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Stepper motor and surface finish

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Mike Poole12/02/2019 17:21:03
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1692 forum posts
44 photos

Stepper motors seem very popular to drive a CNC axis but I was wondering if the motion being steps has an effect on the finish or is it not significant?

Mike

John Haine12/02/2019 17:50:46
2324 forum posts
130 photos

Not significant compared to other effects in my experience. Actually once they are moving at any speed the motion is more like continuous thought the speed will vary during the step cycle, depending on how well the microstepping works. If you approximate curves by straight line segments you can get visible facets but these are much coarser than the step size. For circular arcs most controllers coordinate the motion of the axes at varying relative speeds to form helical arcs, using G02 and G03 commands. It would be nice if they could do more complex interpolation but I don't know any that can.

Ian McVickers12/02/2019 19:07:44
65 forum posts
26 photos

Didn't see any marks on the cut edge on any of the machines I built using stepper motors. As John says when cutting material the motors will be stepping fast enough that it will be near continuous motion. There are various bits of hardware and software out there for control side. A lot of people go for Mach3 but personally I didn't get along with it. I did try Eding cnc and liked it but was part way through my next build which would have been using Acorn but decided to scrap the build and have a go at model engines instead.

mgnbuk12/02/2019 19:52:53
482 forum posts
10 photos

Many Matchmakers with Posidata stepper motor controls in industry back in the '70s, along with Bridgeports with (IIRC) the "Boss" stepper motor control. Acton & Beaver used the Posidata system as well. These used 1/2 step drivers so pretty coarse by modern standards, yet I saw those machines making aircraft & turbine parts and used in goverment research departments.

I took ptenty of those systems off & replaced them with Heidenhain controls & DC servo drive sytems (SEM motors & Indramat amplifiers) in the mid-'80s to mid '90s in a previous employment.. I don't recall anyone commenting on improved surface finish after the conversions, which were usually done to gain reliability and improve useability. Going closed loop with a measuring system & not having to deal with lost steps was also an advantage.

Doing such retrofits died the death when the smaller capacity machines that usually had the stepper motor controls got cheaper new (like Bridgeport Interacts & Spanish/Taiwanese imports) & the cost of the conversions rose over time, so it no longer made financial sense to retrofit an old machine.

Nigel B

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