CNC
Conversion of a Sieg X-3 Milling Machine
By Bob
Berg
Goal
– To create a fairly accurate bench top CNC machine at fairly moderate
price.
Here are
some shop pictures:
The base
mill is a Sieg X-3,
this was purchased from www.lathermasters.com who was the only importer of
this mill at the time. Priced
delivered was about $1,100.00.
This also
shows Shumatech DRO on top of the motor. If your not going to CNC your
mill, you need at least a DRO!
This is my Harbor Freight 9X20
lathe with Quick Change tool post.
The Windex bottle is filled
with Denatured Alcohol I use it to clean EVERYTHING!
Once I
received the mill I completely tore it down and cleaned every piece that was
practical with a brass brush, rags and mineral spirits.
After the cleaning it was amazing how much grit and metal
goo was at the bottom of the cleaning bucket!
The mill was then greased/oiled and then reassembled in its new home.
I used the mill for about a year for some small manual projects.
During this time I got tired at looking at numbers on the hand wheels
and dealing with back lash. I
then built a DRO for it and fitted the X and Y axis with scales.
This single upgrade was time well spent, once you have a DRO you can
never go back!
I knew I
wanted to convert the machine to CNC from the start, so I did a lot of
research on the WEB for information about CNC conversions.
I began to look for components.
I first looked at stepper motors and then servos as many have said
that servo performance will be better.
So I decided on the servo approach.
I first
located some very cheap servo motors from a link I found on
www.cnczone.com.
These are
Clifton Precision servo motors rated for 36VDC with a max torque of about
360 oz/in.
These
motors were purchased for about $10.00 each!
However,
they had no encoders on them, what do you expect for $10.00?
I purchased some 250 count rotary encoders from US Digital for about
$40.00 each and then mounted them to the back of each motor – Now they are
servos!
For about $50.00 each I have a nice
set of servos that should work well.
I’m thinking that the power will be marginal at a 2:1 belt reduction
ratio. I toyed around with 3:1 and finally settled on a 2.5:1 ratio.
If things don’t work out I can always change the ratio.
Pulleys
and belts were purchased from Stock Drive Components and should be here in a
couple of days (2/16/05).
During
the first major shopping trip I purchased 5/8
Pictures
of ball nut components coming soon!
Design
the conversion
As I was
about to start making chips and “design as I go”
I realized quickly that I’m going to make a lot of mistakes and I
need to better plan the whole design before I go to town.
So I quickly taught myself SolidWorks and began to design the various
parts of the conversion. I was
able to model everything in 3d.
This allowed me to see how things would fit and look.
It is like being able to create a virtual model of my machine before
ever cutting a single chip or drilling any holes. I’m sure it has saved me
many hours and dollars of mistakes!
This is
the full assembly of the mill table with all the CNC components.
This
shows the X-axis ball screw details.
The bad
thing about modeling in 3d is that it is so easy to change something you are
constantly
changing
things and never reaching a “Final” design.
Also, there is no surprise when you finish
making a
part, you know what it’s going to look like before you even start!
X,Y & Z
Axis Bearing retainers
These
parts trap the bearing in the bearing plates so there is no axial movement.
The bottoms of the retainers are recessed .100” to the diameter of
the bearing. Based upon the
depth of the bearing plate holes these parts give .015” of crush.
Not that it’s all used of course!
Machined
the ball screws
I think
this was the most difficult part to machine in the whole process, due to the
fact that the ball screw is case hardened to 56C.
When
turning down the ball screw to fit the bearings I wanted to keep the journal
end as concentric as possible in relation to the screw.
Once the ball screw was in the chuck of the lathe I placed a dial
indicator in the thread grove and rotated the chuck by and hand and also
moved the lathe carriage so that the dial indicator would follow the thread.
I had to re-center the dial indicator via the lathe carriage to the low spot
on the thread a little each time as I can’t follow the thread perfectly by
hand. By doing this I adjusted
the lathe chuck so that the screw would run true by indicating off of the
threads not the outside.
Once the screw was centered in the chuck I faced off the screw and drilled a
pilot hole so that I can support the other end with a live center.
The
machining process was begun by taking a hand grinder and removing as much
material by hand as possible
To try to
remove the case hardening.
Be careful not to take too much off doing this method as it’s easy to
do!
I then
turned the rest of the diameter with a brazed on Carbide tool bit.
This worked pretty good once I figured how
much of a cut to take. I then
finished the diameter with some sand paper.
The next step was to thread a portion of the screw for the locknut.
I used a 7/16-20 hand die to make the threads. I tried to use the
lathe to single point the threads but something wasn’t working (don’t know
what) so I did it by hand.
X-Axis
X-Axis
with new ball screw installed with plates and motor mount attached.
All
plates are made from 1” aluminum stock.
I was
able to obtain all the aluminum stock from the scrap bin at work!
The axis
is now silky smooth, in fact I can move the table
by just turning the shaft with
my
fingers!
I think
I’m going to need to put some thought in keeping the ball screws clean.
They are
protected by the table, but I’m sure some chips will get in and gum up the
works!
Y-Axis
Space
Plate, Bearing Holder, and Motor Mount
I just
need to bore the hole in the bearing plate and the Y-axis will be ready to
go.
Here is
the finished Y-axis bearing plate its mating parts and assembly (2/18/05)
Y-Axis
ball nut mount
Y-Axis
with old acme nut removed and new holes drilled for new ball nut mount
Hint: in order to preserve the stock Y
travel. I bored a hole about 1 – ½” deep in to the column here.
