Re: To tool change, or not tool change

Chris,

The main factor at work here (IMO) is that a tool changer has to be
ONE HUNDRED PERCENT FAIL_SAFE! And even the expensive VMC's and CNC
routers still "throw one" occasionally. You only have to be around
this ONCE to understand the importance of the first sentence above!

There is a BIG difference between "allowing for" a toolchange by
having a "toolchange position" and G43,44,49 tool length comp
capablities in the control software; and the reality of implementing
the whole shebang...

A large part of the cost of the toolchange in a hi-freq spindle (like
perske,elte,colombo) is to cover product liability insurance. Really!

The current state of our legal system does not reward innovation in
machine design, and in fact sometimes punishes by assuming that if
something has changed, it means something was "WRONG" to begin with.
Don't laugh. There have been more than a few cases of this legal
argumant winning in product liability...

Anyway, The clues are available online as to how to create a workable
toolchanger by looking at how the big boys have done it in VMC's
(air, "fingers", knobs on the tapered holders, and belleville
washers). But it is more than a trivial pursuit.
Roland Friestad and I talked at length awhile back about how to do
one for the r8 spindle(s) of mill/drills; and I've looked at how the
pcb mills (lpkf) are done.

You are correct that there needs to be a little more added to most
current pc-based control S/W to fully implement a reliable tool
changer; so there is at least some communication as to which tool is
being sought/loaded, and verification of same for safetys' sake. I've
seen discussions of an aoutonomous toolchanger, which only
signals "ready/done" but I wouldn't recommend it.

As to adding some length to a router: The newer "quick-change chucks
available for the Porter-cable 3-1/4 HP routers extend a significant
ways from the original position (so much that the base needs to
have "spacers" inserted). But some have complained that runout is
unacceptable with this tooling... Others love it. One could even
arrange a sort of fork off at one edge of the travel to lock/unlock
this type of device; the problem would be getting the tool lined up
with the collet accurately enough.

I'm quite sure a GOOD/expert machinist could make an extension for
this type of router---I'd use the existing taper which is provided
for the collet, and make a "collet" that was really more like an
endmill holder for a milling machine, with a turned "boss" for the
clamping nut to act upon .The nut would be bored out somewhat)---,
but again, while the design might be trivial, the implementation
needs near perfection. We're talking SHARP bits at 20K+ RPM, here!

By the time you do this (and balance the rotor, improve the bearings,
tighten up the tolerances since the loads are different) you're
really just re-creating the hi-freq spindle again...

FWIW, tyler machinery in TX sells a belt-driven router "head" (to the
ww industry) which might be a good starting point for "longshaft"
mods.

Hope this helps.

Ballendo

P.S. There has been some talk on the MaxNC list that Max (or someone
related) IS coming out with an automatic toolchanger for their small
mills...

P.P.S. I remember working with a 4 head Heian Router ($250K) where
the cleaning of the collet, nut and spindle cavity during tool change
was given near religious attention. A 4 head machine just changes
heads to change tools, but even this expensive machine had thrown a
bit, due to some gunk that got in during a tool change!

--- In CAD_CAM_EDM_DRO@y..., Chris L <datac@l...> wrote:
> A few years back, I had raised a similar question. I was reflecting
on how it
> seemed that the various newer PC based control software offerings
all offered
> Tool Length Comp. and supported tool change G and M Codes.
>
> These offerings would obviously apply for at least someone with
tool holders
> and Not for individuals who have to chuck tooling in a conventional
collet.
> Even to date, There is very little available (mechanically) for
the "hobby"
> and small machine market even though that control software is often
targeted
> directly to that market.
>
> There are toolholder options from companies who make high frequency
spindles
> (like Perske), but the cost factor certainly does not reside in the
hobby
> arena.
>
> It would appear that this would be a very good project for an
enterprising
> individual to develop and build a spindle that may work with some
existing
> toolholder, even if it was a belt driven spindle.
>
> I've even thought it would be interesting to replace existing main
shafts of
> some popular trim and regular size wood routers with a longer shaft
that can
> be set up to accomodate some kind of holder and ditch the collet. I
never
> took one apart to see if you could "press off" the
associated "Motor" parts.
> A "Long Spindle" option would sure make a lot of people happy who
do 3d work
> in soft materials.
>
> Chris L
>
> rainnea wrote:
>
> > Does anyone know of any toolchangers or even plans for one of a
size
> > that would be suitable for the mini-mills and small routers that
many
> > people here use ?
> >
> > Rab
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
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