CNC robotics build your own workshop bot by geoff williams

• Provides step-by-step instructions for building your own CNC mochine
• Greot for use os 0 teoching tool in metol/wood shop
or on the industriol floor

GEOFF

,WILLIAMS
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CNC Robotics
Build Your Own
Workshop Bot

Geoff Williams

McGraw-Hili
New York
London

Chicago
Madrid

San Francisco

Mexico City

New Delhi

San Juan

Singapore

Sydney

Lisbon

Milan

Seoul
Toronto

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./

Cataloging-i n-Publication Data is on file with the Library of Congress

Copyright © 2003 by The McGraw-Hili Companies, Inc. All rights
reserved. Printed in the United States of America. Except as permitted
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may be reproduced or distributed in any form or by any means, or stored
in a data base or retrieval system, without the prior written permission
of the publisher.
3 4 5 6 7 8 9 0 DOC!DOC 0 9 8 7 6 5 4
ISBN 0-07-141828-8

The sponsoring editor for this book was Judy Bass and the production
supervisor wa s Pamela Pelton. It was set in Tiepolo Book by Patricia
Wallenburg.
Printed and bound by RR Donnelly.
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For Margaret, whose help and patience made this book possible.

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Contents

II"

II

I

I

1 ,, 1

1

Design

1

Why Build My Own
Gantry Style
Motors
Lineal Motion
Motor Drivers
Acme Screw

Deciding on the Dimensions of the Machine
Software

2

4

4

9
9
9
10

13

Electronics
Stepper Motor Driver and Computer In terface Boar ds
Stepper Motor Driver Circuit
The Interface Board

3

I

2
2

Making the Printed Circuit Board

13
15
19

77

Tools and Materia l
Artwork
Board Cutting and Cleaning
Toner Transfer
Etching

78
82
85
93

Driver Assembly

99

The Interface Board

III

77

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GNG Robotics

5

Softwa re Setup and Driver Testing
Material Needed
Creat ing Test Files
Triangle Test
Circle Test
Putting th e Elect ro nics in a Case

6

The Frame
Tools and Ma teria l
Bolting
Assemb ly
Bearing Ra il Support Bolt Ho les
Paint the Frame

7

The Gantry and X-axis
T he Gantry
The X -ax is: Insta ll i ng t he Gantry Bearing Guide Rail
Beari ng Holder

8

The Z and Y Axes
T he Z-Axis
The Y-Axls

9

Motor and Lead Screw Insta llat ion
Tools and Ma teria l
X-axis
Y-axls
Z-axis
Lim it Switc h Install at ion
X -axis Limi ts
Y-axis Limi ts
Z-axis Limits

10

File Creation and KCam
KCam CNC Cont rol ler Software
KCam File Require ments
How to Create a File to Import
CorelDraw
ACME Profile r

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113
113
121

122
123
124

13 3
133
138
141
144
151

1 53
153
160
164

175
175
184

189
189
190
199
203
206

208
209
211

215
215
219
222
223
239


Contents

11

Tool Holders and Testing
Tool Holders
Penholder Tool
Router/Dremel Holder
Testing the CNC Machin e

12

245
245
246
252
257

263

Examples
Plotter
Mechanical Engraving Tool
Dremel Tool
Ma ster Craft Rotar y Tool
Router

263
268
271

274
278

293

Sources of M aterial
Electronic Components
L297 /L298 Integrated Circuits
CANADA
United States, California
Lineal Motion
Distributor
Manufacturers
Stepper Motors
Metal

