Excel help, work out circumferance, over and over..

[peige]

Its been years since i've had to do a macro type formula but I need one now, in basic terms, I need to specify two diameters, upper and lower and then work out every circumference between them in 0.1 (this will be a variable) increments, basically giving me the total travel for a spinning part between the outside diameter and the inside diameter, ie all those circumferances added together.

Any pointers ? I'm currently reading up

 

[peige]

Thanks both of you

Ricky, your solution is elequent and simple, Diddyman, you've done it the long way that I had in mind but couldn't do

The aspect that I didn't mention is that I need to calculate the time to cover each circle, the machine maintains a certain surface speed, ie 40m/min. So each circle is effectively done at a different spindle speed. So i think i can take your way Diddyman and add a new line that works out the time to cover each distance at the surface speed that the spindle will be running at that diameter

ie 40m/min will be Circumferance /((40 x 1000) / (pi * D)) will give me the time to travel round a D diameter circle.

Add all those together and I think i've got something that will tell me how long it will take to face the front of a billet of metal off at a given surface speed, well more or less

Thanks !

 

[peige]

As each circle takes a different amount of time I don't think that can work.. in straight line terms the spindle accelerates as the tool point gets closer to the centre of the part.
So
100mm dia cut at 40 m/min means 127rpm and will take 0.404 seconds aprox
50mm dia cat at 40 m/min means 254rpm and will take 0.618 seconds aprox

Unless i'm missing something, which is quite possible given how simple your first solution was

 

[peige]

Oops

Well, you get what I mean !

/edit.. but thinking on you may be correct, if the machine does its job it will cover the whole distance whilst maintaining 40 meters a minute.. i'm going to think about that in a dark room for a bit !

 

[peige]

You may well be correct, i'm trying to get my head around it but if the machine does its job then the tip should be traveling over the job at 40 m/min so the time will be the total distance in meters /40 .. i'm going to think about this for a bit !

 

[peige]

Have a internet cookie, your spot on.. thanks so much for such a simple solution, a new quoting tool for me is born !

Anything that makes quoting easier is great, I hate quoting !

cheers