Picking up the center of a hole on the mill

[Brian Rupnow]

Okay---I have to admit--I've been cheating. Up until now, whenever I wanted to "pick up" the center of a hole in a piece placed on the bed of my mill, I have turned a plug the right size on the lathe, mounted it in the chuck on my mill quill, and jockeyed the mill table around until the plug would fit into the hole smoothly when I lowered the quill. Stone-age, but it worked. today I thought I would get a bit more "machinist" and do it with my "test indicator". Man, it was really hard!!! I have a cheap, one direction only import indicator. Half the time I couldn't decide if the little lever was even touching the inside of the hole, and when I turned the quill around 180 degrees I had to stretch my old neck like a contortionist to even see it, as my mill sets up against the wall. There has to be a better way!! What is it? I'm willing to spend a bit of money if I have to, but this test indicator method is for the birds!!!

 

[Herbiev]

Instead of a plug , I turn a pointed taper, lower it into the hole then tighten things up. Still Stone Age but good enough for me.

 

[bazmak]

I have just bought a cheap chinese electronic one if i can find the correct battery.It has a 10mm ball on 1 end with an LED light when it touchs
Should work well on holes smaller than say 12mm .Will let you know if i get to use it

 

[canadianhorsepower]

There has to be a better way!! What is it? I'm willing to spend a bit of money if I have to, but this test indicator method is for the birds!!!

Brian this is what I use just as good (not as fast) as my co-axe centering tool

hope it helps

 

[aircraftmech]

The way I do it really depends on if it's in the vise or clamped to the table. Like if I want to center a part on the rotary table I put a tap in the collet, press the point into the hole and then clamp down the part. If I'm centering my rotary table I drop a big ball bearing in the hole and press an empty collet on it firmly so it will move the table centered, only takes like 10 seconds.
If it's in the vise I just use the pointed end of an edge finder and line it up by getting the edges flush without the spindle turning, good to about .001-.002". Hope that helps...

 

[petertha]

You might be able to speed up the 'get it to within a couple thou first' process with simpler means before bringing out the precision instruments. I find if its too far off to begin with, the DTI is kind of a pain. Axe first, scalpel second

1) with a pointed finder like pic. If you can snug it in the hole & no burs on the hole edge, you can get the spindle pretty accurate just feeling for any offset difference on the shank.Its quick & dirty

2) with a laser gadget like described here (which I'm keen to make, ebay LED's on route)
http://www.modelenginemaker.com/index.php/topic,4781.45.html

 

[Swifty]

Always used an indicator, I roughly line up the hole with the end of the indicator first, then actually put the point into the hole and zero the indicator, then rotate. It's a bit of a stretch, but it's quick. You could try one of these http://www.machineryhouse.com.au/Q515

Paul.

 

[Cogsy]

About 6 months ago I bought myself a coaxial indicator off ebay and it makes centering holes or round stock under the quill simple and highly accurate. There's no wondering if the probe is touching, the thing is hard up against the part all the time. The indicator body itself does not turn, so it's always facing you and easy to read.

You have it in the spindle and run the mill on it's lowest speed then it's a simple matter of watching the movement in the indicator needle while you move the table and you can quickly zero in on perfect alignment. Mine is a metric version and I can get it to indicate under 0.01mm in less than 30 seconds.

Here's a video as I don't explain it well.

[ame]https://www.youtube.com/watch?v=mU1ewk36zAw[/ame]

And here's an ebay link for one for $70 US http://www.ebay.com.au/itm/COAXIAL-...999?pt=LH_DefaultDomain_0&hash=item1c46cb977f.

 

[kf2qd]

Yeah. Get a COAX style indicator. anything else requires a digital readout...

 

[canadianhorsepower]

I did get my co-axe indicator from Little Machine shop
Love itThm:Thm:
it works great in the lathe also

 

[Gordon]

I have a co-ax indicator but the biggest problem is the head room required for the Z axis. Takes about 6" spindle to part and then when you put in an end mill in the spindle you have to raise the table about 4"

 

[purpleknif]

Try an "interapid style" indicator. Real Interapis cost around $200 but copies are fine for home work. They have both dovetails and a center stem that make them the most versatile indicators out there. Been doing this full time for over 30 years and wouldn't have anything else.

 

[petertha]

Try an "interapid style" indicator. Been doing this full time for over 30 years and wouldn't have anything else.

Likely this has been discussed before elsewhere, but maybe you can elaborate because I've also heard this preference.

I have a Starrett DTI kit which includes a round shank stem accessory that clamps on any of the dovetail rails. Its a friction locking ball & socket so stem/indicator can be oriented in almost any setup direction. I also note Starrett also makes a different 'last word' style set, so presumably offers some other purpose or advantage? Then there is 'interapid style'. Functionally what does that actually mean? The swivel-able stem is integrated into the body of the test indicator? Or a preferable brand name relating to dial / accuracy / repeatability etc?

 

[canadianhorsepower]

these videos should explain it all for round and square

http://www.tormach.com/blog/fab-lab-skill-builder-swing-indicating-part-1/

http://www.tormach.com/blog/fab-lab-skill-builder-swing-indicating-pt-2/

enjoy

 

[Charles Lamont]

and when I turned the quill around 180 degrees I had to stretch my old neck like a contortionist to even see it, as my mill sets up against the wall.

Use a mirror.

 

[goldstar31]

Use a mirror.

Nor I , I couldn't manage without a number of dental mirrors.
One of the ideal uses is to look at tools - lathes, drills and whatever in the tool and cutter grinder. I mark with a waterproof felt tip marker and grind-gently until each worn land is done.

It saves taking the job out to examine progress

 

[Swifty]

Luc, the first video is exactly how I have always done it, the second video is a great idea.

Paul.

 

[barnesrickw]

Try an "interapid style" indicator. Real Interapis cost around $200 but copies are fine for home work. They have both dovetails and a center stem that make them the most versatile indicators out there. Been doing this full time for over 30 years and wouldn't have anything else.

I do what he says. You can use it on holes perpendicular to the mill's Z axis also by mounting the indicator horizontally and moving either the X or Y axis until the peak of swing is found. Did it yesterday on my PMR steam engine cylinder casting.

 

[barnesrickw]

Learnt in at the last machine shop I ran CNC.