Re: bills thoughts and comments.

Well, I guess it's time for me to delurk. This is my first post to
the list.

I am in the final assembly stage of a 5'x5'x2' gantry mill of my own
design. This 2500 lb machine throws a 750 lb moving gantry and in most
places has a design structural stiffness of 100 lb/.001".

The intended control system is LM628 based (Tech80 5638). I have written
c control programs for this many times in the past and it has worked ok.
Motor update is 250 microseconds and trajectory commands can be sent at
1 khz if you pull some tricks.

I am concerned with interrupt latency and the lack of feedforward
in the LM628/pc though. The hard realtime capability of rtlinux EMC
looks very appealing as does the first and second order feedforward
algorithm. The high feedrates and and low following error requirements
I have demand a high performance control. Buying an expensive
manufactured control is not an option.

I'm not a linux or unix guy but this group has me about to take the
plunge. (big mistake? :^) )

It looks like this list is going to be a major resource for me if
I decide to try EMC.

Mabye I can share some of the problem solutions I have found if others
are interested and we can all learn something in one diversified list.

Some of the problems I have been working on are:

- making 7' machine ways to .001" with only a level, 12x18 surface
plate, and hand angle grinder

- Welded tube space frame design using finite element analysis

- active and passive structural damping

- designing and building preloaded ball screw support bearings

- Surplus sources for linear motion components (Chicago area)

My project is for small side business rather than hobby but I think we
might share the need to make cnc machines on a shoestring budget.

Leslie M. Watts
ITW Advanced Technology Group
(847)657-4559
http://www.netcom.com/~leswatts/leswp.html