293

293
293
294
296
296
29 7
300
301

303

Index

vii

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Acknowledgments
I must tha nk my brother Karl who inspi red me to write this book and
my editor Judy Bass w hose fa ith and a ssistance made th e book a rea lity. I'd also like to thank Patricia Wallenburg who assembled my words
and images into book form . Judy an d Patr icia have made this book
project an extre me ly enjoyabl e expe rience. Finally my tha nks go ou t to
a ll the people who have freely shared with me thei r know ledge a nd
assistance wh ile I was resea rchi ng and .bui lding my CNC machi ne.
I must thank th e following co mpan ies for a llowing me to include some
of their cop yrighted materia l in this book.
The NuArc Company, Inc. does n' t p romote, e ndo rse . or wa rra nty an y
modified products. NuArc let me reproduce so me of th e imag es from
the repair ma nua l of th e copy ca mera I disassembled but they don 't

endorse th e use of thei r p roducts for anyt hing ot her tha n the ir origina lly intended fu nction . You can co nta ct NuArc at M&R Sa les a nd
Service, Inc. I N. 372 Main Street , Glen Ellyn, IL 60 13 7, USA or on the
Web at http:/ / www.nua rc.co m.
Kellywa re ha s allo wed me to use sc ree n ca ptures of the progra m
KCa m 4. Kellywa re ca n be contacted at PO Box 563 . Spirit La ke. Iowa
52 36 0 , USA or on the we b at http:/ / www.kellyware.co m.
The p roduct data sheets included with Chapter 2 of th is book have
been reprinted with the pe rm iss ion of STMicroelectron ics . The documents reproduced in this book and many more useful app lication
notes ca n be found at th e STMicroe lectronics Web site loca ted at
http:/ / www.st.co m.
Scien ce Speciali st s, Inc. ha s given me permiss ion to include sc ree n
captures of th e softwa re ACME Profller, Coyot e Version 6.0. Scien ce
Spec ialists, Inc. ca n be rea ched at 1800 Shec kler Rd.. Columbia City,
IN 4675 , USA or on th e Web at http t/ zwwwzfwt.co m/ v. klmble/
sc ispec/scispec. htm .

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Design

Why Build My Own
I first th ought about adding a CNC ro uter to my too l collectio n
after fi nishing a kitchen cab inet renovatio n in my home. I refaced
the cabinets and bui lt 26 new doors. during w hich I d iscovered
t hat door buildi ng can becom e mo noto nou s at best. As always
hap pens w hen yo u tell or sho w yo ur fri ends and fam il y w hat yo u
have don e, som eone w i ll have a sim ilar p roject and enlist yo ur
help . Tha t someone was my frie nd Geoff S. He wanted to do the
same thing to his kitchen-reface and install new cabinet doors. I

agreed to help him and he decided on a style of doo r that can be
ma de from o ne piece of ma terial cut to size and routed to create
th e look he wanted . Of cou rse t he prospect of bu il ding a w ho le Jot
of doo rs and making temp lates to faci litate the routi ng was n't too
thrilling. That's w hen I t ho ught a sma ll CNC machine wo uld co me
in han dy. All th e repeti ti ve rou ting cou ld be asslg ned to the CNC
mach ine and t he doors w ou ld more closely resemble each other
o nce huma n erro r had been removed from t he equation . Now the
project didn't seem too bad at all!
I started to look for an affordable machine to do the job, After
searching the Intern et , I was shocked to find how mu ch the asking
pri ce is fo r a CN C mach ine. I did fi nd a cou ple t hat were under

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CNC Robotics

56000 U.S., bu t I ca n never co nv ince myse lf to buy a too l wo rth so
much . Even if the cost of the ma chin e seems reasona ble you st ill
have ship ping a nd du ties to pay, and in my case the excha nge ra te
be twe en U.S. and Ca na dian dolla rs. All things considered, it was
going to cost me in excess of 510,000 Canadian to get a CNC
ma ch ine in my shed . I can 't afford that kind of pr ice tag! I sea rched
for plans or a book that described what I wanted to bui ld. I did find
some plans on the Internet but either the machine was too sma ll

