Stepper sizing and running as "follower"

[flash319]

So I have my gantry mostly done. I was going to use belts to move the gantry but I am leaning towards rack and pinion (cost). I want to run 2 steppers one at each side of the gantry. The router is 4X8. The gantry weighs about 60lbs and will be running on round linear bearings. Can someone advise on what would be the best setup?

I was thinking bigger is better 2 NEMA 34's with no reduction. Or go with smaller motors with 2:1 reduction belts. I would like to have at least .010 on that axis. Will microstepping get me that resolution? Or is micrstepping not really an option for something so heavy? I am a servo guy and don't know much about steppers. My other axis are running on servos but don't have the money for more.

[ger21]

60lbs is unbelievably light for the gantry of a 4x8 machine. But, if that's all it weighs, then you don't need very big motors. Around 300 oz, and gear them so that 2-3 turns of the motor gives you 1" of travel. That should give you around .002 resolution and pretty good speed as well. What drives do you plan on using?

[Crevice Reamer]

Hi Flash! Bigger is not better if you want decent rapid speeds.

This is what I recommend:

$299 G540 http://geckodrive.com/product.aspx?c=3&i=14469
$078 Two $39 KL23H276-28-4B 270 oz motors for X axis.
$039 One $39 KL23H276-28-4B 270 oz motor for Y axis.
$049 One KL23H284-35-4B 387 oz motor for Z
$129 One KL-5010 50V 10A power supply.
$010 Estop switch
$017 7 Home/limir switches
$009 Straight thru parallel computer cable.
-----
$620 Total electronics cost.

$149 Mach3 cost with above purchase.

$769 To spend at Keling. http://kelinginc.net/

CR.

[flash319]

6lb0 was a bit of a guess. I have a 50lb weight and i lifted it and then lifted my gantry and it weighs a bit more. Maybe more like 80lb. Here is a picture. I started a build thread but was not getting any replies.


Here it is with me holding the Y motor. I do not have a spindle motor yet so i guess that will add about 15 lbs or so. Lets say 100lbs total gantry.


I am running EMC2.

One turn on the rack will be 3.14 so that is only .015. Will microstepping bring that down or should I do the 2:1 thing?

[Crevice Reamer]

The G540 is a 10 microstep drive, so your resolution will be approximately .0015. 2:1 timing belt gearing might be better for cutting force though, and you should still have plenty of speed.

So running Linux adds 20 LBs to gantry weight? Oh! I see you are adding spindle motor weight.

CR.

[flash319]

So running Linux adds 20 LBs to gantry weight? Oh! I see you are adding spindle motor weight.

CR.[/QUOTE]


hehe. Ya I saw that right after I posted. I went and changed it.

[Crevice Reamer]

Oh! Oh! It looks like you already HAVE some huge motors. It may be too late to use G540 then. G540 is limited to only 50V and 3.5A per motor. What size are the other motors?

CR.

[flash319]

The z axis is a 500watt servo and the Y is a 750 watt servo. I have a 2.1 KW servo but the drive is NG. I was going to use it with the belts on the table (25mm wide 8 foot loop) but a drive is going to cost me at least $300+ of Ebay. Plus I would still have to buy Pullies and stuff for a jack-shaft type setup. I figure a rack and pinion on each side will suit me just fine and be much cheaper.

[flash319]

What about two of these 5A drives KL-6050 and 2 640 oz/in Nema 34's?