Rotary Table or Rotary Table and Dividing plates?

[7HC]

Before converting my little Sieg X1 to CNC (maybe), I'm going to get a small 4" rotary table to be able to do circles and parts thereof.
My question is, assuming no production runs or many multiples of the same part, is the addition of a dividing plate setup necessary for equally spacing an arc or circle of points on a part, or can it be accurately done by cranking the table the requisite number of degrees, locking it, performing the necessary machining operation, then repeating the process?

Thanks,

M

 

[atwatterkent]

IMHO, owning a rotary table without a dividing plate attachment and tail stock for that matter is like having a race car that only goes 30 mph. It will do what it was basically designed to do but not all it's capable of doing. You may have no plans to do anything more than simple projects but you never know what will come up down the road. Will you still be able to buy the dividing plate accessory to fit your table in3 or 4 years?

 

[xalky]

Get the indexing. Why go half way.

 

[7HC]

Ok, please bear with me here as you can tell I only know enough to be dangerous.

Would equipping the table with a stepper motor and using a CNC program to control it negate the need for dividing plates?
It's partly a question of cost, 4" table $58......4" table with dividing plates $161, and as I'm possibly looking at CNC in the future I'd rather spend the difference between the two on automating it than on a set of plates.

At the moment my intention is to learn process and technique, then to progress to bigger and better things later on.

Thanks,

M

 

[Sandro]

Ok, please bear with me here as you can tell I only know enough to be dangerous.

Would equipping the table with a stepper motor and using a CNC program to control it negate the need for dividing plates?
It's partly a question of cost, 4" table $58......4" table with dividing plates $161, and as I'm possibly looking at CNC in the future I'd rather spend the difference between the two on automating it than on a set of plates.

At the moment my intention is to learn process and technique, then to progress to bigger and better things later on.

Thanks,

M

Usually CNC is easier than manual. Though one drawback to index plates is the number of divisions available, sometimes the number of divisions you need to cut will not divide into what your dividing equipment will handle. CNC would allow you to do any number of divisions you want not matter how odd the number is. It just depends on how comfortable you are using CNC software as opposed to turning a crank by hand. If you are new to machining and CNC you may have a long learning curve ahead of you. Keep in mind you can start with index plates now and sell them in the future if you do decide to go with CNC.

Hope this helps.

Sandro Di Filippo

 

[Charley Davidson]

I've been thinking about this for a little while. When I ordered my steppers & controllers for my CNC plasma I ordered enough for a 4th axis. Does anybody make a stand alone pogram just for a fourth axis?

 

[8ntsane]

Rotary table without plates would be fine with a DivisionMaster setup, otherwise you could use the program that Marv Klotz has on the net for free, that will get you setup for any number of divisions as well, but more chance for error if your not carefull.

If your useage is minimal, then going to the stepper motor will add a fair bit to the cost. The Division Master unit may be worth looking at. If Im not mistaken, the folks that sell the ELS, Electronic Lead Screw, by Automation Artisans also have been using their kit to power rotary tables.

Other wise, with rotary tables, go the biggest you can handle, you will run out of room for work holding really fast with the small R/T,s. Though a large diameter sub plate could be installed to make it larger.

Rotary tables should be purchased with the dividing plates, and the tailstock will also be a must have item as well. I wouldnt count on some brands of R/T,s to be around , and have plates available down the road, I would get them with the table. The tail stock could be purchased later from many sources, so that could wait.

 

[Tony Wells]

There is a key difference in a stepper motor driven indexer and a true 4th axis. A stepper motor will provide precise index movements in absolute or incremental divisions, true, and seems ideal for stepping off gear spaces or other features with fixed locations. Of course, it is repeatable so that features can be complex, requiring multiple tools such as center/spotting drills, drills and reamers, end mills, and the list goes on. It's not limited to gear cutting by any means.

