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Stevie
04-09-2004, 08:00 PM
I've managed to buy 2 Parker Compumotor AL microstepping drives at a good price

Next question; how can I control them with a PC; they seem to have the inputs that make me think direct connections to the printer port would work; am I right?

vacpress
04-09-2004, 08:43 PM
stevie, a good place to start might be at the gecko website. look at their info on how to setup their geckos, and see what you can infer for your drives. i would guess a bunch are obvious.. just be VERY carefull not to put the motor voltage into the wrong place! most things burn good with 60 or 80 volts at 15amps or whatever.. im not familiar with the drives, so i am only guessing what supply you might be using... look for compumotor manuals and see if they have overlapping info if yours is not available.

hope it helps

Stevie
04-09-2004, 10:15 PM
I found the manuals ok; but they are not really geared to the simple set-up we see here
I'm not too electronic savy; but i feel there must be some way to interface with a PC
Here a shot of an AL drive
http://images.channeladvisor.com/Sell/SSProfiles/20052963/Images/COMPUA.jpg

Stevie
04-09-2004, 10:31 PM
Here's the Compumotor S Drive Specifications from Parker

Performance

Accuracy ±5 arc min (0.0833°) typical.

Unloaded-bidirectional with Compumotor supplied motors. Other motors may exhibit different absolute accuracy.

±1 arc min (0.0167°)

Loaded-in addition to unloaded accuracy, per each frictional load equal to 1% rated torque.

Repeatability ±5 arc sec (0.0014°) typical.

Unloaded-one revolution returning to start point from same direction.

Hysteresis Less than 2 arc min (0.0334°) unloaded-bidirectional.

Resolution 16 selectable choices: 200, 400, 1000, 2000, 5000, 10000, 12800, 18000, 20000, 21600, 25000, 25400, 25600,

36000, 50000, 50800

Waveform Selectable. Allows microstepping shaping for optimum smoothness or relative accuracy. Pure sine; -2%, -4%, -6%,

-10%, third harmonic included.

Speed/Torque Refer to speed-torque curves on page C71.

Motors

Type 2-phase hybrid permanent magnet, 1.8 degree.

Breakdown voltage

(HIPOT) 750VAC minimum

Number of leads 4, 6 or 8

Accuracy Grade 3%

Inductance 0.5 mH minimum; 5.0 to 50.0 mH recommended range; 80.0 mH max

Dimensions Refer to drawings on page C72.

Amplifier

Type 20 kHz fixed frequency, variable duty cycle PWM (pulse width modulated). Current controlled, bipolar type. MOSFET,

IGBT construction.

Number of phases 2

Dimensions Refer to dimensional drawings on pages C73 and C74.

Protection*

Short Circuit Phase-to-phase, phase-to-ground.

Brownout If AC supply drops below 85VAC.

Overtemperature If internal air temperature exceeds 158°F (70°C).

Auto standby If selected, motor current ramps to 75%, 50% or 25% of preset value if no step pulses are received for 1 second.

Rated current levels are resumed upon receipt of next step pulse.

Self test This feature (used primarily for testing and verification of correct wiring) rotates the motor at approximately 1 rps for 6

revolutions in the CCW direction and 6 revolutions in the CW direction.

Step Input High-going pulse, 200 nsec min. width; max. pulse rate is 2 mHz. User-supplied driver for the step and direction inputs

should be capable of providing a minimum of 6.5 mA to a maximum of 15 mA.

Direction Input Logic High = positive (CW) rotation.

Logic Low = negative (CCW) rotation.

User-supplied driver for the step and direction inputs should be capable of providing a minimum of 6.5 mA up to 15 mA.

Shutdown Input Logic High = amplifier disable.

Logic Low = normal operation.

User-supplied driver for the shutdown and zero phase inputs should be capable of providing a minimum of 2.5 mA up

to 30 mA.

Zero phase Logic Low = resets the motor phase currents to the zero state. It is primarily for linear motor applications. The input

must be active for 100 ms before the first step pulse is received.

Logic High = normal operation.

User-supplied driver for the shutdown and zero phase inputs should be capable of providing a minimum of 2.5 mA up

to 30 mA.

Fault Output Conducting = normal operation.

Not conduction = drive fault.

Power Input 90-130VAC 50/60 Hz

Environmental

Operating 32°F to 122°F (0°C to 50°C)

Drive Maximum allowable ambient temperature is 122°F (50°C). Fan cooling may be required if airflow restricted.

