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Author Topic: Setting up a 4th axis?  (Read 11511 times)

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Offline budman68

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Setting up a 4th axis?
« on: July 05, 2008, 02:09:59 PM »
Now bear with me since I'm not a very knowledgable person in this area-  :P

Ok, so I'm interested in setting up a 4th axis (horizontal) on my Taig Mill and I have my stepper and wiring all figured out, BUT, the machanical part of it eludes me a bit. Do I need a gear reducer of somekind? How come you can't just connect a 3 jaw chuck or a drill chuck to the motor shaft itself? Is the resolution too high and you need to lower it by reducing it in some way? I've seen many things used from a small rotary table to a small gearbox/reducer. How do I know what's right for me?

The range of diameters that I would use is probably between 1/4" to 2".

Please help me set this up if you can?
 
As always, thank you for your invaluable time!  ;)

Dave
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Offline Hood

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Re: Setting up a 4th axis?
« Reply #1 on: July 05, 2008, 02:14:10 PM »
You could just hook up a chuck to the motor but you would need a big motor as the cutting forces would be quite high. Gearboxes or rotary tables are used because the reduction increases the torque of the motor.
Hood

Offline budman68

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Re: Setting up a 4th axis?
« Reply #2 on: July 05, 2008, 02:37:56 PM »
Oh, I see, that makes sense, so do you have an idea of what I should be searching for? It seems the idea of a worm gear setup is best for keeping a handle on backplash, but I would have no idea what "ratio" worm and pinion gear to look for. Any ideas?

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Offline Hood

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Re: Setting up a 4th axis?
« Reply #3 on: July 05, 2008, 02:55:16 PM »
Not really, depends on what size motor, what type of motor etc. Have a look at some of the places that sell the 4th axis for the smaller machines and see what they are using, think Sherline and the likes do them.

Hood

Offline budman68

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Re: Setting up a 4th axis?
« Reply #4 on: July 05, 2008, 03:01:30 PM »
Will do, thank you-

Dave
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Offline Hood

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Re: Setting up a 4th axis?
« Reply #5 on: July 05, 2008, 03:16:29 PM »
Just had a look myself and from the sherline pdf it says it uses a 100 ozin stepper with 0.9 degree steps and a 72:1 reduction on their 4 inch rotary axis.
Hood
Re: Setting up a 4th axis?
« Reply #6 on: July 05, 2008, 03:30:05 PM »
http://www.machsupport.com/forum/index.php/topic,6158.0.html
Budman, Here is a neat topic. Gearbox to Axis conv....In case you haven't seen it.
RC

Offline docltf

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Re: Setting up a 4th axis?
« Reply #7 on: July 05, 2008, 03:43:22 PM »
DAVE

most 4th axis are done in degrees.so keep this in mind when you calculate your resolution.the rotory is done with (deg-min-seconds).with the dia you want to use,i would suggest the minimun steps per degree should be 16 full steps.
so figure your gearing with 16 full steps as your base number.then when you go microstep it gets smoother.

bill

Offline budman68

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Re: Setting up a 4th axis?
« Reply #8 on: July 05, 2008, 03:58:48 PM »
Thanks very much fells, been soaking up the info this afternoon and will take all your considerations, for sure. Thanks for the link, RC!

Doc, so a 30:1 gearbox would be fine then? Reason I ask is I may have found a reasonable nice small sized one.
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Offline Chip

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Re: Setting up a 4th axis?
« Reply #9 on: July 05, 2008, 04:05:39 PM »
Hi, Dave

Torque, Accuracy, Speed, Trade Offs.

If you use a 200 step stepper direct, It's 1.8 deg. per step Accuracy, If it's 10 Micro-step, It's 0.18 deg. per step Accuracy.

Depending on the material your cutting, Holding or Moving Torque could be an Issue.

Most rotary tables are 72 to 1, (72 turns to 1 table turn), Have a Sherline Hear.

Steps-Turns-Accuracy & Reduction Values to consider.

Steps 200 X 72 = 14400 steps, 0.025 deg Accuracy. (Sherline/Rot. Table Type)

Steps 200 X 7.2 (10\72 reduction) = 1440 steps, 0.25 deg Accuracy. (Belt/Geared/Stepper)

Steps 200 X 3.6 (20\72 reduction) = 720 steps, 0.5 deg Accuracy. (Belt/Geared/Stepper)

Micro-Steps 2000 X 72 = 144,000 steps, 0.0025 deg Accuracy. (Sherline/Rot. Table Type)

Micro-Steps 2000 X 7.2 (10\72 reduction) = 14,400 steps, 0.025 deg Accuracy. (Belt/Geared/Stepper)

Micro-Steps 2000 X 3.6 (20\72 reduction) = 14,400 steps, 0.05 deg Accuracy. (Belt/Geared/Stepper)

Hope this Helps, Chip
« Last Edit: July 05, 2008, 05:40:27 PM by Chip »