Re: [CAD_CAM_EDM_DRO] Extending the length of ball screw

I will help if you can indicate a bit ...

diameter in mm ?
screw speed in rpm ?
tolerances required ?

Any general info ... what are you going to use this for ?

What kind of ballnut ?
1-start, 2-start or more ?
Rise, or How many turns per inch or mm per turn ?

I think someone commented on this about 1-1.5 years ago ... and they
did it.
If you anneal the ends, and weld, and can machine the grooves at the
joint it may work ... but difficult IMHO.

Better is to drill/(maybe tap) the ends and join two identical pieces of
screw, either with screwed or pressed fitting.

You could use drill rod or precision ground rod, about 1-1.5 times screw
diameter hole,
and have an interference fit about 0.02 mm smaller hole than the rod,
then head the ballscrew to about 120 C, slide the rod in, and let it set.
It would hold fairly large forces, but the things to watch out for may be
your max screw rpm ?
whipping of the screw if its a fast rotation (over 200-400 rpm), will
bend it and create *very* large tension/compression forces on the joint.
This depends on screw rigidity, material, and diameter.

How do you mount the screw ? On bearing or two on fixed end ? Is it
rotating screw or nut ?

My recommendation for this, as its fairly comples/advanced anyway, is to
a. rotate nut
b. have screw use a dual-suppreted fixed end.
c.have the screw under tension (slight tension pre-load), with moving
end having the ability to move away from the fixed end.

Is this for plasma cutter, router, mill, or table positioner ? What are
the loads ?

One example; rotating screw.
Use about 25 mm screw (20 mm is normally enough, but the joint
definitely weakens it)
Rotate max 300 rpm
Fixed end: use 2 dual-row angular contact bearings, separated by 100 mm,
on one end. This is the fixed end.
Use one bearing at the other end. Have the lead (=rise) mach your needed
speed at 300 rpm.

i.e. if you need 2000 mm /min speeds (about 80 inches/min) , at 300 rpm,
its 2000/300 = 6.6 mm rise per turn.
Use nearest rise in 25 mm screw you can get, probably about 5 mm. This
would give you 300 rpm * 5 mm/turn or 1500 mm/min, or about 60
inches/minute.

For a rotating nut, use timing belt to rotate the nut, and tension the
screw maybe about 80 kg, for 100 cm working length,
you would need a screw of about 120 cm.
e.g. 15.9 mm NSK bearing + 100 mm space + 15.9 mm NSK bearing + 100 mm
working are,
plus ballnut (maybe approx 80 mm) + 4-bolt flange bearing about 33 mm,
total 1164 mm == 120 cm.

[ ref: 490-0776 in RS-components
NSK bearing codes:
3202BTNG
YRLN5
508 ]

>
> Hi,
>
> I need a ball screw of total length around 1000mm, but best I can get
> is about 500mm only, so I need to add some length at both ends for
> mounting the screw on the table. Have anyone done this before any helps
> would be much appreciated.
>
> Regards,
>
> Horace.
>