Is a 31 inch diameter Indexer possible?

[cabnet636]

the better the machining the less work one has to do on cleaning up the product, we used 4" grinders with sanding disk (60 grit) and dremal type tools for cleaning up the details, always presand mdf it has a slicker finish than most would think!! i made a lot of mistakes and with a three inch material depth bits are 4" so i broke some of those too, learning to clear enough area for the collet is another challenge

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[cabnet636]

a bit more info


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[Mayo]

Awesome photos James - and awesome work on a complex project! In seeing what is really involved, I may decide to pass on the job and just refer it to you.

Rather than try and reconfigure my table, I had planned on making a dedicated machine just to do the large diameters.

Speaking of loosing steps or resolution, is that due to backlash or something else? This place makes drives with no backlash...
http://www.doughtydrive.com
and check out this machine...
http://www.doughtydrive.com/machine%20demo1.html

[khalid]

Jack.. suppose you have two concentric circles then you know the elementary mathematics..
S =R x Theta

As the Radius grown for the same angle theta, you will get bigger and bigger S...

Now think in this way, suppose you have kept the steps with increment of THETA for indexing...Where THETA will be your fixed angle for each increment...Now see the figure for smaller circle suppose you are using 3mm ball nose and it almost fit on the S of smaller circle.. Now if you use the same resolution (THETA) for bigger circle, then just imagine what will happen...

The "S" changes with Radius "R" whereas the "THETA" is fixed and to be considered in radians...

NOTE:
This Theta will depends upon the steps on the controller circuit i.e. 1/2,1/4/,1/8,1/16 etc, steps of the motor and gearing ratio... This can only be change on controller circuit only... For larger diameter you will change the controller setting to high steps mode...but this will takes more time on the work piece machining with smoother finish..

For a Flat piece you can compare it with stepover value... the greater the stepover the less resolution the smaller the stepover the greater resolution ;)

Sorry for the bad picture..hope it clears the concept...
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[myxpykalix]

Khalid...I know your not here in USA but you need to speak english here! lol You could have been talking serbian and i wouldn't have understood it any better. I appreciate the effort but i barely got thru "readin, ritin, rithmetic" in highschool so that was way over my head! I appreciate the effort though buddy.

I didn't realize till now that james chess pieces were hollow. I would take this project on if i were you mayo.

[Mayo]

Khalid...
I'm not following the math of your explanation (I didn't do well in math in school) but I kind of understand the drawing. However if the design and cutting file takes into account that it is wrapped onto a 30 inch diameter why does the steps matter?
Are you saying that different diameters of work will require changing the number of steps from one job to the next? I would hope if this is true, that the toolpath software would automatically make these changes or compensate for it.

Admittedly, I have little understanding of the whole indexer machining process.

[rb99]

I think he is saying the resolution degrades considerably as you get larger.

RIB

[khalid]

Yes, Richard pointed very well...Mayo, You are also right that the software takes care all these things in the toolpath..but again it all depends on the Hardware too..Fortunatly current days hardware are marvellous and state-of-the-art...microstepping is available in the controller card, the Stepper and Servos are also available in High resolution...

Now , just want to put more thrill in the discussion..consider a stepper motor with 1.8 degree steps, and your controller card can't microstep....Now your CAM program don't know about your hardware resolotuion, however CAM software gives you the toolpath of maximum, optimum, and best resolution..Now here the Hardware Fails... What you will get if your motor can move only 1.8 degree/step and the toolpath command your motor to move 0.8 degree/step????..

The same is true for S=R x Theta, Where S=Arc Length.. As the radius grows the ARC Length will increase for the same Angle...

0.01 degree upto 1meter radius will give you the ARC Length value very small (S= 0.01 x (2xPi/360) x 1) , whereas as the diameter increases , lets say 100 meters, the same Arc length for the same Angle you will Get (S= 0.01 x (2xpi/360) x 100)

The higher the radius the poorer the resolution in Indexer case...

[khalid]

Sorry Guys, currently involving in Turbomachinery vibrations issues...
http://maintenanceforums.com/eve/for...2093#964102093

So my minds goes in mathematical way...

[joecnc2006]

Did you see Arts?

http://www.turningaround.org/