Help with Cnc router mechanical design

[transtar]

Hi all:

I am building a CNC router machine for milling of thin wood (thickness 1.5mm)with the following specifications:

Type: Fixed bed with moving gantry
Travel: 600mm x 350mm x 75mm

Can anyone advise me on the followings:
- Size and brand of stepper motors suitable and capable of driving my
machine
- Size and pitch of leadscrews suitable for my machine
- Do I selected the size and pitch of this leadscrew to suit my machine and
the software will take care of the division / travel distance etc
- Is there any advantage to use a step down timing pulley for Z axis
movement

Thanks in advance for the information

[High Seas]

transtar
1. welcome aboard! You'll find a heap of information here - and sometimes you gotta look a bit - but the members will be glad to help.

2. You sorta gotta define a few things along the way:
how much - to spend,
how tight the resolution,
how repeatable and,
ultimately the accuracy and precision of your machine.
All that will be based on what you want to build. That determines part of your question's answer - size and type of motors and screws...etc

3. What will you use it for? Woodworking - modelbuilding, space support efforts? Cars, Planes, or making signs, plaques, and nice visual items. Members here all have that experience.

4. What you want to make and what you need will answer a lot of the questions regarding size of motors, type of control etc. That you have defined a size for your working space is just a start! Help the member's with a bit of "bounding" the design and you'll be pleasently surprised.
I have been!

WELCOME TO THE JOURNEY! Enjoy
Jim

[tclcpw]

Originally Posted by transtar Hi all: I am building a CNC router machine for milling of thin wood (thickness 1.5mm)with the following specifications: Type: Fixed bed with moving gantry Travel: 600mm x 350mm x 75mm Can anyone advise me on the followings: - Size and brand of stepper motors suitable and capable of driving my machine - Size and pitch of leadscrews suitable for my machine - Do I selected the size and pitch of this leadscrew to suit my machine and the software will take care of the division / travel distance etc - Is there any advantage to use a step down timing pulley for Z axis movement Thanks in advance for the information

Find this web hope can do some help.....

http://www.budgetcnc.com

Regrads

[transtar]

Thanks everyone who has taken the trouble to reply. I am building my machine to mill balsa wood, thin plywood and plastic mainly for modelling. Building of the hardware (machine) is not a major problem cos I am a mechanical engineer by trade and I owned a fully equiped machine shop. As this is my first machine, accuracy and speed is not a major issue, as for budgetry I would like to keep it cheap in fact the machine actual make used of my left over scrap materials including slide etc found in my machine shop.

My problem is that 'Inches' leadscrew is near impossible to obtain in my country of course metric size leadscrew is not a problem. I hope to use a M22 standard pitch leadscrew for my machine. Is the pitch of the screw used must be able to be divided into round figure (movement of the bed) when used in conjunction with any stepper motor?

Thanks and best regards

[High Seas]

Don't know which software you plan on using to run the system - Mach2 is great and; a VERY fair price, well supported, windows-based (not DOS), AND, it doesn't care-inches or metric - you specify in its setup so you don't have to convert. Its available as a DEMO to try before buy too. Hope that helps! Jim

[transtar]

Originally Posted by High Seas Don't know which software you plan on using to run the system - Mach2 is great and; a VERY fair price, well supported, windows-based (not DOS), AND, it doesn't care-inches or metric - you specify in its setup so you don't have to convert. Its available as a DEMO to try before buy too. Hope that helps! Jim

Thank you my fellow machine builder, you just answer my question 'AND, it doesn't care-inches or metric - you specify in its setup so you don't have to convert'. I have heard about this software and I will certain look into it as suggested. Incidentally, I planned to submit the progress during the construction of my machine, hope all the experiece builder like yourself can provide valuable feedback to me.

Btw since we are on the subject on leadscrews, my other few questions that I am seeking answers to is as follows:

1 I notice some of these machines has step down timing belt pulleys on the
Z-axis and X-axis. Is there any major advantages over direct drive from
the stepper motors when this set up is been used? I understand that the
accuracy will improved at the expense of travel speed.

2 Can I use different size of metric leadscrews for the various axis?

3 My proposed design uses an Alu sheet as machine bed with a series of
threaded holes drilled and threaded in a orderly pattern for the purpose of
mounting the work piece. However, I wants to mill thin Balsa sheet of
1.5mm thick and the cutting will need to mill all the way through, the
parts will still be fastened to the stock materials via little tabs surrounding
the parts. My question is that due the need to mill through the materials
thus it will also mill and destroyed my machine bed, what is the usually
holding method for is type of process? In my prototying buisness, we will
actually mounted a board onto our machine bed the stock materials is
actually fastened to this board using double sided tape.

Thanks

[Rance]

Your 'nice' bed can be covered with a thin (1/4" maybe) piece of sacrificial sheet (cheap Luan, for example) so you can cut all the way through your work.

[2 Can I use different size of metric leadscrews for the various axis?]
Yes, each axis can be different. Sometime it is best though to keep the X and Y the same for simplistic reasons.

[Edit] Cheap? You gotta define 'Cheap' in actual dollars (or pesos, etc.)

[spalm]

A note about question #1. Timing belts and pulleys are usually used with servo motors while direct drive is usually used with steppers. You are right about gearing down equals more precision and less speed, but the most common reason is servos like to run fast and steppers like to run slow. See this post for a good explanation.

A note about question #2. Double sticky tape with a sacrificial (throw away) board underneath seems like a good way to cut really thin pieces.

Steve