[Alarm Hero]

Hi everybody,

I'm relativley new to the trade (six months) and I have a question regarding dowels and how to locate them parallel. In this case the dowels are fit into an aluminum tool (car seat mold to be exact) for re-machining and my question is this:

Is it incorrect to bring a dial indicator (in a vertical spindle of a CNC mill) to an approximate position in front of the dowel, then hand turn the spindle until it reads zero? How can you be sure that the arc of the probe isn't off centre, thus giving you a bad reading? I've seen one of the other "more experienced" fellows do this and it doesn't seem right.

IMO you should locate the dowel centre by using the probe of the indicator by indicatind each side on the X axis, then the Y, THEN zero the Y and jog to the other dowel and verify. Am I missing something here, or am I a shmuck?

Thanks guys....

[tobyaxis]

Alarm Hero,

I don't see a problem with indicating center on one Dowel Pin then the next along X axis. It all depends on what has to be done.

Please correct me if I'm wrong, which wouldn't be a first, but Indicating the Center of one Dowel to the next in the "X" Axis is fine as far as I can see. Just make sure the Dowel is Perpindicular to the Table. I other words Check the "Z" Axis up and down around the X and Y Axies to make Sure their is no ERROR FIRST. Then Indicate the Dowel Center X and Y.


tobyaxis :cheers:

[One of Many]

You want the 2 pins parallel to what?

If I presume you mean an axis, then indicate them on one side of each pin to bring them into the same line along that axis. Normally there would be some other machined datum that these 2 pins should be located from. Preferably a longer span than the 2 pins, if there is one with no wear. Once the alignment is achieved, then using the indicator on the spindle will center the spindle over that pin. Set the first one as x,y zero. Then handwheel or jog over the other pin and swing it on center without reseting the origin. This will indicate in the distance between centers.

There is no error in the arc of the probe/indicator, if it is swinging on the spindle bearings. If you have concerns of the pin not being perpendicular to the spindle or Z axis, you can verify this by checking the center swing at the top and bottom of the pins. Which center do you rely on? Hence the need for an outside reference to put them back where they belong. If you intend to move the axis each time you indicate off of another side of the pin, you have a better chance of losing some repeatability with the indicator verses the motion of the table.

If these are alignment pins mating to the opposite mold half. It may be a good idea to to rework both holes as a unit depending on the fit required. Ejector pins can have the same issues.

DC

[NEATman]

Alarm Hero-
The easiest way to indicate two dowels parallel to the axis of travel is to run the indicator along qualified straight edge (even a long machinist scale) touching up against the two pins. This will get you very close, then you can indicate around the pins if you need extreme accuracy.

When I was first learning about machining I had the same question. This simple answer made me think "DUH!"

Hope this helps-

Keith

[Alarm Hero]

Alarm Hero-
The easiest way to indicate two dowels parallel to the axis of travel is to run the indicator along qualified straight edge (even a long machinist scale) touching up against the two pins. This will get you very close, then you can indicate around the pins if you need extreme accuracy.

When I was first learning about machining I had the same question. This simple answer made me think "DUH!"

Hope this helps-

Keith

Sorry, I'm just going over some long dead thread, but thanks for the tip. Still, if one wasn't available the others have given some great advice to go on. Things have been very tough for me career wise as I'm sure it has many of you guys, but I won't bore anyone with the details right now.

Thanks for the help !

[cam1]

Tramming a parallel located against the pins is my methos of choice.
If you are in a shop, you must have some parallel bars somewhere....

regards

[NEATman]

Alarm Hero-
I have to comment on your avitar - it's pretty funny & I haven't seen it before. If you have that in a larger size let me know where you found it. I'll add it to the other cartoons posted on the wall about the Segway, as I'm working at DEKA now... (where the Segway was invented).

Keith