Let the fun begin !!! ???

**PAULRO** · 06-02-2015

i had some play in the fixed bearing blocks (0.3 mm) . stripped them down and set them up again and still had end play. had to make some shims to eliminate it .

**PAULRO** · 06-02-2015

i have gathered power supplies over the years and i'm, hoping to use some of these.i will have to either make a power supply for the drivers or buy one . i haven't decided yet .

**PAULRO** · 06-02-2015

more bits gathered down the years. i hope to use most of these also.

**JAZZCNC** · 06-02-2015

Originally Posted by PAULRO

i had some play in the fixed bearing blocks (0.3 mm) . stripped them down and set them up again and still had end play. had to make some shims to eliminate it .

Well unfortunatly this happens but when shimmed they are fine. Looking at the shim I'm not quite sure your shimming the inner race or outer.?
If it's the inner then the bearings are in the wrong way around. You want them back to back with a shim between outer races.

Regards the Leadshine Closed loop steppers then they are nice but expensive. If your using Mach3 then just attaching encoders to your steppers won't help at all because Mach is not closed loop and all it can do is report the encoder position it cannot correct for error like the leadshine servo stepper drives do.

The closed loop stepper drives actually close the loop within the drive not in the control software so when you see it correcting position Mach doesn't know anything about it. Now this is good and bad at same time.?
It's good that the drive monitors position using the encoder and corrects for any error but at the same time if any error as happened it's still an error which causes a break in continuity between drive and control software. Because the loop is contained within the drive and never reports any small positional errors to mach then In affect Mach becomes in front of the drive for a short period before the position catches backup in that axis. Other axis will carry on in front So Depending on the error amount it can affect the job so the error still shows up in the finished job.!! . . . . . This is also true of servos or any other drive that doesn't have true closed loop system that works in tandem with the control software to sync axis together.

If the positional or what's called following error gets too great then the drive will fault and e-stop the system (which in affect is what Stall detect does but much cruder) This following error can be set in the drive parameters to a small amount so if goes outside parameters then drive faults and system E-stops.
This is how most servos work but like I say the small errors have still happened and at some point will show up in the work.!!

This is why you'll often see people who have experience with both Servos and steppers on slower machines like mills etc say that Servos are no more accurate than steppers if steppers are setup and tuned correctly.! . . . Error is Error and will show in the work with either system.!!
In some ways servo or Semi closed loop is worse than standard stepper system because you'll never know where the Error comes from as each axis have caught back up so when job finished all looks well and in position but the work piece still shows error. With steppers any lost steps can clearly be seen in the axis as it won't return back to where it started.!!

Servo's rule when heavy loads and high feeds are required Or when going point to point very fast like in positioning systems. For Small/Med routers or Small/Med mills steppers can match servos no problem without closed loop.

**PAULRO** · 06-02-2015

ya , that's the way the shims are in o.k bearings back to back and shim in between on the outer races. cheers for the run down on the closed loop . i think i'll stick with the original plan. steppers it is with the AM882 drives.

**JAZZCNC** · 06-02-2015

Originally Posted by PAULRO

y i think i'll stick with the original plan. steppers it is with the AM882 drives.

Good plan but make sure you make use of the Fault output so it E-stops the system when stall detect kicks in.!

**PAULRO** · 10-02-2015

well, i've been reading most of the weekend on the electrics and control side of things and i'm still in 2 minds about my next step. i started on sourcing a power supply for the motors / drivers ( AM882) i was quoted 346 euros + vat for a 60 V DC SUPPLY so i think i will be building my own one !!!
i still have a few queries about the twin motor set up on the x axis ball screws. i'm a bit confused about the homing of each ballscrew separately. am i correct in saying that when i home the x axis, both motors engage and head for home simultaneously but because 1 motor might have lost steps during the course of machining they wont reach their respective home switch together? will the motor that has lost steps get to its home switch eventually albeit some time after the first motor and if so why do we need to home them independently.
i was reading( http://www.mycncuk.com/threads/6418-...-CNC-Mk2/page8 ) about independently homing each axis because of missed steps and the strain it buts on the gantry. so my next question is about the distance they travel away from their respective switches before they stop and return. or have i got this concept wrong also!!

if i did decide to go the 1 motor route and upgrade the motor to a nema 34 and belt drive both ballscrews would the am8882 drive and 60 VDC POWER SUPPLY need to be upgraded also? it a question of cost at the moment and that's why i'm trying to have some upgradability if i do box myself into a corner with dual motors that need regular independent homing. all these choices are really playing havoc with the hamster in the hamster wheel upstairs.

I THINK I FOUND A ANSWER TO THE ISSUE OF HOMINGhttp://www.mycncuk.com/threads/6565-...dy-Eddy/page30 / 32 , I wouldn't mind but i read that before!!

**njhussey** · 10-02-2015

The steppers will generally only lose steps if they're tuned too close to their maximum speed and acceleration from my understanding and reading of Jazz's posts. There's plenty of people on here using twin setups and not many posts to say they're losing steps and racking the gantry. I'm in the same situation as you regarding the twin vs single stepper and I'm leaning towards the single Nema 34 with a different driver. The AM882 will not drive the Nema 34 with any sort of speed, 240V drives are best for them but they are more expensive! I'm going to use my spare 3.1Nm Nema 23 stepper and driver for a 4th axis when I get the Nema 34....

**PAULRO** · 10-02-2015

that's good to know about the AM882 drive. originally i bought 4 nema 23 4Nm with the intention of using 1 each for the x,y,z and a spare for the fourth axis. but soon realized that i would probably need 2 for the x axis. ( 1 on each ball screw). maybe down the road i might just follow you down the road and replace the 2 23s for a 34, now that i know i will just keep going with the 23s and 60 VDC power supply. cheers for that.