Coaxial Centering indicator VS wobbler

[c_mario]

Hi,
I seem to be having difficulty with my new Axial Centering dial indicator as pictured below, VS a wobbler also below.
It seems to me that I get different results finding the center of a hole between the two devices and it appears the the wobbler is more accurate.
I say this because when indicating the center as the start point for a bolt circle and I compare the positions of the bolts circle , the one using the wobblers center position is more accurate. I.e. the position of the bolt holes in the bolt circle are equidistant from the edge of the hole while those indicated using the Axial device appear offset , I.e. closer to the hole on one side of the circle than the other.
What am I doing wrong?

 

[GailInNM]

A common cause of this is the mill head being out of tram.
If you have a knee mill with a quill spindle you can make a quick and dirty check of this by indicating a feature with the quill retracted and moving the knee up make the measurement. Then lower the knee a couple of inches and extend the quill to make a another measurement. If the two center measurements are not the same then the mill is probably out of tram.

 

[danallen]

Something isn't right. I can't imagine a wobbler being more accurate than a coaxial indicator. As posted above check your tram.

 

[Oldiron]

I've had the same problem with a less than Blake quality indicator. To make it work well I had to take it apart and file or stone off the burrs and then lap any sliding surface with very fine compound. I use automotive paint rubbing compound when I need to get very fine. Any lube has to be exceedingly light to not add any stickeyness of it's own. The outer part of the indicator has to move up and down on the inner part with NO friction at all, not even oil drag or your readings will not be correct. The anti spin rod has to bear on a smooth surface, not hand held or it will affect the reading also. The action depends entirely on gravity to work correctly . Good luck, Bob.

 

[rklopp]

I put money on the tram issue. The coax indicator takes up a lot of headroom and requires the spindle to move far from the work compared to where it is when making the holes. Of course some of the issue depends on how accurately your holes end up where your spindle points. I.e., drills wander, single-point-bored holes should not.

To test the alignment (tram) theory, dial-in the hole with a DTI mounted close to the spindle nose and then re-dial the hole with the spindle backed far away and the DTI mounted on an extension so that it will reach the hole. If alignment is off, the DTI will show the hole significantly off-center when the spindle moves away from the hole.

The headroom issue is why I rarely use my Coax, preferring to use a normal DTI. I would not use a wobbler like you show. I might use an edge finder. The wobbler does not self-reset once it kicks off-center. Also, if you don't have a DRO, backlash will kill your accuracy because you need to approach the hole walls from opposite directions.

 

[petertha]

All good points made so nothing to add there. My offshore co-ax 'worked' but also required some TLC to remedy somewhat crude parts & finish. I didn't care for the excessive headroom it occupied & setup time. Now I use a mini Noga arm with standard dial test indicator. One turn of the retention knob & DTI/arm is locked into position wherever its best suited. I find this system very quick & accurate to dial in.

 

[clockworkcheval]

Exactly the same thing happened to me. It is in the design of the axial centering dial indicator. Dependant on the length of the feeler you use, the relation between displacement of the point of the indicator and the displacement of the dial indicator is 10:1. This means that an eccentricity of 0,1 mm gives 0,01 mm on the indicator. As this is the precision of the indicator there is no way you can get better precision than 0,1 mm eccentricity with this method. When you use an edge finder and approach several times till the reading is stable you can get a reliable precision of 0,01 mm.
That being said a friend of mine uses the same axial centering dial indicator with more succes. He dials in till the needle of the dial indicator doesn't 'live' any longer. He estimates a precision of +/- 0,02 mm which in most cases is ample.

 

[ownthesky2010]

Just to clarify, wobbler/wiggler is inherently a very accurate and repeatable method of edge finding. A centering dial indicator is not a more accurate method. It's a more convenient method but it requires a lot more calibration and prep just to be as accurate as the wiggler/wobbler. If you need true precision then use a finger clock as it will beat both methods.

 

[Steamchick]

Thanks for posting this question Mr Mario. Without such questions and the collection of answers, we would all be poorer in knowledge.
Thanks all for the various answers. Another interesting bit of learning achieved today!
K2

 

[JLaning427]

If you need true precision then use a finger clock as it will beat both methods.

Ok, I have never heard of a "finger clock". Can you explain a little, please?

James

 

[SmithDoor]

I use both depending on the work.
For edge work I use a optical type too.

