Formula for calculating the maximum length of a stylus relative to dia?

[[Ri...]]

Is there a formula or rule of thumb for determining the longest functional length/or extension I can use relative to its dia?
I received my .3mm, .5mm, .8mm x 5mm long stylii today.

I have to clear some features to get inside of some small holes and need to know how to determine what my limits are.
Thanks al!

[[Ja...]]

If I am not mistaken, you can use just about any length so long as you don't exceed the probe heads weight/length limit. What you really should be calculating is the feature diameter/stylus diameter ratio.

And who is Al?

[[Ro...]]

Well the 1mm only has a usable length of about 5mm, because the shaft diameter is 0.8mm where the ruby attaches and goes back up to 1mm at 5mm from the ball center. (I have an XT with a 5mm thread)
In the catalogs you should be able to find this data, i think the MLF distance is what you're looking for.

now in the past i have purposely fixtured a part 5º off angle to give myself more room to go deep inside a bore, so i just took a series of half circles on the available side walls.

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[[Ri...]]

t "appears" to me, perhaps erroneously, that I will not be able to qualify one of my styli with the small diameter, 8mm reference sphere that I purchased. I am curious If I am completely wrong here before making anymore moves.

I have received two stylii.

626103-5644-014
DK: 0.8, L: 14, ML: 5, DS: 1, MLE: 4.8, DSE: 0.6, DG: 5

626103-5444-014
DK: 0.5, L: 14, ML: 5, DS: 1, MLE: 2.3, DSE: 0.3, DG: 5

If the MLE of the 5444-014 is only 2.3mm and the radii of the sphere is 4mm, won't I shank out during qualification?

I would just go ahead and see what happens but I have been gloriously allowed one styli for this financial quarter. If I break it I might as well cut the end of the electrical cord off the CMM.

(oh, and al is all, thank you all. 😃)

[[Ro...]]

It looks pretty normal, i don't see a problem qualifying this styli.
I think you got your numbers crossed somewhere.

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[[Ri...]]

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Yea, I just threw it on an adapter plate and jogged it over to take a look. Your absolutely right, its looks good.
Looking at the numbers alone just didn't seem right.

Thank you again. A little assurance goes a long way!~

[[Ow...]]

One 0.3 mm Ø probe is expected to last 3 months?
You can break the dang thing just cleaning it.
Just cut the cord now and enjoy the rest of the summer... 🤣

[[Ro...]]

Styli are "Perishable Tooling", similar to drill bits or end mills.
You hope they last forever, but they've all got a life span, and the smaller the diameter the shorter the lifespan (there must be a correlation somewhere).
My boss may look at me funny when i break an unusual amount of tips in a week, but if they refused to buy more id be like "ok well i guess i'm not checking these parts anymore", or "I guess ill let engineering know that method of measurement for these parts has changed from CMM to...... Calipers"

[[Cl...]]

A few of our programs are using 0.2mm dia stylus. Close the door too hard, it breaks. 😉

Contura G2 VAST Gold XT

[[Aa...]]

I know they've been mentioned here before, but we've found we can save a fair amount of money, particularly on smaller styli like this, by using a different supplier. ITP styli has better pricing and great quality. They still peg-mount a lot of their smaller rubies. No, I'm not on their payroll.

Another way we've saved money on these perishable tooling items is to buy unthreaded styli and put them into the bases for unthreaded styli. I was skeptical at firsts that holding it in place with a set screw would yield good results, but we haven't noticed any appreciable drop in the quality of our results that way. (It was a fairly inexpensive experiment.)

[[Aa...]]

One more thing about switching reference spheres. On the "Reference Sphere" page of the Calibration Certificate of your machine, you'll find a little note to this effect, "The reference sphere is part of the coordinate measuring machine. The mean radius allocated to it is required for compliance with the guaranteed instrument specifications."

Basically, the machine is calibrated using a stylus qualified on the physical reference sphere that came with the machine, with the radius value on the cal cert entered into Calypso. Measuring the radius of the Ref Sphere is outside Zeiss' Scope of Accreditation, and the uncertainty is ridiculously high, but that doesn't matter, since the calibration tech makes software compensations that will offset any inaccuracy in that value (which translates directly to an equal error in all bi-directional measurements), and their traceability is through the stepper gauge they use in calibration.

But that also means that if you switch reference spheres (or if you send the ref sphere out for calibration and enter the new calibrated value into Calypso), that error is different, and those software compensations are no longer valid.

In short, you're best off sticking to the reference sphere the machine was calibrated with. If you need a smaller sphere for smaller styli, the best approach is to use the original sphere with a reduced angle coverage for the static tensor portion (which determines size and location), and the smaller sphere for the dynamic tensor portion (which determines dynamic bending parameters).