Re: [CAD_CAM_EDM_DRO] one for the math gurus.....Squaring an Axis

Chris L wrote:

>Jon Elson wrote:
>
>
>
>>You don't need to do this to determine axis orthogonality. A ball-bar
>>test detects
>>about a dozen different sorts of errors. But, just to detect orthogonality,
>>you just need some way of measuring a distance accurately. If you mounted
>>a ball bearing known to be round to the table, and another one in the
>>spindle,
>>and got them right above each other, and then moved the table some equal
>>distance
>>away, first, say +X +Y, and then the same distance away +X -Y, and measured
>>between the balls at each point with a good 6" micrometer, you should be
>>able to detect this error. Making measurements at all 4 diagonal corners
>>and summing the results might help cancel small errors and magnify the
>>real orthogonality error.
>>
>>
>>
>This looks to be the ultimate method, and I suppose by the time you go
>thru the "cutting" squares out or wrestling with an already "out of
>square" square ( at the home centers around here I don't think any of
>them are square !)
>

The $12 squares at the Home Depot are a JOKE! They are accurate within a
couple of degrees, at best. A good quality machinist's square is good to
tens of arc minutes. That STILL is not good enough for machine alignment
testing. I checked a few of my machinist's squares, and they all have
convex
of concave sides that are easily seen against a known good straightedge.
I mean VISIBLY not flat! So, there's no way to even know what the angle
really is, if the sides aren't even flat. I'm doing alignments on my lathe
bed resurfacing that work out to single arc SECONDS! Over a bed with
a 48" travel, that is still several tenths of curvature, but it is the
best I can
do.

>, You could have this done. I think I am going to
>order a few of those "ball" and shank alignment thingys from Mcmaster. I
>can easily do what you describe, and I guess the Large Mic is the thing
>I'll borrow. I wonder how close I can get with my Mit Digital Caliper....
>I was asking this question because at one time I had my Router as close
>as ever possible. But, a while ago, and in a hurry, I made some blocks
>to raise the whole gantry. I set it back up close, but now only hit
>about within .003" on Circles. ( on a DigiCaliper...) I used to hit a
>little closer and would like to get it back asclose as It was.
>
>
>Are you indicating that no one makes the "BAR" you describe with the
>ball sockets on each end ? That sounds like a handy device.
>

I'm not aware of such a thing. Renishaw makes "ball-bar" testers that
have this sort of
bar with a LVDT linear displacement sensor and a shaft encoder at one of the
fixed ends instead of a simple ball joint. That way, they can plot
error from a true
circle in a circular chart form. If the plot comes out as a circle,
there's no error.

> Can't say
>I've ever seen one, but I lead a sheltered life. I have a thing here
>that someone told me was a SineBar..... Other than a good paper weight,
>I don't know what to do with that either !
>
>

A sine bar usually has some fixed distance between two round bars,
usually 3 or 5" exactly.
You put one of the round bars on a stack of gauge blocks and you can set any
particular angle you want, precisely. Very handy if you need to drill a
hole precisely
at 37.93 degrees in a part.

Jon


[Non-text portions of this message have been removed]