Thanks for the additional info DoN. I thought that I'd remembered from
earlier rotary table and dividing head discussions, that there were details
in Machinerys Handbook. I've known that I should get one (one of the great
procrastinators, ya know).
I haven't used indexing plate sets, and the only differences that I've seen
is that generally, there may be 2 or 3 plates in a set. I wasn't aware that
there were a specific number of sets of holes (six per plate), or other
standards, but it stands to reason since these aspects have been figured out
before the manufacturing of plate sets began.
I'd read that some plates have different divisions on two sides of each
plate.
Other differences would be center hole diameter and number of hole for
attaching the plates (3 or 4).
For simple indexing, I have a 5C spin index, and that's about the extent of
my indexing experience.
What I think would be best for me is a digital readout that displays x
number of degrees with a resolution of .001, to be sure about the settings
before cutting.
The minutes and seconds method is beyond my comprehension (or desire to),
and it seems to be an unneccesarily more complex way of thinking about
locations in a single rotation. It may work well for others that have
experience with it, but it just seems to be way more complex than other
positioning methods.
The feeble grey matter doesn't function at the levels of a CNC computer. I
would see fitting a DRO to a indexing device to be an easier solution.
Encoders have become smaller, and digital counters aren't too complex to set
up, so having a display with 0-360.001 or 0-3600.00 seems to be a good way
to achieve positioning locations.
For any method of indexing, I wouldn't have a clue as to how much error
might be introduced by accumulation, at say, the last tooth on a 100T (or
113T) gear blank, for example. Hopefully, one could make other adjustments
in a design so a 113T gear wouldn't be required.
For cutting 6 splines on a shaft, I would assume this would be a fairly
simple task with indexing plates.
--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html
"DoN. Nichols" wrote in message
...
On 2009-01-06, Wild_Bill wrote:
Would anyone here know what the actual increments/hole numbers are
correct
for a 90:1 ratio Rotary Table?
Do you have a copy of _Machinery's Handbook_? There are tables
in there describing the circles needed to get each number of divisions
and such.
Most are for the 40:1 B&S dividing/indexing heads, which have
three plates of six circles each.
However there is also a table for the Hardinge dividing heads
which have a 20:1 ratio (IIRC), and need a lot more plates.
Also, there are formulas to allow you to calculate what number
of holes is needed for each number of index points, which might be where
you need to start, since you are using a rotary table instead of a
dividing/index head.
Multi-page tables, including differential indexing (which
requires stacks of gears rotating the index plate as the crank is turned
to get some of the figures which don't work out well for a normal 40:1
ratio.
The 90:1 ratio is not chosen for good division ratios, but
rather to get an even number of degrees on one turn of the crank (4 for
a 90:1 ratio). The 40:1 comes out at 9 degrees on the dial which is
more awkward.
Well ... they *will* work on 90:1 for some numbers of holes.
Let's see -- 4 degrees per turn of a 90:1 crank, and divide that by 37
holes (one of the choices on the 40:1 plates) and you get 0.2432
degrees, or 0 degrees 14' 36"
Right -- or adaptable to the RT, with a collar to ensure
centering and various other bits. The main thing is to get the formulas
out of _Machinery's Handbook_ so you can calculate how many holes will
be needed -- and remember that any integer multiple of the number of
holes needed can be used -- for example if you only need four holes, you
can skip over 9 holes per on a 36 hole circle, or 10 holes on a 40 hole
circle and so on.
How different do you expect a plate set to look (other than
overall size)?
Good Luck,
DoN.
--
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