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radkins
03-15-2016, 11:01 AM
Again I did not want to highjack another thread but again someone else asked a question that brought one up of my own, the co-axial indicator.

Using a co-axial indicator for tramming a mill? I have been doing this but I have been told it's not very accurate and is a bad idea, I have also been told just the opposite. I scanned Youtube and again found conflicting advice on this, yes I know Youtube can be hazardous to my machining health, but which is it, is it a Good idea or bad? It seems to work ok for me and I can't see why it wouldn't work but is it just that I am either being lucky or maybe setting my standards too low? An example of what I was told is that a co-axial indicator was not designed for tramming and should never be used for such but then I have also been told that it is often used for that purpose and works great, other than the 'net and asking around I simply have no other way of learning these things and I have been advised both ways.

lakeside53
03-15-2016, 11:13 AM
If a thou or so across say 6 inches , then it works fine. But, are you talking a quality indicator or a cheap import? It makes a difference - too easy to simply believe the dial.

And.. if it's good enough for you, then that's all that matters. I used to obsess about tram, but now don't much care unless I'm doing something that really needs accuracy.

JCHannum
03-15-2016, 11:22 AM
Blake has been manufacturing their co-ax indicator for many years and has remainid successful in the face of competition from import knock offs. This is a testament to the quality of their product.

The co-ax indicator is their only product and its use and specifications are described in detail on their website;

http://blakemanufacturing.com/pages/aboutus.html

Reading the website will lead to the conclusion that the instrument has a singular purpose and is to be used under power. If there were other applications that would add to the use of the instrument and add to its value, I have little doubt that Blake would present them in their literature. They don't.

There are several videos that show the use of a co-ax for mill tramming, and yes, it will work to a degree, and is probably good enough for most purposes. Most of them entail using a long stylus to sweep the table. The longer the stylus, the less the indicator needle will deflect for a given dimension, and the less accuracy the instrument will have.

radkins
03-15-2016, 11:31 AM
If a thou or so across say 6 inches , then it works fine. But, are you talking a quality indicator or a cheap import? It makes a difference - too easy to simply believe the dial.

And.. if it's good enough for you, then that's all that matters. I used to obsess about tram, but now don't much care unless I'm doing something that really needs accuracy.


With the exception of my Starrett Mics and Dial calipers all of my tools are are of the import variety, in this case it's the one Shars sells as their own brand so I didn't expect it to be top-of-the-line but was hopping it was good enough, maybe not? I use a 14" brake rotor, new but trued on the lath anyway, and I can easily get it to within .001 to .002, BUT that's with the cheapee indicator so I suspected it probably wasn't exact. How about I ask this way, if I acquire a better indicator what would be considered a decent indication and over what range?

I have a buddy that has a Blake I could try out and would even be willing to buy one if it's truly worth the difference in my case.

radkins
03-15-2016, 11:35 AM
Blake has been manufacturing their co-ax indicator for many years and has remainid successful in the face of competition from import knock offs. This is a testament to the quality of their product.

The co-ax indicator is their only product and its use and specifications are described in detail on their website;

http://blakemanufacturing.com/pages/aboutus.html

Reading the website will lead to the conclusion that the instrument has a singular purpose and is to be used under power. If there were other applications that would add to the use of the instrument and add to its value, I have little doubt that Blake would present them in their literature. They don't.

There are several videos that show the use of a co-ax for mill tramming, and yes, it will work to a degree, and is probably good enough for most purposes. Most of them entail using a long stylus to sweep the table. The longer the stylus, the less the indicator needle will deflect for a given dimension, and the less accuracy the instrument will have.



Someone else told me the same thing and I have to admit it makes a lot of sense.

dp
03-15-2016, 11:48 AM
This is very easy to test. Use the coax indicator statically on your mill to produce zero deflection on the X axis at two points 180 opposite, then use a dial indicator and repeat the measurement. The length of the probe doesn't matter - it isn't measuring height, it is measuring the relative angle of the quill and the table. The usual cosine concerns don't apply. I demonstrate that here:

https://www.youtube.com/watch?v=8ikS5aJeHG4

Here's a guy who doesn't understand the device at all: https://www.youtube.com/watch?v=sZKf51HG9IQ but it doesn't stop him from giving me a load of crap about it :)

Here's another video I did that proved to be incendiary by those who haven't taken the time to understand the instrument. https://www.youtube.com/watch?v=ZfioLDhBNBQ

Toolguy
03-15-2016, 11:59 AM
DP nailed it. Use the coax first, then do the same operation with a quality dial test indicator. The dial test indicator is the gold standard to compare to. My Blake is good and I use it quite a bit, but for critical dimensions I use the dial test. The Blake is within a thou or 2 of the dial test. I had a Chinese import Blake style, it wasn't worth a crap.

