rotary 4th axis attachment.

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rotary 4th axis attachment.

Postby wood400 » Mon Mar 14, 2016 8:10 pm

Hi folks. i am looking at the chinese 4th axis attachment on ebay. ha sanyone any experience of these . I was wondering would one of the 100mm models be capable of machining a cabriole leg of 70mm square and about 800mm long. EG 23/4 square and 30inches long.
Thanks for your help
Alan
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Re: rotary 4th axis attachment.

Postby IslaWW » Mon Mar 14, 2016 9:22 pm

wood....
a quick search on eBay returned hundreds of results. Yes there were a number that will be up to the task. There are a lot more questions to get answers for before I would buy one tho...
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Re: rotary 4th axis attachment.

Postby anthropod » Mon Mar 14, 2016 9:44 pm

I am very interested in adding a rotary as well.

I see some that say 1:6 Ratio's and ones that says 1:20 Ratios.

Two I am interested are:

http://www.ebay.com/itm/CNC-F-Style-A-A ... Swl8NVXF4S


http://www.ebay.com/itm/CNC-Router-tabl ... SwBLlVOmc4

I have a Geko 540 with one Axis open and I sue Mach3
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Re: rotary 4th axis attachment.

Postby IslaWW » Tue Mar 15, 2016 1:21 am

The reduction should be determined by your max blank diameter and what resolution you require. For example, 6:1 yields .002" step resolution (1/8 microstepping) on a 6" diameter blank. More than ample for rotary wrapped machining up to that diameter. That said, if you are planning on indexed machining, especially off axial center, then the 20:1 may be a better choice. The 20:1 will reduce max rapid speed to around 50-60 rpm, if that is a factor and you may not be able to position it by hand. Are there backlash specs for that 20:1 reduction?
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Re: rotary 4th axis attachment.

Postby anthropod » Tue Mar 15, 2016 3:20 am

I see no backlash specs for the 20:1. Most of what I would be working with should be 2".
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Re: rotary 4th axis attachment.

Postby anthropod » Tue Mar 15, 2016 3:57 pm

What about planetary gears heads? I found a deal on a 4th axis that uses a Thomson Xtrue 100:1 gearhead.

It says that it has a backlash of 13 arc-mins

It comes with a 160oz Nema 23 stepper.

http://www.thomsonlinear.com/website/co ... /xtrue.php
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Re: rotary 4th axis attachment.

Postby IslaWW » Tue Mar 15, 2016 4:33 pm

13 arc minutes is 13/60ths of a degree. This is .00378" backlash at 2" diameter. Unacceptable for may use, YMMV. 100:1 is so much reduction that you may never be able to turn the 4th axis at an acceptable rate.
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Re: rotary 4th axis attachment.

Postby anthropod » Tue Mar 15, 2016 9:16 pm

Im just having a hard time finding a 4th axis to buy to add to my system.

Right now I am looking at three setups:

http://www.ebay.com/itm/261858842965?var=560705631941

http://www.ebay.com/itm/CNC-4th-Axis-Ro ... SwwpdW5mbj

http://www.ebay.com/itm/CNC-Router-Rota ... SwofxUim8K

I'm leaning towards the 50:1 Harmonic Drive.

I will be using 2-3 inch stock and am looking for fine details. I like to make beer tap handles.

Any thoughts?
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Re: rotary 4th axis attachment.

Postby IslaWW » Tue Mar 15, 2016 10:27 pm

If you do go with the 50:1 reduction remember that you must have a controller capable of data output at your required turning speed. A 200 step per revolution (1.8*) will require 10,000 steps per second at 1 revolution per second (60 rpm) which is not fast. You may have to lower rapid expectations to avoid data choke to the 4th axis.
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Re: rotary 4th axis attachment.

Postby wood400 » Thu Mar 17, 2016 5:45 pm

Hi Folks, Thank you for the replies this gives me a help to better understand whats out there.
Thanks alan :D :D :D :D
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