Bugmenot, the guys who were recommending the 23-25x are now saying 20x as the max voltage - you can use less.

But, to get to your main point, where does all this power go....? This is a question for which I would really also like an understandable answer. If I had money/time/space I would be buying all these motors and testing them against each other.

One group of guys have the logic that more power is always better. (Tim). That's fine, but then we must have a reliable way of getting rid of the excess heat. A 300VA supply is easy to cool without blowing it full of dusty air. The big power supplies need breathing air and get choked on dust.

I tend to agree that more power is better than being short of power if optimum performance is needed, obviously considering cost.

Doesn't more current mean more heat, thus the vextras should run cooler? I would really like to know if there is a rule of thumb where more current is better for high speed or vise versa or better for low speed torque, but I guess that is a question for the people at geckodrive.

Generally, current relates to torque and voltage relates to speed. For a given motor, the more current that it has available (up to the maximum rating for the drive) the more work it can do. And in the same way, the more voltage available to a motor (up to the maximum allowed by either the stepper driver or the maximum recommended by Gecko, i.e. 20X or 25X of the rated voltage), the faster the maximum speed will be.

Recent tests on my test bench have shown that a moderately sized motor (PK296B2A-SG3.6) can be spun faster than a larger motor, so, if gearing is available, the PK296 (300 oz*in) or PK299 (600 oz*in) seem ideal for the job. Even without gearing the PK299 size seems to be a very good match.

First post edited to prefer the modern square body motors.

Hi,
New member here trying to gain some knowledge and insight on building a CNC and converting 2 convential machines o CNC. My question is what size motor would you think I would need for a 9" South Bend Lathe and a small Enco knee mill? I'm not well vrsed in electronics so this is pretty much all new to me. Also is there a means of compensating for the backlash in the lead screws without going to ball screws?
Thanks to all you really got an interesting site here and I hope to learn a lot from it.

Hi Glenn, I'm sorry to tell you that we specifically want to cover only "big" CNC routers on this site.

However, having looked at your profile, I feel jealousy (you have a Multicam) and sympathy (you are a schoolteacher(I think)).....

Non-CNC routers are tools that need 2 hands to push around. Small non-CNC lathes and mills can be operated with one hand. Therefore you are needing smaller motors to replace the humans for small lathes/mills than for routers. (Big lathes and mills are a different story). Where we are using NEMA 34's for routers, you should be okay with NEMA 23.

www.cnczone.com would really be the right place for you to get all your answers. Good luck.

Hi Gerald,
Sorry to tell ya, you ain't getting rid of me that easy. LOL I have a second Multicam coming in the next school year (yes I am a school teacher and I appreciate your sympathy). In addition to converting the two machined above I intend to build a mechmate for home. I downloaded your plans and haven't had time to fully review them, but what I have seen and read really look great.
My biggest weakness in in the setup and understanding of the motors and the controls, but have been getting a better understanding from sites like yours.
Glenn

I have been turning over the stepper vs. servo motor option all week. I was wondering if anybody new of a N. American source for servo motors that will work with the gecko 320/340 drives. Most of the Motors i am finding are designed to use their respective manufacturer controllers (I'm finding some that have bus voltages of 325vdc-560vdc!). Any idea would be great. The conclusion is if i can afford a servo setup, that the way i will go, if not, then geared stepper like the $260 ones from oriental. looking to build the controls by june 30, then start in on the steel.

AHHHHHHHHHHH!!!! whew, i feel better now. All this stepper vs servo stuff is making me go bananas. After i posted the above message, i read the servo vs stepper thread. Ok, I need to know a little more before committing to a motor.

How much hand finishing would be required on a circle cut using a mechmate with properly sized and configured stepper motors?

I am believing that a geared stepper motor can hold the stationary axis stationary. Is this correct?

Ok, originally i was typing the desired accuracies of the machine, then i divided out the fraction and realised that even the most basic control system will be more than accurate enough.

So I guess as long as i'm not gonna hafta spend an hour filing or sanding cut parts, it's steppers and little green lizards for me!

Hi Frank

I was hoping that somebody else would chime in here since you all must be very tired of hearing my biased opinions.......http://www.mechmate.com/Forum/clipart/happy.gif

To answer the easy question first; We have un-geared steppers on two tables and we don't have problems holding the stationary axis stationary. My impression is that the people who have reported problems in this area are using Oriental Motors Alpha controller's with feedback from the motors, and that these motors "hunt" to hold a fixed position (The I in PID?).

