Re: Please take a look over my shoulder – CAD CAM CNC Bench Mill System

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "whelenremington"
<wperun1@r...> wrote:

> I've been researching the web for three weeks to figure out how
> to
> select the software, electronics, motors, and mechanicals to put
> together a bench mill system.


> My present system contains a MicroLux Milling Machine #82573
> purchased from Micro Mark. I also have a MicroLux 7x14 Lathe

#82710,

> so I can do fabrication to mount servo motors, and or build new

x,

> and y axis slides. I'll start with the lead screws that came with
> the
> milling machine. Need information about, do I need to modify the

lead

> screw nuts, as an example. I plan to measure backlash.

This is what is called a micro mill. It is light duty and should be
fine for the size and types of parts you describe.

In order to convert any machine to CNC, you need to make it "CNC-
ready"

Here is how I define CNC ready:

1) Thrust bearings to prevent end play on all axes
2) Anti-backlash nuts on the lead screws
3) Motor mounts
4) Flex couplings to adapt motor shafts to lead screws

The X and y axis on a micro mill are relatively straightforward to
accomplish, but the Z is more complicated because of the drill
handle mechanism. Steve Stallings of PMDX has a ball screw Z axis
that he has built on his machine. It avoids the drill handle mess
and substitutes a precision leadscrew. A similar device with an
Acme screw would be sufficient for a micro-mill.

> I guess I want to output .stl files from my CAD software. There

is

> also .dxf, but I don't understand why I would prefer .stl over
> .dxf
> output files.

.stl is for 3D surfaces only, this includes carved and sculpted forms
.DXF can be used for 3d surfaces or prismatic shapes, contours, and
engraving.

> Again what would you suggest for the CAD and CAM software for my
> application? Where do I specify the .stl mesh size? In the CAD

or

> the CAM software?

You specify the .stl mesh density in the Cad software and you
specify the tool cutting pattern and density in the CAM software.

> Next I guess I need translator software. The CAM output files are

G

> code, I think (what is M code?). I find the translator software
> confusing. What is it doing? Is it part of the motor drive
> electronics package, which provides the CNC signals to the motor
> drivers?

See this link:

Creating CNC parts: The software

http://www.cadcamcadcam.com/hobby/creating_CNC_parts.htm

> I might want a tool-path simulation software.
>
> Somewhere in all of this is the ability to set up the 0,0,0
> coordinates to relate the cutter to the work-piece.

Standard item

> Limit switches
> to control run away programs, and something to turn on coolant.

Also

> something must isolate the PC from feed back from the motor driver
> circuits and power supply.

For a desktop machine, these may not be required. Programs do not
run away, and coolant may not be required for your parts.

> I am also aware of IMService SYS-3-4axis complete, ready to bolt

on

> closed loop, servo CNC system with brushed DC servo motors,

cables,

> enclosure, and software. Price approximately $1,424.

This system includes new, USA servo motors with timing belt reducer
assemblies.

It also includes DeskCNC which has a CAM capability to produce G-code
to cut rings with a rotary axis( from .stl files), and Cam
capability to produce pockets, contours, and drilled holes from DXF
files, and text engraving.

It can also probe a target surface directly to an .stl file for
duplication

> Next the Mill and attaching the servo motors
> Will the LowCostCNCRetrofits , Hitachi 100oz.in Cont /500ppr.

Servor

> Motors and chopper driver electronics (motor current and voltage)
> have enough torque for my MicroLux Milling Machine acme lead

screws

> (#82573 purchased from Micro Mark)?

yes, but they may be too big. 100 oz-in on a servo motor is a lot
for a micro mill. You need to know the rpm that they have at the
power supply voltage to determine if they will work well.

> What will be the approximate maximum inches per minute feed rate,
> cutting brass, with a 1/8" dia end mill, cutting 0.040" deep?
> Should
> I connect the servos directly to the lead screws (with flexible
> couplings) or should I provide a timing belt reduction? What

should

> the reduction ratio be, and what is the technical reason for the
> reduction and the ratio (other than more torque)?

You need to reduce the RPM of a servo motor to balance the high
motor shaft rpm to the desired cutting speed and rapids on the
milling machine.

Belt reduction is usually needed for these type of servos.

>What do I tell the
> CAM program about the servo motors, the reduction, and encoder
> frequency? I'll be measuring the backlash in the acme lead
> screws.

Tell the Cam none of this. You will set axis resolution, backlash,
acceleration and speed in your controller.

> Should I replace the lead screw nuts? Do I loosen up the gibs on

the

> slides? Should I lap the ways? What else should I be doing?

You need physical backlash control for CNC. The less backlash, the
better parts you can make. The gibs should be adjusted so the axis
can slide freely. Way lapping may not be too useful if your machine
is already fairly accurate. The quality of these machines varies
quite a bit and yours may be fit well enough as it stands, that no
rework is required.

Fred Smith - IMService
http://www.cadcamcadcam.com/hobby