and inaccurate or the plans were expensive and requ ired the use
of expensive components. I cou ldn 't find any books in print about
a similar project. I won't buy plans that I can't get a good look at
first , so the Inte rnet plans were out of the qu estion. I prefer books
bec a use I ca n ho ld them and flip through the pages before I hand
ove r th e cash. Books also cost less.
I decide d to build my ow n ma ch ine us ing some off-t he-she lf
linea l mot ion co mpo ne nts a nd so me co mpone nts tha t I salvaged
or modified to suit the project . I thou gh t the most logica l thing
wo uld be to docum ent my p rogress a nd share the inform a tion
through a book . To sum ma rize, I deci ded to build my ow n ma chin e
because I love a cha llenge a nd I learn mo re whe n I have a pra ctica l project; a lso, I ca n keep the cost low. It's that simple.

Gantry Style
In my op inion, a gantry styled CNC mach ine is sim plest to imp lement. A few years ago , I built a ba nd saw mill fram e and gantry,
so the design of a more accura te system didn't seem too to ugh a
pro ject. I a lso like the idea of moving the tool over the material
ra th er tha n the mat er ial under the tool. A mach ine built to move
ma teria l would not have as la rge a wo rking a rea for a given footpri nt. Con sidering my work shed is only 22 X 12 feet , a gantry
mach ine is most suitable.

Motors
The first purchase to make was the stepper motor. My loca l
Princess Auto has a grea t s urplus department, so I headed there
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first. Sure enoug h, they had some step- syn motors (seen in
Fig u res 1.1 and 1.2) . They ar e Nema frame size 34 , draw 1.4
amps per cha n nel , and have a rating of 4.6 volts.
Figure 1,1
Ste p-Syn steppe r motor
side view.

Figure 1.2
Step-Syn ste pper mot or

top view.

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CNC Robotics

These motors we re used in an IBM produ ct-probabl y a pr inter.
They are unipolar, but if yo u run th em as bipolar the y produce
more to rqu e (see Figure 1.3).
1 also discovered that these steppe r motors work better if t hey are
given 12 vo lts ins tead of the 4.6-volt rating on th e motor body. The
strength of a s tepper motor is rated in ou nce inches of holding
torque. The ste p-sy n information 1 found ind ica ted tha t these
motor s ar e an ywhere from 90 to 220 ounce inch es. I so metimes
wo rk ba ckward s, and bu ying the motors first is ce rta inly just th at !
Norma lly, you would calculate w ha t strengt h of motor yo u nee d to
run th e machine and then p urc ha se a s uita b le motor. Here's how
to calculate the st re ngt h of motor you need to run this mach ine. If
you can 't find any surplus mo tor s, investigate a company called
Pacific Scientific-they ha ve a va riety of s teppe r motors and also
make available soft ware for do wnloa d, w hich you ca n use to

determine the size of motor yo u ne ed . Spe a king with them , I was
impress ed with how we ll I wa s treated, cons ide ring 1 would only
need th ree of the ir motors.
Remember that although brand new motors ar e expe ns ive, you
kno w the y will work and you ca n match the s trength to the
machine. New motors could also speed up the ma ch ine considerabl y. When 1 sa y "speed up ," it is important to not e that I am
referring to travel s peeds, not cutti ng s peeds . Cutting speeds for
most material s will be slow with this sty le of machine, rega rdless
of whi ch motor you choose; you ca n't run a route r thro ugh wood
at 200 inches per minute and ex pect the cut to look good . Cutting
speeds of 10 to 30 inch es per minu te define t he ra nge we can
expect from th is mach ine wit h these motors. A faster ma chine can
be expected to travel quickly w hen not cutti ng and slow down
when cutti ng through mat erial.

Lineal Motion
There are a va riety of off-the-shelf lineal motion products , but
mo st of the systems we re too expensive for thi s proj ect. Thinking
th at it would be useful some day. 1 acq uired a NuArc co py cam era
a few years ago (se e Figure 1.4 ), so 1 took it apart and found it
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Chapter 1 /

Design

STEP-SYN 103-820-0240 4.5V 1.4 AMP 2DEG/STEP
WIRING DIAGRAM

RED

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Wiring diagram of a
Step-Syn stepper motor.