The tricky question, "how much sanding on circles". It won't help you if I honestly replied that we never sand any circles, because we simply don't do any post-cutting finishing service. Our clients do that themselves and we don't compete on their turf. The few times that I have made things for myself, and have wanted to remove the chatter marks that occur on parts of circles only, I reckon that it took about 10 strokes with 80grit paper?? Can anyone else give a better answer to this valid question?

Realising that we have direct drive motors, the general client feedback is that they are happy with MDF and softwood cut for them, but that they want better for acrylic plastic (perspex). If we had gearboxes, we could probably also satisfy the plastics guys.

Hi,

Here is my 2 cents.
I don't really know how much "mill mark" there will be when cutting circles using ungeared motors since I haven't used them yet so in that respect I can't comment.

How about someone posting some pics with wood and plastic?

I do know this, if was to cut circles say with my bandsaw, I would have a considerable amount of sanding with a power sander then alot of hand sanding. If all I have to do is sand 10 strokes with 80 grit sand paper, I will be most pleased. I have purchased the ungeared motors from Oriental (as recomended) and will using them. I will play around with them when I get them moving. I would think that no hand held or hand propelled power tool would be able to hold any kind of smooth transition through a radius. I don't know if this is a better answer but I will take a router cut over my bandsaw any day much less my jig saw.

Guys, thanks for the info. I agree with the notion that 10 strokes of sandpaper is nothing, I always dress cuts anyway. And Gerald, your opinions are what got me thinking i could build one of these things. And the guys in this forum reaffirm that. So anyhoo, I guess now I'm on the hunt for some motors. Any thought on the gecko drive? 202 v 203. Can't figure out what the differences are from the blurbs on there site. I'll keep reading and can't wait to start posting pics.

Hi all, Gerald.,

Can?t seem to find posts on the MechMate speed ( ipm) subject.
I?d like to know more on the possibilities of its cutting & transient speed capabilities of a tipical MechMate set up. Don?t get me wrong here, I?m not hopping to get anything like this ?Tim Allen type? worthless supersonic speed !!
No?no, just curious on what to expect and hopping to find out more & the how on the ipm achievable?
Thanks, Robert http://www.mechmate.com/Forum/clipart/happy.gif

Robert,
A search of (ips) will find the topics.
Never have been sure which to quote - IPS or IPM

I use 7.2 reduction and a 35 tooth pinion.
It will surface the spoilboard at 400 ipm
At 575 ipm it loses steps.
The Mechmate is able to cut much faster than I am comfortable with.

DocTanner

Thanks doc,
It?s what I was hopping to get!! http://www.mechmate.com/Forum/clipart/happy.gif
Later, Robert

This motor
 

Is this motor enough to drive the Mechmate... it's rated at 3.33Nm so it should be strong enough, or am I missing something...
http://motioncontrolproducts.co.uk/p...products_id/83

KM

Kim, the smallest one is 3.33Nm which is a bit light. You should be looking at FL86STH80-4208 at 4.51Nm minimum. They are calling it Nema 23, but the sizes look like the Nema 34?

Frank, if you are still reading this, you may want to look here for pics of various cut qualities with different machines and speeds. We normally get much better than the best of those with the MechMate.

Thx Gerald....

I will go with the 4.51Nm version then, it's only £42 a piece, which is very cheap... Maybe I'll even go with the 6.5Nm version to get bigger torque... And possibly more control of the gantry...

I don't know what the shipping costs are like, but it might be worthwhile to buy only one of each now and test them. Put the "worst" motor on the z-axis where it doesn't work so hard, and get the better motors for the other axes. :)

Doc
Have you any further comment on your setup with the 7.2 geared motors? Is the 1A sufficient or do you see the possibility of needing a 2A motor? What sort of jog speeds, and move speeds while cutting are you achieving?
I am getting close to making a decision on motors and would appreciate your input.

In browsing the oriental motor website, I noticed that they now have 9, 10, 18 and 36 to 1 gear ratios available in this motor line. Gerald, or anyone for that mater, what do you think about going higher than 7.2 : 1? The higher torque might give a better cut quality.

Also, the 2 amp motor seems to have a lower voltage coil and a lower inductance. Seems to me that if your driver can handle the 2 amps, then maybe this would be a better choice than the 1 amp? Lower inductance should mean better acceleration and torque?

Any comments anyone?