Motor 212°F (100°C) maximum motor case temperature. Actual temperature rise duty cycle dependent.

Storage -40°F to 185°F (-40°C to 85°C)

Humidity 0-95%, non-condensing

AL drive is very similar; just it has 3amps max to the motor

I got an S drive too; so I have 2 AL's and 1 S; 3 drives for the mill project
If I do end up needing some kind of inderxer; I'll just have to get one; bit I still feel a PC can connect to it; it needs step and direction

ger21
04-09-2004, 10:43 PM
I think this is the right manual for what you have. http://www.parkermotion.com/manuals/a-ax/a_ug.pdf
If so, page 26 shows you how to give step and direction pulses to run the drive. So you SHOULD be able to use these with Mach2 or TurboCNC. It looks about as simple as electronics get, but I don't know what I'm doing either.

One problem I see, though, is that these supply the motors with 170VDC, at up to 3a/phase. If this is not adjustable (I didn't read that far), you need to use motors that are at LEAST 7V or more (25x overvoltage is ~ 170V), or you'll probably damage your motors.

PS. The airport was on exit 9. And you didn't remind me it would take 45min to go through AFTER I was over the bridge. :D

Stevie
04-09-2004, 10:49 PM
Hey Gerry; you took 45mins to drive to the airport from the bridge; wow; was it the trucks all lined up
I thought it was pretty simple; I've done it a lot quicker

Stevie
04-09-2004, 10:56 PM
Yeah I had that .pdf too; looked it over; I'm lost; hehehe

But I've found if you study things long enough it starts to make sense

ger21
04-09-2004, 11:09 PM
No, it took me 45 minutes from you're side of the bridge to the booths. About 400 yds. Then, 5 minutes to the airport. I thought I'd pull up as the wife's plane was landing. I was half way to the booth when she called asking where I was. Apparently, the entire city of Sarnia travels to the states on Sunday's and goes back home around 5:00. No trucks, either.

You shouldn't need an indexer, just the simple circuit I pointed out in the manual.

Stevie
04-10-2004, 09:06 AM
Sorry about the wait Gerry

Still back to the Compumotor microsteppers; I've been buying them off eBay; got some sweet deals too; got a Vexta 5 phase for $26 and it looks brand new (list is over $839)
http://www.plccenter.com/Detail_New2.asp?PartNum=UDX5114N&Manufacturer=VEXTA
THe Parker Compumotor AL's I got 1 for $69.95 and the other for $56; the first $69.95 is brand new in box; both these listed for $1500 new
I've also bought a Zeta4 with motor for $100.50; (list $1076 without motor)
Finally a Parker Compumotor S6 for $86 again with motor (list was $1301 witout the motor; new)

Pricing provided by
http://www.plccenter.com/partlist.aspx?VTI-GROUP=0&R1=2&T1=COMPUMOTOR

I feel this is a better way than the drives most use here; at least there are plenty of drive protections built in; even if I did have to buy some fancy indexer; I'v still not spent anymore than Gecko's

The 5 phase I want for my lathe for the X axis (it will be smooth for sure) The Zeta4 will be for my Z axis

The 3 Compumotors will be for my Japan servo steppers 300oz/in Nema 34; all for the Mill project

This has got to be the way to go with stepper drives; eBay is full of them if you know where to look

If you want 2 5 phase drives look at these
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42894&item=3808514478&rd=1
I bid on the last pair to $90; they went for $160 (so I'm cheap) but as these are the second batch I feel they will go for less; maybe $100; for a pair of drives this is very cheap; I'll bet about 1/10 of the original cost; and they look like new

ger21
04-10-2004, 09:40 AM
If you don't go the step and direction route I mentioned above, and you go with the indexer, what software will you use? I'm assuming that the indexer won't accept step and direction, since it appears that it outputs step and direction. The popular (and cheap) software everyone uses (Mach2, TurboCNC) output step and direction. Quite possibly, the money you saved on the drives will be aeten up (and then some) by the indexer and special software needed to run the thing.

I could be wrong, this is just an assumption I'm making here. The beauty of what everyone uses here, (Xylotex, Gecko, Mach2, TurboCNC...) Is that everythiing is relatively cheap and it all works well together. Although you can get the high end stuff for cheap on Ebay, making it all work can be a different story.

I'd try to hook them up with the step and direction circuit, if I were you.

