Steppers or Servos for a conversion??

[Brass_Machine]

I am getting ready to start my conversion for my little X2. I had ordered plans from Fignoggle last year and I am almost (finally) to the point of where I can start it. I noticed on the Keling Tech site the have some 230 & 350 oz-in servos for a decent price. I have a little extra money and am thinking of going that way. Can anyone tell me why or why not this would be a good/bad idea? Which of those peak torque servos would I want to use?

This mill will be used for some hobby and minor production work.

Thanks
Eric

 

[BobWarfield]

I have used both. My current IH Mill project uses servos, and I have a little router with steppers as well as a lathe I've played with steppers on.

Steppers are a lot easier to get running. Servos, if you can handle the added complexity can deliver more performance. The question will be whether you're set up to take advantage of the performance.

For example, my IH mill can rapid at 140 inches per minute. I'm scared to jog at more than maybe 30% of that. It is quick!

However, my spindle goes 1600 rpm and I spend most of my time cutting at less than 10 IPM. Until I get a much higher speed spindle, I can't really use all that speed.

Servos will typically need to be geared down with timing belts as well.

All things considered, especially for a smaller mill, I'd be real tempted to stick to steppers and git 'er done sooner/cheaper/easier.

You'll think of something else you need to spend that money on!

Cheers,

BW

 

[Brass_Machine]

Thanks Bob.

You had told me once what you are using for a controller... smooth step was it?

Eric

 

[RonGinger]

This is Holy War #1 in the hobby CNC world. There must be thousands of pages of argument on it.

I Strongly believe the following points are true;

1) a stepper motor of correct size will NEVER loose a step as long as its operated with in its capability. There are thousands of commercial machines in operation daily making lots of parts that prove this.

2) Steppers are always lower cost- if nothing else simply because they do not need an encoder.

3) Servos can be tricky to tune. There is no tuning to do to a stepper.

4) Steppers are limited to about 300watts - or abut 1/3hp. If you need more power servos are the only way.

For an X2 class machine I have no doubt that steppers would be the way to go. Any servo would be a serious overkill. Save your money, buy some more cutting tools, or make a 4th axis or do something useful with it. Only a guy selling servos will tell you otherwise.

I did my Jet knee mill with a 7x30 table first with servos. The tuning was a pain, the growling nose was annoying and one eventually burned out due to a failed brake. I switched to steppers and have a great machine. I get 75ipm rapids- I dont want to see anything faster than that. I dont cut any material anywhere close to 75ipm. I have run 3 hour long job making molds and have never lost a step.

Oh, I elevate the knee and table on my machine, which must weight a couple hundred pounds with a stepper. Works fine.

If you are using Mach take the money you saved on the steppers instead of servos and buy a Smoothstepper. It is more than worth its cost. Ive done 6 or 8 machines with parallel ports, but from here on everything I do will have a smoothstepper.

 

[Brass_Machine]

Thanks Ron!

What do you recommend for peak torque on the steppers for the X2?

Eric

 

[BobWarfield]

Yes I use a Smoothstepper.

RE noise, my servos are MUCH quieter than my steppers in every regime but dead stop, and even then they're quiet just not quieter. Ron, I do wonder about the tuning if yours were so noisy.

Be that as it may, as I said above, I'd lean towards steppers for your mill. For a larger mill, I don't regret the servos though. Just be ready for the increased complexity involved if you choose that path.

Getting back to the Smoothstepper, I like it, BUT...

Not all Mach3 features work for it yet. There are two in particular that I find annoying to be without:

- There is no backlash compensation. But wait, you say, with good ballscrews you have no backlash! Not true. You just have a lot less, and backlash comp can still improve your machine's performance. If you're not running ballscrews with preload nuts you will likely really miss the backlash comp.

