Re: X-Y Table, Rotary Table for CNC INFO

Hi Ballendo,

If I am correct, about 80% of machinine is drilling holes. that
means the table should be capable of speeds for feeds of drills.


Although more expensive, I thought about a rotary table style screw
for the Z. the large, screw would spin thereby raisisng the table.
I think the sizzors is too fragile. The lifting members have to
undergo tortonal stress, compression and expansion.

Dave



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo <ballendo@y...>"
<ballendo@y...> wrote:

> Ray,
>
> Thank you. As I mentioned before, I'm only pursuing this as a

thought

> experiment, since I believe the economics won't work out. But
> someone else may not agree. So here's some more...
>
> (added on re-read. If you ARE interested in this as a real item,
> please see the PS below this message.)
>
> In the simple single scissor I have in my head, there would be a
> SIN/COS relationship to leadscrew nut movement versus vertical
> movement.
>
> The single X of the scissor is arranged this way: (of course there
> are two X's, and the nut would act on the lower leg of both, but

for

> the example, we'll just look at one of the X's)
>
> pivot points at left bottom, crossing point, and left top. Nut is
> attached to right bottom, with motor hanging out past the left
> bottom. (The leadscrew remains horizontal at all positions.) The
> right top will slide "captured" in a slot. A ball bearing carrier
> with 2 or 3 bearings riding on either sidewall of the slot will

allow

> this final pivot point to be in line with the left top (which is
> needed to preserve accuracy), while eliminating this otherwise
> possible source of backlash. Similarly, the right bottom legs of

the

> x will need to travel without vertical backlash in a straight line
> (the axis of the leadscrew).
>
> Now here's what we have. At exactly 45 degrees (the X legs are all

at

> right angles to each other), one unit of movement of the leadscrew
> wil result in an equal vertical movement. Less than this, it will
> take "more" leadscrew, and above this point it will take "Less"
> leadscrew movement. (following the SIN/COS angular relationship) So
> let's keep the error "single ended" by restricting ourselves to

less

> than 45 degrees... We choose "less than" so that the table can be
> kept compact vertically.
>
> Anyway, Hope this makes sense. This is a very "buildable" method

for

> any who wish to pursue it. I would be glad to help any who want
> to "go there" with comments or ideas offlist.
>
> Ballendo
>
> P.s. I actually have a pretty complete design for this in my head.
> I'd like to hear from anyone who thinks this might be an item worth
> having: How much table force/load would you want? What "accuracy"
> would you need to have to consider REALLY buying one of these? And
> finally, At what price would you REALLY buy one, given that your
> specs were met? (Speedwise, I'm thinking that 100 IPM would be

easily

> done.)
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Ray Henry <rehenry@u...>
> wrote:
> >
> > Ballendo
> >
> > The z motion compared to the rotation of the screw is really

riding

> along
> > an arc or a cam. The leadscrew comp produces a linear

compensation

> > between points. This should be okay for most of the arc but like
> you say
> > it would be big as you approached the top.
> >
> > Till Franitza built a little hexapod using a a crank shaft and
> connecting
> > rod to get linear motion. This would be very similar to the

motion

> of
> > the scissor table. If we get serious about this, I can see if we
> can get
> > him to explain it to us.
> >
> > Ray
> >
> >
> >
> > On Saturday 18 January 2003 04:56 am, Ballendo wrote:
> > > Message: 2
> > >    Date: Sat, 18 Jan 2003 04:18:32 -0000
> > >    From: "ballendo <ballendo@y...>" <ballendo@y...>
> > > Subject: Re: X-Y Table, Rotary Table for CNC INFO
> > >
> > > Ray,
> > >
> > > Good point.
> > > But it would be repeatable, and therefore possible to correct in
> > > software. Possibly even with EMC's leadscrew correction, though
> the
> > > error is "squished at one end" of the travel.
> > >
> > > Ballendo
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, Ray Henry <rehenry@u...>
> > >
> > > wrote:
> > > > 
> > > > >    From: "ballendo <ballendo@y...>" <ballendo@y...>
> > > > > Subject: Re: X-Y Table, Rotary Table for CNC INFO
> > > > <s>
> > > > > Think scissor lift table. A couple of accurately placed
> pivots;
> > >
> > > ONE
> > >
> > > > > screw, lots of force. Problem: Stability in the direction
> perp. to
> > > > > the scissor. Fix that with a vertical guidepost (or two.

Note

> that
> > > > > these DON'T need to be heavy duty linear motion component
> quality;
> > > > > they are just keeping the structure stable in one axis
> (resisting
> > >
> > > only
> > >
> > > > > side loads).
> > > > 
> > > > With a scissor you will need to be a bit careful where you

place

> > >
> > > the
> > >
> > > > screw.  The usual place is in the middle between pivot arms

and

> > > > perpendicular to the motion.  Many car jacks are made this
> way.  
> > >
> > > With
> > >
> > > > something like this, z motion would NOT be linearly related to
> > >
> > > rotation
> > >
> > > > of the screw.
> > > > 
> > > > Ray