Wanting to Build a 4th Axis / Rotary

Group,

I am wanting to build a fourth axis for my machine ( an upgraded 1985 SuperMax YCM-30 ).
This seems to be on of the most knowledgeable groups - so I figured I'd pick your brains first before I start out on this journey.

I'm thinking of buying a 6" or a 9" rotary table from Enco.. something with a 90:1 ratio.

Has anyone here done this?
Some questions:

What did they do about the backlash? How did they take it out ?
Did the further reduce the gear reduction?
What driver are they using to control it? (I'm thinking of using a stepper on it...and driving it with a Gecko drive... )

Any help is appreciated.

Thanks,

Joe

Quote:

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Originally Posted by CNC-Joe

Group,

I am wanting to build a fourth axis for my machine ( an upgraded 1985 SuperMax YCM-30 ).
This seems to be on of the most knowledgeable groups - so I figured I'd pick your brains first before I start out on this journey.

I'm thinking of buying a 6" or a 9" rotary table from Enco.. something with a 90:1 ratio.

Has anyone here done this?

Some questions:

What did they do about the backlash? How did they take it out ?

[I observed quite a bit of backlash - about 2 degrees. There wasn't any way to minimize it in the particular Asian rotary table I had, although I've heard that some allow this.]

Did the further reduce the gear reduction?

[No, there's already plenty of reduction - what you'll lack is speed, not torque.]

What driver are they using to control it? (I'm thinking of using a stepper on it...and driving it with a Gecko drive... )

[That should work fine, as long as you give it enough power.]

Any help is appreciated.

[It will probably work okay, as long as your cuts are really light and you don't change direction in the middle of a program - then the backlash will be quite evident. If you're just planning on using this for an indexer, and plan on locking it down between positions, it should be fine. But if you want to cut while the table is moving, you might look for something better.]

Thanks,

Joe

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Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

Thanks for the information.

I hope that others chime in.

I am wanting to use it for rotary machining. Therefore - the backlash should be reduced. I am wondering how others did this.

Thanks for your help.

Joe

if you go for a vertex they are really good and that is the unit that i converted.

the backlash is taken out by the cam action and careful setup.

i am using a g540 with mine and 300OZ motors which is overkill to be honest. they are self locking and don't really require any holding torque. mine was direct drive as the setup.

table video

You need to make sure you buy a rotary table that has backlash adjustment for both worm engagement and for worm shaft thrust. In addition you need to be able to preload the main table bearings. Then the remaining issue that is capable of causing backlash and that is difficult to correct is eccentricity of the table axis and the worm axis. The only practical solution to this is to buy a half decent table. I converted an 8" Vertex and have less than .0004" backlash at a 4" radius. I used a 640 oz.in stepper with direct drive. It's powerful enough to turn the table with the table locks on without losing steps.

Phil:)

Thank You Fragger and Philbur!

I really appreciate your input. I had no idea that there were rotary tables made that had backlash adjustment in them.. I can see that I'm going to have to make some phone calls.

I did notice that in one of the Digital Machinist magazines - there is an article about converting a rotary to a fourth axis...

I always attempt to gather (ok steal) as much information as I can before spending money on a new "paper weight" with a bunch of "I wished I would have known......"

Anyone that has built one - and can tell me what worked and what to avoid -it would be greatly appreciated. I would like to make one that does not have to be locked during machining - so that I can rotate constantly when needed (ok - you know that's the next question: What software supports the 4th axis/rotary? Aspire I believe does. I know with Cut3D, you make 4 different cut files - one for each "side" (Front, top, back, bottom) and machine. I think MeshCAM supports 4 axis too - but not sure (Ger will probably answer this one, as he's a Mesh CAM expert.... see I told you that I have a lot of questions......)

Fragger: I'm not sure what you mean about the cam statement. I guess your rotary table has a cam lock on it? For rotate-lock -machine type machining? Most rotary tables that I've seen have a sort of screw lock on them.. I like the idea of the cam lock).

Thank You to everybody for pitching in.

Joe

So - I've learned a good bit so far about rotary tables, and the size motors that everyone is using.. what about SoftWare ?

What Software are people using with their 4th axis / rotary?

Then download DeskProto - it will work for free for a month, so if your machine is together, you'll have ample time to try it out. It can handle large complex STL files, and generates a few types of 4-axis toolpaths very quickly. If you want to buy it, let me know - I can get you a good deal on it right now, especially if you're a hobbyist.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

when i was refering to a cam i was talking about the worm pinion gear is usually held in place with a CAM arrangement that allows the backlash / engagement to be adjusted.

as for locking, usually not required as rotary axis are stiff out of the box.

