Work has commenced, many questions

[Tabor]

Hey guys

I have started to build a CNC machine and have a few questions.

My machine is made out of Aluminum, and has a working area of around one A3 sheet of paper.

I have linear bearings for the X and Y axis running on 20mm High Tensile Precision Ground Bar. The Z axis is using sintered brass sleeves on 1/2 inch PG bar.

The first couple of questions have to do with the "ball screws".

Is the machine best made with the same pitch threads?

I am not using proper Ball Screws yet but have decided to use precision threaded rod with wide Brass Nuts, Two nuts on each rod with a spring to seperate them. and a housing around the two.

I am hoping this will be suitable to reduce backlash????

Any comments??

Cheers

Tabor

[jcc3inc]

Dear Sir:

Can you tell me the size of "A3" paper? Also what is a "PG" bar?

Regards,
Jack C.

[Tabor]

A3 is Approx 11.5 x 16.5 inchs

PG bar is just precision Ground Round Bar.

Tabor

[Graham S]

If you use belts between the screws and motor then you can match the mechanical advantage of each. So if one has half the lead/pitch of the other you might use half the gear ratio. If you are going to run direct drive with steppers then probably best to keep X and Y pitches the same.

Graham