Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Curtis_F on July 07, 2009, 01:38:59 PM
-
Greetings all,
I'm new to the hobby-cnc world, and am reading everything I can get my hands on to try and get up-to-speed, or atleast not appear ignorant. ;D One thing I have decided on is to use Mach 3 as I've read hundreds of good reviews from people who have home-built and/or retro fitted CNC machines.
My current/first project is the design and construction of a CNC mini lathe (4" x 12") and I'm hoping for some reccomendations on Spindle Encoders that are known to be 100% compatible with Mach 3.
I've been looking through the archives here and found posts of people asking for help with some encoders, but I didn't see many posts that talked about encoders working on the first go.
One thing I did learn in reading all the posts is that I really need to have a USB (Smooth Stepper) interface to handle higher RPMs.
And while I'm at it I'm going throw out a really ignorant question: :-[ For a lathe where I'm going to be doing single point threading is a VFD or a Servo better for the spindle motor?
Thanks for reading, and any enlightenment will be greatly appreciated,
Curtis F.
-
Aaaaaaaaaand I forgot to mention that I'm looking for an encoder "kit" that'll fit on a 50mm OD shaft. :-[
I'm desiging the spindle around the C5 collet standards and will be pushing a max operating RPM of about 15k (wanted 30k, but scaled back the design due to bearing costs), which immediately kills most encoders with integreal bearings, thus the "kit" option.
Though I'm still interrested in any recomendations as there's a Mill project after the Lathe and it'll need encoders as well.
Thank you for your time again,
Curtis F.
-
You dont actually need encoders as Mach just uses a single input pulse per rev at this time and it works well.
As to what is a better motor for the spindle I would say Servo everytime over Induction/VFD. Obviously if you use a servo for the spindle then it will have an encoder so if it has the index pulse you can use that for input to Mach via the SS.
Hood
-
You should check out the thread "Success, mini machining center . . . " in this forum. I just finished building what amounts to a lathe head using a 5C spindle and it is servo driven. You might get some ideas there.
A servo motor is basically a precision purpose build DC motor (read expensive). There is no point to using one on a spindle unless you are going to use gears or timing belt drive. The typical flat or V-belt arrangement (which you will probably use at the RPM you are talking about) erases any advantage the servo has.
You will have to rig the encoder and also an index, I would think. Unless you can find an encoder with an index rated to 15k. Here again, really no purpose to the encoder if you don't use a servo, which there's no purpose in if you use a v-belt. Catch-22
15k RPM is a dangerous neighborhood to be playing in. When things go wrong at that speed, a lot of major damage gets done in an instant. You might consider a smaller collet size for that kind of speed.
There are occasionally precision lathe heads for 3C (I think) on ebay that sell for about $350, so you might consider that option.
-
Curtis,
Curious, what are you turning at 30,000 RPM??
RICH
-
Big benefit of an AC sero (not sure about DC) for a spindle is you have full continuous rated torque from Zero RPM right up to full continuous rated RPM, a VFD will drop off rapidly on torque when you get low on the speed. Another good thing about AC Servo is you use Step/Dir so you have very accurate speed control and if using Swap Axis you can also position the spindle, could be handy for an auto tolchanger.
Bad thing about AC Servo is the cost but deals can be had on eBay and the Chinese ones are forcing the price down.
Hood
-
Hood,
My bad. I hadn't even considered an AC servo. The OP is talking 4" x 12" lathe. You could probably fit that whole thing on your cross slide :D
Do they make tiny AC servos? If so . . I may feel the need to tinker . . . .
-
I could probably fit it in my toolpost ;D
Yes AC servos can be had in all sizes, saw one the lat day that was 200Watt and I am sure you get even smaller.
Hood
-
Simpson,
Yes, AC servos are available in a wide variety of sizes. Got one on my Emco Compact lathe spindle. Yet another big advantage of an AC servo is its small frame size for the same power rating as DC motors. Mine is 1/3 the size and weight of the original 0.44KW DC motor and is 1.3kW!
Hood,
DC motors are the contrary to VFD - they have max torque at zero speed and it drops liniary as you increase the speed. At max speed the torque is zero.
Daniel
-
DC motors are the contrary to VFD - they have max torque at zero speed and it drops liniary as you increase the speed. At max speed the torque is zero.
Daniel
True only for DC steper motors.
I have read that AC servos have superior holding power . . an important consideration for my 4th axis application.
A huge disadvantage of an AC servo is that my wife will kill me if I spend any more money on this CNC project . . . LOL!!
-
A huge disadvantage of an AC servo is that my wife will kill me if I spend any more money on this CNC project . . . LOL!!
