My parts list - would like opinion

[haku]

Can someone let me know if I am picking good parts to build my first machine with.

1 LMC16 x 650mm rail bearing shaft XYZ table CNC router (Y Axis)
1 LMC16 x 4 pc linear ball bearing XYZ table CNC router (Y Axis)
2 24" 1/2-10 ACME Lead Screw w/ Delrin Nut for CNC Router(Y and X Axis)
1 12" 1/2-10 ACME Lead Screw w/ Delrin Nut for CNC Router(Z Axis)
2 3/4" Round Precision Ground Rod 24" (X Axis)
1 1/2" Round Precision Ground Rod 24" (2 x 12") (Z Axis)
2 SC20UU x 4 pc linear ball bearing (X and Z Axis)
1 3/4" 4'x8' MDF
1 G540 4 axis controller (when it comes out)
3 282oz-in stepper motor 2 phase

I am looking for opinions

Thanks
Haku

[ger21]

Use 1/2-8 2 start or 1/2-10 5 start acme.

[haku]

What is the difference??

Thanks
Haku

[ger21]

You'll get 3-5 times more speed than with single start 1/2-10.

[haku]

I mean what is the physical difference, a different pitch??

Thanks
Haku

[waltm]

I'm still learning this stuff as well so you might want to wait for someone to confirm but this is my take on it.

You can think of each start as a separate spiral running the length of the rod. A 1 start has a single spiral groove like a normal screw. A 2 start has 2 spirals, like a double helix, so you you would get an effective 4 tpi out of a 1/2-8 2 start or .25 inches per revolution. A 1/2-10 5 start would give an effective 2 tpi so for every turn of the screw you would move .5 inches.

[ger21]

Yes, 1/2-8 2 start is 4 turns per inch. 1/2-10 5 start is 2 turns per inch.

[BobF]

Plus higher efficiency. Multi-start screws are usually higher efficiency than single. Some of the motion screw manufacturers publish information about there screws.
Look here.
http://nookindustries.com/acme/AcmeAvailability.cfm