[Zathras]

Well Keith, I sit corrected!

I took a look at the specs and it does say zero alright. Well, I suppose it's virtually unmeasurable.
The old Mectrol site says;
"Accuracy. All bearings are precision class 6 bearings. The cam follower bolt circles are held concentric to 0.0002". This gives positional accuracies down to seconds of arc."

Now that would be nice!

[Clementvs]

Hi all,

there is a way to have a zero backlash rotary table. You may use a patented worm gear.

This is made specifically for high precision rotary table, and well used in the mmk-matsumoto product.

The point is that zero backlash limit the rotation speed, therefore the system can be precisely adjusted to the minimum acceptable backlash.

In some cases you may need fast rotation (backlash) then precise positionning (zero backlash). Therefore the backlash might be adjusted dynamically.

another solution is to use a multiple start shafted worm set with zero backlash. You get a appreciable speed and don't need to adjust backlash dynamically.

here are links to more technical data of these technologies :

1) Worm gears zero backlash for rotary table :
http://www.allytech.eu/index_fichier...dwormwheel.htm

2) backlash adjusted dynamically (called OTT-MATIC):
http://www.allytech.eu/index_fichiers/OTTMATIC.htm

Hope this help anyone.

Clem

[Zathras]

Hi again,

For those who don't require full 360 deg rotation from a rotary table, I think the cable drive could work. I found this old link again by Don Clement used for a telescope drive.
http://www.clementfocuser.com/images...rive_Print.pdf

He reports very high torsional stiffness with this drive system.

Also check out "Roto-Lok" system, essentially the same thing, here;
http://www.sagebrushtech.com/prod-rotolok.php

Also here;
http://www.avltech.com/vehiclemountm...&back_id=21233

[Jay C]

Haven't seen the link to this video yet:
http://www.smcyclo.com/modules.php?name=Pages&sp_id=277
I was finally able to see the roller bearing and pins you guys were talking about.

[Zathras]

Just another device for "zero" backlash rotary motion I found looking around.

Check it out (with a video link);
http://www.cim.mcgill.ca/~rmsl/Index/Speed-o-Cam.htm

[Herbertkabi]

Just another device for "zero" backlash rotary motion I found looking around.

Check it out (with a video link);
http://www.cim.mcgill.ca/~rmsl/Index/Speed-o-Cam.htm

Its like one version of cyclo drive ... at least by my opinion ...
cheers,
herbert

[Zathras]

Its like one version of cyclo drive ... at least by my opinion ..

I really don't see it myself. These designs are rim driven by cams not orbiting gears.
Here is the paper for a more detailed look;
http://www.cim.mcgill.ca/~rmsl/Index...c98-990510.pdf

[petecul]

I made a drawing and realized that the worms would need to rotate in the same direction in this configuration :P

The dual servo version seems more and more appealing!

You could use a right and left threaded worn screw but in your desing, backalsh is transfered to the bevel gears!!

Keep going on design, i am also interested in a rotary axe.

thanks
petecul

[bgriggs]

Now i tested to machine the reducer Zoidberg draw for me and it works. :banana:

Very nice! Do you have any update pictures of the drive installed?

Bill

[aystarik]

here is my reducer again... now with thrust bearings
don't have access to CNC mill, so it will stay virtual unless someone picks it up... anyone?

[aystarik]

I've added simple tolerance check for hypocycloid plotter.

[Mike Everman]

I want to build a rotary table that can handle continuous milling!
Do you think my drawing would work?
The upper gear belt pulley can rotate freely on the axle, and is connected to the axle via the spring, and is preloaded.

Not sure I understand what coupling via the spring is doing, but generally this approach would need perfect coupling between worms, that is zero backlash in itself. otherwise it will bind up when changing direction, assuming you got it going first...

[morphious69]

has anyone considered using a high powered magnetic substance to mill a worm and worm gear out of? these magnets can be quite powerful and I would think possibly the answer for that. Before anyone dissmisses this I suggest you think about how a stepper motor works. it is entirely magnetic power that causes it to not only move but also hold it's position!

ofcourse it may be possible to make a rotary table that is essentially a stepper motor too! this would eliminate the need for having the motor hanging off to one side of the unit. since the motion would be handled buy the very mechanism of the rotary table it's self.

[morphious69]

has anyone considered using a high powered magnetic substance to mill a worm and worm gear out of? these magnets can be quite powerful and I would think possibly the answer for that. Before anyone dissmisses this I suggest you think about how a stepper motor works. it is entirely magnetic power that causes it to not only move but also hold it's position!

ofcourse it may be possible to make a rotary table that is essentially a stepper motor too! this would eliminate the need for having the motor hanging off to one side of the unit. since the motion would be handled buy the very mechanism of the rotary table it's self.

