Accurate threaded rod help needed

James,

I am putting the stage together for caustic testing, like the Gaviola test to be found in ATM III. I'm not interested in interferometry testing at this time.

Thanks, Ed

Reply to
endo
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This book looks like exactly what I need for the design of this project. Thanks. I'll get it.

Ed

Reply to
endo

Robin,

Thanks,

You've given me good questions which help to clarify the questions and design that I'm looking at. I'll try to describe the instrument a bit better.

I am not measuring any parts. It's not like an outside micrometer or caliper where you put the part between two jaws or anvils and gently bring them together. I need to be able to set up the stage at a known zero (the null for the center of the mirror I'm testing) and then back off the stage to specific measurements from that known zero. Once at the specified measurement I take two measurements with the Y axis and then back the x axis off to another specific distance from the known zero.

I'm constructing the x-y stage to measure the caustic curve of a parabolic mirror under test. It is a very accurate test but depends on the accuracy of the stage that I use.

The x stage will be spring loaded to pull the stage back against the adjusting mechanism. The mechanism can be a simple screw that pushes the stage against the pull of the spring(s). The distance could then me measured with a DRO, a dial caliper that's clamped in place, or a dial indicator that has the correct amount of travel (3").

I don't know exactly what the tolerances are for the x axis and I need to find this out. I do know that I need to measure to .001" along the x axis and can probably be off by .001" over a 3" travel. I need 3" of travel in order to test the largest mirror I have reason believe I will make.

I want to design one of these stages and make it right rather than have to make a bigger one later. Of course there's always redesigning it later and making changes to accomodate the needed distances and accuracy.

This is exactly the kind of rule of thumb that I'm looking for.

To tell the truth, a DRO sounds about right. I can get measurements to .0005" and the accuracy is to .001".

The thing I still don't understand... when accuracy to .001" is stipulated, what does that mean? Is it accurate to .001" over an inch? Is it accurate over the whole of the 6" travel of the instrument? It seems there's a part of the information missing from the "advertising copy."

Is there an understood shorthand that everyone that's a machinist knows that goes like this? When they say it's accurate to .001" they mean over 1.0". I hope I'm making this clear. I'm just trying to understand the stated specifications so I don't make a mistake when I order a part.

Thanks,

Ed Stevens

Reply to
endo

Reply to
Eric R Snow

You can buy individual gage blocks from J & L Industrial supply. The cheapest ones are +/- .0001 or ten times your required accuracy. They are about $3 each and range in size from .050 to 1.00

Dan

snipped-for-privacy@hant> I need to be able to set up the stage at a known

Reply to
dcaster

Combine that with an inexepensive micrometer head that runs to an inch and he has absolute accuracy over, say, six inches, down to 0.0001 level.

At this point the largest source of inaccuracy will be the mechanical translation stage. Optics folks go to considerable effort to get this right:

Jim

Reply to
jim rozen

Another good book from lindsay

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Reply to
Jack Lai

Ed,

IMO, you should go with a brand-name dial indicator. They're simple to use, very accurate, easy to mount and easy to read. These indicators need only a hole with a simple clamping mechanism and they are spring-loaded so you don't have to worry about whether the indicator is making contact with the stage.

I would look at Mitutoyo first. Their stuff is reasonably priced, and you know you're buying quality (guarenteed). If you have any questions regarding accuracy, repeatability, etc. you can just call Mitutoyo and talk to a techie.

While you will pay more for the indicator, you'll be investing in your process. You can probably buy a "made in China" 3" indicator for perhaps a quarter of the price of a Mitutoyo, but you never really know how accurate the unit is, and the quality/craftsmanship will certainly be less.

Good luck with your project. Let us know how it works out when you're done (with pictures, of course.)

Regards,

Robin

Reply to
Robin S.

While you're there, could you look to see if you have an illuminator for a Zeiss medical microscope? Jpeg available if a description would not be enough.

Jim

Reply to
jim rozen

Hmm ... this allows certain other possibilities, depending on the answer to another question:

How many different measurements will you need? If only a few, which are repeated, I would suggest that you retain the spring-loaded idea, but instead of using a micrometer screw or the like, that you make up stacks of gauge block (the "Jo" blocks which someone else mentioned elsewhere in this thread) to the precise measurements which you need. In particular, you could quite easily get the precision needed out of one or two cheap sets of the Chinese ones. Those are supplied within

0.000050" (50 micro-inches) each. The typical set contains say a 1.000", 2.000", 3.000", 0.100, 0.200, 0.300, 0.400, 0.500, 0.600, 0.700 0.800 0.900 0.110, 0.120, 0.130, 0.140, 0.150, 0.160, 0.170, 0.180, 0.190 0.101, 0.102, 0.103, 0.104, 0.105, 0.106, 0.107, 0.108, 0.109 0.1001, 0.1002, 0.1003, 0.1004, 0.1005, 0.1006, 0.1007, 0.1008, 0.1009 and 0.100050

You can make up a stack of these, "wringing" them together, to certainly gain any distance between 0.100" and your 3.000" for the full range. (None are smaller that 0.100", because they then get thin enough to be easily bendable or breakable.) Most measurements can be accomplished by a stack of four of them within 0.001", or five within

0.0001" Assuming that all of the errors are maximum and in the same direction, that would be no more than 0.0002" off for a stack of four. More expensive sets will give you even greater accuracy, but I don't see the need of that. (I know that I have a set of gauge blocks ranging from 0.100000" through 0.100010" in steps of 0.000010", but that is well beyond what you appear to need.)