AdminCrew
04-10-2004, 09:46 AM
Much of the Compumotor drives and indexers work with their "X language" which is not G-code and use a serial port rather than a printer port, so be careful.

Stevie
04-10-2004, 10:10 AM
I think 5vdc + or - is not really dependant on which port is emminates from; if the drive needs 5vdc for step and direction just the same as the cheaper drives most use here; whats the differance; the only other input I see is the shutdown input
I'll paste it in here
The inputs are optically isolated and may be driven (activated) by providing a positive pulse to the plus input with repect to the minus input. These inputs may also be differentially driven. The input drivermust provide minimum of 10mA (20mA maximum).
Step-Pulse_Input
The step pulse input has the following limitations
500 nanosecond-pulse minimum
40%-60% duty cycle at 15mA (750khz max pulse rate)
Input currents greater than 15mA may result in lost steps at high pulse rates

Direction-Input
This input meets the input specifications listed above.
A Minimum of 2ms of set-up time is required before and after the receipt of the step pulse

Shutdown Input
Amplifier Disable
Tjis input has the same electrical characteristics as the STEP input. you can enable it when the motor is not moving. The input must be activated for 100ms to disable the amplifier. The shutdown input must be deactivated for 100ms before the first step pulse is received

The last part is what I'm not sure about; now if the software like Mach2 has the pulses and the direction; the only thing I'm not sure about is the mA from the printer port

ESjaavik
04-10-2004, 10:46 AM
Those drives seems like an excellent deal to me!
Ger21: I don't know what you mean by that "indexer" needed between the parport and the drive? Most software I've seen outputs step and direction. That is what that drive needs. The indexers I've seen are devices that translate from step/direction to phase signals. This is a function inside this drive. If however your software outputs phase signals (unlikely) you would need a function converting this to step/direction. ( a rexednI ? )

Also this drive have (as most quality drives) galvanic barriers for protection. And the input current limiting resistor indicates that 5V will be enough to drive it. The drive have all the right features to make the motors efficient both at low *and* at high speeds. Forget 5-phase, these microstepping drives give as good or better motion at a lower price (retail prices of course). 5-phase are on their way out.

But Stevie, I understand you're sceptical. I could give you my address so you don't need to go through the trouble of getting rid of these drives as hazardous waste. :-)

Stevie
04-10-2004, 10:58 AM
ESjaavik; I am the type of guy that gets an old computer given to him at the local discount store because it's old and out of date (SX486-25) pulls the SX chip out and replaces it with a DX 33; runs Turbocnc and gets 414.5hz; no where near enough; back to the drawing board
But then finds another Pentium 75 free again; pulls the MB out replaces it with a 120 pentium S and now my Turbocnc went from 414.5hz to 22809hz; all in 2 days and cost me nothing (well at the time I bought them yrs ago; it did) but the time and fun playing around with it all

So I think I can make these work for me; like you say the protections built into them may prevent me from blowing them up; and I can enjoy trying to make them do what I want

Stevie
04-10-2004, 11:18 AM
What put me into the position of looking at these drives is the fact they just need mains voltage; I don't have to figure out the sep/power supply for the drive system; just provide a bus bar with 110vac; the drives all must have the transformers built in; I'm sure they are all choppers and setable for the amps to the motors (by dips) the volts to the motors might seem high; but if they are choppers and the system is as good as the original list price represents they should be very good stepper drives :cool:
What was cool also was 2 of the drives came with matching motors; the 5 phase drive needs a 5 phase motor; but I found several on the web for not bad prices (surplus)

Stevie
04-10-2004, 11:49 AM
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3808597146

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42894&item=3808632242&rd=1
want a 12amp stepper drive; chk these out; monsters :cool:

ESjaavik
04-10-2004, 11:50 AM
I think those drives would rather compare to a 2GHz P4 than a 486. The drives are very good, by today's standard, not yesterdays. And look at the smiley at the end of my last paragraph.

Stevie
04-10-2004, 11:52 AM
I knew you where joking; chk out the last post of mine; need any 12amp stepper drives?

AdminCrew
04-10-2004, 02:15 PM
A $70 obsolete, single axis 3 amp drive when there is a Xylotex board for less with a proven track record and all the help you could possibly need. Why?

