[nikbrewer]

i did a search an could not come up with a answer i liked. I am starting to build my first cnc. 36" x and y lead screws, 4" z leads screw 1.75 hp PC router. proballt 350 in/oc steppers. I am wanting to do a over head lead screw on the x and have the x rail up lust below the y axis. i want this so the cnc can be placed on somethign and cut into it, such as flooring. I will also build a vacume table for it to sit on. I plane on using 1 1/16" chrome hafele closet rod for the x and y rails. this stuff is over 1/16" wall thickness and super smooth. I have a nesting router cnc a work to cut my parts.

here is my idea. can i cut half circles out of 1" thick derlin and use it for slides? i would run 2 on top of the rail, about 6" apart, and then one under neith between then, tighend up just to barely touch so the gantry cant lift off the rails. WIll these be smooth enough? i am not looking for a super fast cnc, and it really only needs to be acurate to about 1/32 of an inch. This seams easier then building the carts with scate bearing, though i cna do that too.

On a side note, i bought my z axis with a stepper attached and can see how to get the lead scerw off. are they pressed onto the shaft? could i get it off with a blow torch and heating it up?

thanks in advace

[stefn]

I'm looking to do something similar. Here is my design.

What are your thoughts?
:cheers:
Stefn

[dertsap]

i would be concerned the delrin will get distorted with the constant weight on them ,
what i used on my first machine was oil impregated bushings which worked well ,they are cheap and may be an alternative

[Geof]

i would be concerned the delrin will get distorted with the constant weight on them ...

Delrin is pretty good for not distorting under constant load. We make a rotating mechanism which uses a tapered Delrin bearing under spring pressure to get a controlled drag to the rotation. The torque needed to move the mechanism remains constant within about +/-10% for two years or more, and through hundreds of movements.

But there is a minor problem which could affect a machine under a heavy load. When the Delrin bearing is stationary for several days, and especially if the temperature changes up and down, it seems to 'settle in' and you have to put use extra force to get it moving. Once it has been moved it goes back to the original torque.

[dertsap]

thats good to know
ive concidered using it for a slide assembly in the past but ruled it out due to the concern of distortion by weight and forces from cutting
i had some delrin bushings kicking around ,where they are now is beyond me , the stuff slides beautifully and a little oil makes it pretty slick , if it is that stable then i would imagine it would work much smooter than the oilite bushings i had used