Tell her once you have it perfected you will be able to make all sorts of fancy ornaments for the house and jewellery for her, that should allow you some tinkering money ;)
Hood
-
Simpson,
This is true for any DC brushed motor. You may want to review this link:
http://lancet.mit.edu/motors/motors3.html#tscurve
Actually, it is even true for AC servos, but the torque of an AC servo doesn't fall that rapidly with increasing the speed as in DC motor, and the motor can still deliver torque at its max speed. Thus, practically an AC servo may be considered as delivering a constant torque through its practical operation speed range.
Haven't heard about the superior holding power. I think the same power rated DC and AC servo would have the same holding capability.
Yes, AC servos are quite expensive. I'm looking for one as well to replace the DC motor on my mill's spindle and can't find anything reasonably priced for my pocket...
Daniel
-
It is really only useful to speak in terms of power. Torque is a static measure, and has no meaning by itself. For example torque being zero at max speed is not meaningful because that is no load speed and the motor is not doing any work. As soon as you place a load on the motor, it slows but begins to produce a measurable torque. The more load is placed on it, the more static torque it produces, hence the torque curve you referenced.
Some confusion results when torque is discussed as if it is power. Seems I have contributed to that in this instance. Power is what moves things and power is work done over time. In the case of motors, power is torque x RPM so the faster the motor rotates the more power it is generating until the point where the torque is dropping faster then the speed is increasing.
In the case of steppers, the torque falls off very quickly per speed increase and therefor they are actually making significantly less power the faster they go. Servos on the other hand, continue to make relatively contant power over their RPM range. From the actual power curves I have looked at for servo motors specifically (as opposed to a regular DC motor as for a treadmill, etc) the motors are not linear in response. That supposedly is the difference in a servo motor and hence the high cost comparatively speaking. The skewed rotor designs have something to do with that, but that level of tech is over my head.
I don't know how or why AC motors are different performance wise, but I have read in enough places (including manuf who make both types) where the AC motor's superior holding power are cited as as justification for the higher cost, that I believe their must be some credibility to that claim.
-
Thank you for all the replies!
Sounds like an AC Servo is the way to go.
There is some posistional data loss when using anything but a direct drive coupling system, but if Mach 3 will work with a Servo that'll be more than close enough for my work.
-----------------------------------------
Curtis,
Curious, what are you turning at 30,000 RPM??
Rich,
I, and a bunch of my friends, do model building that often requires very small pins and screws. Here's what I posed on the CNCZone.com forums when asked this same question:
The Machinery's Handbook 26th edition says; when cutting Brass with a Carbide cutter the optimal Surface speed is in the 440 to 1170 Feet Per Minute range.
The major diameter of a #0 thread is: .060"
The major diameter of a #2 thread is: .086"
The major diameter of a 1/2" thread is: .500"
Therefore:
Optimal RPM for turning the major diameter of a #0 screw is: 28,000 to 75,000 RPM
Optimal RPM for turning the major diameter of a #2 screw is: 20,000 to 52,000 RPM
Just for comparison;
Optimal RPM for turning the major diameter of a 1/2" screw is: 3,400 to 9,000 RPM
After researching bearings a little I found that the off-the-shelf ones of the size needed to fit around a 5C collet spindle (45mm I.D.) topped out at a little over 30,000 RPM if oil lubrication is used.
Here's a link to the thread at the CNCZone if you're really bored. :-) http://www.cnczone.com/forums/showthread.php?t=84133 (http://www.cnczone.com/forums/showthread.php?t=84133)
---------------------------------------------------
You should check out the thread "Success, mini machining center . . . " in this forum. I just finished building what amounts to a lathe head using a 5C spindle and it is servo driven. You might get some ideas there.
I'm going to read that right now!
Thank you again,
Curtis F.
-
Just an FYI . .
I am awaiting a new servo drive from a company called American Motion Technology. That same company makes a very reasoanbly priceS ($180) AC servo DRIVE as well as matched small AC servo motors. I have not found pricing on the motors, but they seem to be new and have not made it into the product lineup for the US.
Might be worth a look see.
http://www.americanmotiontech.com/Products/
-
Thats Leadshine stuff, Chinese, but the stepper drives certainly seem to work well so no reason to think the Servo ones be different :)
Hood
-
Might be worth a look see.
http://www.americanmotiontech.com/Products/
I checked the link out and it does not seem very clear as to if they are true AC servo's drives or DCBL, they do use UVW hall input commutation, which occasionally is used by AC sinusoidal at start up, rather than continuously as in DCBL.
They mention a trapezoidal test signal.
Nosmo
-
Hood,
The factory is ISO 900x in contrast to some of this stuff that seems to be made with a soldering iron at the Kitchen (http://en.wikipedia.org/wiki/Vance_Miller) table . . . not saying there is anything wrong with that, but ISO certs are not handed out like candy and I woud not be surprised if China now has more of them than any other country. You know where the money is coming from for the stimulus, yes?
NosmoKing,
I only wish I had a clue what you just said . . :-[
EDIT: Seems you know your way around the AC servo areana. Any chance you might cruise ebay and pick out a couple of (hopefully sub $100) motors that would be compatable with the Leadshine AC drive?