JCHannum
03-15-2016, 12:48 PM
The effect of probe length is simple physics. It is nothing more than a lever and fulcrum, the longer the lever, the less the work will move.

I don't have a long stylus for my Blake so I made a 4" long straight to use. Using the standard Blake stylus, a 0.010" feeler gauge resulted in a 6-3/4 division deflection of the needle, the 4" extension resulted in a bit over 3 division deflection, that means that it is more than one half as sensitive with the longer stylus.

I do not understand the angle measurement statement, the instrument is indicating the difference in the vertical location of the stylus tip at different positions. I believe that is height.

As I have said, the co-ax will sort of work, and probably is adequate in most cases. If you have one, use it being aware of its shortcomings. I would not recommend purchasing one for that sole purpose.

Danl
03-15-2016, 12:57 PM
The effect of probe length is simple physics. It is nothing more than a lever and fulcrum, the longer the lever, the less the work will move.

I don't have a long stylus for my Blake so I made a 4" long straight to use. Using the standard Blake stylus, a 0.010" feeler gauge resulted in a 6-3/4 division deflection of the needle, the 4" extension resulted in a bit over 3 division deflection, that means that it is more than one half as sensitive with the longer stylus.

I do not understand the angle measurement statement, the instrument is indicating the difference in the vertical location of the stylus tip at different positions. I believe that is height.

As I have said, the co-ax will sort of work, and probably is adequate in most cases. If you have one, use it being aware of its shortcomings. I would not recommend purchasing one for that sole purpose.

I'll admit I don't use Youtube for research on how to use some of these measurement instruments, but the idea of using my coaxial indicator to tram my BP seems ridiculous. Some folks don't use them at all, don't even want them in their shops. I don't use mine very often, but it can save time in some situations.

But using it to tram a mill? Really? hmmmm......


Dan L

Carm
03-15-2016, 01:32 PM
I've never used a co-ax for tramming and probably never will, nor to measure angles.
It is a device of relativity though. Of course it will work. Sine error really has no bearing.
Should you? Dunno, but I'm not a tool purist. You can drill with a mill and braze with a cutting tip.

dp
03-15-2016, 03:16 PM
The effect of probe length is simple physics. It is nothing more than a lever and fulcrum, the longer the lever, the less the work will move.

I don't have a long stylus for my Blake so I made a 4" long straight to use. Using the standard Blake stylus, a 0.010" feeler gauge resulted in a 6-3/4 division deflection of the needle, the 4" extension resulted in a bit over 3 division deflection, that means that it is more than one half as sensitive with the longer stylus.

I do not understand the angle measurement statement, the instrument is indicating the difference in the vertical location of the stylus tip at different positions. I believe that is height.

As I have said, the co-ax will sort of work, and probably is adequate in most cases. If you have one, use it being aware of its shortcomings. I would not recommend purchasing one for that sole purpose.

When you understand this video you will understand the coax indicator when used to sweep a horizontal surface. And there is nothing in the design of the instrument that suggests you cannot or should not use it for this purpose. It doesn't care.

The granite plate is at an arbitrary angle that doesn't change throughout the test. The different length probes indicate identical readings because the instrument in this configuration is reporting the angle of the rocker relative to the body of the instrument. Because the angle of the plate is fixed the two probes report the same angle. That is, the magnitude of the dial readings are identical. It is counter-intuitive. This result doesn't happening when over a bore or a pin - in that configuration the probe length is very much critical.

The side of the plate to the left of the tool center is higher than the side to the right of the tool center. This is evident by the rise and fall of the blue body. As the probe length becomes longer that probe tip travels farther vertically than the shorter probe hence the identical readings. We don't care about the probe tip vertical distance traveled because the object is to remove all that when tramming. When the granite plate is exactly 90 relative to the quill the indicator, regardless of probe length, will read zero deflection (within the geometric accuracy of the instrument).

https://www.youtube.com/watch?v=8ikS5aJeHG4

JCHannum
03-15-2016, 03:40 PM
The video proves my point. The longer stylus must move a greater distance for an identical movement of the pointer. Thus, it is less sensitive.

dp
03-15-2016, 04:00 PM
Of course it does - that isn't disputed - that is how angles work and also why the probe length is unimportant. In a right triangle of a known proportions the angles and proportions are constant regardless of the size of the triangle. And it (the system) isn't less sensitive or the two indications would be very different and they are not. The magnitude of motion of the different length probes compensates and the result is the magnitude of the angle presented to either probe. That, btw, is the same thing you wrote the last time we had this conversation.