Re: [CAD_CAM_EDM_DRO] Re: Is this motor workable?

cnc_4_me <cnc4me@...> wrote:


You make it sound like the table will crash and pin a jackrabbit...It
will slowly work its way to the ground...

// I've never seen 1200 lbs slowly work its way earthward. The screw would get up to speed in no time flat. No resistance for the 1200 lbs to work against. Just a couple of bevel gears and pulley out in the breeze. If that be the case Mr Otis wouldnt have needed such an elaborate brake and simply relied on drive gears to slow an elevators descent. Oh and I havent seen any jackrabbits in the shop since I quit the liquid lunches.

:-)

Second, a acme screw for the same lead will take aprox 2x more power.

Third, most people who power the knee mount gas springs on it to take
most of the load off the motor and stop it from falling...

"
From: Peter Renolds

Date: Thu Aug 5, 2004 2:02 pm
Subject: Re: [DIY-CNC] Bridgeport NC conversion.


Hi Steve,

This subject has been discussed several times - try some different
searches to find the threads such as cnc'ing the knee etc. You will
need something to stop the knee crashing to the bottom. I have
installed a servo on my Z axis (knee) and had to fit two 150lb (or
thereabouts) gas springs to counterbalance (so to speak) the static
weight of the knee. It has worked perfectly for the last almost 3
years. The gas springs were from McMaster Carr and cost about $20 ea
incl the end fittings.

I have a couple pics in the CCED Photos folder - look for NEMA42 - Gas
Springs - It show the steppers I started with, now it is servo motor
driven via belts.

Cheers, Peter"


Note: the above dosn't mean you have to use ballscrews, several
people have posted both ways work, ballscrew and acme...

Wally


--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers
wrote:

> Assuming I change out my lead screws
> to 4 or 5 tpi ballscrews is there a "suggested" torque requirement

for the

> screws on a b'port size machine? The knee would obviously have to

have a

> bigger motor or more reduction. Quick side question...is there any

reason

> to change the knee to a ball screw? Seems like there really isn't a
> backlash issue on a knee.
>
> //There is no backlash. Using a ballscrew on a knee driven Z is a

waste and its not safe. There is a very little resistance in a
ballscrew and if the servo belt broke the weight of the Z axis (about
800 pounds) could feed the screw in the nut and the table would fall.
Ron//

>

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