How to use Coaxial Indicator

[Bill Pace]

Lower speeds tend to make reading and adjusting simpler.

McNeill's procedure is as good as any. Once the concept of operation is understood, application is rather intuitive.

I agree, McNeill's procedure is the way I do it also - except the rpm, having a VFD I take it down to 50-100 rpm. And, as you say, Jim, once you do it a couple times and get visuallised what its doing, I think its rather a simple and efficient way to get center.

Laz -- again, having the VFD, I also edge find at slower speeds - probably around 150-200ish-- just enough to get the 'kick'

[mochinist]

You can't trust a fast spinning co-ax.

I like double check expensive or tight tolerance parts anyways, I do have a blake and use it at around 200 rpm's on the manual and 500 rpm's on the cnc mills. I've gotten out my indicol holder and a tenth indicator on numerous occasions to double check the hole zero location on a tight tolerance part and the blake is always within .0005", manual or cnc.


I will say at that rpm especially on a aluminum part, it is helpful to put a dab of some oil on the surface where the co-ax indicator point will be touching, otherwise it will screw up the surface

[Peter Neill]

I have one of the cheaper LDL co-ax indicators and have found it to be more than precise enough, and very useful.
I also use it the same was as Carl does, with a spanner on the drawbar and turn it by hand, then zero in one axis first, then the other.
Very quick and simple, and it needs less headroom than changing from a collet/collet chuck/drill chuck.

Peter

[Glenn Wegman]

I dont' often speak w/ such pronouncements, but allow me...

lower the indicator such that it is just above the hole/boss you're indicating. spin it by hand. eyeball it in the x direction one side, then the other. adjust. repeat. then y. adjust. repeat. lower it into the hole/over the boss. Rotate by hand, comparing value for x left/right. adjust halfway. same with Y. maybe do it a couple of times. engage the spindle and run it at 500 rpms and tweak it such that the needle stops vibrating. If it takes you any longer than 2 or 3 minutes, you're doing something wrong.

Disclaimer: I only know what I've taught myself. I could be way off accepted practice.

-Phil

Not to criticize Phil's post but...

By the time you do that, a DTI on an Indicol (clamps ON the spindle, not IN it)is as quik or quicker, and there is no doubt about the accuracy! Along with that, the DTI can be used for numerous other operations around the shop. If you have neither a DTI or a CoAx, it may be a matter of preference, but if you already have a DTI why spend the money on a CoAx?

There may be the odd occasion where a CoAx would be a better choice over a DTI, but not very often!

[Peter Neill]

Not to criticize Phil's post but...

By the time you do that, a DTI on an Indicol (clamps ON the spindle, not IN it)is as quik or quicker, and there is no doubt about the accuracy! Along with that, the DTI can be used for numerous other operations around the shop. If you have neither a DTI or a CoAx, it may be a matter of preference, but if you already have a DTI why spend the money on a CoAx?

There may be the odd occasion where a CoAx would be a better choice over a DTI, but not very often!

I think you're missing the point entirely.
With a co-ax indicator, the dial is facing straight at you 100% of the time. No mirrors, no straining your neck round the back or the sides, no parallax errors from viewing it at odd angles.
That's what makes it so simple to use, without even mentioning the extended probes so that the indicator can be down the bottom of a long bore whilst the dial is above the bore in plain sight.

Peter

[jdunmyer]

I have one of the Chinese co-ax indicators, but have gotten away from using it. Instead, I use a TDI clamped in an Indicol and now can center a part pretty quickly:

Spin the spindle by hand with the indicator point above the part until it's "close". Put the TDI point in contact with the part. Adjust the 'X' axis so the indicator reads the same on both the Left and Right sides; I'll usually tweak the 'Y' axis a bit at the same time. Once I'm happy with the 'X', I'll make sure the 'Y' reading is the same. Note that during this procedure, I turn the spindle only 180 degrees, keeping the face of the TDI in view at all times. When I'm done, I might crank the spindle so the face is to the rear and check it with a mirror, but if the part is round, the reading is always the same as at the front.

Here's a hint for using a TDI: Do NOT try to use the Zero reading on the dial. Always adjust the dial so that pressing 'more' on the point makes the reading go 'up' or increase. My TDIs are bi-directional, and it used to be a problem figuring out which way to move the table until I learned this trick.

[lazlo]

With a co-ax indicator, the dial is facing straight at you 100% of the time. No mirrors, no straining your neck round the back or the sides, no parallax errors from viewing it at odd angles.

Exactly. Plus you don't have to mess with the getting the DTI up/down on the Zero-Set beam. With the various tips, a Blake can indicate an 8" hole/cylinder. You need to make a beam to do that with a DTI.

Not a huge advantage either way. Different strokes...

[gwilson]

I actually have a Blake. I don't think any of these replies have been very complete. I think the Blake type co-ax is wonderfully handy to have.

The first thing I advise you to do,is first screw on the long straight handle that you hold in 1 hand to keep the Blake from rotating. I run my unit SLOW.

Next,and VERY important,when getting ready to center something like a hole,put on the shortest leg you can,and run the leg round and round close over the hole. Adjust the mill's table until you can see that the hole is pretty well visually centered below the probe you selected. IF YOU PUT THE PROBE INTO THE HOLE WHEN IT IS TOO FAR OFF CENTER,THE PROBE CAN REACH ITS LIMIT OF TRAVEL AND BREAK THE SHAFT OFF OF THE BLAKE!!!!!!!
This last info is VERY important to remember. I saw a broken off Blake in a professional machine shop.

Running the mill slow is very adequate to indicate the hole onto center by manipulating the X and Y axes until the indicator's needle stays in 1 place. You can zero the needle's position by rotating the bezel if you want to. The important thing is to get the needle to where it moves as little as possible,with just the smallest tremor. Running the mill faster just makes centering the hole(or whatever) more difficult.

I also got the needle tip for centering punch marks,which is very handy to have. This needle tip is spring loaded,which it needs to be as the needle tip goes in and out as it is used to center the punch mark. DO NOT ATTEMPT TO USE A HOME MADE,NON SPRING LOADED NEEDLE TIP. It will break your Blake.

I have heard bad things about the Chinese Blake clones. I hope yours works o.k..

[Glenn Wegman]

With the various tips, a Blake can indicate an 8" hole/cylinder. You need to make a beam to do that with a DTI.

Not a huge advantage either way. Different strokes...

Ever check the accuracy on that CoAx with the arm at a 45° angle to the axis? Or the wrap up on a long arm?

A properly setup DTI does not suffer from that with diameter changes.

DTI's also come with dovetails on the upper surface!!



There is no need for a mirror if mounted vertically anyway as you only need to sweep three sides of a bore if it it round. Left on X axis, 180° right on X axis, and toward you on Y axis. If you are not sure and want that warm feeling, a final check on the far side.

I also have a Blake.............that lives in it's box!

[John Stevenson]

Don't even start the spindle.

Use one of these and you'll never go back to a co-ax or DTI



Watch this video.

http://www.youtube.com/watch?v=RTzxe...eature=channel

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