Need Help to Measure a Thin Gap

[GT-6 Racer]

Can you get in the gap to measure with feeler gages? 0.001" maybe a little tricky,

66B English Thickness Gage

The Starrett Imperial Thickness Gage is used in automotive, aviation, diesel and farm equipment manufacture and service and also in jig, fixture, gage and experimental work. Especially useful in adjusting tappets, spark plugs, distributor points, checking bearing clearances and gear play...

www.starrett.com

Thickness / Feeler Gage Stock

www.starrett.com

0.0005 and 0.001 are available as stock.

If you can generate enough force the soft lead is an excellent choice as well, used that many times in the Navy. I have used plastigage, frankly not a fan other than maybe an error check against math errors with the micrometers.

Epoxy may work but the film will be thin (beware of shrinkage on curing) and maybe OK if you can get an outside mic over the part to measure the thickness or maybe with a DTI on the surface plate.

I'd suggest a few different methods as a cross check if the measurement is critical including an "unloaded" measurement of the separate parts on the surface plate.

 

[woodchucker]

I didn't see a response to why feeler gauge would not be the answer. Is it a possibility?
Just remember, everything you measure, alters the thing you are measuring. Even a bar of steel.

 

[extropic]

I didn't see a response to why feeler gauge would not be the answer. Is it a possibility?
Just remember, everything you measure, alters the thing you are measuring. Even a bar of steel.

In the OP I wrote "I want to measure the gap to .0001" resolution."
Standard feeler gage stock, AFAIK, can't get me there.
I don't have a surface grinder in service (yet), and I don't want to tackle the necessary range of custom feelers without one.

 

[extropic]

I guess it's time for an update, of sorts.
The project is 1000 miles and an unknown number of days away, so the thread was for planning purposes, not immediate application.

I think I'll do some testing to choose the method/technique before I attempt the intended project measurements.
What I have in mind is using solid (no holes) 1-2-3 blocks as test substrates because they are fine surface texture, hard and suitably large enough.
I can use AWG 36 (.005" OD) electrical conductor wire (and smaller) to set a representative gap. I can do tests of the various methods until one, or more, seem to be workable.

I plan to update this thread with the testing descriptions/results.

Thanks again to all the contributors.

 

[MikeWi]

are the pieces short enough to measure from the ends and thus directly measure the change? If not, how about gluing blocks at three places around the cylinders and measure before and after that way?

 

[extropic]

are the pieces short enough to measure from the ends and thus directly measure the change? If not, how about gluing blocks at three places around the cylinders and measure before and after that way?

It took a minute for me to "get" your questions, but they did soak through.
I think the "from the ends" option would be difficult because the overall length is on the order of 2 feet and I'd have to jury-rig some sort of gage. The delta T (on the gage), from one reading to the next, would also add uncertainty.
The "three blocks" was a real head-slap moment for me. It sounds like the most finicky set-up (block faces must be precisely parallel to each other and very parallel to the gap, but doable and the measurements would become very simple and quick. The available space in the proximity may be a problem but adding temporary reference surfaces outside the parts is definitely worth serious consideration. Thank you.

 

[B2]

Key word for search: "Solder balls" or "Solder Spheres" in the diameter range of your interest. Some times called Reballing solder balls. They are used in circuit repair or screen printing patterns.

Pre-made Solder Balls

These are the leaded solder balls that we use for reballing larger chips, such as iPhone 6/6+ baseband CPU. Placing solder balls in a stencil as an alternative to solder paste ensures that the formed balls are all perfectly even. Solder balls in this size are the ones we use for reballing most...

ipadrehab.store

or
Digikey has an assortment. Even for sale on Amazon, in kits of sizes.

Prices, thousands of balls/$10

I think these things are very uniform in size, but you can check by microscope measurements. This means that you do not have to mechanically measure their compressed thickness. Just use a microscope to see/measure the flat surface diameter (of the flattened surface) and the final overall diameter to determine how much they have flatten out. You can calibrate this. Just recall that solids are in-compressible so the volume is conserved. You can use a bunch of them to get some statistics.

 

[extropic]

Key word for search: "Solder balls" or "Solder Spheres" in the diameter range of your interest. Some times called Reballing solder balls. They are used in circuit repair or screen printing patterns.

Pre-made Solder Balls

These are the leaded solder balls that we use for reballing larger chips, such as iPhone 6/6+ baseband CPU. Placing solder balls in a stencil as an alternative to solder paste ensures that the formed balls are all perfectly even. Solder balls in this size are the ones we use for reballing most...

ipadrehab.store

or
Digikey has an assortment. Even for sale on Amazon, in kits of sizes.

Prices, thousands of balls/$10

I think these things are very uniform in size, but you can check by microscope measurements. This means that you do not have to mechanically measure their compressed thickness. Just use a microscope to see/measure the flat surface diameter (of the flattened surface) and the final overall diameter to determine how much they have flatten out. You can calibrate this. Just recall that solids are in-compressible so the volume is conserved. You can use a bunch of them to get some statistics.

Now I want to know how they manufacture commodity quantities of 0.20 mm (.008") solder balls? LOL

 

[ChazzC]

Key word for search: "Solder balls" or "Solder Spheres" in the diameter range of your interest. Some times called Reballing solder balls. They are used in circuit repair or screen printing patterns.

