higher torque 5 start, vs lower torque 2 start

[carvemylog]

Hi, this is my 1st post, but I've been reading alot on here for the past few weeks. I'm planning on making a 2'x3' router that will mainly be used to make guitar bodies and necks. This would assume I'm mostly cutting hardwood. I would like to get the speed reasonably high within cost limits and the limits of a G540. I have two questions:

1. Assuming I have a G540 with a 48V PS, would it cut faster/more accurate with 425oz steppers and an ACME 5 start, or with a smaller stepper (270oz) with a 2 start screw? Or to keep the torque up, would two smaller steppers set up as master and slave on the X (longer axis) be better?

2. Would a few of you mind sharing what stepper size/screw size and speeds you are acheiving with them?

Thanks

Mike

[ger21]

Faster and more accurate don't go hand in hand. Usually, to go faster, you do so at the expense of resolution. Fortunately, even 5 start should give you plenty of resolution, along with plenty of speed.

It's very hard to answer your question without actually trying both combinations, but the most popular screw choice these days is definately the 5 start. I'd go for the dual/slaved approach, use the 5 start on each, and somewhere around 300 oz-in motors. Maybe these when they become available at keling.

http://www.kelinginc.net/KL23H2100-35-4B.pdf

[johnmac]

While the smaller motors can run faster, I wouldn't count on the extra speed to make up for the 2 start screw. I would use the larger motors and 5 start screws. You can gain resolution with fractional stepping.

Unlike regular motors, steppers produce their best power when running slow, so don't "gear it down" as with fine pitch screws, to get extra power.

John

[FandZ]

What is special about those steppers? If it is what I think it is, I'm going to have to sell my steppers on ebay.

Originally Posted by ger21 Faster and more accurate don't go hand in hand. Usually, to go faster, you do so at the expense of resolution. Fortunately, even 5 start should give you plenty of resolution, along with plenty of speed. It's very hard to answer your question without actually trying both combinations, but the most popular screw choice these days is definately the 5 start. I'd go for the dual/slaved approach, use the 5 start on each, and somewhere around 300 oz-in motors. Maybe these when they become available at keling. http://www.kelinginc.net/KL23H2100-35-4B.pdf

[ahren]

FandZ,
These motors are optimized to take maximum advantage of the Gecko G540 in terms of inductance and current rating. Keling already has some other motors that are very close to this maximum (they have 4.1 mH instead of the 2.8 advertised here), so this won't be a huge change.

Ahren
www.cncrouterparts.com

[FandZ]

Thanks Ahren, that's what I thought they were. That 48oz difference is going to drive me nuts untill I get them lol. I do a lot of over clocking on pc's. I'm always looking for the most I can get out of my components and go to great legths to get everything perfectly balanced. This will turn out to be the same case..haha

Originally Posted by ahren FandZ, These motors are optimized to take maximum advantage of the Gecko G540 in terms of inductance and current rating. Keling already has some other motors that are very close to this maximum (they have 4.1 mH instead of the 2.8 advertised here), so this won't be a huge change. Ahren www.cncrouterparts.com

[jsheerin]

I have the G540, a 48V PS, the Keling 425oz motors, and 1/2-10 5 start acme screws with dumpster cnc nuts on my 4'x4' cutting area router. I have dual x motors and screws driving a gantry that's ~100lbs. I get rapids around 270ipm. For the Y axis, I get somewhere over 400ipm (I forget exactly), and even higher on my z, but I have that set at 400 as well. I have the acceleration turned down on the x, but the y and z are pretty snappy. I'm still getting started on cutting - I was cutting test shapes today to square up the gantry - so I can't tell you how fast I can reliably cut at. For resolution / accuracy, I'm typically seeing errors of around 0.001"-0.003" in my cuts and can move a a few thousandths if required. I think a lot of the error I see is due to the lead errors of the screws though. It typically returns to the same position within less than 0.0005". Anyway, this should be plenty accurate for wood. Hope that helps.

After I bought my electronics and learned some more, I was looking at one of the lower torque Keling motors - maybe a 387oz-in?. If you look at the torque curves of the 425 vs that one, the 425 had higher holding torque obviously and higher torque up to a certain rpm, but above that the smaller motor had more torque. I had figured out where the crossover point was in speed for my setup, and I seem to remember it being higher or right around the fastest that I planned on cutting at, but that would be something you might want to look at.

[carvemylog]

Originally Posted by jsheerin I have the G540, a 48V PS, the Keling 425oz motors, and 1/2-10 5 start acme screws with dumpster cnc nuts on my 4'x4' cutting area router. I have dual x motors and screws driving a gantry that's ~100lbs. I get rapids around 270ipm. For the Y axis, I get somewhere over 400ipm (I forget exactly), and even higher on my z, but I have that set at 400 as well. I have the acceleration turned down on the x, but the y and z are pretty snappy. I'm still getting started on cutting - I was cutting test shapes today to square up the gantry - so I can't tell you how fast I can reliably cut at. For resolution / accuracy, I'm typically seeing errors of around 0.001"-0.003" in my cuts and can move a a few thousandths if required. I think a lot of the error I see is due to the lead errors of the screws though. It typically returns to the same position within less than 0.0005". Anyway, this should be plenty accurate for wood. Hope that helps. After I bought my electronics and learned some more, I was looking at one of the lower torque Keling motors - maybe a 387oz-in?. If you look at the torque curves of the 425 vs that one, the 425 had higher holding torque obviously and higher torque up to a certain rpm, but above that the smaller motor had more torque. I had figured out where the crossover point was in speed for my setup, and I seem to remember it being higher or right around the fastest that I planned on cutting at, but that would be something you might want to look at.

Thanks, that is what I was looking for. I'm likely going to end up with a set up similar to yours and now have an idea how fast it will be. In fact it is faster then I thought it would be. I suppose the other dumb question to ask is to get your dual X motors working did you use a breakout board to send the "X" signal to two of the G540 drives and just invert the output of the slave drive motor? And one more question, would it make sense to put a 2 start on the Z axis since speed there isn't as important and I might be cutting guitar inlays etc? Would more accuracy in the Z axis make sense here?

[jsheerin]

Glad that helped. You can slave the X and A axis in software. I did it in Mach3 with no problem. You can also home them separately to square the gantry, but I haven't gotten my limit switches going yet so haven't tried that one. The G540 basically contains a breakout board, so no need for another one. As far as a 2 start on the Z, maybe - I'm not familiar with that kind of work. If you did want more resolution on the Z, that could be a good way to go, but especially there you might want to look into the smaller motor as the force from the lower lead would be higher for a given motor torque. So less low rpm torque could give similar force, but higher torque at high rpm could allow you to still run at decent speeds while giving more resolution from the lower screw lead. However another factor to consider on the 2 start is that the efficiency is lower. This is one I would put in a spreadsheet to figure out the differences and see if they would get you what you want.