With only a few values needed, you could make permanent stacks and keep them pre-packaged to drop in.

For values between 0.100 and 0.299, you have the problem that the individual blocks would add up to as much as 0.300 just to get the number of significant digits, so you make a stairstep of three gauge blocks as your stationary resting point. Steps of 0.100", 0.200", and

0.300" would be sufficient to allow you to move from 0.000" up through 3.000". The highest step would be used as the starting point of values which could be reached without need for corrections. The other two would be used to subtract 0.100" or 0.200" from the stack. (Sine plates often have a step of 0.100" for this very purpose.)

Obviously, if you need to use many distance values, you would have to build up an individual stack each time you do measurements.

You will want to carefully wipe the mating surfaces each time you use a stack, because at these dimensions, a piece of dust or a hair can throw you off too far.

Gauge blocks would be sufficiently accurate to achieve this -- even the cheapest sets.

Understood.

It depends on what the manufacturer (or vendor) wants it to mean. With gauge block, you know what it means -- and even if you don't use the system I have suggested, you can use a set of them to verify your own digital caliper.

Note, that some DROs have a scale of glass or quartz, with a pattern printed on it by metalizing, and the whole thing enclosed in an aluminum spar. The thermal co-efficient of expansion of the steel of a machine tool and the quartz or glass of the scale in the DRO can differ by enough so precise metalwork is done only after the machine tool reaches a stable temperature.

A micrometer, which is made of steel and cast iron, is subject to this expansion as well. Accurate ones will often have an insulating plastic handgrip on the frame, so the thermal expansion will not change the readings as you hold it longer. This is especially so in the larger ones, where the expansion near one edge or the other can bring the anvil and spindle closer together or farther apart. These micrometers are reading in 0.0001" increments by a vernier.

It really depends on who is relating the specs.

*Test* what you get. Or perhaps you can get the manufacturer (e.g. Starrett or Mitutoyo) to tell you in writing.

Looking at an old Starrett catalog, I see a micrometer spindle (for building into your own tool) with a range of 0-2.000", and resolution of either 0.001", or 0.0001" (with vernier).

It is the model 63, with different suffixes to denote options:

63P Plain -- 0.001" resolution, no ratchet, no lock 63L 0.001" resolution, lock but no ratchet. 63RL 0.001" resolution, lock and ratchet T63L 0.0001" resolution, lock but no ratchet T63RL 0.0001" resolution, lock and ratchet.

For your purposes, the vernier (tenths reading) would be difficult to read (as you have to look around the barrel), and the ratchet is not needed, as you are not tightening against a firm stop, but you might want the lock, to keep vibration from shifting the reading.

However, the tenths reading should be usable without using the vernier to read to 0.001", and it should be accurate enough for your purposes. The only additional thing needed would be a 1.000" gauge block, to extend the range by an additional inch.

Good Luck, DoN.

Reply to
DoN. Nichols

Don,

Good food for thought in your post. I'm now leaning toward using the gage blocks and a micrometer head that reads to .0001". I have an old Starrett 363 with .0001 read on a vernier. The micrometer will be plenty accurate even if I don't read the vernier. I'm still puzzling over how to set up the machine to use the gage blocks appropriately and not have the x stage run into the stand that holds the micrometer. I think I need to figure out a way to add an extra 1" shaft onto the micrometer. Hope this makes sense.

Because of the nature of the measurements that I need to take and the delicacy of the positioning I want to disturb the x-y stage setup as little as possible. I'd like to change only one block or two at the most by changing out the 1" block or 2" block. Setting up separate blocks sounds like a good idea until I think about doing that for eight different mirror sizes. I'd need somewhere around 60 individual gage blocks, one for each mirror size.

I'm playing with different designs right now. The main idea I have for using gage blocks right now is to place the micrometer on the base plate that holds the moving stage. The gage sits against a stop block on the stage and the micrometer pushes the stage and block together. Of course, it just occurred to me that I could mount the micrometer to the stage instead. That might solve some of the problems I've been having with how to change out the gage blocks. Back to the drawing board.

Thanks,

Ed

Reply to
endo

How about a depth mic with changeable rods? This would give you virtually unlimited range with .001 resolution relatively cheaply.

