Re: CNC flame/plasma cutter

Let me add a few thoughts about racks and pinions..
They work very well in cnc applications but suffer from two problems. One is
the pitch diameter of the pinion. The second is debris that that clogs the
teeth and jam the mechanisms.
The pitch diameter for the smallest pinion that works on a neam 23 motor is
.5"D. Thus it will travel .00785" per step at 200 steps per rev and half
that for 400 steps prer rev. Generally a nema 34 motor is used and this
would have to have a 1" pitch diamter so that there is enought meat for the
pinion to be bored for .3755. Then the resolution increades by pi*D or 3.14
for 1 rev at 200 steps=.0157 per step and half that for the half step mode.
You will get very fast travel. I have one system that ran no load at over
600" per minute with 150 oz in nea 34 motors.
An alternative is to then use a belt drive to drive the pinion then you can
increase the resolution by the pulley ratio. Some people just use timing
belts cut and both ends secured for non critcal tolerances.

Dan
-----Original Message-----
From: Tim Goldstein <timg@...>
To: CAD_CAM_EDM_DRO@onelist.com <CAD_CAM_EDM_DRO@onelist.com>
Date: Wednesday, June 23, 1999 9:15 PM
Subject: Re: [CAD_CAM_EDM_DRO] CNC flame/plasma cutter

>From: "Tim Goldstein" <timg@...>
>
>
>My friend only got the table parts from Torchmate. He is using a bi-polar
>chopper drive stepper controller (better torque and rpm than a unipolar)
>that he built from a kit he purchased from Dan at Camtronics. For the
>software he is currently running DeskNC DOS version which does handle
>g-code. But, we are soon going to move him over to EMC and Linux as it

seems

>to run a stepper machine much smoother.
>
>As far as ball screws v/s rack I think it is not a question of what is
>better, but more a question of what is most appropriate for the job
>considering the cost. A ball screw is more accurate, but is the rest of the
>machine such that the added accuracy will ever be noticed? If you are
>thinking of a machine that can handle 4' x 8' and figure the cheapest
>ballscrew material is $1/in and nuts are $20 you will have over $200 in
>just the parts and I don't think you will see any difference.
>
>Tim
>[Denver, CO]
>
>> -----Original Message-----
>> From: smcdonal [mailto:smcdonal@...]
>> Sent: Thursday, June 24, 1999 1:11 AM
>> To: CAD_CAM_EDM_DRO@onelist.com
>> Subject: Re: [CAD_CAM_EDM_DRO] CNC flame/plasma cutter (was Stepster)
>>
>>
>> From: smcdonal <smcdonal@...>
>>
>> Tim Goldstein wrote:
>> How does the torchmate handle files? Can it read standard g code or does
>> it use some other format?
>>
>> Also would like to know if rack and pinion is better then ballscrews?
>>
>> Thanks
>> Stan
>>
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