What's new
What's new

WTB: A teeter-totter type DTI accessory, 3 inch min reach

extropic

Stainless
Joined
Dec 3, 2010
Location
WA, USA
I'm looking to buy something that will allow me to indicate circular runout (.00005" resolution) on elements (1" min dia) at 3" deep into the part while it's mounted in a lathe chuck.

I'm thinking of a teeter-totter type thing that mounts on a .00005" reading DTI (TESA 18.20013).

I don't know if such a thing is commercially available (I've never seen one) so . . . :confused:

Can you post a link to a source for such a thing?

Am I going to have to build it?

I'm open to considering other approaches that will achieve the inspection in situ.

Any help out there?
 
I wouldn't trust such a thing. Brown and Sharpe used to have a .00005 indicator with a long needle that would probably be the best you could get for that.
 
I wouldn't trust such a thing. Brown and Sharpe used to have a .00005 indicator with a long needle that would probably be the best you could get for that.

I hear ya. Maybe that's why they aren't common.

I think one COULD be made to be completely "trustworthy" (for my application). I'm just hoping I can buy it, rather than have to build it.
 
I kinda think it would need an air bearing to get it to work. Been thinking of something like this for indicating .223 barrels. And not willing to go that far.

Full chamber depth? That would be a more difficult task because the length vs diameter ratio is about 2 times what I'm trying to do.
 
I hear ya. Maybe that's why they aren't common.

I think one COULD be made to be completely "trustworthy" (for my application). I'm just hoping I can buy it, rather than have to build it.

Not so easy.

At that level of sensitivity, it would need a bearing functional first-cousin to a Swiss watch balance staff or those old Agate and knife-edge bearings on uber-sensitive lab balances back in the day before electronics obsoleted them. Fragile stuff.

Pragmatically, electronic measuring is where you'll have to go for this task, costs according, of course.

Mechanical means would want far too much f***-with time for many, many readings averaged, each one a PITA to take.

I've got a pair of store-bought Indi-cals - bought brand-new. Two so I can check same task with two different DTI and "go in search of the truth".

INDI-CAL INTERNAL GROOVE GAGE

"In theory" I could plop a ten-millionths per-divison Hamilton DTI onto one.
Or a half-tenth's Tesa.

But just how good - and how repeatable - can the pivot be? How about bending? Then there are thermal effects.

So.. "In fact", not theory, I'd not trust such a "universal" rig any further than splitting ONE thou. If even.

Too tedious by half, that "searching for truth" part can be.

GOOD electronics. Or a bespoke gage set or gaging system.
 
long island indicator sells long (up to 5" i think) contact points for various brands of DTI's

You cant just put a 5" long contact point on your DTI unless you are willing to live with the fact that the marks that were once .001 are now .010.
Doing so reduces the resolution of the DTI by the ratio of the arm lengths.
Teeter-totter here too. Imagine a 50ft long indicator point, lots of tip motion for the same at the short end as .001 with a .5 inch long tip.

If your indicator has a reasonable spring pressure or spring loaded you can make such an arm as above with a sloppy bronze bushing or even just a drilled and reamed hole and it will work just fine.
I understand the thought that you would need jeweled accuracy but it is not true here. Such a device will not like you reversing rotation direction as it will jump but will indicate a bore nicely.

Bob
 
You cant just put a 5" long contact point on your DTI unless you are willing to live with the fact that the marks that were once .001 are now .010.
Only if the ratio is not identical, both sides of the pivot-point...
Doing so reduces the resolution of the DTI by the ratio of the arm lengths.
Or INCREASES it. In theory, at least.

Hard to actually DELIVER that reliably, but a variant of it is done inside certain high-amplification direct-camming DTI that do not rely (entirely) on micro-gearing.

Teeter-totter here too. Imagine a 50ft long indicator point, lots of tip motion for the same at the short end as .001 with a .5 inch long tip.
With a "nearly ENOUGH perfect", eg: non-bending, beam, now reverse that, if you will.
If your indicator has a reasonable spring pressure or spring loaded you can make such an arm as above with a sloppy bronze bushing or even just a drilled and reamed hole and it will work just fine.
For one reading perhaps. What about taking three readings off the same part?
I understand the thought that you would need jeweled accuracy but it is not true here.
It IS true if you need a device you can trust to repeat and to not be uber-sensitive as to how it is stored, held, presented to the target workpiece. More "fragile", yes, but there you are. High-precision DTI are always a tad fragile.

Or DTI would be rubber-banded or glued together out of stampings and injection-molded parts.

Oh.. wait.. some actually ARE! Clever people, those Chinese!

:)
 
Only if the ratio is not identical, both sides of the pivot-point...
Or INCREASES it. In theory, at least.

Hard to actually DELIVER that reliably, but a variant of it is done inside certain high-amplification direct-camming DTI that do not rely (entirely) on micro-gearing.

With a "nearly ENOUGH perfect", eg: non-bending, beam, now reverse that, if you will.
For one reading perhaps. What about taking three readings off the same part?
It IS true if you need a device you can trust to repeat and to not be uber-sensitive as to how it is stored, held, presented to the target workpiece. More "fragile", yes, but there you are. High-precision DTI are always a tad fragile.

Or DTI would be rubber-banded or glued together out of stampings and injection-molded parts.

Oh.. wait.. some actually ARE! Clever people, those Chinese!

