ELS for BOXFORD AUD

[mgnbukParticipant @mgnbuk]

the Nema23 stalls under certain conditions.

Your Dip switch settings for SW5 -8 for the steps per rev suggest 6400 steps per rev according to the stepperonline description for a DM556T drive which yours looks like it may be – difficult to see from the picture & you don’t specify as far as I can see. A description of this given under item 3 on  here where 32 microsteps operation (6400 ppr) is shown as having only around 5% of the rated motor torque compared to full step operation.

Best torque is with full or half steps, so maybe you could try resetting both drive and ELS to run at, say, 400 steps per rev and see what happens ? Also up the current to the drive maximum of 4A, as the motor picture shows the motor is rated ar 4.2A and it will only give the rated stall torque at that current value. I would not expect that you could stall a 3Nm motor by hand – I have a  3Nm Nema 24 stepperonline motor driven with a stepperonline DM556N drive from a 36V no-name switch mode psu set for a low microstepping rate & can’t stop it rotating with a 30-ish mm diameter timing belt pulley fitted.

Nigel B.

[John Haine]

On John Haine Said:

On Robert Atkinson 2 Said:

……
A ELS on a conventional lathe has one disadvantage over a typical CNC system, you can’t ramp the speed up, it has to be syncronous with the spindle which you have no control over.
It seems to me that 840RPM is very fast for screwcutting.

Robert.

P.S. Hoping to fit a electronicleadscreweu single axis to my ML7 over the holidays. All the bits are in.

If that’s the case it is a poor design!  Even Mach3 does better than this.  The trick is to have a 1ppr index pulse and use that to trigger the acceleration from a fixed start position for each pass, returning to the same start after the cut.  You can also have an encoder to give finer control of cutting speed as in more advanced lathe CNC controls.

Maybe I wasn’t clear enough. My comment applies to thread cutting. If you accelerate the the cutter you get a variable pitch thread. You can accelerate before the cutter stsrts cutting but that is not always possible.

Robert.

 

[Robert Atkinson 2Participant @robertatkinson2]

Just seen Nigel B’s post and I agree entirely. Microstepping is not a good idea for this type of application. Set for half step.

Robert.

[John HaineParticipant @johnhaine32865]

Robert, I just don’t see what you are getting at.  An ELS isn’t going to be able to cut full depth at one pass, so for each pass it has to somehow move the tool back to the start.  Unless the spindle reverses (with the tool withdrawn of course) and the L/S turns backwards, you have to withdraw the tool, send it back to the start, feed in again and synchronise with the spindle.  Just like “hand”threading, the tool will start each pass clear of the end of the stock and has some clearance to accelerate before the next cut starts.  Provided there is at least a 1ppr spindle index pulse synchronisation is pretty trivial.  Obviously you can’t accelerate the tool once it’s cutting, though actually small adjustments to feed rate are made in more advanced controllers to allow for spindle speed variations caused by cutting force.

Just for information, the Z leadscrew on my S7 is driven through a 2:1 pulley from a reasonably beefy NEMA23 at 3A coil current, with microstepping set to 8 (i.e. 1600 steps per rev).  In all the time I’ve been running this (14 years) I cannot recall a single time I’ve missed steps other than when I’ve managed to stall the spindle with an over enthusiastic cut.

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