[DDMODS]

Hi everyone, I'm currently building a new cnc machine with dual y axis steppers driving ballscrews on each side on individual drivers just 1 being a slave axis over the other with mach 3. When i was testing out some max feeds on the y axis it come to the attention that 1 coupling had come loose so at one point 1 motor was pushing the gantry along on 1 side while the other was not so the gantry was twisting itself around so to speak (not much but maybe 5mm over the 1300mm span which is enough to concern me).

i haven't had a problem since tightening the coupling but it is of some concern that down the track a similar problem occurring or driver failing or stepper failing etc that 1 side of the axis will continue to drive while the other will remain stationary and end up causing the machine to break something somewhere.

My machine is a steel construction and the steppers would probably end up clutching out before actually breaking something but i thought if there was an easy limit switch arrangement others have come up with for this then i might as well install it.

I was originally thinking of having limit switches running on either side of the gantry (front to back not side to side) to the main frame and just off being triggered so that if 1 motor stops the twist in the gantry will end up making the limit switch activate and estop requested.

has anyone thought of anything for this situation?

i have new linear rails to go on each side so that will reduce any ability to twist the gantry anyway but im just worried as to what would happen if 1 motor fails etc...

Any help is appreciated cheers

[James Newton]

Sorry I don't have any advice, but it's an interesting question and I'd love to hear what anyone comes up with.

[Al_The_Man]

In my opinion the mechanics should be such that it would survive and suffer no ill effects from a motor failure and the result would be a stepper stall first before any damage occurred.
Where both sides of a gantry is driven it is common to make only one side compliant and the other side non-compliant. to avoid binding etc that may occur if some slight out of parallel condition exists.
It sounds like you have the gantry set up for the whole gantry to travel in the Y? rather than the Y across the Gantry? Although It is optional which way to set up a gantry.
Al.

[ger21]

There is a board available with a Mach3 plugin that uses encoders on the motors to monitor their position, and stop the machine if an error occurs.

[Les Bidgood]

A miniature chain and sprocket can be used to couple the 2 ball screws together. This provides a belt and braces solution.

[DDMODS]

In my opinion the mechanics should be such that it would survive and suffer no ill effects from a motor failure and the result would be a stepper stall first before any damage occurred.
Where both sides of a gantry is driven it is common to make only one side compliant and the other side non-compliant. to avoid binding etc that may occur if some slight out of parallel condition exists.
It sounds like you have the gantry set up for the whole gantry to travel in the Y? rather than the Y across the Gantry? Although It is optional which way to set up a gantry.
Al.

My y direction is end to end of the table and my x is across the table or paralley with the gantry so to speak. im sure the new gantry now will have no issues with breaking but it was just a curious issue.

There is a board available with a Mach3 plugin that uses encoders on the motors to monitor their position, and stop the machine if an error occurs.

Do you know where i could find this board or what its called? id be interested to see maybe

A miniature chain and sprocket can be used to couple the 2 ball screws together. This provides a belt and braces solution.

I had thought about that but the way its setup now would be difficult to attach a belt or chain to the ballscrews as there isnt an available end or room to modify the ballscrew to fit a sprocket or similar

[ger21]

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[UA_Iron]

what kind of coupling are you using? It might be cheapest to go with a better coupler and still remain blind to such failures.

Schneider M-drive motors have an external encoder option -EE that allows for a linear external encoder. You could build into the m-code routine the handling of such events. In fact, I have dealt with this exact [loose] coupling problem on an Mdrive setup with external encoder - I was scratching my head at the stall flag that was being raised.

These are one of the cheapest linear encoder options:
US Digital | Products

Fairly accurate too - the biggest source of error on those things I believe is from the environment in which they print the mylar strips: they do not temperature control the environment when printing - still probably more accurate than a lot of magnetic linear encoders.

[DDMODS]

what kind of coupling are you using? It might be cheapest to go with a better coupler and still remain blind to such failures.

Schneider M-drive motors have an external encoder option -EE that allows for a linear external encoder. You could build into the m-code routine the handling of such events. In fact, I have dealt with this exact [loose] coupling problem on an Mdrive setup with external encoder - I was scratching my head at the stall flag that was being raised.

These are one of the cheapest linear encoder options:
US Digital | Products

Fairly accurate too - the biggest source of error on those things I believe is from the environment in which they print the mylar strips: they do not temperature control the environment when printing - still probably more accurate than a lot of magnetic linear encoders.

At the moment have a few different ones. The Ones I'm using are the flexible aluminium sprung ones where the grub screw grips the shaft but I have another one that the grub screw clamps the sleeve around the shafts. Also have solid couplings but I think a bit of loctite on the grub screws should work

Thanks for the encoder options I'll see how it goes should be a lot better now with the new gantry rails too

[UA_Iron]

At the moment have a few different ones. The Ones I'm using are the flexible aluminium sprung ones where the grub screw grips the shaft but I have another one that the grub screw clamps the sleeve around the shafts. Also have solid couplings but I think a bit of loctite on the grub screws should work

Thanks for the encoder options I'll see how it goes should be a lot better now with the new gantry rails too

For frequently rotating components I would never use a hard coupler - but it sounds like you have some options for securing your current couplers down better. Use some permanent loctite in the 420, or 422 range - it can still be removed at some point if need be, it's just a pain in the ass.

Just like with the Mdrive motor+controller, there are other ways to solve this problem, but they get expensive and it's usually all solved at the motor controller level, not at the mach3 level. I have seen that encoder interface board that Ger21 posted, but unfortunately there's not a huge use of that board on the forum. Hopefully Rogersmachine would give good support for that product.