Re: [CAD_CAM_EDM_DRO] Re: Z-Axis problem - Not Enough Torque?

Chris,

I now fully understand what you, Brian and others were pointing out to me
regarding the advantage of putting counterweight in the Z-axis mill head.

However, as I have pointed out in my previous post, I am not driving the
whole Z-axis head but only the quill. I think the coil (?) spring in the
existing manual Z-axis serves as the counterweight.

Best,
WT

----- Original Message -----
From: Chris Horne
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: Friday, November 10, 2006 1:48 AM
Subject: [CAD_CAM_EDM_DRO] Re: Z-Axis problem - Not Enough Torque?


WT

I read the your reply to Brian after I posted, but I still think it
may be worth you counterweighting.

The big advantage is this..

If you have a slightly heavier than exact counterbalance the leadscrew
nut will be pulled up on the leadscrew.. (you can adjust simple
weights much more easily than pneumatic type counterbalances)

When you drive the tool into the workpiece, there will be ZERO (I mean
ZERO) backlash no matter how much backlash you have in the leadscrew
itself.

The advantage is obvious..

The only time this doesn't help is if you are machining upward with a
tool that reaches underneath the work (very unusual)

Counterbalancing is worth it just for this, the need for less power in
the drive system is a bonus.

Another bonus if you are using ballscrews is the reduction of load on
the leadscrew which pretty much prevents the hilarious spectacle of
the head descending under its own weight when the power is switched off.

The only disadvantage is the increase in inertia, I have not found
this to be noticable in practice, and in fact I have added weight to
both the head and the counterweight which has had a vibration
dampening effect.

And the principles of counterweighting the head are the same no matter
what the size of mill...

honestly... it works...

Cheers

Chris

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "WT" <pharmapack@...> wrote:
>
> Hi, Chris.
>
> 1. I noticed a lot of advise from others regarding counterweighing the
> Z-axis head as well. Maybe I am missing something here. Is it a must
or a
> better solution to do a Z-axis by counterweighing? Kindly look at my
earlier
> post reply to "Brian Worth" regarding this.
>
> 2. Timing belt/pulley reduction may be the first thing I will try.
>
> Talking of pulley, can someone point me to a web resource where I
can get
> the DXF or SolidWorks file for an XL timing pulley for CNC GCodes
> generation?
>
> Thanks,
> WT
>
>
> ----- Original Message -----
> From: Chris Horne
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Sent: Thursday, November 09, 2006 7:28 AM
> Subject: [CAD_CAM_EDM_DRO] Re: Z-Axis problem - Not Enough Torque?
>
>
> In your shoes I would try the following in this order.
>
> 1. Counterweight the head with a weight, steel cable and a couple of
> pulleys. Make the counterweight greater in weight than the head.
> The exact amount more than the weight of the head you can find by
> experimentation, but at some point it will take up the backlash on the
> leadscrew, killing two birds with one stone...
>
> 2. Toothed belt drive reduction on the 'Z'.. most of the time you
> will hardly notice the reduction in speed..
>
> I can't stress enough that the counterweight actually works... and it
> is also probably the most effective, easiest and cheapest option.
>
> Chris