PMINMO A3977 or L297-8 Driver?

[cnc-newb]

after a year or so of health issues i am back at it again and this time have adjusted my goals to deal w/ my situation. will be making a small unit just to do it. if i go larger, then so be it, but i just want to build now and get more understanding of cam and see everything working together.

machine will be something small, probably w/ sizes of 6"x6"x4" or possibly 10"x10"x6" at most. will be cutting either some types of acrylic/plastics, pcbs (if resolution is suitable), some wood and that is about it.

was looking to do this w/ the PMINMO drivers/bob setup, either the A3977 based or the L297-8 based unit. only problem is i don't know which one to go with. they seem to be very close in specs, and i am a bit worried about my skills soldering the 3977 chip, so please chime in. i do have a 15 and 25W iron w/ very small tips on them - the 15W tip is very pointed, like a nail.

steppers are small -
nema17
1.8 degree
1.0A, up to 2.0A (the sticker says 1.0A but i called the company and they said i could go higher but to make sure the stepper doesn't go ove 50C - does this sound correct?)
bipolar - 4 wires
24V (in this area i was told i could use 12V and it would just mess w/ speed - is this correct? would a computer psu be ok just for testing to make sure all electronics work ok before buying a 24V+ psu?)
63oz in - again, just a small unit

will probably be using a 1/4-20 leadscrew so i don't think i will need 1/4 or 1/8th step but may, not sure. speed is not a concern.

if the 3977 setup is recommended, i will go that route and be careful, but please give me your insight/recommendation for this endeavor.

http://pminmo.com/ is the page w/ the information - do plan on buying his commercially made boards and parts kit for whichever setup you guys think would be better.

thanks,
newb

[irving2008]

personally I'd go the 297/298 route - they're easier to solder, less likely to damage, cheap to replace and will do for what you want. With 20tpi leadscrews you'll theoretically get 1/4000" resolution per step on a 1.8deg stepper, but the stability of your construction will probably not be that good. So you definitely wont want microstepping. 63oz steppers will probably suffice on a small a machine as that as long as you are not trying too deep a cut, have not too heavy a gantry and reasonable quality slides... milling PCB's should be fine. 12v wil certainly work to start, just dont expect too much performance.. but again good enough.

If you've not bought the steppers I'd consider going for unipolar ones and using an even cheaper driver circuit like the one on www.instructables.com, but there's not a lot in it...

[cnc-newb]

Originally Posted by irving2008 personally I'd go the 297/298 route - they're easier to solder, less likely to damage, cheap to replace and will do for what you want. With 20tpi leadscrews you'll theoretically get 1/4000" resolution per step on a 1.8deg stepper, but the stability of your construction will probably not be that good. So you definitely wont want microstepping. 63oz steppers will probably suffice on a small a machine as that as long as you are not trying too deep a cut, have not too heavy a gantry and reasonable quality slides... milling PCB's should be fine. 12v wil certainly work to start, just dont expect too much performance.. but again good enough. If you've not bought the steppers I'd consider going for unipolar ones and using an even cheaper driver circuit like the one on www.instructables.com, but there's not a lot in it...

thanks for the info. steppers are already on the desk. they were cheap, and seemed to be ok for what i wanted. i don't putting them on a 24VDC psu, but want 12V just for testing.

should i go more like 1/4-16, 12 or 10 instead of 20? or does it really matter for my needs not caring about speeds?

also, i have looked around on many sites including the one you listed but i can't currently make pcbs, so i figure it would be cheaper to buy a diy kit. looking at keeping total ~$200-$250+software, so looking for deals all around

will probably run mach3, but may start out w/ kcam since it is free, at least for 500 lines, and also contemplating the linux setup, so i need to make a decision for that. i may go some free version and if i really enjoy it, then buy something else, unless the free cam software does basically everything the paid for version do w/ the exception of the support, or support other than forums.

again, thanks and any other suggestions?

[student1616]

if its bi polar then L297-298 is the only option.bcz soldering A3977 need very good soldering skills .if u have unipolar motors then u can go for controllers like LInistepper,SLA..etc.they are easy to make and can do micro stepping
so are u planning for a router design? have u made any prototype drawing?

[pminmo]

You really don't want high tpi screws as steppers power curve leans to slow rpms. See: http://pminmo.com/PMinMOwiki/index.p...chanical_Power

[cnc-newb]

sounds good. i have done some smd in the past but it was 15yrs or so ago and my eyes aren't near as good, so the 297-8 is looking more and more appealing.

for a design, possibly a mix of the cartesian mcwire and tim(or tom) mcwire design and add to them - again, this is just for proof of concept as i have access to a lot of industrial cnc equipment, i just want to "play" at home and don't have the room for a real machine and since i don't have the room, i figured something real cheap would at least satisfy my learning.

but that could change, i first want to get the electronics going as i think they will be the hard part and if need be i could get larger steppers.

[cnc-newb]

pminmo, thanks for the info. i was looking at different screws/nuts and unforutately found that for this project, the best i can do is 1/4-16 2g threads, if at all possibly i would move up to 2c but i can't find any nuts that are cheap - seems they are all a bit expensive once you get past the regular V type thread.

if anybody has any other info regarding this it would be very helpful - delrin, bronze, plastics - don't care the material as the loads will obviously be minimal.

out of curiosity, how hard is it for a machinist to cut 2c threads in say some version of an Al block i could use? the rod isn't too expensive but the nut portion is. i do have that access but don't know how much of a pita it would be for them to make me basically 3 small pillow block type Al "nuts" - please forgive my lack of the correct terminology. is this easy for a accomplished machinist? or a time waster? also, if i am using some sort of steel rod, would Al be an ok choice for the nut or would it gall? what material would be ideal?

i figure this will give me the reslolution but it also can't eat up 90% of the budget since it is just a small "how does it work" setup and for me to mess w/ cam.

also, pminmo, do you also feel the 297-8 would be in my best interest as student1616 stated? if i were to put a heatsink on the 3977 before soldering would that help or would it still be fragile since i am connecting directly to a pin?

again all, thanks in advance,
newb

[irving2008]

Originally Posted by cnc-newb if anybody has any other info regarding this it would be very helpful - delrin, bronze, plastics - don't care the material as the loads will obviously be minimal. out of curiosity, how hard is it for a machinist to cut 2c threads in say some version of an Al block i could use?

Its easy to make a delrin nut. Take a length of the screw thread you plan to use, angle grind 3 or 4 slots/flutes in the side and taper the thread slightly - its easier if you have a lathe to taper it, but a short length (3" or so) can be chucked in a drillchuck and spun against a grinder. this makes a perfectly good tap for delrin...

[pminmo]

This 1/2-10 is pretty good for the price: http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=56714652 and enco has good price on standard nuts if you don't want to make some: http://www.use-enco.com/CGI/INSRIT?P...PARTPG=INLMK32 HDPE also makes a good easy nut. If you buy the standard enco nut they JB weld to a washer and hold well.

If your motors are 2A and under and your concerned about soldering skills then the L297-8. The L297-8 combination are audibly noisey when sitting still , and that bothers "purest" electronics people who don't run machines... When a spindle is running you don't hear anything but the spindle and cutting, and when the machine is stopped it is smart to disable the drivers anyway.

[cnc-newb]

appreciate the ideas and links, thanks so much

[nhatson.elec]

more current, you can use l297 with l6203