Stevie
04-10-2004, 02:21 PM
Because there is a built in power supply; there are more protections built in and the thing cost $1500 new; might be old but the design is probablly way better than a Xylotex; which is only 2.5 amps and the heat sink is puny compared to the compumotor
Plus the compumotor has micro step up to 50,800 step

ger21
04-10-2004, 02:34 PM
Plus the compumotor has micro step up to 50,800 step

Mach2 can only send 45,000/second. That will give you 0.26 rpm with a 200 step motor, if I did the math right. Not a terribly useful feature, imho :D

Stevie
04-10-2004, 02:54 PM
wait a min; if the signal sent is micro stepped by the drive; then each step sent by Mach2 would then be subdivided by the set microstep count in the drive; is that not the way this works?

AdminCrew
04-10-2004, 06:52 PM
A 50,000 step/rev resolution is slooow, try it.
Light milling or engraving right off a stepper shaft could be an interesting project though
The drives may have been $1500 but they are obsolete and are only worth what you can get for them. You need to be very careful with ebay, dumptser divers are making some good money.
Last year I purchased from a motion control company some brand Compumotor OEM-750X drives (7.5 amp) which are still being produced and I paid $80 apiece. I also purchased from the same outfit some brand new AMP HT23-401D steppers rated at 264 oz/in for $10 apiece. It seemed too good to be true but it wasn't.
Ebay can be good but you need to beware. There are some large outfits that are liquidating equipment from companies that have not survived the hightec meltdown and their stuff is current.
Then there are the scavengers with wire brushes and WD-40.

AdminCrew
04-10-2004, 06:57 PM
A 50,000 step/rev resolution is slooow, try it.
Light milling or engraving right off a stepper shaft could be an interesting project though
The drives may have been $1500 but they are obsolete and are only worth what you can get for them. You need to be very careful with ebay, dumptser divers are making some good money.
Last year I purchased from a motion control company some brand Compumotor OEM-750X drives (7.5 amp) which are still being produced and I paid $80 apiece. I also purchased from the same outfit some brand new AMP HT23-401D steppers rated at 264 oz/in for $10 apiece. It seemed too good to be true but it wasn't.
Ebay can be good but you need to beware. There are some large outfits that are liquidating equipment from companies that did not survived the hightec meltdown and their stuff is current.
Then there are the scavengers with wire brushes and WD-40.

Stevie
04-10-2004, 06:59 PM
I'm not planing to use the 50,000 step; with a 0.05pitch leadscrew it would be silly; but the mill I plan to build might have 10mm lead; then a good selection might be usefull; I just don't know yet

I know some might be dumping; but for what I paid it's worth the risk; and as i said; I'm a tinkerer; even the power transformer section could be used by removing it; who knows :rolleyes:

ESjaavik
04-10-2004, 07:33 PM
Use as high number of microsteps as your PC and software can manage. I have tried 5 and 20 microsteps, and there is a marked difference in smoothness and lack of resonances. (5=2000 microsteps/rev, 20=8000 microsteps/rev). One common misconception is that microstepping is used to get a better position resolution. It's not, but you gain in smoothness, stress on mechanical components, torque and noise level.

I got mine (Phytron) on eBay, and have no complaints. You may get some crap, but so far the price of the really good ones will outweigh that in my case. Your mileage may vary, etc. etc...

ger21
04-10-2004, 08:12 PM
Originally posted by Stevie
wait a min; if the signal sent is micro stepped by the drive; then each step sent by Mach2 would then be subdivided by the set microstep count in the drive; is that not the way this works?

Not with a Xylotex or Gecko. When I set my Xylotex for 1/8 step mode, I need to send it 1600 steps/revolution. Your's might work differently, though.

Stevie
04-10-2004, 08:21 PM
hummm; well that got me thinking; whats the point of the microstep in the drive if you have to send more steps per second from your PC; if the motor has 200; I thought the drive simply subdivided the steps from the PC and microstepped the motor accordingly; I must be missunderstanding the whole concept here

But thats not a surprise; I've been wrong before (had 3 marriges) hehehehehe :D

Stevie
04-10-2004, 10:19 PM
I've been reading about the LPT port tonight; it might be a bit low on the mA side to actually control the drivers direct; I might have to brew a board to bring it up to the 15mA the drives need to operate; but i know feel that control of the Compumotor drives is quite possible with the current "cheap" software controlers avilable; like Mach2 or Turbocnc
Opto isolation would be nice; I'll have to see just what devices can bring the LPT ports out-put of only a couple mA to a useable 15mA

