Interesting 4th Axis

[BanduraMaker]

I'm in the market for a 4th axis and in my search, I came across this one:

eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices

I imagine it's probably a knock-off harmonic drive but maybe that's not such a big deal for a medium duty basement shop machine.

I'm wondering if anyone's tried it or anything. If it's of decent quality, $380 would be a fantastic price!

[cyclestart]

It looks as if mini-lathe pieces like a 4-jaw chuck would bolt right on.
The thru-hole probably only extends about 3" but that's only another guess, the listing is a bit short on details.
Great price for sure.

[JerryBurks]

Looks very interesting. If I had not already bought a rotary table from Sherline, I would probably give that one a try since it is a turnkey solution and rather less expensive.

I would prefer a good wood turning chuck like the Oneway Talon because it holds on to lumber better but that could probably be mounted as well.

[BanduraMaker]

I was planning on going the Sherline route as well but heard some rumors that the quality was down a bit and that backlash could be significant on the workpieces of the size I'm planning.

I started investigating DIY harmonic drive setups when I stumbled across this. The vendor told me via email that he's willing to remove the chuck and even the stepper to drop price and shipping cost. I need a four jaw since I'll be unsung 4" x 3" stock but I might buy with the 3 jaw just to have if I actually go for it.

[JerryBurks]

I noticed some backlash on the Sherline rotary (have not measured it) but I think that is as good as it gets with a worm drive. Since it is reduced by 1:72 it should not be substantial (I hope).

But now I got the itch of using the Sherline for something else and buy the gadget that you found. Can you please explain this to my wife?

JB

[harryn]

Jerry, just tell her that you want to make something for her and it won't come out right using the one you have.

All I can say, is that I hope your sherline stuff is more rigid than an old lathe that I was given. The main benefit of it has been the training - I can readily see every deflection with my eyes so that I won't be fooled (as easily ) by other tools.

[BanduraMaker]

Jerry,

I'll tell her why you need it next time I talk to her

As to the backlash, from the Sherline site, backlash should not be adjusted to better than 0.1 degrees to protect the worm gear from excessive wear. At 2" out, .1 degrees works out to be .0035" so, with 4 inch wide stock, that would be .007" difference from one side to the other.

I've never used a 4th axis so I don't know how this works practically but, apparently the worry is that the backlash will cause the part to move depending on whether you're plunging, climb cutting, conventional cutting and whether or not you're using upcut or downcut bits etc. Because I'll be using this 4th primarily for indexing, a swing of .007" across the part would not be acceptable to what I'm doing.

I'm currently using a 4 sided vacuum fixture to machine some parts and I'm probably getting a max error of about .004" and for my purposes, that's not good enough (which is one of the reasons I'm looking at a 4th axis).

I know full well that over time wood can't hold a tolerance better than .004 but, for the process of machining, .004 is significant enough to cause major ridges, non flat surfaces etc.

Harmonic drive isn't perfectly accurate when it comes to positioning but, that can be compensated for in Mach. It is zero backlash which could be a very big deal in terms of surface finish and squareness between sides.

Thoughts?

[JerryBurks]

Thanks...appreciate your help But it is not that bad. It is bonus time anyway and I guess I have some money socked away to spend on such indulgences.

Actually, since I am a kind of impulse buyer, I ordered it already.

If you have the time to wait until it arrives and (more problematic) until I have it hooked up I can tell you if it is any good. On the to-do list before I get to that is:
- finish my dust boot
- make some hand wheels for the stepper axis sticking out
- Improved dust cyclone
- upgrade the control box with higher voltage stepper supply and 4th axis drive

Since I have it now anyway, I may make the Sherline a 5th axis sometimes (many moons from now). No real idea what I would use it for but a perfect toy for me. I have the DeskProto software that will support 4-axis and limited 5-axis CAM.

Anyway, thanks for the tip!!!

[HorridHenry]

You vould always buy these items.....
LittleMachineShop.com - Spindle, Mini Lathe 7x14
LittleMachineShop.com - Headstock Casting, 7x14
LittleMachineShop.com - Lathe Chuck, 3-Jaw 3"
Some bearings and a stepper and you're away.

[BanduraMaker]

Wow Jerry, you move fast! I don't really need my 4th axis until late this year so I'll definitely be waiting to hear your review of the product. My fingers are crossed!

Henry, something like you proposed is my plan "B"

[HorridHenry]

Henry, something like you proposed is my plan "B"

Ok,maybe this might be plan "C"

http://www.youtube.com/watch?v=DwB2FmsjByM&list=PLEF16F2DE81B7BCD2&index=10&feature=plpp_video]RoboCNC X1 Router 10 : Making a 4th Axis / Indexer / Rotary Axis / A-Axis - YouTube

[JerryBurks]

Wow Jerry, you move fast! I don't really need my 4th axis until late this year so I'll definitely be waiting to hear your review of the product....

I know, I am a horribly impatient person with little restraint when I find interesting stuff. And a pack rat too, which is why my garage is so cluttered and I am not allowed to go to a surplus store.

Give me a month or two and I think I will have it set up. I will post the results here.