g251's w/SS BoB or g540

[MarshMan]

I plan to have a dedicated laptop, Dell D600, for my CNC set up.

Planning to use Keling steppers KL23H284-35-4B 387 oz-in on my 7x12 lathe as suggested elsewhere.

From a suggestion, I have the choice of going with g251's w/BOB or g540

My question is, if I go with 2 g251's and a BOB is needed, I assume I will need a smooth stepper board, being I have a laptop?....OR can I be OK to use the g540 being it has a BOB?

Will be using Mach3

Thanks!

[CoAMarcus]

Does your laptop have a parallel port? If it does not, then you will need to use something like the SmoothStepper or G100 to get the step pulses to your drive. If you do not have a parallel port the convenience of the G540 will be mostly lost and the G251 will be the easiest way to go.

Marcus

[MarshMan]

yes, the laptop has a parallel port.

If I went the g251 way, which BoB would be a good choice?

Thanks!

[CoAMarcus]

If you have a parallel port then the G540 is a good option. A motion controller will not be necessary unless you need a VERY high step pulse frequency.

We recommend buying a BOB from four places:

www.pmdx.com
www.campbelldesigns.com
www.candcnc.com
www.cnc4pc.com

Those are all active breakout boards using 74ACT logic onboard, and we have heard good things about all of them.

Marcus

[jhowelb]

Originally Posted by MarshMan I plan to have a dedicated laptop, Dell D600, for my CNC set up. Planning to use Keling steppers KL23H284-35-4B 387 oz-in on my 7x12 lathe as suggested elsewhere. From a suggestion, I have the choice of going with g251's w/BOB or g540 My question is, if I go with 2 g251's and a BOB is needed, I assume I will need a smooth stepper board, being I have a laptop?....OR can I be OK to use the g540 being it has a BOB? Will be using Mach3 Thanks!

You may experience the same problem I had with my lathe conversion. The lower voltage required by the G251 may not deliver enough speed for threading operations.

I used G203V's which thankfully allowed me to use Kellings 72 volt power supply. I was running Kellings KL23H286-20-08b steppers at 495 oz-in. I have never regretted "over engineering" the little lathe and it has always delivered after the voltage boost.

I am using the G251's on a router with only one small glitch which I expect to have worked out soon. The lower rotational speed isn't as crucial in this application.

[TOTALLYRC]

Originally Posted by MarshMan I plan to have a dedicated laptop, Dell D600, for my CNC set up. Planning to use Keling steppers KL23H284-35-4B 387 oz-in on my 7x12 lathe as suggested elsewhere. From a suggestion, I have the choice of going with g251's w/BOB or g540 My question is, if I go with 2 g251's and a BOB is needed, I assume I will need a smooth stepper board, being I have a laptop?....OR can I be OK to use the g540 being it has a BOB? Will be using Mach3 Thanks!

Mach3 is not supported on laptops unless you use something like a smooth stepper/motion controller. Says it right on their website.
That being said, many people are using it on laptops.

I went to the local computer shop and told him that I needed a cheap computer, gave him the min specs from the mach3 website and he sold me a used Dell desktop with a fresh install of winxp for $200. It has the certificate of authenticity on the case making it perfectly legal. Plus I can add a second pport if I need to.

If you really want to use the laptop, get the smooth stepper and read the manual first.

http://warp9td.com/documentation/Smo...ManualV1.0.pdf

The way that I read it is that you need a breakout board in conjunction with the smooth stepper.

[MarshMan]

Thank You Gentlemen!

[TOTALLYRC]

Originally Posted by jhowelb You may experience the same problem I had with my lathe conversion. The lower voltage required by the G251 may not deliver enough speed for threading operations. I used G203V's which thankfully allowed me to use Kellings 72 volt power supply. I was running Kellings KL23H286-20-08b steppers at 495 oz-in. I have never regretted "over engineering" the little lathe and it has always delivered after the voltage boost. I am using the G251's on a router with only one small glitch which I expect to have worked out soon. The lower rotational speed isn't as crucial in this application.

The 387's are much closer to what the 251's max ratings are than the 495's, which is why you may have suffered from insufficent speed during certain operations.

Going from G251's to g203v's is a very large cost jump.

Originally Posted by MarshMan Thank You Gentlemen!

Alsways glad to help. Please post on which drivers you get and how the whole thing works out.


Mike

[jhowelb]

If one really reads my previous post he might presume that I was recommending the G203V/KL23H286-20-08b 72 volt perfect match over the mismatch described by pairing the G251/KL23H284-35-4B. I know what caused my problem, described it and was trying to help someone else avoid a costly disappointment.

[TOTALLYRC]

Originally Posted by jhowelb If one really reads my previous post he might presume that I was recommending the G203V/KL23H286-20-08b 72 volt perfect match over the mismatch described by pairing the G251/KL23H284-35-4B. I know what caused my problem, described it and was trying to help someone else avoid a costly disappointment.