AdminCrew
04-10-2004, 11:28 PM
for some reason microstepping not only stops set screws from vibrating themselves loose, it also increases the speed and usefulness
A few years ago I purchased a very highly recommended 5amp
1/2 step bipolar driver kit. I assembled it with great difficulty, fitted in an aluminum box with a fan and got it rigged up to control a small lathe I purchased for the task. I ordered a bloody great 24v 20 amp power supply and off I went
It was terrible, I could not get a good finish, the ratchety movement transfered itself throughout the machine causing vibration patterns on the work and it lost steps all the time. I gave up on it and did my turning on my usual lathe.
I eventually purchased a small very cheap unipolar microstep (1/8) drive built on an Allegro SLA7044 chip, whipped a 36 volt power transformer from an old audio amp, connected it up and it was pretty amazing. This tiny little unpolar drive more than doubled my speed, the finish was perfect and the lost steps was a thing of the past plus the motors sang rather than rattled.
I have since purchased other microstep drives but the lathe is working just fine and will not be upgraded.
I am sure that the disappointment of those primitive 1 and 1/2 step boards based on hobby circuits was the prime factor in driving the home tinkerer to servo systems.

Stevie
04-11-2004, 07:33 AM
I built the kit-rus board a couple of weeks ago; my little girl enjoyed making it with me (she has way better eyes for the resister colors)
Anyway it's fried already; must have messed up with something; prob powered up without a motor or something like that
Thats what forced me to look at boards with built in open-short-fault and any other (I've got a stupid owner) devices to maintain the health of the drive

Anyone know a way to up the LPT port to 15mA from the standard output?

Stevie
04-11-2004, 11:58 AM
Ignore that post with the 15mA; i just played with 3 diff LPT's
1 on the 120 pentium I intend to run turbocnc; 1 on my 866 and the 500mhz of my little girls computer

all had slightly diff values

the 120 had 59.8mA @ 3.8vdc
the 500 had 43.7mA @4.9vdc
this (866) has 45.9mA @ 5.1vdc

I need to reduce the mA to 15 for the compumotor; I should be able to do this with a pot (I think)

Strange all the pages i looked at on the web said the mA would only be 2-3mA per pin

AdminCrew
04-11-2004, 12:45 PM
Steve,
I am using Compumotor OEM drives and I took a look at the A drive manual I believe the the imputs to be the same.
15 MA is the maxand should not be exceeded so it should work straight from the printer port. Mine do
You need to use pin 1 for step + input and pin 2 for direction +
You must ground out pins 14 and 15 (step - and direction -) This is important, If you do not do this it will not work. I also grounded out pin seven which is the ground pin on mine and could be on yours.
Try it, I'm sure it will work, you can't ruin anything.
I got the above information from Parker - list experts should be a last resort;)
You lose a lot of features by not using the Indexer (which I removed) but I wanted to use g-code rather than learn the Compumotor X language.

Stevie
04-11-2004, 01:13 PM
Hi Cutfinger

Mine are still in shipping
some are coming right to me; the others are heading to my buddies in Michigan; I'll get them next weekend

But I'll be sure to try it with the printer port once they arrive

I just figured I did'nt want to blow-up Gecko's or the Xylotex products; that why I went this way; plus I'm the kind of guy that walks the less tread path :rolleyes:

PS. where in Canada are you

ESjaavik
04-11-2004, 01:28 PM
Stevie: You don't say how you measured these figures. Was that when connected to the Compumotor drives? If not, try to connect to the drive and measure the current. It doesn't matter if the drive is powered up or not as you're driving the input diode of an optocoupler. Actually better if it isn't connected as then the motor will not do strange things.

Stevie
04-11-2004, 01:31 PM
hi ESjaavik

No; just my multimeter connected to the LPT ports #2pin
I have an old add-on port I took the back off and removed the old com2 port connecter wire; the nice thing is it will make a good connecter

:D

Stevie
04-11-2004, 02:47 PM
I downloaded Paraport

copied to a 3.5 floppy

enjoyed playing with turning on and off the pins of the LPT1 on the 120 pentium; I'm not bothered if I mess this computer up i built it this week with old parts I had laying around

But the program worked great; i had to change the address of the LPT but that was simple

I got readings of 3.9vdc again but with 59.9-61.2mA
This is just my dig multimeter connected to the pin outs and ground

I love playing around like this (I learn stuff too) :D

I should try a load; but how?