High ratios could be useful if:
- There is a true higher torque. Even the 7.2 gearbox doesn't allow you to use 7.2 times the torque of the ungeared motor. Mechanical limitations on bearing loads, shaft strengths, etc.
- There isn't any additional backlash.
- Your computer/controller/drive can run at the higher frequency required.
If you want to do some experimenting, let us know what you find :)

The 1 Amp motor with 3.6:1 gearbox developed sufficient torque to break 1/2" cutters. Can't an obvious reason why a 2 amp motor would be "better".

Gerald,
Do you think the 3.6 geared motor provides better resolution and better cut quality than the direct motor? I was thinking of the 10 : 1 motor as it would be a nice divisor and provide more resolution for better cut quality?

The main problem with high gear ratios is the number of steps per second that it takes to move along an axis. For instance, using the popular 30 tooth pinion that has a pitch diameter of 1.5 inches, moves the axis 1.5 X pi or 4.71 inches. Because a Gecko G20x stepper driver requires 2,000 pulses to rotate the shaft one time, each stepper pulse on a 1:1 (non-geared) motor would move the axis 4.71/2000 or 0.002355 inches, which is also 424.628 steps per inch. If we were to use a 3.6:1 geared stepper motor, it would take 424.628 X 3.6 = 1528.6608 pulses to move an inch. Mach 3 has a top speed through the parallel port of 45,000 pulses per second (on my computer). That means that Mach 3 could move/jog an axis at 29.43 inches per second with a motor geared 3.6:1 (if the ramping was perfect and no gremlins were active on that particular day; however, getting 1/2 that speed would still be a notable feat).

Going to 10:1 gear reduction would require 4246.28 steps per inch. Top jog speed would be reduced to about 10 inches per second (with 5-ips being more realistic).

More importantly, as Gerald pointed out, the gearboxes used on the PK296A1A-SG series motors are NOT famous for being particularly strong or accurate. The are limited in the amount of torque that they can handle and they have some backlash. For most normal CNC work, I would pick the 3.6:1 gearbox or the 7.2:1 gearbox. Personally, I have four of the 3.6:1 gearboxes on my test bench. If and when I ever get around to building a MechMate, I'll most likely use those motors.

Going by all reports, and following common logic, the 3.6 geared is better than direct, though I have no personal experience of it. The 7.2 seems to be the even better option (again, going by reports). 10:1 is not spoken of, and it is not even slightly important to use "nice" numbers.

Mike, Art recently found a way to get much higher speeds out of his Mach engine, which is apparently standard now. (Something like 100khz without changing the PC?)

Gerald,

Thanks for the info about the higher Mach 3 speeds. I haven't downloaded anything from Art since the stable G100 plugin became available. (I receive dozens of Mach forum messages every night, but usually I just quickly scan the headers to see if there's anything I need - somehow I totally missed the higher speed pulse rate.) At any rate, I've just downloaded the latest software and will soon be testing it at my test bench.

Mach 3, at 100kHz, is wonderful! For the first time, I can make the motors on the PMDX/Gecko G202 test bench act as though they were the motors on the G100/G203 test bench.

At 100kHz, gear ratios higher than 7.2:1 could be used, but, in my opinion, either the 3.6:1 or the 7.2:1 would still be my preference.

Edited: We need to remember that, even though Mach 3 at 100kHz can spin the motors much faster, the torque requirements on a motor will probably dictate that the motor be used at moderate speeds, the speed range where a stepper motor has the most torque. What I am thinking about, however, is that higher ratio geared motors could be used if good quality gear boxes were used (expensive, more than $800 per gear box) or that brushed servos could be used (also expensive because the ones I've tested are useless without a high ratio gear box). The advantage to using servo motors is that the torque curve seems to be constant throughout the motor's speed range, but the available torque is only a fraction of that available from a smaller and lighter stepper motor. For instance, I have a 34-size brushed servo (ID33004) that is long and heavy and has only 170 oz*in of torque at 70V. However, at 70V, that motor can run all day long at 2,200 RPM. So, with a 7.2:1 or 10:1 gear box to multiply the torque and to divide the speed, that particular motor might be useful on a CNC router. The problem of course is that even though the motor and Gecko G320 servo driver costs almost the same as a Gecko G20x stepper driver and a 600 oz*in stepper motor, the servo requires a gearbox - meaning that a MechMate with servos would probably cost at least $4,000 more than a MechMate with steppers.

Hi All,

How about http://www.linengineering.com/site/products/8718.html , i have a quote from them for model 8718S-05P around 250 USD each. Do you all think vexta is better, i think i should find a dealer for vexta here in bangalore

rgd
IRfan

Suggest you first find the Vexta price before you decide which company is the better supplier. On paper, the motors are very similar.