Dear jhowelb.

If this quote was meant for me, I was in no way denagrating you or anything that you said. I think the 495's with g203v are an awsome combination and will deliver tremendous amounts of power along with excellent rapids.

I also agree that the 495's are "overengineered" for a lathe this small as you said earlier and I appreciate your honesty in this.

However, based on the other posts that this gentleman has made regarding his conversion, the g251's/385's will give him the best bang for his buck.

He can go with 2 g251's and a 48v ps plus breakout board for the lowest cost that gecko offers and with the new 385's that keling is selling, his lathe should be all he wants for a reasonable sum and well within his budget.

Unless I am completely off my mark ( and it won't be the first time) the 385's should be more than enough to run a 7x12 lathe.


Mike

[Mariss Freimanis]

OK, I have to do a friendly rant (and motor review) here. People, don't think that holding torque is the end all, be all specification on step motors. If you do, you may paint yourself into an unpleasant corner. Consider this:

Motor holding torque determines low speed torque.
Motor inductance determines motor power.

Power is what gets things done. Power is speed times torque. Power runs end-mills through metal to produce a lot of metal chips, power runs router bits through wood to produce a lot of sawdust. A properly geared low inductance motor will always beat a high holding torque motor with lots of inductance at the same power supply voltage. Why? Because it has more power.

How do you pick? Compare the square-roots of the candidate motor inductances against one another; the roots will tell you how much power the motors will generate at the same supply voltage. Let's pick a couple of motors mentioned here and another candidate of mine as a 3rd choice:

Candidate 1:
Keling KL23H284-35-B
Holding torque: 387 in-oz
Inductance: 4.1 mH

Candidate 2:
Keling KL23H2100-30-B
Holding torque: 495 in-oz
Inductance: 7mH

495 in-oz sure looks better than 387 in-oz but let's take the square-roots of their inductance. SQRT 7mH = 2.65, SQRT 4.1mH = 2.02. Divide one root by the other to get a ratio. The lower inductance motor (KL23H284-35-B) will get you 30% more power, (2.65/2.02). It's counter-intuitive but real none the less. Gear the 387 in-oz motor 1.3:1 lower than the 495 in-oz motor and you get 30% more thru-put across the board.

My candidate:
Vexta PK268-03A (Oriental Motor Company).
Holding torque: 240 in-oz
Inductance: 1.6mH

This is one of the silkiest-smooth motors I have ever tested. Beats the pants of of anything Keling has for smoothness because it is a "prime-lamination" motor. It is optimized for smoothness (microstep accuracy) instead of raw holding torque. You can have one or the other but not both.

Take the square-root of its inductance. You get 1.26. Run the ratios against the other candidates. You get 2.1 and 1.6 respectively. That means it will deliver 2.1 times more power than the 495 in-oz and 1.6 times more power than the 387 in-oz motor.

It means you will get somewhere between 1.6 and 2.1 more times work out of it. You will also get a servomotor-like smoothness (not even a hint of vibration) while the other two will vibrate a little bit at some speeds below 3 revs a second.

240 in-oz may seem small but it doesn't matter. Gear it down 2:1 to match the 495 in-oz motor. At higher speeds it will beat the 495 in-oz motor better than 2 to 1 in performance while turning with no vibration at all. To be fair, it is a $100 motor versus a $50 motor. Also to be fair the "horsepower per $" is the same yet the smoothness is a huge advantage and it's "for free".

As always, my reviews are based on side-by-side lab testing. I run into something good, I let you know about it. Vexta doesn't even know we exist.:-)

Mariss

[TOTALLYRC]

Thanks to you, Mariss, we finally have drives that will let us run stepper motors at faster than a crawl without having to worry about them suffering from midband instability/resonance. I have always wondered about gearing a stepper.

Now that we have morphing drives that will really let the motors shine,I have a for instance. On an X3 Z axis I believe it is, everybody says you need a high holding torque motor to get the job done, possibly an nema 34. What you are saying, is get a good solid motor and gear it to match the load being moved and you will be better off. I think that the resolution will be even greater because of the steps/inch, but which may get some of us in trouble with step generation thru the pport, but that is a different story.

The only draw back to using the vexta over say the 495 keling, is the added complexity of the reduction system, which the newbie doesn't want to/can't do. But if the end result is as good as you say it is, maybe many of use should reconsider how to build and design stepper driven machines.

I personally don't have the stepper motor experiance that you do (not that many people do) and I make recomendations on suppliers that I have used and products that I have used or have heard good things about, such as Gecko drives. Which in my case is both.

I also take into account peoples spending desires/budget when giving advice. I have learned the hard way, buy right, not twice, but the average newbie doesn't want to here it will be $300 more to get the good stuff. Especially when the other stuff he is looking at is said to be "just as good".

I will however put the vexta into my recomendation pile and if I need to buy more steppers, I will give them a try if the budget allows.

Thanks again.

Mike