AdminCrew
04-11-2004, 10:02 PM
Stevie,
I'm from the province where the federal government has to leave the till open to stop the babies crying.
I get my stuff sent to northern NY, we get really screwed if we have stuff shipped up here

Stevie
04-12-2004, 06:02 PM
I posted about this problem in a forum all about electronics; I got the right answer about if the LPT gives more than the spec input for the Parker

Add a 500 ohm res to the LPT pin and this will limit the output to 10mA@5V

Stevie
04-12-2004, 06:06 PM
Originally posted by cutfinger

Light milling or engraving right off a stepper shaft could be an interesting project though


You'll never get enough RPM to do this; an engraver would need 60,000 for good cutting; if the motor had enough balls; you might cut with a 3/16" dia at the top speed of most steppers

Stevie
04-12-2004, 06:19 PM
it really works too; I don't have a 500ohm; but a 11K just cut it to .35mA; so the solution is really quite simple

Stevie
04-12-2004, 08:26 PM
Just got an Email from Art of Artsoft about the compatablity of Compumotors with his software; he feels the specs fit the bill nicely :D

AdminCrew
04-12-2004, 09:55 PM
Originally posted by Stevie
You'll never get enough RPM to do this; an engraver would need 60,000 for good cutting; if the motor had enough balls; you might cut with a 3/16" dia at the top speed of most steppers
FOR CRYING OUT FRIGGING LOUD STEVIE, You use a dremel or a router if your machine can handle it for the Z axis and and the 4th axis would be a large stepper with a resolution of 50,00 steps/rev.
Instead of using a rotary table or dividing head you could rig up a platform and work off the stepper spindle.
The more powerful step motors have 1/2 dia shafts and large bearings. I did say light milling and engraving.
Imagine engraving the names of your wives around the circumference of a cylinder, it could be like the Stanley Cup in a few years :D
Please, does anyone know how I can get off CNCZONE, it brags about membership but there appears to be no way to unsubscribe like the Google groups. I do not just want to log off, I want want completely out with no spams from CNCZONE
Thanks
Before I forget Stevie, your drives require motors with an impedence of 20mH minimum (see section 3) This will severely restrict your choice on more ebay 'bargains"

Stevie
04-12-2004, 10:05 PM
Originally posted by cutfinger


Before I forget Stevie, your drives require motors with an impedence of 20mH minimum (see section 3) This will severely restrict your choice on more ebay 'bargains"

I can always buy compumotor steppers; there are tons on surplus sites

Stevie
04-14-2004, 05:29 PM
I got home tonight to find the Zeta4 drive with maching motor; all the cables and connecters and manual were also in the box; this was a great buy; it all looks brand new too

The cable is already setup for step and direction; just need to strip the wire back on the motor lead and attach to the supplied plug; I think I'll try series wiring as the drive manual says the motor will run cooler :cool:

The thing I love about this type of microstepper drive is the built in PS

Stevie
04-17-2004, 04:07 PM
The drives work just fine without grounding pin 7; it did add a 150ohm resistor inline to limit the current to 15mA; I used Turbocnc to move the steppers via the LPT1 port

I have had the S6 (6amp) drive working and the Zeta4 (4amp) still need to test the new AL drive; but i need to make up special connectors for this one; the motor and AC have some strange assed plug that you can't find locally

One other very weird thing; Radio Shack in Canada sells everything you might need to build electronic boards; but not a single bloody resistor is avilable; now who thought that up
:rolleyes:

tohlsson
11-15-2007, 09:35 AM
FOR CRYING OUT FRIGGING LOUD STEVIE, You use a dremel or a router if your machine can handle it for the Z axis and and the 4th axis would be a large stepper with a resolution of 50,00 steps/rev.
Instead of using a rotary table or dividing head you could rig up a platform and work off the stepper spindle.
The more powerful step motors have 1/2 dia shafts and large bearings. I did say light milling and engraving.
Imagine engraving the names of your wives around the circumference of a cylinder, it could be like the Stanley Cup in a few years :D
Please, does anyone know how I can get off CNCZONE, it brags about membership but there appears to be no way to unsubscribe like the Google groups. I do not just want to log off, I want want completely out with no spams from CNCZONE
Thanks
Before I forget Stevie, your drives require motors with an impedence of 20mH minimum (see section 3) This will severely restrict your choice on more ebay 'bargains"
20mH "inductance" not impedence; electornics 101 eh!