Frame Build - Lead screw Q

[viroy]

Hello again all!
I am making progress on my first build and have gotten to the point where I need a little help.

Im building a CNC for cutting small aluminum boxes (3"x4"), and PCB's.
I have the bottom of the frame designed using Autocad 2008 with the 8020 add-on (im making the whole frame from 8020).

Questions:
a) I need to design the bed which holds the lead screw on the bottom... but I dont know how they mount. I imagine when I purchase the lead screw it will just be a rod and I will need to get 2 bearings? Is there a standard size or attachment method? Can someone fill in the details please

b) I need to decide on a lead screw to purchase. I havent purchased an X or Y axis motor yet (I already own a 'Paul Jones instant Z-Axis Kit').
But I do not know how to properly decide what lead screws to get for my X and Y axis.
I see alot of talk about IPM and speed/torque conversions, but I am new to this. I'm worried I may need to do something like gear up/down.
Can someone please fill in the details on how I should proceed?

Thanks for help in advance!
I have attached a picture of the instant z-axis kit and also the Autocad design I have made thus far.
J

[viroy]

Ive been reading alot through the forum and have come to the conclusion that a Recirculating Roller Screw would be the best option for precision.
This is the link that sold me:
http://www.linearmotion.skf.com/en/8...rews__SV_.html

[ger21]

Not sure if you'll find any homebuilt machines that use those. Extremely expensive, unless you can build your own. And the one in the link has a 1mm lead, which will give you an extremely slow machine.

1/2-8 2 start or 1/2-10 5 start acme are the most common choices. The 1/2-8 will give more resolution, but less speed. The 1/2-10 5 start will give less resolution, and more speed. If you don't have any idea how fast you want or need to cut, then one of the two choices I gave you will get you started at a reasonable price.

[viroy]

Originally Posted by ger21 Not sure if you'll find any homebuilt machines that use those. Extremely expensive, unless you can build your own. And the one in the link has a 1mm lead, which will give you an extremely slow machine. 1/2-8 2 start or 1/2-10 5 start acme are the most common choices. The 1/2-8 will give more resolution, but less speed. The 1/2-10 5 start will give less resolution, and more speed. If you don't have any idea how fast you want or need to cut, then one of the two choices I gave you will get you started at a reasonable price.

Oh are they not very common? I wish they had a price list... I was just looking at that link to get an understanding of that design.
What does the "start" mean? im guessing the firs number is the width? 1/2"? and the "-8" is the pitch?

[ger21]

1/2-8 2 start

1/2" diameter, 8 threads per inch. 2 start means there are two separate alternating threads, each with 4 turns per inch. So one turn of the screw moves 0.25".

[viroy]

so the more starts the better?
Is there a thickness rule for going 48 long"?

I guess I should decide on the lead screw to purchase now so I can get dimensions for the proper fixed mount system...
right now im not sure but im thinking something like 5/8" 4 start, sound good?
I have no idea what inches per minute this will turn out to be, or what i need.