Here's a teaser pic:

You can see more pics on my blog along with some design notes.
http://timf.anansi-web.com/wp/possible- ... -shapeoko/
The offset is in the plane the V-wheels perform best. The carriage twists in the plane of the V-wheels at least an order of magnitude less than in the two perpendicular planes. There will be some additional error, but it should be very small.cozmicray wrote:Are you concerned about the torque created because offset
of leadscrew and center line of mechanism?
Difference between drive point and resistance point.
I can. There are no spacers on the V-wheels, which makes a big difference in rigidity, especially important in the weaker planes (see above). Also, the spindle is closer to the Z V-wheels, and overall closer to the gantry, so its weight and the cutting forces have less leverage over both the Z and the X V-wheels.cozmicray wrote:I can't see how it is MORE rigid?
Yes, but that's the normal way of running a leadscrew. A longer leadscrew will be even more constrained (e.g. a block with two angular contact bearings, spaced well apart and preloaded, at each end -- four bearings total), to prevent whipping.cozmicray wrote:Will the leadscrew be over constrained with bearings
at top and bottom?
By what "Normal" spec?cvoinescu Yes, but that's the normal way of running a leadscrew. A longer leadscrew will be even more constrained (e.g. a block with two angular contact bearings, spaced well apart and preloaded, at each end -- four bearings total), to prevent whipping.
I am not a Mechanical engineer but I can read / listen to what the say?If you rigidly constrain a component at more places
than are needed, you will start a fight between these places. This
is overconstraint. As an example, three bearings on one shaft
do not work. It is not luck you need in trying to fit the shaft
through three bearings, it’s sympathy — it won’t go! -----
Understanding how to transform basic physical principles
into working concepts with predictable behavior is the key to
achieving high accuracy, high speed, and high reliability.
http://multimechatronics.com/images/upl ... 0Fight.pdf
I'm not an engineer, so I can't quote specs at you, but http://blog.helixlinear.com/lead-screw-end-mounts and http://web.mit.edu/people/kripa/publica ... dsmc04.pdf and http://www.cncroutersource.com/leadscrew.html are just a few examples that come up with a quick search.cozmicray wrote:By what "Normal" spec?cvoinescu Yes, but that's the normal way of running a leadscrew. A longer leadscrew will be even more constrained (e.g. a block with two angular contact bearings, spaced well apart and preloaded, at each end -- four bearings total), to prevent whipping.
Well, do that then. I got my information about how to mount a leadscrew the same way.cozmicray wrote:I am not a Mechanical engineer but I can read / listen to what the say?
Wha...?cozmicray wrote:Have seen simulations on spacecraft instrument drive mechanisms
and the REAL thump -- thump -- thump that permeates thru entire spacecraft
when the instrument is scanning with leadscrew drive?
More H, and the willingness to admit O may not be sufficiently informed, would be nice.cozmicray wrote:IMHO
Charles Darwin wrote:Ignorance more frequently begets confidence than does knowledge.