This e-mail I like!

morgan · Post by **morgan** » Thu Mar 13, 2008 10:34 am

I put out a few 'feelers' in the right places for equipment that may be of use for stacking etc and this e-mail came today.....

Hi Kev, Lou here. This is your lucky day! Ivor has just brought
home a fantastic piece of gear for you and we're chuffed to bits,-
taken from a machine that was going to be scrapped.
It's a 2 axes micrometer movement from a shadowgraph
( used to measure small radii of blades etc).
There's a 1 inch total movement in both axes. Micrometer movement
accurate to 1 tenth of a thou i.e. 0.0001 inch.
You'll have to mount it on a solid piece of wood or something.

Do you think this will be OK? and has anyone seen this sort of gear in use?

augusthouse · Post by **augusthouse** » Fri Mar 14, 2008 8:08 pm

hi morgan,
I suspect that the items on their way to you may be somewhat similar in concept to the pictures below. The image shows an XYZ and XY configeration from Newport Corp. Thorlabs, Parker Daedal and others make these types of positioners.

Are they any good? You bet!!!

http://www.newport.com/460A-Series-Low- ... alog.aspx#

Craig

augusthouse · Post by **augusthouse** » Fri Mar 14, 2008 9:57 pm

I did a search on eBay for Shadowgraph and Comparator.

Some images below.

Craig

rjlittlefield · Post by **rjlittlefield** » Sat Mar 15, 2008 12:48 am

Ah, now that would be a fun little positioner!

They're not quite as wonderful as they appear at first glance, however.

Micrometer screws are typically 0.025" per rotation, with either fine ticks or a vernier scale that allows them to be read to 1/250 rotation = 0.0001". The last image is consistent with these numbers.

In contrast, the machining table that I use is 0.100" per rotation, so 4X coarser there, but the dials are also about 2X larger.

Bottom line is that under manual control the shadowgraph positioner will probably make movements only about 2X finer than my table will, maybe 4X if the movement is very smooth.

I'd still love to have one, mind you!

--Rik

morgan · Post by **morgan** » Sat Mar 15, 2008 4:05 pm

Thanks for the info all.
I got my sticky fingers on the positioner today and it seems to be a very smooth running bit of kit.
It has a roller bearing movement and, with what appears to be, no backlash at all.
Once set up it should be ideal for my use.
Watch this space.

Harold Gough · Post by **Harold Gough** » Sun Mar 16, 2008 3:01 am

You can find them on eBay:

http://cgi.ebay.co.uk/4-Way-Macro-Shot- ... dZViewItem

Harold

augusthouse · Post by **augusthouse** » Sun Mar 16, 2008 4:02 am

Morgan,
Nice positioner! Lou and Ivor should be given a medal for rescuing that beautiful gizmo. Looks really smooth!

Craig

rjlittlefield · Post by **rjlittlefield** » Sun Mar 16, 2008 9:54 am

Harold Gough wrote:You can find them on eBay:

http://cgi.ebay.co.uk/4-Way-Macro-Shot- ... dZViewItem

Harold

Umm...no...very different beast. That unit on eBay uses two direct-drive racks. It will make movements of 1/2 mm easily and 1/10 mm (0.004") if you're very careful, in contrast to the 0.0001" markings (and finer movement possible) for morgan's unit. I use one like eBay's for XY positioning, but its movements are nowhere near fine enough for high magnification stacking.

--Rik

augusthouse · Post by **augusthouse** » Mon Apr 07, 2008 2:07 am

Rik wrote:

Micrometer screws are typically 0.025" per rotation, with either fine ticks or a vernier scale that allows them to be read to 1/250 rotation = 0.0001".

What does 1/500 rotation = ? (for the non-mathematician - me)

I just received a similar xy unit. The giant micrometer actuators (30mm diameter) allow 1" travel, 50 TPI with 500 increments per turn. The actuators offered slight resistance until I pulled them apart and removed some old, dry lubricant - now it glides with finger-tip control.

The unit is marked EP01 New York - Made in Germany. The actuators are marked Made In West-Germany DIN 863/1. Stage area is 5 1/2" x 5 1/2".

Here's the eBay listing picture. It looks much better now after some TLC.

*edited typo

Craig

Harold Gough · Post by **Harold Gough** » Mon Apr 07, 2008 3:16 am

Am I right in thinking that the positioning stage on a decent research microscope would give the fine movements necessary? If so, there might be more "for spares" of those available than of these more exotic machines.

Harold

DaveW · Post by **DaveW** » Mon Apr 07, 2008 3:25 am

I have one of those focusing slides Harold. They are OK for average macro work or perhaps even low level photostacking, but nothing like as precise as the dual axis micrometer slides shown above. They are akin to the normal fore and aft movements on bellows, being a similar rack and pinion slide.

DaveW

Planapo · Post by **Planapo** » Mon Apr 07, 2008 5:55 am

Craig,

I interpret the data of your positioner as follows:

50 TPI, i.e. 50 turns giving 1" of movement, then
1 turn giving (1/50)" of movement (compare: the value given by Rik says 1 turn giving (1/40)" )
with 1 turn being divided in 500 increments, then
1 increment giving (1/50)" x 1/500 = (1/25000)" = 25.4 mm x 1/25000 = 0.001016 mm

So, one increment of rotation would give you 1.016 Micrometer of movement.

But then, are there really 500 increment markings on that actuator knob with a diameter of 30 mm??? I can´t imagine this.
On my microscope stand there are 100 increment markings on a knob that has a diameter of 30 mm. How is it done with 500 increments on your 30 mm knob?

--Betty

Planapo · Post by **Planapo** » Mon Apr 07, 2008 6:04 am

Harold,

Yes, the fine focus of the stage drive of a better microscope will give you the increments of movement necessary. That is what I currently use with good results.

--Betty

rjlittlefield · Post by **rjlittlefield** » Mon Apr 07, 2008 8:44 am

Craig, I confirm Betty's calculation. 1/500 turn at 1/50 inch per turn = 1/25000 inch = 0.00004" = 0.001016 mm = 1.016 microns (micrometer, µm).

Nikon MicroscopyU quotes the DOF of a 20X NA 0.40 as being 5.8 microns, so you will have lots finer control than you need.

However I share Betty's headscratching about 500 increments around a 30 mm diameter dial. The circumference of that dial will be pi*30 = 94 mm, implying a spacing of 500/94 = 5.3 increments per mm. I have never seen tick marks that close together intended to be read by naked eye. It is common for such fine movements to be encoded using a vernier scale (image below). You can certainly make a movement of 1/500 turn. Just be sure you are reading the indicator correctly.

Harold, what Betty says is correct, but I'm not sure you two are talking about the same thing. The fine focus of pretty much any microscope will work fine, if it has enough total travel. However, slide positioners (XY, not focus) are typically just direct drive to a small rack and pinion. Those do not have enough precision/accuracy for fine stacking.

Betty, the linear scale on axis is used to keep track of how many full turns. Small analog micrometers typically have three scales that the user must read separately, then add together as shown below. The shadowgraph positioner shown by morgan does not have the vernier scale. I can't tell from the picture what Craig's unit has.

--Rik

Planapo · Post by **Planapo** » Mon Apr 07, 2008 2:09 pm

Thanks much, Rik for this image and your explanation of this complex scale on the analog micrometer. I´ve never worked with such a gadget.

BTW, I wish I had more lecturers like you: You answer my questions without me even having asked them!

You can either read my mind, or my previous edits!

--Betty