I got the quotes from Vexta distributers its almost 300USD for the ungeared and around 365USD for the geared (3.2) without taxes.

ho ho.............

Have you considered importing from Motionking, China? They might even tell you they have a stockist/agent in India.

i guesst you just answer my first Q?

is funy geral i just read this hall and you send me back here lol

well a bit about my motors i have a set of super vexta 5-phase motors with there drivers here is a picture of them in my small machine

this are the drives
http://i15.photobucket.com/albums/a3...cdrives002.jpg
and this are the motors
http://i15.photobucket.com/albums/a3...cdrives004.jpg

can any one tell me if any of this is good to install in my machine

Here's a link to an Oriental Motor document that shows the why there are 2-phase motors and 5-phase motors:

http://www.orientalmotor.com/MotionC...hase-intro.htm

Read it carefully, and it will answer most of your questions.

My own opinion on the matter is that I would NOT use 5-phase motors. Using 5-phase motors means that I would NOT be able to use Gecko G20x stepper drivers. To me, the 5-phase motors are like the Oriental Motor Alpha drivers/steppers that I have on my Shopbot PRT-Alpha machine. The motors and the drivers are a package - a very expensive package. Just one motor/driver costs about $1,100 retail. Gecko stepper drives cost less than $150 each and the motors cost about $200 each. So for about $1,400 plus another $100 for a power supply, I can buy four motors and four drivers and a power supply that has much better resolution that the Oriental Motor Alpha driver/stepper.

Right now, I have two of the 23 frame size 5-phase stepper motors and drivers and one of the 34-frame size 5-phase stepper motors and driver. None of them have ever been used. Very possibly, none of them will ever be used. Why? Because, if I build them into a machine, I will have to support them and replace them in the event that one fails. That costs too much to make it practical. So, unless I find a way to use them in one of my own projects, I probably won't use them at all. (Please don't ask me to sell them at 10 cents on the dollar. Deep down, I am a business man and as a business man, I don't give away expensive parts and pieces. Sorry, but there is a line between giving advice freely and giving away parts and pieces that cost a lot of money to buy. Even though those motors and drivers may have very little value to anyone else, they still cost more than $3,000 to buy. As far as that goes, I also have about $15,000 worth of Ziatech STD-32 controllers on hand. I bought those shortly before Ziatech was bought by Intel. Those boards are all factory new - but will never see life in a new machine for the same reason - it's simply much cheaper to buy a Z-World processor and design a process control computer around the Z-World processor than it is to use the Ziatech parts that are sitting on my shelf. Just so I don't sound too mercenary, how would you feel if I sold you a process control computer that had all new parts but when the machine broke I told you that the manufacturer had gone out of business; therefore, I couldn't service your brand-new machine? Sometimes we get a little bitter when suppliers that we trust suddenly close their doors without warning us. That happened to me with Ampro computers and their Little Board Z80, with Ziatech with their STD-32 line and with Oriental Motors with their 5-phase Vexta line. In the case of Oriental Motors, they still make other fine 5-phase motors and drivers, but I've decided to use their 2-phase motors with Gecko drivers to get the best value for my money.)

Manny, have you tested those motors and drives? Do they work smoothly for you?

What is the diameter and length of the output shafts? (Notice that all three motors are different). We are looking for a 1/2" shaft more than 1.25" long.

There is a chance you might be able to use a motor for the z-axis . . . .

(PS. I spent nearly an hour looking for specs on those Vexta motors in the photo. At $150/hr (my day job rate), you owe me about ?? beers ;))

geral D my motors are 1/2" shaft and 1.25" long and i am working with them in my machine now they do work really good and smoth

btw

i have a 24 pack:D:cool:

this is my machine now the pictures are old i do have 3 of the motors and the drivers are the same.
http://i15.photobucket.com/albums/a3...ics/cnc006.jpg

There is a *possibility* that these motors could work for the y and z-axis. I am afraid that you will have to experiment.

how about if i get the new motors and use the drivers i have now if you see the in the pictures those are the vexta drives the model number is UDX5128NA

i was reading on the page about the 5 and 2 phase i probably will be able to get away with it

5-phase steppers are basically obsolete, a museum might be interested in that driver and motor. :( (I seriously spent a long time looking at your drivers and there was just no info, which means they probably went off the market before the internet existed)

i guest i least words lol don't use them i will have to go with the ones you recomend well ebay will have some new items now i am looking to start this machine really soon