Another option is an inside mic laid in a trough that acts as a stop opposed to your spring loaded stage.

Or a couple mic standards to lay in the trough and 1" dial indicator to interpolate. An uncalibrated screw provides the stop. This is a variation of the end measuring rods used in jig borers, boring mills, etc., in the days before DROs.

Ned Simmons

Reply to
Ned Simmons

If you use a one inch micrometer and gage blocks your largest source of error will be the stage itself. You need to be sure it has precision guideways, and that the guide ways are truly orthoginal.

What you don't want happening is for the X position to begin shifting around inadvertently as you are scanning in Y.

Jim

Reply to
jim rozen

Which kind Jim? Twin fiber optic probes or a flat stage?

Please send a pic as to what you are looking for.

Gunner

"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown

Reply to
Gunner

Hmm ... how about a shaft extending from the moving part of the stage in line with the micrometer. This way, they could meet in the middle somewhere.

And as for how to hold the gauge blocks, I would suggest a piece of aluminum angle stock, mounted to allow both the micrometer spindle and the shaft on the moving part of the stage to pass close to one side. The typical gauge block is something like 1" wide, by perhaps 5/16" thick (this without going downstairs and measuring mine,as these dimensions are not really important, usually).

There are also "spacer blocks" (which should be sufficiently accurate for your needs), which are round, and would rest easily in a piece of aluminum angle stock. Yet another option would be the ones which are about 1" square.

I would suggest that the shaft should stick out at least a full three inches, so it will clear the aluminum V even at the zero setting of the micrometer. If you thread the end of the shaft, screw it into a tapped hole in the stage, and provide a setscrew to lock it in position once set, you will be able to set the zero position of your stage to coincide with the zero on the micrometer (if this matters). It might be that this does not matter, and only the relative positions matter.

That is why I asked how many different settings you would need. Obviously, the stacks of gauge blocks would be awkward under these conditions. (Note, BTW, that gauge blocks which are "wrung" together will hold as a single object until some force is applied to separate them. (Except that the cheap Chinese ones with the 0.000050" accuracy, tend to have a poorer surface finish, so the wringing is not nearly as strong as a really good set.)

Yes, this could work fairly well -- as long as you have some kind of "cradle" (such as the angle aluminum which I suggested) to allow the gauge block or spacer block to slide, and the spring on the stage is strong enough to overcome friction with no doubt.

BTW normal steel Gauge blocks need to be kept oiled when not in use, or they will rust and destroy their accuracy. I would suggest that you get the ceramic gauge blocks for this, which will not need to be oiled when putting them away, and cleaned of oil prior to each use. They are quite expensive in sets, as they are made to higher precisions than the Chinese ones which I have been mentioning -- but since you only need two

1.000" and 2.000" (or even just a 1.000" if you get a 2" range micrometer head. A pity that they don't offer a 3.000" range one. :-)

That might result in more disturbance of the workpiece, if bumping the sage can disturb that. (I don't know whether you have something just resting on the stage, or firmly attached to it.

You're welcome.

Good Luck, DoN.

Reply to
DoN. Nichols

It's for a Zeiss medical microscope, the kind with the big roll-around stand. The illuminator in question is pretty much nothing more than a gray cylinder with a light bulb in it. Because the microscope I salvaged out of the dumpster at work (no, really, they throw out perfectly good Zeiss microscopes there) was missing the illuminator, I've been borrowing the one off a co-worker's rig. Because I'm not using mine at the moment, he's got it so I'll need to borrow it again after the monday holiday to snap a jpg.

I could dropbox it, or send it right to you.

Jim

Reply to
jim rozen

Email it directly to me. Ill see what I can dig out. Most of the illuminators I have are the high intensity boxes with a port for a fiber optic "hose" , most of which are split into a T for illumination from two sides. They came from a motherboard manufacturer so are largely used for surface illimination, but I do have some bits and pieces of Stuff, along with busted microscopes and whatnot. I may have some Bausch and Lomb illuminators like you are refering too. Ive several zoom type microscopes that I use for examination, including one with a reticle identical to that in optical comparitors, that came out of a swiss screw machine shop that specialized in micro parts.

Tell me what you are trying to illuminate and Ill set you up iff possible.

I also have a friend who is a manager at her fathers company

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who is good about giving Gunner Discounts.

Gunner

"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown

Reply to
Gunner

Thank you. I'll send a pic along next week after I borrow the item in question.

The lamp attaches directly to the microscope, and provides light directly through the objective lense on whatever is being viewed.

I like to use that microscope for working on cryogenic equipment because it has a very long working length and very crisp optics. It allows me to work on the instruments while they're hung on a rack on the wall, with the microscope a comfortable distance away. It give me enough room for tweezers, wrenches, etc.

Jim

Reply to
jim rozen

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