Programing a 4th axis can be as complex or as easy as you want it to make it. If you are basically using it as a indexer then 2 1/2D CAm will do it with you inserting the code when you rotate the part. however if you are looking for continuous moved then you will be talking some serious money if you don't want to just load a model and have a generic cutting strategy applied.

I just ordered a 6" phase 2 from enco with free shipping and 10% off (codes MCTEN + MCUPS only good till 5/20/11)

I wanted the 8" and was going to use the standard free shopping code, but for some unknown reason the 8" is coded for "freight truck" only even though it is 30lbs less than their posted ups maximum weight??? even tried calling and begging.

ended up getting the phase 2 6" for less than $230 on my door step (well-arrives monday) and with the savings I bought an 8" plain back independent 4 jaw chuck and way oil to fill the rotab with both with free shipping and 10% off.

I think the shipping for the 8" was going to be $89 IIRC

standard free shipping code is FSC + (3 digit month abbreviation) "FSCMAY" "FSCMAR" ETC

Thanks for the input Group!

I am leaning toward building my own now - mainly to get the backlash completely out. I know I would loose some resolution versus a 90:1 drive.... but.. at least I can getthe backlash out by using timing belts and pulleys.

Quote:

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Originally Posted by CNC-Joe

Thanks for the input Group!

I am leaning toward building my own now - mainly to get the backlash completely out. I know I would loose some resolution versus a 90:1 drive.... but.. at least I can getthe backlash out by using timing belts and pulleys.

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Have you seen my 4th axis page take a look for some ideas.
CNC Projects
cheers

i think you will be disappointed as there will be more flex and issues with a belt than you would get with a worm drive. it will have to be locked in position and very likely oscillate during cutting.

what are you planning to machine? i get 10-20 microns of backlash on a 4" rotary table. i have experience of machining part to sub micron accuracy on a rotary table that has 30 40 microns of backlash.

With rotary axis it can be more about program than the axis, if you only rotate the axis in one direction then you never have backlash. I would aslo suggest that you have more backlash in you linear axis than you would ever have in a rotary one.

Hey Bob,

No- I hadn't seen your work - but now I have -very nice work there!
That's exactly what I'm leaning toward.. a timing belt driven device.

Thanks again for sharing.

Joe

Hi Fragger,

Ok - now you're making me re-think the whole thing. Certainly with a rotary table - I will get resolution and mechanical advantage to hold the cutting forces (assuming I put a stout stepper on the input handle shaft....)

But I am still concerned that I can't dial the backlash out of a rotary table...

With a worm drive gear you probably can't remove it all. What fragger is saying is that unless you are precision machining wine barrels the backlash you can get to may be well within tolerance. Also you can design the cut to force the work in the direction that backlash is already taken up from. I see many folks seem to rate the stepper high enough to drive the table with the locks dragging which helps to add more resistance to the table shifting in it's backlash


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I have built a cnc rotary table and adjusted the backlash out.

The worm gear is mounted on a cam and the engagement can be adjusted. with my rotary table you can completely lock the drive by changing the engagement.

With a Worm drive you don't need to hav large steppers as you have mechanical advantage which you don't have with a timing belt.

What i was saying about backlash in a rotary axis is that you can program to move in only one direction and avoid the backlash. this would be like cutting a gear as you would never reverse the drive.

What are you trying to make?

A rotary with backlash is likely to cause chatter with a tool of any significant size
unless it's locked down.
Hoss

A rotary table is kind of a standard for the DIYer, you can get backlash down to a level where it has no appreciable effect. If you want to go the next step then you should look at Harmonic drives. They are backlash free so of course they are expensive, although they turn up on ebay for a good price.

Phil:)

The worm shaft also may include backlash adjustment of the thrust bearings. The 6" and 8" Vertex do. This is equally as important as the worm/gear engagement adjustment.

It is not always practical to CNC machine in one direction only, for example profiling or pocketing.

Phil:)

Quote:

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Originally Posted by fragger6662000

I have built a cnc rotary table and adjusted the backlash out.

The worm gear is mounted on a cam and the engagement can be adjusted. with my rotary table you can completely lock the drive by changing the engagement.

With a Worm drive you don't need to hav large steppers as you have mechanical advantage which you don't have with a timing belt.

What i was saying about backlash in a rotary axis is that you can program to move in only one direction and avoid the backlash. this would be like cutting a gear as you would never reverse the drive.

What are you trying to make?

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