Newbie- Centering problem

[daanmuller]

Hi,

I am trying to machine something with a 36 mm hole in the middle that I have to turn over to machine the other side.

So first I machine one side with x0 and y0 at the center.

Then I flip the piece over.
I then have to center the mill again. I do this in in the following way:

I pick up an edge from the 36mm hole with a laserfinder.
zero y axis.
Jog over to the other side till I pick the other edge.
Note the distance traveled on y.
take halve and move y back by that amount.
zero y

Repeat this for the x axis.

I think that I should be centered again now. But then I start cutting again and I am always off on both my x and y axis by at least one mm and always in the same direction x+ and y+

What am I doing wrong?

[One of Many]

Using the laser edge finder is the problem. They are not accurate enough to reset or place the origin to the center of an existing hole. Between the beam width and exponential runout the farther above the edge, the worse it can influence human error. I wouldn't trust one expecting under .015 position tolerances.

Use an indicator in or on the spindle to reference the origin to your part. You can find indicator holders like the Indicol clamp or tool holder mounted style. The indicator resolution may also be of importance. If you expect finer than .001 centering, use a .0001 resolution indicator. Once you have the indicator pointer stable at four quadrants of the bore, boss or hole, set your origin and you should be good to go within the capability of the machine.

I should also add that it is essential to check your head is trammed in to the table. If the head is not true perpendicular, there will be a mis-alignment from where the origin is set to where the cutter actually places the next cut(s) if the Z distance changes between tools. Not to mention the new feature at an odd angle of what is expected.

DC

[djr76]

this tool will be your friend, use it for finding center of the hole.

[daanmuller]

Thanks.

I ordered one of these:

[One of Many]

One of those does not use the spindle bearings to center it about the spindle. If there is any offset in the method that is held, you can still be off center from the feature being located.

DC

[daanmuller]

They can be alligned to be precisely in the center of spindle with 4 setscrews. Or do you mean something else?

[One of Many]

At least there provisions for centering it in the spindle. Provided you place it in a dedicated tool holder and put the tool holder in the same orientation each use.

This adds some pains in using it in a drill chuck or moving it from one holder to another if it must be checked for running on true center each time before using it to reference an origin.

Possibly just personal preference, since I like my trusty Indicol clamp or dovetail swivel post mounts. I can transfer any of my indicators to either setup depending on the operation circumstances at hand.

Indicol Clamp and universal swivel styles

DC