However, a true 4th axis typically is linked with encoders on the other axes, so that movements are coordinated with the other axes. For example, if you wanted to machine a helix on the OD of a cylinder, you would need to establish a start and stop point in both the -B- axis and the -X- axis that are synchronized, and establish a feedrate that takes both movements into consideration. If the cut must be taken in multiple passes, this B0,X0 must be established and repeatable. Since the stepper motor is not really designed to control feedrate from a CNC control, as an indexer is is not useful as a true 4th axis. And typically, the code to move the -X- axis and the indexer are not synchronized like they are in a true 4th axis command. I have made this work though, in a pinch, but it had to be done in one pass, and the results required a bit of experimentation to get the movements coordinated. I had to guess the lag in executing the code for both the stepper motor and the servo on the table.

 

[7HC]

There is a key difference in a stepper motor driven indexer and a true 4th axis. A stepper motor will provide precise index movements in absolute or incremental divisions, true, and seems ideal for stepping off gear spaces or other features with fixed locations. Of course, it is repeatable so that features can be complex, requiring multiple tools such as center/spotting drills, drills and reamers, end mills, and the list goes on. It's not limited to gear cutting by any means.

However, a true 4th axis typically is linked with encoders on the other axes, so that movements are coordinated with the other axes. For example, if you wanted to machine a helix on the OD of a cylinder, you would need to establish a start and stop point in both the -B- axis and the -X- axis that are synchronized, and establish a feedrate that takes both movements into consideration. If the cut must be taken in multiple passes, this B0,X0 must be established and repeatable. Since the stepper motor is not really designed to control feedrate from a CNC control, as an indexer is is not useful as a true 4th axis. And typically, the code to move the -X- axis and the indexer are not synchronized like they are in a true 4th axis command. I have made this work though, in a pinch, but it had to be done in one pass, and the results required a bit of experimentation to get the movements coordinated. I had to guess the lag in executing the code for both the stepper motor and the servo on the table.

Yesssss..........that's way in advance of my present level of understanding at the moment.

Your first paragraph was exactly along the lines I was thinking, but your second seemed to squash that idea.
Here's a silly question. Doesn't the software instruct the stepper motor to execute a certain number of revolutions then stop, then do it again, etc., etc.
For example, say I wanted to use the table to mark a disc in degrees, wouldn't a stand alone automated table work well for that.

At this point I'm just thinking about a stand alone rotary table with a motor, driver, power supply, and some software; not a complete XYZ as well.
I'm also thinking that if I'm milling something circular, a stepper motor would be able to provide a much steadier and more controlled feed than I could mamage by hand.

Finally, if it's practical to automate a stand alone rotary table successfully, I'd find it a great learning step in understanding both the mechanical, electrical, and the programming aspects of setting up a CNC system at a reasonable price.

Thanks,

M

 

[Tony Wells]

A stepper driven indexer is available as a stand alone system. I have run one on a small Webb CNC 3 axis knee mill. It had two basic modes of operation. You could set up the tool with all the parameters for the operation for that tool, execute an index move and the indexer would stop. Then the CNC control would go through all the code for that feature, whether it had one tool or ten. Once the program was finished for that particular feature, and homed out, you I would hit the "index" cycle start button on the separate control for the indexer, which would move to the next position. Cycle start the main control and repeat all tool operations on the next identical feature. Repeat as necessary. The control for the indexer was separate from the CNC controller for the mill. It was more of an accessory. It worked very well, within its limits.

As I recall, there was the facility to link the two so that the end of cycle on the main control could trigger an index move, so the entire part could be done without operator intervention. It's just that you could not program a feedrate into the indexer. It was wide open speed or nothing. and like I said, no way to connect the to to coordinate the start/stop between the indexer and the other axes.

Remember though, that was a while ago, and only one make of indexer, but that's how they are all designed to work, as far as I know. I have seen people set up repetitive hole drilling jobs even on manual machines like Bridgeport mills with a microswitch at the top of the quill so that after each hole was drilled, manually, the indexer would move to the next hole location. I think basically, the understanding is that they are intended to move to a new position rather than cut along the way to the next programmed position.