Re: EMC Bug???

[Jon Elson <elson-at-pico-systems.com>]

Richard wrote:

> Hello Jon,
>
> Sunday, September 1, 2002, 1:05:39 AM, you wrote:
>
> JE> 20.0 In/Sec^2 acceleration.  So, I set my acceleration to 20.0, and the
> JE> velocity fluctuation was reduced to a minute blip.  But, of course, real
> JE> milling machines can't accelerate at 20 in/sec^2.
>
> Interesting you should say that as I was going to go higher
> than that. That rate is going to take very little torque, so
> what is your reasoning?
>
> What accelaration would be normal for a small CNC mill?

I'm using 2 Inch/Sec^2, some other people are using 5 Inch/Sec^2.
Think about the acceleration.  At 20 I/S^2, at the end of the first
second, you'd be doing 20 IPS, or 1200 IPM.  At the end of the 2nd
second, you'd be moving at 40 IPS, or 2400 IPM.  These are pretty high
feedrates, on the order achieved by the very latest $100,000 machining
centers.  How much motor power does it take to accelerate a machine
table to 1200 IPM in one second?  Does this apply to a Sherline, with
a 1 Lb table, or a Series-II Bridgeport, with a 500 Lb table?  Obviously,
it makes a difference.

Anyway, I left the acceleration at 20 I/S^2 on my servo-controlled Bridgeport
Series-I machine, until I broke a drive belt after only a week or two of use.
I figured out that the accleration must be exceeding the capacity of the
belt.  I moved it down to 2.0, and it doesn't seem to cause a significant
slowdown,
or sluggish feeling on the machine.

By the way, I don't have any desire to go over 100 IPM on my machine.

Jon