+ MOTOR SUPPLY

UNIPOlAR CONNECTKlN

..lAllA}

Figure 1 .3

PHASEA

BLACK
REDiWH lTE -

BLUE
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PHASEC

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PHASE D

BIPOLAR CONNECTIONS
BIPOLAR HAlF WINDING (MORESPEED)

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CNC Robot ics

Figure 1.4
Exploded illustration of the NuArc Model SST 1418 supersonic horizontal camera. Part 21 is the carriage
that travels on the guide rails using lineal bearings.

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Chapte r 1 / Design

uses lineal bearings r un ning on guide rails to mo ve th e copy board

as we ll as the bellows.
Th e slide employed to mo ve th e bellows and cop y board wo uld
work we ll as th e y-axis for my CNC machine. And it w as comp let e
wi th beari ngs and ho lders built in to th e sli de, as pictu red in
Figures 1.5 and 1.6.
Figure 1 .5
NuArc Camera, part
number 82 is the

guide rail.

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85 86
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CNC Robotics

Figure 1 .6
Closeup of the slide
showing the bearings
numbered 40 and the
location of lead screw

nut numbered 33 .

Of the eight bearings, I found that onl y four were st ill in satisfactory condition fo r use. I decided that the x-a xis could be built in the
same ma nner, employing open linea l bearings running o n a ra il
tha t ha d been drilled a nd ta pped to allow the use of s upport bo lts.
I also ch ose to ma ke my own bearing ho lders for th e x- ax is beca use
the co st of preb uilt p roducts was more t han I co u ld justify. Rail s up port ma teri al is ava ilable a s we ll, but the cos t of th is prod uct made
me belie ve it wasn't required a nd t hat the bolts wo uld give the rail
e no ugh su pport. I noti ced th a t t he copy came ra d idn't have any
ext ra s up port under the rails. If you wanted extra s upport in a pro ject like this, it co uld be fashioned from two pieces of angle iron
with a spacer, but the su rface it would be mounted on-conside ring the rail would be in con tact with the support-would have to be
perfectly flat. As I had no intention of using perfect steel to bu ild
this machine, having the bolts pro vide the support meant that they
could be adjusted to bring the rail to a flat plane.
Simi lar beari ngs an d ra ils cou ld be used for the z-axls, but I decided ins tead to use a sw iveling TV tray assembly bo ught a t the
Home Depot. The glides ar e ra ted at 100 Ibs. to ho ld a te levisio n
hori zontall y. My p ro ject would use the glides vert ica lly, so they
would be p lenty s trong, w ith la rge ba ll be a rings an d e nough tra vel for the z-a xls. The NuArc ca mera used 3/4 -i nc h bearings and
support ra ils, so I decided to use th e sa me bearing and rail size on
th e x- axis.
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Chapter 1 / Design

Motor Drivers
At thi s point in the proj ect 1 had al read y pu rchased motors, so I
looked at simple driver so lut io ns. The be st solution was found in
th e form of th e 129 7 and 1298 integrated circuits manufactured by
ST Microe lec tronics . The ir Web site ha s all the information needed to build a bipol ar stepper moto r d river using these two integrated c ircuits, w hich ar e often refe rred to as "chips." A driver built
from these ch ips can ea sily pr ovide th e vo ltag e and amperage
needed by the step sy n motors.

