Cable stuff was Re: Stuttering stepper

Hello,

Jon has covered the basic things already, but let me add something:

The cables themselves. Inside the insulation. Broken wire(s). A cable
not expressly made for continuous motion can fail VERY quickly. And
it/they can take out one or more drives as they go...

Very few homebuilt cnc machines I see on the net use anything NEAR
proper cables or cable "management". And I am familiar with your
Blacklab machine (from pictures, at least), and can say that it
appears to be one of these which considers cabling
an "afterthought"...

A few years ago I had an interesting conversation with a Belden (well-
known wire mfr.) app engineer. At the time they were trying to get
into the robotics/machine tool cable business, and were having life
problems with their product.

Anyway, he told me that for a given cable used "tick-tock"fashion
(this means it hangs from two points, or slodes along a table/surface
from two points), a typical life expectancy was on th eorder of
30,000 cycles. Okay, but get this: the SAME cable use in a "rolling"
way (as in a cable track, or supported so that it works similarly),
will have a life in excess of 6 million cycles! That's 200 times the
life, just by using the cable properly.

Recently I was looking through the Olflex catalog, which says that
there should be 15x cable diameter from the fixed points to the
rolling part...

And don't forget the effect of oil/solvents, if that fits your
situation.

Hope this helps,

Ballendo

P.S. If you can't afford to use continuous motion cables, at least
try to use the finest wires within the cable that you can; i.e., 7x19
is MUCH better than 7x7. Foil sheilds wil beak down in a jiffy if ANY
torsional action is taking place. Braided sheilds are better, but if
there's torsional movement, try for a spiral wrapped shield of fine
copper wire.

P.P.S. Obviously, a first step is to try to route the cable paths so
there is a minimum of flexing, and with as great a radius as possible.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "walldawg1"
<tony.marshall@e...> wrote:

> I bought a cnc router from Blacklab machine(Ebay) and the machine

has

> worked fine for a couble weeks now all the sudden one stepper

(vexta

> pk268-03)seems to stutter and and STick
>
> It doesnt seem to be mechanical as far as the machine goes just

that

> one stepper all the others are smooth.
>
> Thanks in advance for your suggestions
> Tony