This allows for a longer ball screw as it can go into the
column when the Y table is at its maximum.
This actually allowed me to gain more Y travel then
stock. With out
this modification, I would have had less travel because the ball
nut is longer then the stock nut. And you don’t want to let the
screw go half way out of the nut or you will loose your balls!
J Ask
me how I know!
Limit switches are important to keep that from happening!
Y-axis
new nut mount installed. The
electronic device mounted on the left is a reader head from a harbor freight
6” electronic caliper.
This is
used for the Y-Axis DRO Scale.
When I put the Y-table back on the scale just slides back inside the
head!
Z-Axis –
I still
need to design how I’m going to approach the Z-axis.
I will most likely drill a hole in the top of the column and mount a
bearing plate and motor mount for the ball screw on the top.
I will need to make a new mount for the ball nut.
I’m not sure if I will need to support the screw from the other end
with a radial bearing. I’m also not sure if I will disconnect the hand wheel
gear or make so that I can engage and disengage the hand wheel from the ball
screw. If I do use the hand
wheel I will definitely need to support the other end of the screw.
Before
conversion:
After
Conversion
Here is
the new ball screw, preloaded nut and mount installed!
I decided
to support the screw at the opposite end.
I used the existing bearing holder, removed the thrust bearings and
replace with radial bearings. I
have decided to leave the crown gear off so the hand wheel is now
disconnected. I don’t need it
anyway!
Here is
the pulley and empty motor mount on the side of the mill.
The
plates are 1” alum.
The
little white switch on the left is the upper Z limit/home switch
Here is
the X axis ready to go!
And the Y
Just need
to finish up some wiring!
The
following is a list of all the “major” components that I used, approximate
cost and source:
|
Vendor |
Web Site |
Part Number |
Description |
Approximate Cost |
|
Stock Drive Products |
A 6A 3-20DF03708 |
Motor Pulley -.200 (XL) Pitch, 20 Teeth, Aluminum Alloy Timing
Pulley |
$9.25
|
|
|
Stock Drive Products |
A 6A 3-50NF03710 |
X & Y Pulleys .200 (XL) Pitch, 50 Teeth, Aluminum Alloy Timing
Pulley |
20 |
|
|
Stock Drive Products |
A 6R 3-082037 |
X Belt - .200" (XL) Pitch, 82 Teeth, 3/8" Wide, Neoprene Belt |
$5.55
|
|
|
Stock Drive Products |
A 6R 3-102037 |
Y Belt - .200" (XL) Pitch, 102 Teeth, 3/8" Wide, Neoprene Belt |
$6.01
|
|
|
Stock Drive Products |
A 6A 3-17DF03708 |
Z - Motor Pulley - .200 (XL) Pitch, 17 Teeth, Aluminum Alloy Timing
Pulley |
$9.21
|
|
|
Stock Drive Products |
A 6A 3-50NF03710 |
Z Big Pulley.200 (XL) Pitch, 50 Teeth, Aluminum Alloy Timing Pulley |
$20.91
|
|
|
Stock Drive Products |
A 6R 3-102037 |
Z Belt .200" (XL) Pitch, 102 Teeth, 3/8" Wide, Neoprene Belt |
$6.01
|
|
|
|
|
|
|
|
|
Industrial Hobbies |
http://www.industrialhobbies.com/ |
|
5/8" |
$22.00
|
|
Industrial Hobbies |
http://www.industrialhobbies.com/ |
|
5/8" 5 TPI
|
$51.00
|
|
Industrial Hobbies |
http://www.industrialhobbies.com/ |
|
3 Gecko 320 Combo (Servo Drives) |
$342.00
|
|
VXB Ball Bearings |
http://stores.ebay.com/VXB-Bearings-Skateboard-and-Slotcar |
7201B 12x32x10 |
Angular Contact Bearings (2 Per Axis Back to Back) |
$15.00
|
|
ColdFusionX |
Ebay |
|
Digital and Analog Panel Meters |
|
|
Ebay |
|
Controller Box |
75 |
|
|
Cabelldesigns |
BreakOut
Board |
Parrallell
Break out board |
137 |
|
|
US Digital |
E2-250-250 |
250 Count Encoders (For the servo motors) (3
Pcs) |
120 |
|
|
Avel
Lindberg |
http://avellindberg.com/index.html |
Y236951 |
30AMP Toroid Transformer (32Volt) |
82 |
|
CNC Zone. |
http://www.cnczone.com/forums/showthread.php?t=2082&highlight=cheap+servos |
|
Surplus |
$30.00
|
|
Jeff Davis |
http://www.homecnc.info/cnc-main.html |
|
Preloaded Ball Nut Plans - Also Sells Servo Motors that would be
good for the X-3 |
7 |
As of now I have completed the CNC conversion of the mill a few years ago and everything works perfect! The Z axis has been converted to ball screw and has full range of motion and works great, the servo has no problem lifting and lowering the head. I have since remove the hi-low speed change gears and now have a direct belt drive from the motor to spindle. I have also replaced the stock motor with a 3 phase 1/2HP Motor and a VFD from Automation Direct.
I’m
currently running about 100 inch/minute in rapids.
I could get it to run faster, however for the size of the machine I
don’t need it any faster. Most
of my cutting is under 20 in/min.
It has ton’s of power, able to snap 3/8 end mills and keep going like
nothing ever happened!
The X
travel is 16.6 inches and Y is 6.4”, this is more then stock!
Not sure about Z but it also has more then stock.