Acme Screw
The qu estion of how to move the gantry and a xes slides was a lso
res olved by co st. I had originally conside red using ball screws, but
afte r co mpar ing th e cos t of the ball screw wit h that of an acme
screw, it didn 't ma ke se nse to spe nd three times a s mu ch on ba ll
screws. The ad vantage s to usin g ball screws ar e tha t a sm aller
motor ca n be used to move a given load, and with a pre load ed nut,
the re is ve ry little ba ckla sh in the system. As mentioned ea rlier in
thi s c ha pte r, this is a machine th a t will not s peed through its
a ssign ed jobs so we can compe nsa te for ba ckla sh in the softw a re.
Thi s mean s the project ca n be built usin g les s expensive a cme
screws.
I also had to de cide how many turn s per inch to put on the acme
sc rew. My experiments w ith ready rod proved t hat too man y tu rns

made fo r a nnoyingly slow movem ent and too few turn s redu ce s
th e qu al ity of resolution tha t a llows t he machine to make sm all ,
pr ecise movem ents. 1 sett led on a 1/2 -in ch acm e screw with eight
turn s per inch, and a 6- foot length with a nut at a co st of $ 135
Canadian.
'

Deciding on the Dimensions
of the Machine
Earlier in th e cha pte r 1 expla ined tha t I made t he deci sion of
ma chine footprint size based on the a rea in my wo rks hop.
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CNC Robotics

Becau se I on ly have a space 12 X 22 feet a nd tools and mate ria ls cu rrently occupy most of th a t space, my mac hine wo uld o nly
be ab out 7 fee t lo ng a nd 4 feet wide. The next step in this projeci
was to ge nerate concept drawings, since I was going to use some
of the components fro m the NuArc horizontal camera. The
dimensions of the frame ended up being longer than the support
rails in order to accommodate the bearing holders and the motor
mount with a little roo m 10 spare. The width of the frame is a few
inches sho rte r than the balance of a 6-foot acme lead screw, after
the length needed for the z-a xis has been cut from it. The follow ing illustrations are the concept drawings 1 created to guide the
co ns tr uctio n of the machine. Figure 1.7 is a drawing of the
ma chine fro m the side.
Figure 1. 7

View from side of
proposed machine.

The next illustrati on, Figure 1.8, is the width of the mach ine,
viewe d from the front.

Software
After figur ing out the approximate shape and dimensions and
de cid ing on stepper motors and drivers, the next questio n was
which software to use to control the machine once finished. 1
looked a t a variety of software solutions and , since my level of
experience wit h CNC machinery was nonexistent, I wanted a pro gra m tha t was easy to use. To communicate to the stepper moto rs
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Figure 1 .8

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how to move so th e tool being used will follow the desired path, a
p rog ra m is w ritten in G-code and M-code . The G- and M-codes are
used to tell the machine w here to go in the xyx-axes areas of travel a nd what to do when it ge ts there. Very simple programs
describing th ings like boxes o r circles are not ve ry comp licated to
w rite yourself. 1 wa nted software that wo u ld allow me to create my
own desig ns in a drawing program like CorelD raw and then import
the drawi ng a nd a uto matica lly cre a te the necessary G- and Mcode file. 1 looked at some freeware but was disa ppointed by t he
level of d ifficulty to imple me nt t he so ftware and get it doi ng what

I wanted. Furt her research revealed software ca lled KCam that
wou ld do exactly w ha t was necessa ry. See the screen capture from
KCam in Figure 1.9.
KCam isn't freewa re, but it ce rtai nly isn 't expe nsive e ither at $100
U.S. pe r copy. The fact that KCam is not expensive s ho uldn't lead
yo u to be lieve it is ineffective softwa re. It is extremely easy to use
an d a llows yo u to customize the use of the p rinter port . KCam will
11

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CNC Robotics

Figure 1 .9

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also import H PGL files crea ted in Corel Draw 9 or OX F files created
in CAD soft ware like AutoCa d or in CorelDraw 9.
In this cha pter I sha red design choices for my CNC machin e and
t he rea so ns beh ind them, as well as t he choices of stepper motors,
drivers . an d software. At this point in the project. we need to start
t hinking abou t t he elec tro nics. th e topi c of t he next chapter.