- There is no feedrate override. I really like FRO. For example, my programs often cut air for a little while to allow for variation in the initial rough sawn workpiece. With FRO I can crank my feed way up and get done cutting air sooner. I often restart programs, and may not know exactly where I need to run to (i.e. which line of code). I can crank FRO and get done cutting air sooner. Lastly, the feedrate can vary surprisingly much based on what the endmill is doing. Most CAM software doesn't take this into account unless you have an expensive high speed machining option. Having started out a manual machinist, your eyes and ears can do a pretty good job. You can nurse that FRO and get done cutting your part sooner, or avert a problem of too fast a feed without having to stop the program and modify it if you have FRO.

These features are supposed to be coming, but the guy who invented Smoothstepper is not very responsive or communicative. You can go weeks on his forum without him saying anything. I worry sometimes about orphaned products if the guy's priorities in life change. I have had this happen to me twice now with CNC electronics and it is really painful to have spent the time and money only to discover you have to rip it back out or live with the limitations because the device is orphaned.

I am not saying this will happen with Smoothstepper, and I love mine, but it is something to think about. I don't think you want to be too far off the beaten path with Mach3.

Best,

BW

 

[RonGinger]

These features are supposed to be coming, but the guy who invented Smoothstepper is not very responsive or communicative. You can go weeks on his forum without him saying anything. I worry sometimes about orphaned products if the guy's priorities in life change.

I would not worry about that with Smoothstepper. He is also working on an industrial version of the board, and a lot of major business plans are in place for it. I am very sure he is fully committed to this, and I also know Brian Barker is fully committed to mach support for smoothstepper. They will be around for a long time.

The only workaround for feed override is to code the job for the max feedrate and then run it slower- you can slow down feed, you cannot increase it.

MY servos were using geckos, and they are well known for the growl problem . Marriss has just recently talked about a new driver the he says will be very quiet. I may try them when they are available on my router.

I am still firmly convinced for any machine smaller than the low side of bridgeports steppers are the way to go. Big bridgeports and up must be servos. An X2 with servos would be silly.

I think an X2 machine would be fine with any of the new 300-400 oz-in NEMA 23 motors.

 

[ianjkirby]

Hi,
The guy at http://www.cncteknix.com has a very good servo controller. The web site is a little dated because he is working mainly by himself, and spends time on the product rather than the website, but it is a good unit. The servos he uses are brushless dc, and they are silent in all modes of operation. I am not connected with him other than as a visitor and occasional customer.
Regards, Ian.

 

[Weldsol]

Hi there I know this company is UK based but I'm sure the products are available anywhere.
I got a full system (Stepper)for the machine I'm making and I went for the biggest steppers / drives / power supply in case I decide to do other things.
As it turned out the system would run my Bridgeport if I needed to

http://www.motioncontrolproducts.co.uk


Paul

 

[Tin Falcon]

Jack 282s should be plenty big for and x-2
Tin

 

[Krown Kustoms]

I have previously posted, a company Probotix sells a kit for around $300, it includes everything you need except wiring and enclosure.
I am putting together a series on how to set it up with Mach 3.
I have been using it for a while and the only mod I have done is a cooling fan in the enclosure because I am set up at 1600 steps/rev.
I have it attached to a Grizzly mini mill. It has enough power so far and is pretty user friendly.
You can also mix and match steppers per your aplication in the kit.
I cant remember off the top of my head but I think my setup has 240 oz steppers.
forgive the mess in the pic

 

[kuhncw]

Hello Jack,

You might try Jeffery Birt for an E-stop switch.

http://soigeneris.com/CNCParts.aspx

Regards,

Chuck

 

[Tin Falcon]

http://www.kelinginc.net/CNCPackage.html


http://www.alliedelec.com/Search/SearchResults.aspx?N=0&Ntk=Primary&Ntt=e-stop+button

Tin

 

[shred]

I got one from Surplus Center a while back-- big red twist-to-reset button and everything. Always worth a visit even if they don't have what you're looking for

 

[vlmarshall]

Surplus Center switches is a great source of stuff like that. I recently ordered a pair of E-stop switches, along with a bunch of other parts for a CNC router... steppers from Keling, switches from Surplus Center... both places were easy to deal with.

Oh yeah, and a stepper controller from Gecko. After wiring THAT up, I'm seriously considering swapping out the Xylotex in my little mill.