:)

Bill, the reference was to "long tips" on otherwise standard indicators. With that restriction, no playing with "ratios" is available.

Also, Your comment regarding three tests. That would impose very high standards for location in any plane on any "teeter totter" pivot..

More, surface finish of the part, and any "drag" or friction resulting in distortion would throw one of those "zeros" into the meaningless catagory. ;-)

It's a tuff one.

Myself, I would like to pick up the 3 inch teeter totter, that was useful to .001". I've got a look out, but haven't had one jump out at me....yet ;-)
 
I would think that a teeter-totter as described here would need very good bearings to locate the pivot, as any "sweep" of the contact tips on either side of the T-T would throw off the contact height, either in the bore or on the tester needle contact ball.

There's a manufacturer of flexure pivot bearings (Infinite Life, Frictionless Pivot Bearings and Custom Engineered Bearings | Flex Pivots) which if stiff enough against loads aside from pivoting might be a great choice for a DIY T-T setup. I used these ages ago for precision pivots when no-lube was a requirement (space application).
 
Bill, the reference was to "long tips" on otherwise standard indicators.
That crept-in, but no, the thread itself was about "teeter totter" devices. Equal ratio or otherwise. Plus - what Bob described actually exists INSIDE some DTI. Unequal ratios as multipliers for at least part of the system. The construction won't much help the OP on the outside. Not unless he wants to write a many-figure check to the likes of Dorsey Metrology.

Also, Your comment regarding three tests. That would impose very high standards for location in any plane on any "teeter totter" pivot..
And does do.

But look at the sort of measurement the OP sought.

...allow me to indicate circular runout (.00005" resolution) on elements (1" min dia) at 3" deep into the part while it's mounted in a lathe chuck

That .. 50 millionths of an inch, is it? Is a seriously challenging set of numbers to hit, regardless...

Not all lathes even have spindle bearings that good.

I double and triple-check measurements a hundred times less precise. Shit moves, temps change, dirt and debris get involved, I get tired or careless, etc.

More, surface finish of the part, and any "drag" or friction resulting in distortion would throw one of those "zeros" into the meaningless catagory. ;-)

It's a tuff one.

Myself, I would like to pick up the 3 inch teeter totter, that was useful to .001". I've got a look out, but haven't had one jump out at me....yet ;-)

It is very much a tough one. Hence bespoke gaging or seriously good electronics.

Not having deadlines or production costs to worry about, I can take all the time I need, and harbour "enough" different TI that there's no need to add that sort of gadgetry to them. I just use a different one, better suited.

The exception are the Indi-Cal's. Meant for internal grooves, but all-around useful where the DTI itself may not reach, or may not have suitable tips. Not terribly expensive, brand-new, those, even if needed but once in a year or more.
 
snip

Myself, I would like to pick up the 3 inch teeter totter, that was useful to .001". I've got a look out, but haven't had one jump out at me....yet ;-)

So . . . if I end up making one, maybe I should make two? :D

Milland,

If I need to make the thing, I agree that a double ended flexural pivot is the way to go.

To all,

I'm getting the idea that what I thought I wanted isn't commercially available.
Can anyone describe a commercially available alternative that will resolve .ooo1" circular runout, 3" deep in a 1" bore while the part is in situ on a lathe spindle/chuck? Working links appreciated.
 
So . . . if I end up making one, maybe I should make two? :D

Milland,

If I need to make the thing, I agree that a double ended flexural pivot is the way to go.

To all,

I'm getting the idea that what I thought I wanted isn't commercially available.
Can anyone describe a commercially available alternative that will resolve .ooo1" circular runout, 3" deep in a 1" bore while the part is in situ on a lathe spindle/chuck? Working links appreciated.

A "solution" - several - may be commercially available. Just not as cheap as a teeter-totter.

Given that your spec just moved by a multiple of five? There'll be more compromises. Costs, to name one.

So.. you should be able to find a solution you can AFFORD as fast as anyone else.

I think you will need "non-contact" metrology. Air, optical, Laser beam, capacitance, wotever...

You are not even close to the first Pilgrim with a need, after all.
 
One other DIY option could be a small bar with a sapphire contact ball to ride the bore (sapphire has low inherent friction), and the bar has a flexure cut into it just past the ball. Put a high sensitivity strain gauge on the flexure and read with the appropriate amplifier. Not quite as simple to make work as described, but doable (I think).

Could an air gauge head that reads variations in flow as eccentricities pass by work? I've always been a little unsure of how they work when a surface might have roughness variations around its circumference.

[No good links, I'm afraid]
 
With an inch bore to play with, you can swallow much of the indicator. Indeed there may be an electronic one so small you could swallow the whole thing and read from a cable to display. Anyhow, could be the combination of a long barrel indicator and the longest standard tip would get you close? I'm pretty sure the Mahr 800 EWL with a long tip would go about 2.5" deep with the digital "dial" still visible.

I do think with that much extension (and thus deflection) and some inevitable slop in the system (with a lever arm), that getting .0005" accuracy could be tricky with a lever type device. But if you're just aiming to center things, might be OK.

If you're just trying to center things up there's probably some sort of expanding plug that would bring an accurate center further out; assuming you have a machined bore. Think expanding collets or the guts of a bore micrometer; both of which will repeat to around .0002" If you're trying to measure the bore and lobing within it, well, a bore micrometer.
 








 
Back
Top