4th Axis from china

[tangocharlie123]

Has anybody had a look at these

http://www.ebay.com/itm/CNC-Router-Rotational-Axis-4th-Axis-axis-engraving-machine-/260878973637?pt=LH_DefaultDomain_0&hash=item3cbd993ac5

if so can you give feedback Please

Pete

[tumutbound]

Pete,
Take a look at this one (http://www.carving-cnc.com/rotation-axis.html), very much the same but much cheaper.

I'm looking at getting one for the 6040 CNC router they sell. I have one of these routers but from a different seller.

Regards
Geoff

[bradm]

Those seem a little small for the MM; if you're planning on working on small pieces with small bits, it could work, but I would look carefully at whether or not that ungeared nema-25 is strong enough to hold your work in place under cutting forces.

[smreish]

A general "rule of thumb" for any motivated device in a rotary or winch fashion that the motor can be back fed from the part requires either a load brake or a 40:1 gear reduction via a double reduction worm gearbox. Now, this is a really vague rule, but when resisting loads, it nice to know the power transmission can stay put while being used. I'm not an engineer - but my automation mentor beat this rule in my head for years when winching people off the deck. 40:1 double reduction worm is considered "self locking" and doesn't back feed.

So, for instance on my rotary axis that was moving a 4' x 4' x 8' block of foam, I used a 80:1 double reduction gearbox fed with a Nema 34, 4.5A stepper motor. I think it was the PK299-4.5 with exceptional results.

[tangocharlie123]

Thanks for the replies and for your input.

Regards Pete

[smreish]

Pete,
You can also see a very recent 4th axis done by Jimmy.
His is moving a fairly small part area (and load) with a 4:1 reduction. I might have been short sighted in not clearly showing the large circumference and load that I was utilizing.

Sorry if I misled you with partial information.