Re: CNC Plasma Help

I got mine from Mc Master Carr. Get the smallest diameter pinion that will
fit your stepper motor. I would say that you would probably want at least
150 oz in torque sot that you will have good speed for thin material.
Dan
-----Original Message-----
From: Mark Ehle <markehle@...>
To: CAD_CAM_EDM_DRO@onelist.com <CAD_CAM_EDM_DRO@onelist.com>
Date: Tuesday, December 28, 1999 4:11 PM
Subject: Re: [CAD_CAM_EDM_DRO] CNC Plasma Help

>From: "Mark Ehle" <markehle@...>
>
>Jay -
>
>Can you give us an idea of the mechanics of the rack-and-pinion drive?
>Diameter / pitch / # of teeth / size of driving motors?
>
>I have acquired all of the necessary parts to put together an O/A table,
>about 4 feet by 5 feet. The only thing I lack is the drive system, and

after

>reading your post I have pretty much decided to go with rack and pinion. I
>was thinking of using a section of timing belt or lead screw, but It would
>be slick to be able to disengage the motor from the rack to move the
>carriage quickly.
>
>I need to know how strong a stepper motor to use and what size rack to use.
>Also, where is the best deal on racks?
>
>Anybody out there got some ideas / answers?
>
>Thanks!
>
>Mark Ehle
>Battle Creek, MI
>
>----- Original Message -----
>From: Jay Hayes <xmas4lites@...>
>To: <CAD_CAM_EDM_DRO@onelist.com>
>Sent: Tuesday, December 28, 1999 11:23 AM
>Subject: Re: [CAD_CAM_EDM_DRO] CNC Plasma Help
>
>
>> I have a commercial unit and it has rack and pinion drive on both X and

Y.

>The servos, gear reducers and drive pinions are
>> mounted on a spring loaded mount that allows the drives to be engaged or
>disengaged from the rack. This removes the backlash
>> between the rack and pinion. Rotary encoders are also driven by the

pinion

>shaft. This arrangement negates any backlash from the
>> gear box.
>>
>> You don't need to go overboard on high precision drive components on a
>plasma or O/A burning table. The nature of the cutting
>> process will not yield a high precision edge regardless, unless you're
>running a "High-definition" plasma torch or laser. If
>> you can hold .010 inch, you are doing good.
>>
>> More important is the ability of the drives to negotiate the contours of
>the cut at the proper velocity at any given point along
>> its path. This requires the software to look ahead and allow for corner
>slow down for sharp cornering, but allow constant
>> velocity on gentle curves. Software that allows a slight pause anywhere
>along the cutting path, will introduce a defect into the
>> part being cut. Likewise, taking a sharp corner at a high velocity can
>cause over travel of the torch and or over stress the
>> drive components. The momentum of the gantry flying down the track can be
>substantial.
>>
>> The good news is if most of your cutting is thicker material, than the
>torch doesn't have to move very fast. But if you mainly
>> need to cut thin gauge material, than you need higher cutting speeds to
>achieve a quality cut.
>>
>> Hope this helps.
>>
>> Jay Hayes
>> Weston, WV
>>
>> Don Robertson wrote:
>>
>> > From: "Don Robertson" <dnrobert@...>
>> >
>> > The surface will be flat and the shapes will have all kinds of curves
>and
>> > angles. Accuracy well I think the ball screw method will be best from
>what
>> > I have seen in comerical units.
>> >
>> > What kind of motors would I use with ball screws?
>> >
>> > I assume I will build a rack system to support the axises and hold the
>> > torch. Any suggestions on bearing configurations?
>> >
>> > The mechanics dont really seem to be the problems the real problems are
>with
>> > wiring the motors to respond to computer.
>> >
>> > Software Well I am open to suggestions there I plan to scan graphics
>and
>> > convert to line drawings that the plasma will cut like a plotter

prints.

>> >
>> > Thanks Don
>> >
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>> > List Manager
>>
>>
>>
>>
>> >
>> --
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>>Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the

discussion of shop built systems in the above catagories.

>To Unsubscribe, read archives, change to or from digest.
>Go to: http://www.onelist.com/isregistered.cgi
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>bill,
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