Why Rostock?

There's a video of a rostock moving with a dial indicator on its head. I'll look it up later when I'm home.

Impossible to read the indicator though.
Could someone with a rostock do a simple weighted test?
That is, place a known weight on a string and attach to a tall point on the towers, flip weight over a corner and down so it pulls sideways.
Then measure the deflection with weight. My Rostock clone wiith 600mm long 10mm dia rods is fairly stiff, but my 800mm machine is quite wobbly. A slight increase in length has a lot of impact on stiffness, or lack thereof.

Dark Alchemist Wrote:

> Don't have the money for an ACME screw setup, or a
> ball screw setup? Then use a thread rod with two
> nuts and a spring inbetween them with a harness
> holding the two nuts. The spring keeps the nuts
> up againt the edges of the thread so the backlash
> is pretty much gone and gone on the cheap.

You can have a very good steel Z10 mm trapezoidal screw in 1m with bronze nut for about 20€ (7.37€ for screw, 13€ for long bronze nut, cut it in 2 put a spring ==> 0 backlash ) so price is hardly a problem. Ball screw are costly yes.

And we should use that as lead screw, not standard M8 or M10. Standard M rods have absolutly no guarantee of straightness and eveness of step.

alj_rprp Wrote:
-------------------------------------------------------
> Dark Alchemist Wrote:
>
> > Don't have the money for an ACME screw setup, or
> a
> > ball screw setup? Then use a thread rod with
> two
> > nuts and a spring inbetween them with a harness
> > holding the two nuts. The spring keeps the
> nuts
> > up againt the edges of the thread so the
> backlash
> > is pretty much gone and gone on the cheap.
>
> You can have a very good steel Z10 mm trapezoidal
> screw in 1m with bronze nut for about 20€
> (7.37€ for screw, 13€ for long bronze nut, cut
> it in 2 put a spring ==> 0 backlash ) so price is
> hardly a problem. Ball screw are costly yes.
>
> And we should use that as lead screw, not standard
> M8 or M10. Standard M rods have absolutly no
> guarantee of straightness and eveness of step.

Most M rods are cold-rolled.
They are each pulled from roll and straightened or preformed in extrusion, then drop into roller and get shaped in a single movement.
If they fall in a tiny bit crooked the threads come out crooked too. I had this issue on my cnc with a z error repeating every turn with +/- 0.25mm on a 1.25mm/turn rod.
The press-type method is used for short cheap rods as it can run fully automated. I know there was a clip on how it's made showing this process but can't find it online.

There is also some machines that produce threaded rod by long or continous lengths. These can oscillate causing odd periodic errors.
[www.youtube.com]
They are used for long rods.