This.
Somebody wiser than I am tought me that me that you can't ever
totally eliminate backlash on a screw and nut setup. You can
lessen it so it is less obnoxious, but you can't eliminate it. So
you will have to live with it. Since you have to live with it
there it doesn't make much sense to jump through major hoops to
get rid of the last little bit.
So you do what Carl said, the last motion is always in the same
direction, and is larger than the backlash. Sometimes that means
you overshoot and come back more than the backlash. Or if you
overshoot you come back more than the backlash and go in again
more carefully.
Ideally that last motion should be in the opposite direction than
cutting forces are going to try to move the cutter. This way the
cutting forces have something to push against instead of pulling
the cutter into the backlash zone where it can float around.
On 4/5/23 15:28, Carl wrote:
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Hi
Gang:
As a
toolmaker we learned to always turn the cranks the same way,
usually clockwise. This has fallen to the wayside with ball
screws and digital read outs.
Carl.
On 4/5/2023 2:26 PM, Herman de Leeuw
via groups.io wrote:
Hi Jpow,
Having come the same way as you do,
I just would like to toss in here my humble 2 cents of wisdom
without any claim to UNIMAT 3 lathe mastery at all, but here
goes:
In this rather comprehensive (and
recommended) , published by the then importer for Unimat in
the Netherlands, in Utrecht (still in
existence), I stumbled upon the below passage on page 58 (see
scan).?
The main point here is about the "transporteurs"?
- the spindles for the different movement feeders
(longitudinal, cross-slide and tailstock). According to this
manual, the backlash ("speling") on the spindles is on
purpose and one should not try to reduce the backlash. Coming
to the field of metalworking as a woodworker, I was not
surprised: when dealing with cast iron woodplanes, one
encounters the same backlashes when adjusting the cutting
iron.?
What one should do is to 1) either
keep a record when the cross slide spindle starts to engage
and the slide starts to move, or 2) avail oneself of a set of
adjustable handwheels that allow you to set the wheel at zero
the moment the spindle engages.?
As much as I would want to take out
the backlash (I have a history of maintaining motorcycles,
mopeds and bicycles, where it is all about reducing friction
and taking out backlash) I have come to live with it now.?
Now hoping to hear from a few others
whether this makes any sense,
Herman
?
Hey all,
I'm having this really irritating problem with backlash
coming from the Unimat PC cross-slide handwheel.
My understanding is that backlash (for the Unimat) can come
from two sources
A) Play in the slide lead nut / screw itself; OR
B) Having too much of a gap between the threaded
handlewheel and the cross slide itself.
My main issue is with B)
Following the Unimat instructions, I screw in the threaded
handlewheel all the way, and back it out JUST a bit, before
tightening up the locking nut (on the outside).
For the life of me, I can never get it "just right". If I
tighten enough so everything JUST rotates smoothly, the
backlash is too much (0.07mm). If I tighten anymore, the
backlash is a bit better, but the handwheel starts to bind
and it is difficult to turn freely.
(The binding is strange in the sense that "tightness"
occurs at certains angles of rotation only, rather than a
constant heavy friction).
Could this be some issue with the bushings or something? I
tried putting in small thrust bearing between the
handlewheel and where it is mounted, but it didn't help
much.
Appreciate any advice thanks :)
