1/4 - 20 generic vs acme?

[9xnet]

I am building a Rockcliff Router and am wondering what the diference is between generic 1/4 20 treaded rod is and the acme rod?

I do you think 5/8th is enough for the x y z rods? i will be making the cnc 18 x 18 cutting area vs the 12 x 12 base design.

Thanks for all your help.

[rockcliff]

Originally Posted by 9xnet I am building a Rockcliff Router and am wondering what the diference is between generic 1/4 20 treaded rod is and the acme rod? I do you think 5/8th is enough for the x y z rods? i will be making the cnc 18 x 18 cutting area vs the 12 x 12 base design. Thanks for all your help.

Hi
1/4-20 is about as fine of a thread pitch as you would want to use, 20 threads per inch will give approx 20 to 25 inches per minute running speed, and about 18 lbs of force with a 200ozin motor. Using an acme thread can give higher travel speeds as the thread pitch can be more coarse, using a more coarse pitch will also lower the amount of force to the slide, your project size of 18 x 18 is only 6 above base model , there will be some flex in any unsupported rail setup, but the amount will be acceptable for cutting softer materials like wood or plastic, for a 5/8 shaft, you can increase the size to 3/4 if you want a little more strength and want to stay with the base model design see don's machine http://www.cnczone.com/forums/showth...ight=rockcliff he used 3/4 on the y axis and 5/8 on the x and z Another possible combination is to use 3/4 on X and Y and to use 1/2 on Z But if your planning to cut harder materials see the commercial bearing model or the DIY slide. hope that helps
Nick
http://www.rockcliffmachine.com

[9xnet]

Ok cool, i guess i will go for the acme.

Heres another question, since you say the rods will flex under harder materials why cant i put bearings under the y table that would just ride against the wood under it? would that not support it enough?

[rockcliff]

Originally Posted by 9xnet Ok cool, i guess i will go for the acme. Heres another question, since you say the rods will flex under harder materials why cant i put bearings under the y table that would just ride against the wood under it? would that not support it enough?

The 5/8 unsupported shaft will be acceptable for cutting most materials, if you want a more rigid machine build version D see drawing set D1 to D10

[9xnet]

one last question before i send my order off.

I have been looking at

6061K447

Hardened Precision Steel Shaft 3/4" OD

It costs a bit more money then the ones in the plan but i was wondering if thats becuase its stonger?

Edit: I wonder if im over engineering this as its my first cnc router?

[rockcliff]

Hi
Hardened shaft will give a very small amount of extra strengh, over un-hardened it should only be used for use with linear ball bearings, I would not recommend it with bronze bearings, unless you wanted to use linear bearings in the future, also with hardened shaft you cannot cut it with a bandsaw or hacksaw you will need to use an abrasive cut off wheel

http://www.rockcliffmachine.com