Dave

Hi,
I seem to be having difficulty with my new Axial Centering dial indicator as pictured below, VS a wobbler also below.
It seems to me that I get different results finding the center of a hole between the two devices and it appears the the wobbler is more accurate.
I say this because when indicating the center as the start point for a bolt circle and I compare the positions of the bolts circle , the one using the wobblers center position is more accurate. I.e. the position of the bolt holes in the bolt circle are equidistant from the edge of the hole while those indicated using the Axial device appear offset , I.e. closer to the hole on one side of the circle than the other.
What am I doing wrong?
View attachment 132243 View attachment 132244

 

[ChazzC]

Hi,
I seem to be having difficulty with my new Axial Centering dial indicator as pictured below, VS a wobbler also below.
It seems to me that I get different results finding the center of a hole between the two devices and it appears the the wobbler is more accurate.
I say this because when indicating the center as the start point for a bolt circle and I compare the positions of the bolts circle , the one using the wobblers center position is more accurate. I.e. the position of the bolt holes in the bolt circle are equidistant from the edge of the hole while those indicated using the Axial device appear offset , I.e. closer to the hole on one side of the circle than the other.
What am I doing wrong?
View attachment 132243 View attachment 132244

I'm going to ask what may seem to be an obvious question (and apologize in advance): did you remove the white plastic split ring at the top of the blue body?:

The instructions that come with these indicators (see attached) don't always tell you to remove this ring, which is put on at the factory to limit movement of the assembly and protect the indicator during shipping. The mechanism will work with the ring in place, but since the travel is limited to about one dial revolution, you can get wacky readings. I keep the ring on my CoAxial Indicator only because I don't use it very often: I have a label inside the storage box that reminds me to remove the ring.

My indicator works very smoothly. I purchased it a few years ago from LMS on special at Cabin Fever: while LMS does sell items that appear to be identical to others sourced from China & India, I have noticed that LMS does a good job of weeding out poor quality manufacturers and I can always trust what they sell.

In addition to a copy of the instructions that came with my indicator, I have attached a pdf with info from Blake: instructions, table of dial values for different length feelers and the original patent drawing & description. Enjoy!


Charlie

 

[rklopp]

Finger Clock = Dial Test Indicator = DTI.

Interapid is a known good brand.

 

[JLaning427]

Finger clock = DTI. Got it! Never heard that one before.

James

 

[c_mario]

I'm going to ask what may seem to be an obvious question (and apologize in advance): did you remove the white plastic split ring at the top of the blue body?:

View attachment 132302

The instructions that come with these indicators (see attached) don't always tell you to remove this ring, which is put on at the factory to limit movement of the assembly and protect the indicator during shipping. The mechanism will work with the ring in place, but since the travel is limited to about one dial revolution, you can get wacky readings. I keep the ring on my CoAxial Indicator only because I don't use it very often: I have a label inside the storage box that reminds me to remove the ring.

My indicator works very smoothly. I purchased it a few years ago from LMS on special at Cabin Fever: while LMS does sell items that appear to be identical to others sourced from China & India, I have noticed that LMS does a good job of weeding out poor quality manufacturers and I can always trust what they sell.

In addition to a copy of the instructions that came with my indicator, I have attached a pdf with info from Blake: instructions, table of dial values for different length feelers and the original patent drawing & description. Enjoy!


Charlie

Thanks Charlie. I have instructions with the device much the same as those you posted and I did remove the plastic ring. As suggested by others here I also trammed the mill again. I was comparing the wiggler , the Co-axial indicator and a norga style arm with standard DTI. The wiggler and the standard DTI setup seemed more reliable than the Co-axial indicator. I just wanted to get on with the job so I went with the standard DTI in the norga style arm. I will give the co-axial indicator another go when I have time.

 

[petertha]

Just for the record, the company name is Noga (says the Noga-holic haha)
https://www.noga.com/
The other thing I learned is poorly made lookalike arms are also not your friend. Not knocking all clones because there are some decent ones out there too, but also a lot of crappy ones & hard to tell the difference from a picture. You might want to check some of Stefan Gotteswinter YouTube videos, he has some good comments around indicator arms - pros, cons, likes, dislikes... He favors the 'C' style which might even be a shop made if memory serves. Like most things, your mileage may vary by preference or application.