Geo wrote:
I have read the threads and checked the various calculators. I assume you want to strive for the entire 8x4 sheet in the green when using the above referenced. But some mentioned the belt angle but I do not under this 100% yet.
Which belts are compared and what is the happy range angle (or the extremes to avoid)?
So what the green/white/red areas in my calculator are all about is the belt
angles.
background:
The arms can pivot on the router, but at some point they hit the uprights. The
entire sled can then rotate until a 2nd arm also hits an upright, at that point
you don’t stop being able to move, but the belt no longer makes a straight line
between the anchor and the center of the bit. This makes the distance from the
anchor to the center of the bit be a little less than the maslow thinks it is.
This increases the tension on all the belts, and makes the sled position be just
a little off.
From the earlier theoretical tests (see
Maslow 4 frame size checker - #77 by arjenschoneveld ) the error
starts out small ( 0.5mm at 130mm beyond the green) but grows non-linearly
(2.5mm 400m beyond the green). This is a theoretical calculation that does not
take into account the fact that the belt doesn’t translate directly into error,
it translates into increased tension and belt stretch (and longer belts can
stretch more than shorter ones)
according the Bar’s design, the arms get blocked when they get to within 20
degrees of the verticals (i.e. no two arms can get closer than 40 degrees to
each other, or furhter than 140 degrees from each other), my view of cad gives
it just a little more, and I have a version showing what I think would happen if
you removed the verticals around the leadscrews and clipped the top clamp to
avoid problems. That is the ‘angles’ pulldown on my calculator. As you can see,
the wider the angles, the bigger the green area.
How this applies:
When you get close to the edge, the belts to the two closest anchors get far
apart. The red area is where those belts will both hit a vertical.
When you get near a corner, the two belts to the corners of the opposite
diagonal both run into the verticals (so as you are nearing the top left corner,
the bottom left belt and top right belt get to their limit). That defines the
edge of the white area of the graph.
So in the green area, the angles all work and you should have no problems
(although if you get to really small frames, the Z angle and diameter of the
sled start to be a problem, the theoretical green area on a 20" square frame is
a lot larger than the 4" square that you can cut and still have the 16" sled
clear the side of the frame, and that close to the anchors the Z distance to the
anchors needs to be small)
Now, ALL OF THE ABOVE IS THEORETICAL, the default frame that @bar built does not
work according to theory, but he was able to cut out the world map without
noticing big problems. It’s all going to depend on what your accuracy
requirements are, and that can vary from project to project.
The testing being done in this thread is an attempt to see how much of this
theoretical error translates into practical distortion.
Does this (long) explination help? At this point all we can say is you want to
keep as close to the green area as you can, and we have seen a number of people
propose frame layouts that are longer than is useful, resulting in the top and
bottom red areas reaching deeper in, while the green area is longer than the
workpiece they are planning for. In those cases, moving anchors in from the ends
can actually create a more usable machine.
For example, compare a 10x8 (default size) from with a 12x8 frame, and then look
at a 11x8 frame which seems to be better than both
David Lang