CNC Torch Table/Research Development/Previous Version

'''NOTE: This is an older design, superseded by the self-replicating Torch Table Build. 4/21/11-MJ'''

The following have useful info that should be gathered here
 * See blog posts on torch table - http://openfarmtech.org/weblog/?cat=214
 * initial testing of the computer controlled torch table
 * Category:Torch Table



The torch table is a computer-controlled device that can move a plasma cutter or acetylene torch. Plasma cutters and acetylene torches are devices for cutting metal. By attaching these to a computer-controlled arm that can move very precisely in any direction, we create a device that can cut metal into any shape you can imagine. This is very useful for making machine parts.

The self-replicability comes from the fact that the entire gantry and motion structure, minus electronics and stepper motors, can be cut out on the table itself.

The table is readily adaptable to industrial duty routing. Accuracy is not sufficient for circuit fabrication. Cost of the table is about $1500 for materials, and we aim to produce these tables for an additional $500-1000 in labor costs for a total of $2000-2500.

=Torch Table Design= Here is a design that is based on review from the CAD_CAM and DIY CNC Yahoo groups as well as feedback from other sources. The drive is obtained with stepper motors and rack-and-pinion style direct drive with a 1" pinion gear. Using 425 in oz stepper motors, this allows for direct coupling and ~50 pounds of force delivered to move the gantry. Linear bearings and ball screws were replaced with rack-and-pinion drive due to cost considerations. Using direct rack and pinion drive, good accuracy is possible: theoretical 2/1000 of an inch for a 1 inch pinion gear with 1/8 stepping. The limiting factors will be straightness of the guide rail (1 1/4" cold rolled steel rod) and resolution of the pinion gear.

Notable design goals:
 * 1/32" accuracy is sought for general acetylene torch cutting (or plasma cutter) applications
 * Ball bearings ride directly on guide rail on the drive side
 * Bearings ride directly on structural metal on the non-driven side
 * Direct coupling of stepper motor to metal rack via a single pinion gear; no gearing involved
 * Stepper motor speed: 10 RPM for ~30 inch per minute (IPM) motion with ~1 inch diameter pulley
 * Fast rapid motion should be possible, 100 RPM for 300 IPM
 * Traction of rack-and-pinion drive is obtained via the weight of the gantry
 * Gantry weight: ~40 lb
 * Frame is 6" wide U-channel, 5/16" thick
 * 4'x8'x1' maximum working object dimensions

Design Details
The initial concepts above have been refined to the following detail for the main precision rail. The red part is a rectangular tube 4"x4"x1/8".

Design rationale:
 * Traction for the rack and pinion is obtained by gravity through the weight of the gantry and drive system
 * Long-axis alignment is secured by the main guide rail, with 4 guiding ball bearings in the long direction (x)
 * The shaft for the pinion gear is supported on both ends
 * Direct coupling of motor to gear is utilized
 * 10 rpm of stepper motor yields 30 inches per minute travel - the max desired speed for cutting with an acetylene torch
 * Rapid travel of torch ~300-600 inches per minute
 * Pinion gear radius = 1 inch; circumference ~3 inches
 * Driving torque is 425 in oz yields about 50 pounds of force for a gear radius = 1/2 inch
 * Gantry weight ~40 lbs, so approximately 1 g acceleration is possible
 * Pitch of rack and pinion is 20DP-20PA (6.3662 Teeth per Inch)
 * 200 step stepper motor is driven with 1/8th steps for theoretical 2 thousandths of an inch resolution in the x direction
 * Straightness of guide rail will be the limiting factor

Frame


Initial 3D views:



=3D Views=

Gantry




The Gantry assembly bill of materials falls out of this:


 * X Rails

Z Axis


=2D Views=

X Rail Detail, Front View


Pinion gear bearing:

Stepper Motor to Pinion Gear Coupling via Flexible Shaft Coupler




X Rail Detail, Top View


The assembly on the bottom left is the guide rail system detailed in the above 2 pictures. The gantry that carries the torch head consists mainly of the same type of guide rail as found for the long exis (x axis).

Y Axis Drive Detail
The y rail is the blue part of the above 2 diagrams. The detail of the y-direction drive is shown below:



Initial Designs
see Torch Table Initial Designs

=Design Reviews=


 * Dave from Xylotex user group
 * Gene Haskett
 * CAD_CAM_EDM_DRO yahoo group
 * http://www.cnczone.com/forums/showthread.php?p=605553

=Bill of Materials=



Details:

Rack is also available from Moore Gear and Manufacturing. 
 * Rack from Standard Steel Specialties. Quick response, great price on the rack.


 * Pinion from McMaster.com, item 5172T12
 * [[Image:pinion_gear.jpg]]


 * Pinion holder - square tube 2" x 2" gauge 12 .109" x 2ft - weight: 2.802 lb/ft * 2ft = 5.604 lbs


 * rectangular tube 4" x 2" x gauge 11 .120" x 2' - weight: 4.75 lb/ft * 2ft = 9.5 lbs


 * Xylotex motors and controller -


 * Bearings from vxb.com -
 * [[Image:bearings.jpg]]


 * Small bolt prices at boltdepot.com -

Wheel



 * http://cgi.ebay.com/---CNC-Track-Roller--V-Groove-Bearing_W0QQitemZ270349417490QQcmdZViewItem
 * http://cgi.ebay.com/MCGILL-VCF3-1%2f2-TRAKROL-BEARING-W%2fV-GROOVE-ON-OD-NEW_W0QQitemZ250310140048QQcmdZViewItem
 * http://www.vxb.com/page/bearings/PROD/V-Groove-Bearings/Kit8408
 * http://www.google.com/products?hl=en&as_q=v+groove&num=10&scoring=r&as_epq=&as_oq=cam+follower+bearing+wheel&as_eq=&price1=&price2=&as_occt=any&show=dd&safe=off

Fixed bushing for #2 V wheel V-groove wheel #2 Item Number: 302010 Wheel bushings: Add one eccentric bushing per wheel Edit this product $15.02 		$60.08 		V-track for #2 V wheel V-track for #2 V-groove wheel Item Number: 302040 G dimension from left or Right?: Left Over all length of each piece - Enter L dimension in inches. ie. 23.62. Tolerance is +/- .05 inch.: Answer: 18 Enter number of pieces ( order each length seperately ): Answer: 8 Edit this product $0.96 		$7.68 	Remove Update 	Subtotal: 	$67.76
 * need something like this with the stuff that goes with it. Not too expensive.
 * whole number
 * whole number


 * http://accuratebushing.thomasnet.com/Category/smith-trax-bearings
 * http://www.modernlinear.com/components.html
 * good
 * http://www.qbcbearings.com/BuyRFQ/LinearB_Guide_W_VG_IS.htm#
 * http://www.atlanticdrivesnc.com/products.html
 * http://cgi.ebay.com/Butcher-Boy-Table-Roller-V-Groove-Bearing-BB00811V_W0QQitemZ270349418206QQcmdZViewItem

=License=

This design is placed explicitly in the public domain and under a Copyleft License.