Re: CNC Plasma Help

For those of you interested, BERG makes linear gear
drive racks and bearings. These are based on a round
shaft and incorporate the bearing and drive in one block.

Steve

----------
From: Mark Ehle <markehle@...>
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] CNC Plasma Help
Date: Tuesday, December 28, 1999 4:10 PM

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
> >
> > > > Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the
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>
>
> >
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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
Log on, and you will go to Member Center, and you can make changes there.
For the FAQ, go to http://www.ktmarketing.com/faq.html
bill,
List Manager