Fine Centering Scope

This is the key for me, I think. The problems with parallax and with not being able to see the scribed lines well enough really slows things down, and causes errors. I'm convinced, and will buy the Enco scope.

I couldn't tell, although the comments were to the effect that reflections off the workpiece degraded accuracy in practice. In fact, the description at littlemachineshop.com says just that, and they sell an accessory (the polarizer) to solve the problem.

Which models have the zeroing knob?

The item at littlemachineshop.com looks like a computer-generated image of what it ought to look like, not a photograph of what it does look like. But it does gave holes in the side that look like they give access to adjusting screws.

Would the scope be any better? Sounds like the bulk of the machine would be in the way. I did see a centering scope sold in the UK where the arm is perpendicular to the centering axis.

Joe Gwinn

According to Joseph Gwinn :

O.K. It is pretty much as I remembered.

"Moves the reticle line" is the same as adjusting the centering to compensate for slightly off-center collets or spindles. If it does that, then it does everything that the other does.

It only does the focusing of your eye to the hairline to make it good and sharp. Focusing of the image of the scribe line would be done by Z-axis motion -- either the quill or the knee -- whichever is easier and gives sufficient range.

I must admit that I had originally though that the bottom knurled ring (just above the objective lens) was for fine focusing of the objective, so you don't have to tweak the Z axis as closely.

O.K. Though I don't think that there *is* "another hair" -- you only need one to do what the scope is for. You rotate it 90 degrees to do the other axis, once you've zeroed it for the axis which lets you swing the eyepiece both ways. As mentioned above, you can't do the zeroing with the Y axis because you can't get your head between the eyepiece and the column -- though one with a TV camera built in and a TV monitor on a shelf nearby would allow that as well.

I note that the Enco one says the length is 3" (which I suspect means from the step at the bottom of the shank to the end of the lens), and the lens then needs an additional inch to focus (working distance).

It looks to me as though the eyepiece tube on that one is closer to six inches long, if the end of shank to lens tip is three inches.

Enjoy, DoN.

According to Joseph Gwinn :

O.K. It sounds as though it is the thing for you -- especially if you set to scribed lines often.

Oh -- you were talking about the one with the laser beam generating a single dot (with the Airy ring surrounding it).

I *think* that the Laser one's knurled ring is for focusing the dot to the smallest possible -- but I guess that it could be for zeroing the offset. In that case, I would guess that the easiest way to zero would be to set the spindle speed at the slowest, and watch the circle generated by the dot -- and grip and release the knurled ring (if the design allows that), watching the effect on the circle size until it is zeroed (stationary even with the spindle rotating). Since I have never seen one of these, all I can do is to guess.

I think that none of the Laser diode ones do. And it appears that the Enco does

Those may be for original zeroing at the factory. Though you might have to tweak it if you drop or bump it hard.

The scope is what I was talking about there -- not the Laser diode one.

That would still be difficult to adjust, because the eyepiece would probably hit the overarm as you swung from 0 degrees to 180 degrees. (And hit the table, swinging the other way.)

Enjoy, DoN.

So it would appear.

Billy Hiebert said that the lens to target distance needs to be about

I'm hoping for a crosshair.

I read about the calibrated TV cameras. Seemed like far too much trouble.

Well, I ordered one. When I get it and have used it a bit, I'll post a report.

Joe Gwinn

We shall see. I've ordered one.

Yes, that's the one, that's the issue.

What I don't understand is why the laser center doesn't have a knob to vary the intensity. The polarizer sounds like a clumsy workaround for what should have been simple to fix. It would be far easier to vary the current through the laser.

Me too. I have only that copmputer-generated picture.

OK. Maybe someday.

I guess video wins here.

Joe Gwinn

According to Joseph Gwinn :

I believe that Laser diodes turn off below a certain current, unlike LEDs which simply get dimmer. And the "knob to vary the intensity" would either waste power in a series resistor, or require active circuitry to control the current (a better but more expensive solution).

You might be able to reduce the apparent intensity by PWM (Pulse Width Modulation) -- though I'm not sure that this would eliminate the appearance of the Airy ring.

I guess so -- except that the camera module would still probably be put on on a long arm to maintain the maximum sensitivity.

Enjoy, DoN.

True enough, but lasers are linear above threshold, so all that's necessary is an offset, so zero on the pot is near the lasing threshold, and max on the pot is at max allowed current. (Or duty cycle, if using PWM; discussed below.)

I think that most laser pointers and modules made today have a little IC in them, not just a resistor. PWM would certainly work. Perhaps the ICs already work that way.

The Airy ring disappears simply because it becomes too dim to see with the unaided eye, especially in a well-lit shop, not because it isn't there.

Depends on the camera lens. One would expect that what is being used is a low-power microscope objective lens.

Joe Gwinn