ebay indexer/4th axis

[donek]

I am considering purchasing one of these:

http://www.ebay.com/itm/4axis-Rotary-Axis-For-Cnc-Drilling-Millin-g-Engraving-Machine-Cnc-Router-/280863982083?pt=LH_DefaultDomain_0&hash=item4164cc4203

http://www.ebay.com/itm/CNC-Machine-Accessory-F-Style-A-Axis-4th-Axis-Rotary-Axis-with-80mm-3-Jaw-Scro-/261111159467?pt=BI_Tool_Work_Holding&hash=item3ccb701aab

http://www.ebay.com/itm/cnc-router-4axis-rotary-axis-4th-axis-A-axis-for-the-engraving-machine-/221167774248?pt=LH_DefaultDomain_0&hash=item337ea06a28

to use on my PRS Standard. I am told I will need a RBK controller to run it. My primary purpose at this point is the ability to easily machine on multiple surfaces of quite small parts.

Does anyone have any experience with one of these? Can you provide any insight into their function, quality of build, accuracy? Will I have any significant difficulties getting any of them to function with the shopbot?

[Brady Watson]

The RBK driver is the most elegant in terms of ease of installation. If you just want to use it as a part flipper, it should be fine...but automated part flipping via an indexer leaves a lot to be desired & this depends on the shape of the part itself + material density. Workholding is tricky, and minimizing vibration that is not present when the part is fully supported or up against a spoilboard will be a challenge. It's not impossible, and is part/shape dependent, so think about this a little before you take the plunge.

Aside from this, I don't know much about these units, but there isn't a whole lot to them. The one thing that stands out in all of the units you listed is the very small drive pulley, in order to get some gear reduction. There aren't many teeth engaged on the small pulley and this will affect holding capacity, and may even cause some cogging.

If you do get one, report back so others can get in on it if it is deemed worth it...

-B

[donek]

Thanks for the input Brady. I have looked a bit closer. I think these are the two I am now considering:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250977194397&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250994978988&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en