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Please recommend a micro adjustable DTI holder

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awemawson:
Recent alignment work on the lathe and it's turret has revealed a hole in my measuring equipment - a micro adjustable DTI holder.

I have a couple of the Noga style articulated arm holders that are very good so long as you lightly lubricate the internal locking wedges, but these only get you 'into the ball park'. What I'm after is a similar holder but with a micro-adjustment facility.

Now in the past I've had the style (picture below) where a clip / spring clamps two plates together that are riveted onto the ends of bars, but all that I've had were of nasty construction - the riveting works loose, or the clip flies across the workshop at the least opportune moment.

So educate me - what is out there that combines the benefits of  the articulated arm style, and also has a well engineered micro-adjustment that doesn't fall apart in normal use?

chipenter:
Stefan Gotteswinter made an adjustable indicator stand with micro adjustment its in two parts .

PekkaNF:
Noga indicator stands are economical, but not that great.

It all depends what you do, greater public is not aware how flexible indicator stands are until you need to measure machine and rotate the indicator. Few pretty good demostrations on web:

Richard King demonstrating indicator sag.


Stefan Gotteswinter - Machineshop Physics: Indicator sag - Durchhang von Messstativen


Andrew is no doubt familiar with this, hence the question.

Do you have a shop that has Fisso stands and you can try them? Personally I would not try anyting lower quality than these if I need anything better than bog standard stand:
https://pmtshop.de/messzeuge/messstative/fisso-messstative/fisso-base-line/2936/praezisions-magnet-messstativ-fisso-lxs25-base-line-hoehe-277-mm


An my answer is to keep all arms as short as possible and avoid fine adjustment alltogether, if there is a way. Sometimes adjustement is good, I have used two ok andother was russina with flexture and separate push/pull screws - you loosen one screw, then adjust with one and finaly lock with the another one. One is fisso flexture type, and this one is not thet great if you need to rotate the stand but works really nice if you need exact fine adjustment, it's sold as a spare of Strato µ-Line fine adjustment:


I think I have seen these under 100€, still not cheap, but you shoud try how it works, whole better than standard fisso/mahr and different league than noga.

https://pmtshop.de/messzeuge/messstative/fisso-messstative/fisso-zubehoer/385/fisso-praezisions-feineinstellung-strato-line-8mm/m8


In priciple a stiff flexture on the stand (instead of of at the end of the arm) should be fine with stubby arms, but I don't have experience on those.


Do you have something spesific measurment problem in mind?

Pekka

awemawson:
Pekka,

Yes Richard did that demonstration when we had the scraping class here the other year. The flexing and sag is not really surprising when you consider the length of the arm and the fact that the DTI will show a few microns movement.

What triggered my interest recently is that I am repeating the measurements and adjustments that I made on the Beaver Turret for alignment. I am getting a discrepancy between sweeping the bore of an axial holder to set centre, and the mounting face of a radial lathe tool holder that implies that the turret rotation relative to the Curvic Coupling isn't spot on. Now it is possible, but I think very unlikely, that it has moved since I did the alignment. So I want to set up a very rigid measurement system. The real issue is that to keep the DTI mounting arms short and rigid the turret has to be right up against the chuck making access neigh on impossible to read the DTI. To over come this I intend to use my electronic Tessa gauge so that the indication can be remote, but I need to improve it's mounting. Hence the question!

PekkaNF:
I don't get that exactly, if it is like I think there are two similar type measurement problems:

Bore and arbour on the same line---this is often soleved by installing close fitting bushing (pin) to bore and maching diameter pin or arbour, then arbour and bore (pin) measurements are clocked with DTI. DTI does not rotate, arbour usually can be rotated with relative ease.

Another measurement problem I am aware is alingment of the two shafts (gear coupling assembly ot such) that used to be abiach, before laset aligment units came common. Measurement guy had to lug along heavy suiticase of measurement fixtures. Smallest one had a prism that rode atop of the shaft, tightened with a strap (or chain) and had pipes to mount DTI, something like this:

That one looks the part, excluding the "bolt" that mounts the DTI. We used 20 mm hydraulic pipe, sag was neglible in 150 mm extension....tested that on proofing bar, because one mechanician did not believe on sag with his easier magnetic stand

I am pretty sure you have used or seen one used. Am I right?

if unknown/flexible mount was used the trick was to rotate the assembly and use another DTI to measure "sag" - it is the arm/mount that sags and not the DTI....but this takes some experience and an analythical mind set.

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