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so, as some of you know, i have a novakon nm200 (as well as a nm145).
i am not the first owner but if worked with it since it was nearly new. its a long and stupid story, but what it ends with is the nm200 is now mine.
the original owner used the machine often, but was not very skilled with it. at some point this year he seems to have damaged it, and it now has 0.002" backlash in the y ball screw, and 0.013" in the x ball screw. ive measured and checked thoroughly and the play is definitely in the ball nut. my assumption is that one of his many crashes with the machine damaged the ball nut leaving it with play. when the machine was newer, i had measured it, and it had near zero backlash. the Z still has no measureable play.
so, i decided this was an oportunity to upgrade and overhaul the beast.
first on the list is new X and Y ball screws. i decided to skip any attempt to repack and repair the old ones, as quality new screws from taiwan are not very expensive. so with the new screws will come the first 2 enhancements:
1 - ill be using 2510 screws this time. double the pitch of the stock ones. this will put the steppers into a better rpm/torque range, and should easily improve rapid speeds to 200-250IPM with solid reliability.
2 - i will be altering the X travel. right now i get up to 28" travel, overrunning the table on the non drive side about 7.5", and on the drive side about an inc and a half. this seems to let the table sag a little on the extreme end which i dont like. so ill be recentring the screw and offsetting the motor mount so that the table over travels the saddle 5" on each side. this will give me a comfortable 29" travel, and be more stable than it is now.
3 - im rigging the limit switches to estop the machine 1/8" from the hard stops. steppers seem so innocuous when they "bounce" off an obstical, but i have the strong feeling this causes real damage, especially with those huge nema42 motors. ill have a push button override to allow you to job back into the safe area.
george at xzero in toronto will be providing me with the screws, i just need to get the ends machined with good precision. ill be using standard grade 7203B angular contact bearings in custom steel blocks for supports. i think higher precision grades are overkill for this application. total cost should be under $500. ill post more as things progress.
since there is not document on machine assembly/dis-assembly please take lot of pictures. will help me to disassemble the machine and take it to the basement. i will get the movers, but i do need to tell them which screws/pins to take out.
PS: not successful yet but still have few months to convince Khai to re-crate the machine before shipping. in that case movers just have to safely slip the boxes through 29 inch door down the stairs.
so, while i wait for the ball screws, i am looking ahead to see what i can do for a spindle motor.
the stock spindle motor is perfectly fine functionally. its a big induction motor with 2hp at 3500rpm.
there are 2 drawbacks for me though.
1 - its too slow for the primarily wood, plastic and aluminium work i do.
2 - the inverter is annoying, and i never seem to get mach to display the correct speed - or know if the spindle is actually going the correct speed. novakon came over and set it once, but at some point it lost the settings. not sure how.
3 - the motor is too large physically. it leaves no room for a power drawbar.
so, i went looking for motor options, and no induction motor of the same power is any smaller, and a nice inverter is $283 and would be able to bump the speed to 4-5k, but do little else for me.
so i started looking at servos. keling has a nice 1kw delta model for $1000 including drive, but its a little under powered, and has no really usable peak torque.
i scoured ebay and found a few parker servos with 1.2kw at 5000rpm, but no matched drives, and a still hefty price tag.
so then i remembered i had this in a box:
these are shiny new siemens 1ft5046af7 servo motors. ive actually only got one left, but basically, they are 92mm frame servos with 3.3NM continuous torque at 4000rpm, and 6NM torque at 3200rpm on a 25% 10 minute duty cycle. with a good fan and heatsink cooling the motor i could probably increase the duty cycle to 30 percent.
what that means, its with a 2:1 belt i will give 1.85HP continuous at 8000rpm and 2.7HP 2.5 minute duty at 6400rpm and still up to 3NM torqe at lower speeds. thats quite good enough for the nm2000, in fact, maybe a perfect match.
its 92mm square, so it leaves enough room for a 4" SMC air cylinder ive found (more on that later).
the added bonus of using a servo is i can do rigid tapping and home fortool changing. i have some renco 1024 line encoders that will mount on the servo nicely (it came stock with a resolver).
so that little guy cost me $150 10 years ago
now, heres where i need help. i need a drive for it. the reason we can get these awesome siemns motors for so cheap is they run at 600V. thats out of the range of most drives. i did find one from AMC, but its $2200 new, and thats not cool. baldor makes one, and ive found a handful of used ones on ebay for under a grand, but in the spitit of this overhail, id like to find something cheaper
anyone have any ideas?
novakon is supposed to have a servo motor option for replacing the 145 spindle motor setup soon. i was told $1500 for the motor and drive. i believe it was siemens??? i can not remember what the hp/tq was, but i believe 6k rpm was the goal. hopefully they get that right this time, the dc motor fiasco was quite brutal for them.
yeah, something for the 145 is easier. as i mentioned theres a delta 1kw motor/drive set for $1000. a 2:1 pully will get that to 6krpm nicely.
a siemens servo kit for $1500 seems unlikely. retail on the motor alone i have here is $3000+. but then, this is meant as a drive axis and the heidenhain resolver is probably half the price.
im wonderig if theres anything like a VFD that works with brushless motors. something more simple - and cheap compared to a full blown servo drive.
so there is a yaskawa vfd and a parker vfd that run brushless ac motors. the yaskawa seems to be about $500, the parker about $900. they have similar options, but the parker has full blown servo operation add on interfaces. this both take in 480v ac 3 phase, which will give me my 600vdc bus.
im still looking for alternatives.
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