Making a 4th axis?

[lilricky2]

Has anyone converted a 4 or 6 inch rotary table into a 4th axis? Just wondering which rotary table and how you synchronized it to your software. I have Bobcad V21 and an early version of Mach2. My mill runs with 1/4 HP servo's. Will I need something that stout or does it matter? Any pointers would be appreciated.

Rick

[replicapro]

I just finished my 4th axis today.
I used http://www.littlemachineshop.com/pro...ProductID=1810

and made a plate that sticks out the side

[lilricky2]

Sweet! I never thought about that approach. What kind of software are you running?

[replicapro]

I have mach 3.

The servo is a 420 oz with a 3 to 1 pully ratio.

The plate is connected to the exsisting 2 holes that were factory stock on the rotary table.
I cut the plate with the holes and the servo mount slots then just bolted it on. The servo is sitting a bit shallow and the belt is riding on the edge, but I will put a 1/4 " spacer on the plate to bring the servo closer so the belt rides more in the center.

The hardest part is keeping the backlash down on the table. This table was the cheapest, so that accounts for some of it. However mach 3 has backlash compensation so it is not a problem.

[philbur]

Trouble is the backlash is not uniform over the whole 360 degree.

If you use a belt drive you have to consider the load/wear issue if the worm spindle has only plain bearings. Direct drive is better from this point of view. I fitted my 8" table with a direct drive 640 oz-in stepper, it works find. The only thing you need to do with the software is tell Mach 2 the number of units per step (Or is it steps per unit?) and whether it’s linear or annular interpolation.

Regards
Phil

Originally Posted by replicapro The hardest part is keeping the backlash down on the table. This table was the cheapest, so that accounts for some of it. However mach 3 has backlash compensation so it is not a problem.

[philbur]

Yes but not so sweet if you also want to use it with the axis vertically.

I don't think software is an issue for the table design. The 4th axis only sees pulses from MACH2 or whatever control software you use. If your software produces gcode for a forth axis then you're in buisiness if it doesn't then you are writing/editing by hand or transposing axis (not sure if that's the correct terminology) in MACH.

Regards
Phil

Originally Posted by lilricky2 Sweet! I never thought about that approach. What kind of software are you running?

[philbur]

The tricky bit for me is correctly installing the 4-axis driver without any expensive smoke.

Also you have to look carefully at how to mount the drive motor to the table. On many rotary tables the method of adjusting the backlash (excentric worm shaft housing) makes this a bit tricky.

you should search the archive, all these topics have been previously discussed extensively.

Regards
Phil

Originally Posted by lilricky2 Has anyone converted a 4 or 6 inch rotary table into a 4th axis? Just wondering which rotary table and how you synchronized it to your software. I have Bobcad V21 and an early version of Mach2. My mill runs with 1/4 HP servo's. Will I need something that stout or does it matter? Any pointers would be appreciated. Rick

[lilricky2]

Good points. I'm still learning so some of your terminology is Greek to me. (annular, interpolation) I do want to use it vertically and horizontally. Don't I need to use a servo if my other drives are servo's? I am hoping someone has a drawing for an adapter to connect a specific servo motor to a specific table. I can cut or purchase hubs and coupling elements. I'm just curious as to what motor adapts well to what table and how the software integrates. I did do a search, but most of what comes up are posts about what A axis someone purchased for there Taig or X3. I don't really think of those as conversions, more like add ons. I'll dig a little deeper in the search function. I'm not all that worried about backlash. After 20 + years as an industrial mechanic/manual machinist, I can remove mechanical backlash from a gear box. It's the cnc stuff that confounds me the most.

Rick

[henryblowery]

You can buy a kit from this guy.....

http://www.jfettigmachines.com/

Gray