand after import duties etc & to be honest I don't even need the extra size (it a 3020...not that big...but still bigger than my 2015)...just the accuracy. Now to me, a grand seems a lot to pay for the small gain in accuracy I seek over my present machine!

    That said it seems well made & specced, for example, here's the innards of the control box ...

    )

    (at least it's not a woeful Yoocnc stepper driver single pcb board in there!)

    So then I wondered could I just simply upgrade the leadscrews on my existing machine to ballscrews/ballnuts (total cost would be approx 100 - I like!) ...having done the measurements & looked at ballnut dimensions, I think I might just be able to get away fitting SFU1204-3 ballnuts onto my present machine ....but my Sabel 2015 machine has small nema17 motors with 5mm shafts...would this be a crazy match for 1204 rods? (alas, IMHO it's not going to be practical to upgrade the motors to nema23...on account the present nema17 casing edges are flush with the rear of the CNC gantry uprights...if I replaced with nema23....two of the NEMA23 mounting holes would see fresh air at the back (ie they'd had nothing to screw into)...at a push I guess some form of plate could be made to allow me to use nema23, but then the project gets bigger (& like I say, I suck with anything involving metal/accuracy!)

    therefore I think I might be stuck with nema 17s...so like I say, would nem17s be be too much of a mismatch for 1204-3 ballscrews/nuts, the spec of the motors on my machine is here...

    1. Step angle: 1.8 degree
    2. Number of Phase: 2
    3. Hold torque: 4.4 kg.cm
    4. Rated current/Phase: 1.68 amps.
    5. Phase resistance: 1.65 ohms
    6. Voltage/Phase: 2.77 VDC


    Thanks in advance.
    Last edited by HankMcSpank; 18-06-2013 at 09:25 PM.

  2. #2
    If the machine moves now with standard screws then it will be easier to move with any ballscrew.
    Will there be enough room for the ball nut!
    Have you thought of smaller ballscrews 10 mm!

    Peter

  3. #3
    Hank 1204 will be fine but you will need to mod the Z plate to take the Ballnut by the looks of it?
    If the nagging gets really bad......Get a bigger shed:naughty:

  4. #4
    Thanks guys

    Quote Originally Posted by Swarfing View Post
    Hank 1204 will be fine but you will need to mod the Z plate to take the Ballnut by the looks of it?
    I haven't taken the Z backplate off to have a look, but I think the X axis ought to take a 1204 ballnut (which according to the spec sheet - http://images.tiu.ru/22699355_w640_h640_sfu1605.png ...top entry, not the highlighted entry in that table!), should fit...



    Can anyone tell me the difference between a 1204-3 & a 1204-4? (& no smart replies saying 1 please!)

    I think I'm gonna stay with this machine a little while longer, cos yesterday I found & ordered a dedicated spindle which looks like it suits my needs (& until yesterday I didn't even know existed)....




    a video of it in action (spindle porn!)...



    the spiindle, motor & mounting plates (everything in the picture) only totals 66 plus 15 delivery - which to me seems very keenly price (nice & quiet too...and 10,000RPM ought to be enough - my present spindle only goes up to 5,000rpm)...so I pulled the trigger & should have it in about 10 days.
    Last edited by HankMcSpank; 20-06-2013 at 09:25 AM.

  5. #5
    Great news sounds like it is all working out in the end. Will you stand the stepper off so that you can get a support bearing in there?
    If the nagging gets really bad......Get a bigger shed:naughty:

  6. #6
    I think the Z axis is gonna be a challenge (it doesn't appear to be the same as the X axis & not sure I can fit an sfu1204 ballnut in there at all :-( )
    Last edited by HankMcSpank; 21-06-2013 at 08:07 PM.

  7. #7
    Is there space between the linear bearings? could always make a new block up so as not to ruin the existing.
    If the nagging gets really bad......Get a bigger shed:naughty:

  8. #8
    That spindle assembly looks really good and excellent value. I can't comment about the noise as I can't hear it!!!(only the cleaner). G.

  9. #9
    Quote Originally Posted by GEOFFREY View Post
    That spindle assembly looks really good and excellent value. I can't comment about the noise as I can't hear it!!!(only the cleaner). G.
    Ironically, having just bought asbo's 300W spindle (which is a surprisingly fine spindle type for the price) ....the one I've now just gone and bought afterwards (above) looks to have exactly the same driving motor on it - they are just gearing up the motor's RPM with the pulley (I note they quote the motor at 24V vs. "upto 48V" that the 300W spindle motor is normally spec'ed for - I guess the spindle that the motor is driving only has modest bearings & wouldn't cope well with RPM above 10,000RPM - actually, perversely, I'm hoping the spindle *doesn't* use ceramic bearings & therefore the spindle shaft might be groundable - is that a word?)

    Re the noise...as someone who mainly mills PCBs, I'm a sucker for a quiet spindle, and yes it's very quiet, which is why I pulled the trigger so quickly (the seller had sold 4 & only had one left)...only last week, I was comtemplating water cooled spindles, but I'm pleased I didn't now...I really don't need the extra grunt (& complexity/weight) that it yields.

    Quote Originally Posted by Swarfing View Post
    Is there space between the linear bearings? could always make a new block up so as not to ruin the existing.
    It's all too easy to reason that most members on here are of a solid engineering background ilk...I'm not - really small children laugh loudly at my output (I often hear them muttering things like "FFS, that bloke should have used angular contact bearings on his Z axis"...I have no idea what they're going on about).

    I'm a reluctaant CNC'er ...I potter along blindly, then hit a problem ...& spend way too long trying to find an inadequate solution! (whereas, I'd much rather be playing my guitar & gulping on a cool one)
    Last edited by HankMcSpank; 22-06-2013 at 01:00 AM.

  10. #10
    LOL! Hank no inference from me on that score, firm believer in you can only do what you can only do :-)
    If the nagging gets really bad......Get a bigger shed:naughty:

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