[aystarik]

it is possible to have belt driven rotary table with almost no backlash... The problem is it will not provide much torque for heavy milling and if you use a stepper, number of steps on rotary table may not be sufficient for fine engraving work.
The same applies for homemade stepper made rotary -- it won't be accurate for fine work and it wont be strong enough for heavy work.
There are several designs of axial permanent magnet motor generators (3 phase), used in wind power generators, with proper AC servo drive you could use it as servo rotary table... It should be accurate, not sure about strength...

[NEATman]

http://www.kollmorgen.com/website/co...s/c_series.php
There are motors out there that are designed to be used without gearing, such as the ones in the link above. The main problems are the cost (huge motor & drive needed) and the power consumed while in operation...

Keith

[Moriquendi]

Hi all.

I've been reading this thread for a while now as a lurker and I thought I'd join in the fun.

ZincBoy, I've downloaded the python script you wrote for generating hypocycloid cams, it's great. I wrote a spreadsheet for generating epitrochoids when I was building a Wankel engine in Inventor but using a script is much easier. I wonder whether you would mind briefly explaining the parameters that your script uses? I'm having difficulty modifying it to my specs because I don't understand some of the variables.

Specifically could you explain the relationship between Tooth Pitch (p) and Pin Bolt Circle Diameter (b)

Thanks

Moriquendi

[handlewanker]

Hi all, just read through the whole thread and I don't think the problem of a "backlash free rotary table" has yet been conquered in DIY terms, come to terms with, yes, but not eliminated.

Personally I was wowed by the ball screw type of worm drive mentioned some time back in this thread, but it was pointed out that it was not capable of supplying much force for driving a rotary table against the load of a cutter!!!!!....What are they saying....This design is similar to the forces that are present in the normal ball screw pushing against a load on any linear router/mill/lathe et al, and all it takes is sufficient ball size to worm wheel dimensions to carry the load.

The fact that ball screws need two nuts against each other to apply preload means that the same factors apply to a rotary table.

First the design is out of the realms of the home worker, due to the need for a worm wheel requiring hardened and ground teeth for the worm balls to impinge against.....accurately....otherwise you could just make a steel wormwheel to the ball profile form, and get it case hardened and polished, but dimensionally the accuracy of the pitch would vary around the rim of the worm wheel, (unless ground), the same as it would if a linear ball screw was machine cut, case hardened and polished as if you were screw cutting a normal screw thread.

The same would apply to the worm which has the ball thread form cut into it with recirculating path, but all hardened and ground.

The parameters of ball bearing technology apply here.

The design IS truly backlash free, same as the ball screw IS truly backlash free, but ball screws, either linear or rotary, are out of the realm of the DIY circle, which is a pity, because it's the only solution to a very real problem.

Even that very clever arrangement with the split worm of the OTT design that impinges on a bronze wormwheel is flawed, and eventually will be worn like the bronze nut and Acme thread of linear transmissions, even though they both can be adjusted to take up wear, clearance and so backlash is present.

The regular rotary table with bronze wormwheel and steel worm, is a non starter when it come to attempting to mill using the rotation of the table to apply the job to the cutter, not only due to the failiure to be able to not accept climb milling mode when reversed rotation, but in the lost motion when reversing.

Any form of steel worm/bronze wormwheel clearance reduction only leads to wear.

So, if the Chinese designers are taking notes, we might just see a cost effective rotary table with ball screw drive soon, (totally backlash free).
Ian.

[georgebarr]

Has anyone tried using the Camnetics product called GearTeq for creating accurate CAD models of the Cycloidal Speed Reducers? I plan to make a 200:1 version for a rotary table which will go into a 5th axes setup to cut metal projects.

I bought some harmonic drives, but someone says the tension springs (I think that is what they call it) may not be stiff enough to handle the heavy loads.

[RICHARD ZASTROW]

Ref post #218: Ian is correct, the ball driven rotary table is capable of backlash free milling.

The reason I know this is it was done back in the 1990's. We had a project to mill blades for LARGE gas turbine engines. The milling machine was a 5 axis Hermle and a Detlaff Hofmann (sic) ball driven rotary 4th axis.

This combination worked perfectly. No backlash and took heavy cuts, no problem.

Accuracy was spot on. Prior to this testing, we had never had blades 100% in tolerance. The results from this test; all blades in tolerance with one exception, a cutter pulled out of a collet to cut a groove in one blade.

The surface finish was within requirements. all we had to do was buff the blades to get the grain of the finish in the air flow direction.

Dick Z