Turntable use ... i dont get it :(

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May 10, 2012
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Thread starter #1
I tried to use at pottery turntable to center my work under a microscope. I centeret the scope and the middle of the turntable. The turntable has rings and when i spin the turntable, the rings are perfect centered with the view through the microscope.

In theorie, if i now place my vise under the scope i just need to place the section i want to engrave in the middle of the scope view and it should be turning in the center of the view when i turn the turntable. No matter on which position of the vise the part is that should be engraved? Am i right?

But that does not happen for me. It always turns in big O´s .

Again, my steps ...

- Center of the turntable is exactly ind the center of the scopes view
- double ckeck turning the emptie turntable and it runs perfectly centered, no concentric movements of the inner turntable ring to see when looking through the scope
- i place the vise with the engraving part under the scope
- i place the area i want to engrave exactly in the middle of the scopes view
- i turn the turntable - not the vise
- the section i want to engrave always turns off center

First i thought maybe i moved the turntable while i put the vise in the middle. But thats not the case. When i remove the vise then the scope and the turntable are still exactly centered.

What could be my mistake here?
 
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#3
It's hard to define straight down because ... A stereomicroscope gives perception of depth because the left and right eyes get different images from two different optical paths in the microscope. Your brain reconciles the different images, typically preferring one eye over the other (The dominant eye. You hold your graver in your dominant hand and look at it "predominantly" with your dominant eye. The dominant eye and hand are not necessarily on the same side) Those optical paths are not parallel, but converge upon the a spot in the center of the field of vision at the level of focus. I'm guessing that you did not focus upon the turntable, but instead saw it's unfocused image, making it easier for your brain to favor one path over the other. Try this: make a cylinder with square ends (dowel for example). The length should be equal to the height of your vise + thickness of the work piece. Put a dot in the center of the top end. Put the bottom of the dowel in the bulls eye on your turntable. Center the focused dot by moving the scope. Spin the table. Replace the dowel with the work. Spin. If it rotates, there is a different problem.
 

mitch

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#4
what Marty said. if you want your scope tilted a slight angle, the turntable needs to be tilted, too.

also, your vise needs to be dead upright on its donut. you might want to try hot gluing it to the donut to keep it from tipping out of alignment.
 
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#5
l have the same setup and find it impossible to center the turntable by itself. So I start off as you have in order to get a gross centering. then I place the vise on the turntable, turn up the magnification, and complete the same steps as before. I focus on one hole on the top of the vise, or maybe a pin or even a dot with a sharpie. Make very small adjustments by tapping on the side of the turntable, recenter the dot as viewed through the scope and spin again. Your theory is correct and when the turntable is truely centered your work will spin centered.
 
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#6
Interesting reading. I always thought that it was a macro vs micro centering issue but perhaps it was an angle issue. There is a good 4-5” from the top of the turntable to the work piece which could have changed the effective center. In either event when I recentered the turntable base as described above it works for me.
 
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#7
To circumvent the centering issues, I glued a 2x2cm piece of technical drawing paper (bears a 1mm blue grid) onto a printable magnetic label (less than a mm thick, prints in inkjets). This I place on top of the engraver ball’s jaws, center the vise on the turntable (no precision needed) and look trough the scope onto the square. When the turntable is rotated and the center of rotation is somewhere on the square, it will be visible (like a hole in the blur the other squares make while rotating) and one could center the microscope to it. My scope is at an angle, and I use 2 different ball vises. Works all the time. The slightly magnetic backing keeps the paper in place during rotation. Should have patended the idea...

Best regards,

Ralf
 
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Thread starter #8
Thank you for your answers!!

also, your vise needs to be dead upright on its donut. you might want to try hot gluing it to the donut to keep it from tipping out of alignment.
Maybe thats the issue ..
But i tried it again and i had the same struggle. I went back to the positioning pin vise for the moment.
 
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Thread starter #10
Thank you, Sam!

I found that video. There was also a nice hint on how to center when the vise is on the bench Instead on a turntable. That works great with the positioning pin vise.

Since i only have a microblock xl its not that easy to get it perfect leveled. Maybe you can see a tilt better on a bigger vise?
 

Borzzza

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#11
Make sure your vise is straight, not tilted. I put a rubber ring under the vise to keep it from tilting for example.
Move your turntable with the vise on it to center it, and check if the position continues to be good just leave it like that))
 
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#12
As an afterthought to my former post, I made another magnetic label that bears a 2D dot pattern with about 0.3mm spacing. It’s printed with a b/w laser printer on white paper. Works better because of the enhanced contrast and finer structure.
Place it on your work piece or on the ball vise jaws. Center the vice roughly on the turntable, precision is not important here. Look at the dot pattern through the microscope. While rotating the turntable, the center of rotation becomes visible in the rotating dot pattern. Center the microscope to it. Microscope viewing angle is no longer crucial here.

Best regards,

Ralf
 

Chujybear

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#15
Make sure your vise is straight, not tilted. I put a rubber ring under the vise to keep it from tilting for example.
Move your turntable with the vise on it to center it, and check if the position continues to be good just leave it like that))
should be able to do it with a tilted vise.. but it is much simpler if your vise is planar.. in which case, dont't bother with an engraving vise at al, just glue your work to a big steel slug, or even a block of heavy hardwood.
 

dhall

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#16
As mentioned, it can be a challenge to get everything "straight" (vise, turntable, scope). Don't rely on "eyeballing" your setup. Use a level to at least get all the components parallel to one another, and then slide things around under the scope until it lines up, as described above. If the scope seems to be a challenge, use the barlow lens frame on the bottom of the scope, so your level will be underneath the scope.

You'll get there!
Doug
 
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#17
If you use a turntable vise, no matter how you tilt it it will stay centered. There’s no need for dowels or anything. Just rotate the table with the vise on it and observe the pivot point. Move your scope over it to where the pivot point is in the middle of the field of view. Takes two seconds.
 
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#20
i use a nickel to center my scope. i place the coin in the center of the vice then place the vice on the turntable. Give the turntable a spin and watch through the scope the way jeffersons eye pivots around the center of view. I keep my scope in the same place and move my turntable and ball vice at the same time by sliding the turntable under the scope until the eye is in the middle of my field of vision. To confirm I'm centered i zoom all the way in and make sure the eye of the coin is perfectly zeroed. hope this helps
 

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