-
I looked at the manual this time and it appears they are AC servo drives, they use the hall effect commutation pulses to start up and then use the encoder for commutation, so you need to look for a AC or DCBL motor that has encoder and the 3 Hall effect outputs which now a days has them simulated on the encoder disk, so you also need a motor with encoder with these features.
When looking for a motor, beware that many AC motors have resolver, which cannot be used with these drives.
I look for Tamagawa, or Applied Motion, which are the same motors, also good, Aerotech, DMC, & Reliance, which are now owned by Allen-Bradley.
And it also depends on what torque range you need.
There are many Yaskawa motors, which are supposed to be excellent but I have never personally used these.
I would get the 60v versions as the drive is 80vdc max and they also state to not used any supply that is more than 5v of the rated motor voltage.
Nosmo
-
I really do appreciate your effort, but you're over my head. I'm going to need to do a lot of homework on this topic obviously.
If I want to dabble in the AC servo game, I should start with a NEW drive and motor from the same company.
Check this out! Already set up to work with MACH3! Do you have any opinion on this?
http://www.dmm-tech.com/Pricing.html (http://www.dmm-tech.com/Pricing.html)
-
Hood,
The factory is ISO 900x in contrast to some of this stuff that seems to be made with a soldering iron at the Kitchen (http://en.wikipedia.org/wiki/Vance_Miller) table . . . not saying there is anything wrong with that, but ISO certs are not handed out like candy and I woud not be surprised if China now has more of them than any other country. You know where the money is coming from for the stimulus, yes?
I was responding to your earlier post which said
I am awaiting a new servo drive from a company called American Motion Technology. That same company makes a very reasoanbly priceS ($180) AC servo DRIVE as well as matched small AC servo motors.
That seemed to suggest to me that you thought they were American made and I was simply letting you know where they came from. As I said their stepper drives seem good, I have them on the coil winder :)
Hood
-
I knew they were a Chinese company. Sneaking the word 'American' into a company name set up to operate in the US is nothing new. That just shows that the marketing people understand the American mind set. I was just making the point that the ISO designation is meaningful, no matter what country the factory is located in. The Chinese companies had a leg up on their world wide competition because there was so much government subsidizing of their 'development', but as far as I know, even the government can't buy an ISO certification, so hopefully it will remain a standard by which manufacturers can be compared.
*soapbox off*
What appealed to my Geek side was that I could tell right away just by the way the Leadshine literature reads that AMT is populated with 'pocket protector' types . . gives me a warm fuzzy . . . :D
How did you come to select Leadshine stepper drives? I'd be interested to know your take on the dmm-tech products?
-
Check this out! Already set up to work with MACH3! Do you have any opinion on this?
http://www.dmm-tech.com/Pricing.html (http://www.dmm-tech.com/Pricing.html)
Well they claim it works with Mach, I could not see any mention of Step/Dir? Unless I did not dig deep enough.
I wonder why they feature an Absolute encoder? Generally this is reserved for Robotic applications?
This will show you the relationship with the 3 windings and the commutation, although BLDC, but informative, nonetheless.
http://users.tinyworld.co.uk/flecc/4-pole-bldc-motor031102.swf
Nosmo
-
Just be carefull what you try to match up. AC sinusoidal & DC trapezoidal are two different critters. Trying to run an AC off a trap drive can lead to cogging instead of a SMOOTH rotation
Just a thought, (;-) TP
-
How did you come to select Leadshine stepper drives? I'd be interested to know your take on the dmm-tech products?
I used Leadshine stepper drives simply because I could get them next day delivery in the UK. The ones I have dont have LeadShine on them but that is normal for Chinese stuff, I have a DRO on a lathe called a Sino, I have seen it on the net under a dozen or more different brand names. Oh and I have had that DRO for 5 or 6 yrs and its switched on 24/7 and has never missed a beat :) Same with the Knuth (Top10 or whatever you want to call it ;) ) DRO on the other lathe, Chinese can produce quality stuff just like anyone else :)
The DMM drives look like they are ok but without testing them and having something to compare them with it would be hard to say. They will work with Mach, the specs say they can take Pulse/Dir signals which is just another word for Step/Dir. If I remember correctly Yaskawa call it Pulse/Signal, many names for the same thing ;D.
Only thing I am not keen on with these smaller drives is you need a seperate DC power supply where the more industrial orientated drives take mains. Not had a good look at the specs to see what the power supply requirements actually are however.
Hood
-
My next toy will be Advanced Motion Controls model DX15CO8
Snagged it on ebay for $25, so . . . worst case can't be that bad :P
I need a CAN interface for it, but I can definately get a surplus UBS to CAN adapter for $50 . . . I'm trying to get it for $25, we shall see.
AMC does make models that will interface with RS232, but a new one of those babies is something like $600 . . . . WAY outside the 'dinking around with toys' department.