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RI R2 R3 R4 R5 R6

4k 4k 4k 4k 4k 4k

Electronics

Stepper Motor Driver and
Computer Interface Boards
This chapter deals with the design and construction of the electronics required for controlling stepper motors using a computer
and Keam software. The requirements for the drivers are based on
the step- syn motor purchased in the previous chapter from the
surplus department of Princ ess Auto (see Fig ur e 2.2).
Figure 2 .1
The finished boards.

In addition to these surplus motors, I also bought three new
motors from Pacific Scientific , also mentioned in the previous
chapter (see Figure 2.3).
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CNC Robotics

Figure 2.2
Step-syn stepper motor.

Figure 2.3
Pacific Scientific

stepper motor.

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Chapter 2 / Electronics

All the motors d raw 1.4 amps pe r chan nel, but the step-syn
mo tors are rate d at 4.5 volts and t he Pacific Scientific motor can be
given a maximum of 170 volts. Alt ho ugh I'm not using Pacific
Scientific moto rs in this project, if yo u are unable to find suitable
surplus steppers you may w ish to purchase new ones. WARNING:
The stepper motor driver boards described in this chapter can d rive
both of these motors, but you can only use up to 36 volts for motor
power-too many volts will fry the L298 integrated circuit. A com pa ny called ST Microelectronics has gracious ly given me permission to reproduce the data sheets and app lic at ion notes in their
entirety in this chapter (see pages 22 through 75). These docu ments are the basis of th e driver board design . Read t hem thoro ughly to ga in a greater understa nding of the strengths and lim ita tions of t he L297 /L298 integrated circuits (referred to as ICs) in
t his app lic ation .

Stepper Motor Driver Circuit
The stepper motordriver boards are th e mu scles of th e CNC ma chine.
Th ey receive signa ls fro m the co mp uter t hat in d icate w hic h directi on that ax is w ill travel and how fa r it wi ll move. Th ey are the
mu scles becau se as they receive d irect io n and step signa ls from

Figure 2. 4
L297 stepper motor
contro ller IC.

Figure 2.5
L298 H Bridge IC.

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CNC Roboti cs

the computer, they translate the information into higher voltage
and amperage signa ls to send to the stepper motors. The power
sent to the stepper motor coils is distributed to the coils in a
sequence that will move the shaft in the desired direction as ma ny
steps as are needed to traverse the distance required on that axis .
For th is project we need t hr ee d river boards. one for each ax is of
travel. The boa rds are designed usin g a set of in tegrated circuits
manu factured by STM icroelect rion ics- t he L297 and L298 . The
nic e thing about using th ese two chi ps is that th e boa rd design is
quite simple. o nly req uiring a min ima l number of co mponents. A
second benefit is that w hen com bined, t hese two chips create a
very powerful drive r boar d capable of handli ng up to 36 volts and
2 amperes per channe l. A lot of bipolar and uniploa r stepper
motors currently manufactured or available as surplus. which are
strong enough to be used for this machine. are well within the tolerances of these chips. T he steppers that I decided to use are
Sanyo Denki step-syn and are rated at 4 .5 volts and 1.4 amps per

channel wi t h a resolution of 2 degrees per step. T he powe r rat ings
are well wi th in the to lera nces of th e drive r boa rd. You can refer to
the schemat ic (Figure 2.6) to dete rm ine the co mponents requ ired
for this board .

Table 2-1
Driver Board
Components

Part

Quantity

Description

Ul

1

L298 Dual full-bridge driver

U2

1

L297 Stepper motor controller

Dl-D8

8

FR304 Fast recovery diode

Cl

1

3.3 NF capacitor

C2,C3

2

0.1 UF capacitor

C4

1

470 UF capacitor

C5, C6

2

lNF capacito r

Rl, R2

2

0 .5 ohm power resistor

R3

1

lK ohm resisto r

R4

1

22K ohm resistor
(continued

on next page)

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