Stepper vs Servo?

[Pretorien]

Still pondering my route to CNC - the best overall hardware base for my application appears to be the Taig unit (small parts, mostly brass & aluminum, hobby use - speed of production not really an issue, small (<1/8" tools) - thus high spindle speed an advantage.

There are a lot of stepper driven units available - either as turn-key or kits, and a few servo systems (one, in particular, uses relatively small Globe servos with reduction drive to the leadscrews)

Conceptually, the servo system, with a closed loop control mechanism, appears to be the better choice albeit typically a bit more expensive.

Are there other factors to be considered? - Disadvantages to servo control?

My objective is to use a CNC mill as a tool for my hobby - it will not be a hobby itself.

thanks

EM

[philbur]

Its my understanding that servo sytems are more difficult to tune. Also servos mostly come into their own when you want to push the machine close to its limits (as in commercial use) with respect to lost steps. So for hobby use I would not bust a gut in order to have servos. Pricing the two alternatives might help you to decide.

Regards
Phil

Originally Posted by Pretorien Still pondering my route to CNC - the best overall hardware base for my application appears to be the Taig unit (small parts, mostly brass & aluminum, hobby use - speed of production not really an issue, small (<1/8" tools) - thus high spindle speed an advantage. There are a lot of stepper driven units available - either as turn-key or kits, and a few servo systems (one, in particular, uses relatively small Globe servos with reduction drive to the leadscrews) Conceptually, the servo system, with a closed loop control mechanism, appears to be the better choice albeit typically a bit more expensive. Are there other factors to be considered? - Disadvantages to servo control? My objective is to use a CNC mill as a tool for my hobby - it will not be a hobby itself. thanks EM

[wizard]

Servos have some technical advantages as well as some disadvantages. Generally from the standpoint of pursuing an hobby I see steppers winning for most uses.

The issue is costs foremost. In your case it should also be an easier system to setup and maintain which is a very good thing if your goal is to support another hobby. The only gotcha here is that you have to be sure that th steppers will be smooth enough at the speeds you will be feeding those small tools. This coming statement may lead to arguments but believe it is much easier to get high quality results from servo systems as opposed to stepper systems.

I have no experience with the Taig, from what I hear though it will be an easy machine to get up and running as they do a very nice job of building the machine. That would likely be one of the biggest detractions of converting an import mill.

Do realize though that once you have a CNC mill making use of it requires a chain of software tools to generate the code and the drawings from which the code is generated. You of course can hand code CNC code and even use the CNC software to drive the mil manually. It is just that the more complex items require a tool chain to build the CNC code required to generate the product. You may already be aware of this but I point it out due to many not taking into account the software chain needed nor the efforts required to hand code G-code.

Dave

[LongRat]

Sounds like you would be best looking at steppers, not being after ultra speed etc. Also a point to note, hobby servo systems all run on brushed DC motors which can wear out. Stepper motors are zero maintenance brushless. Good if you are after a hobby tool, not a tool hobby

[in2steam]

Originally Posted by Pretorien Still pondering my route to CNC - the best overall hardware base for my application appears to be the Taig unit (small parts, mostly brass & aluminum, hobby use - speed of production not really an issue, small (<1/8" tools) - thus high spindle speed an advantage. There are a lot of stepper driven units available - either as turn-key or kits, and a few servo systems (one, in particular, uses relatively small Globe servos with reduction drive to the leadscrews)

Since you are only going to be doing fairly small stuff and light cutting, I would go with steppers, in fairness you can with a small amount of work make stepper units closed loop, but it would add to the cost and put you nearer to a servo system. Servos can be more unforgiving when it comes to operator errors and with 1/8 tools your tools won't last should there be a fupar. Not that steppers won't cause things to snap but you are less likely to damage hard components such as screws, tables, and gibs. I own a taig lathe and its an execeptional machine for its size, I would personally get one of the ebay units for around $1500 deepgroove being one of the more popular, for no hassle its pretty much plug in and play save the computer and software.
The micro stepper drives on those machines produce good results, albiet a little on the slow side, they do very fine work such as engravings and ring work very well.
I kinda wish taig made a larger unit.....
chris.

[NC Cams]

Do a stepper and servo search on the website.

There is a very detailed cost/benefit posting by Maris that has been reposted SEVERAL times either via cut and paste or via link. Pretty much ALL the gives and takes are well documented.

Each has benefits and liabilities that the user has to be the judge of.

BTW, Bridgeport made a lot of machines that used DC brushed motors on VMC's and ExTraks and V2XT's - BPT hardly made whay you'd consider a "hobby" system.

[in2steam]

Originally Posted by NC Cams Do a stepper and servo search on the website. BTW, Bridgeport made a lot of machines that used DC brushed motors on VMC's and ExTraks and V2XT's - BPT hardly made whay you'd consider a "hobby" system.

Yeah I know, slighlty off topic, I pulled one apart when I went to school a few years ago(machine repair/millwright), again lots more power then you ever need(this one was near to a 1 HP in size), I used to work at leeson electric(engineering dyno test tech) for awhile, we had products that we purchased and rebranded both steppers and servos, for there size and weight steppers can do allot more then brushed servos at low rpms, its the high rpm(above 600) were servos come into there own. AC servos now those are really cool, but they cost as much as most of these entire systems for a small one(not including the drive). Hardinge sold there tm series with a stepper drive on it, so it goes both ways, of the two I can see hardinge universal (with a vertical head)finding its way into my garage long before a bridgeport ever will.
chris

[ger21]

Steppers vs Servos

Steppers and Servos...

[holbieone]

I've used both in the field and for hobby

you can't beat a servo but for what you are doing it maybe a bit over kill

i would add up the total cost of both systems and let that be your deciding factor

[NC Cams]

This too:

http://www.cnczone.com/forums/showth...078#post214078, post #15

[Pretorien]

My thanks for all the responses - take-away lesson # 1 - do a thorough search before asking a question! - Lesson # 2 "For every complex problem, there is a simple answer - and it is wrong"

EM

[rc-monster mike]

I think I would have a hard time justifying servos myself. Granted, my stepper system wasn't exactly cheap, but for small machines like mine(Minitech Mill4), I can't imagine much value to a servo system over my current Camtronics Gecko setup. I can easily get over 400ipm reliably with the setup, and without limits, its nice to know that an error will result in lost steps and not destruction or damage to a machine component.