Pre-made Solder Balls

These are the leaded solder balls that we use for reballing larger chips, such as iPhone 6/6+ baseband CPU. Placing solder balls in a stencil as an alternative to solder paste ensures that the formed balls are all perfectly even. Solder balls in this size are the ones we use for reballing most...

ipadrehab.store

or
Digikey has an assortment. Even for sale on Amazon, in kits of sizes.

Prices, thousands of balls/$10

I think these things are very uniform in size, but you can check by microscope measurements. This means that you do not have to mechanically measure their compressed thickness. Just use a microscope to see/measure the flat surface diameter (of the flattened surface) and the final overall diameter to determine how much they have flatten out. You can calibrate this. Just recall that solids are in-compressible so the volume is conserved. You can use a bunch of them to get some statistics.

Clever approach, but gap measurement is desired to be +/- 0.0001”, which means the ball needs to be spherical and homogeneous within that tolerance in order to calculate the smashed thickness based on the microscope reticle diameter.

Use of the solder balls is good, but I stand by my recommendation to measure the flattened thickness with a comparator stand and 0.0001” drop indicator.

 

[B2]

Now I want to know how they manufacture commodity quantities of 0.20 mm (.008") solder balls? LOL

My guess? Inexpensive, mass produced? Spray them out as a liquid from a hot very small nozzle at a consistent speed and pressure. It is probably a process that existed even before inkjet printers. Surface tension on a liquid drop results in a very spherical shape. They cool then become a solid as they are in flight. I have seen machinery that makes very precise ball bearings this way. Somethings are done like this via spinning wheels so that droplets fly off. This is some times even done in vacuum. I know that you can simply use a consistent drop size to achieve spheres of glass/beads. So the precise size is determined by the dropping or ejecting process which can be extremely repeatable. In inkjet printing, where the spheres can be only a few microns in size, there is a puddle formed on the end of the spray nozzle and then piezoelectric impulses can be used to push the puddle surface outward causing a drop to be ejected. In some setups a pair of drops are formed and ejected, the first being larger followed by a tiny secondary drop. Electrostatics can be employed to deflect them and so select one.... and so one can only use the larger or the tiny drop. Inkjet however, is usually a liquid carrier of dyes and do not dry into spheres in flight as these might not stick and flow into the paper. If you have ever used a paint sprayer or even a spray paint can you may have observed that if you spray into the air and your substrate is too far away, the paint particles just turn into a dry dust before they ever reach the substrate.

The one I want to know about his how they make ceramic ball bearings.. very high temperatures. Perhaps they again just make lots of them in a similar manner, but with harder to control process and then size them, but most ceramics do not melt at reasonable temperatures.

Clever approach, but gap measurement is desired to be +/- 0.0001”, which means the ball needs to be spherical and homogeneous within that tolerance in order to calculate the smashed thickness based on the microscope reticle diameter.

I think they can be.. Is the exact size of the ball even required? I think not. As long as they are all the same size one can calibrate things for preciseness. Whether measurement to +/- 0.0001” (~+/-4 microns) accuracy is achieved is some what dependent upon what the spacing is. What @extropic said was

The magnitude of the gap is .001" to .005". I want to measure the gap to .0001" resolution.

So 0.001" is ~ 40 microns while .005" is ~200. So the ball has to be larger than the expected gap in order to be deformed by the squeeze. The larger the resulting cylinder shape the more likely the optical measurement will be accurate. Anyway, observing 4 microns differences is pretty easy with a decent microscope.

There is another approach to this which requires bit more expensive ($10K) and dedicated instrument. Mechanical profilometers' probe tips are usually a polished gem stone which is dragged across the deformed ball and the height measured directly by deflection. These are commonly used to measure surface roughness and the ones I have used commonly operate to give height profiles that are considerably smaller than 1 micron. We sometimes use these to calibrate the thickness of thin films being deposited in vacuum. By knowing the time and other processing conditions one can get a deposition rate and then control the thickness very well. I made lots of 20 to 4000 Angstrom thick vacuum deposited metal films (10,000 Angstroms = 1 micron). This calibration process almost seems crude, but it is standard practice and works well.... Before depositing (like evaporation) onto a (very clean smooth) substrate you cover a portion of it with a knife edge (sometimes just tape) and make a deposit. Peal off the knife edge and then run the profilometer probe across the surface at this transition region and measure the bump as the probe tip moves from no deposited film to the deposited film.... height step. These things are standard process equipment in a thin film deposition labs. The search term can be Surface Profilometer or Roughness Profilometer. By the way, there is another common instrument used to capture a 3-D images of surface roughness and shapes at the Angstrom scale called an Atomic Force Microscope (AFM) or Scanning Force Microscope (SFM). It was invented in the mid 80's and is now a standard instrumentation tool ($100-200K). It scans in x and y directions of an area of only a few microns and measures the surface heights. These have been used to study the roughness at the atomic level and lots of various applications. https://en.wikipedia.org/wiki/Atomic_force_microscopy . Today, these things are necessary tools in the semiconductor and magnetic storage manufacturing industry as well as others. One last little extra. If you deposit a magnetic material on the AFM probe tip then it will sense the changes in magnetic force with respect to the x-y positions of a magnetic material deposited on a substrate. This way you can actually observe magnetic recording patterns. (Magnetic Force Microscopy---MFM). https://en.wikipedia.org/wiki/Magnetic_force_microscope
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