this is a device that was used when I was a machinist,for quick location on a Milling machine.You need………a small piece of plasticene,the type that kids play with(don't know about playdough,never used it,it was'nt in use back then)and a pin.The pin you should make yourself.Chuck a piece of rod in the lathe,and file and polish it to a point,cut off about an inch long.

How to use it.:

                   You wan't to drill a hole in a component on your mill,you have coated your component with marking fluid,and marked it out with scribe marks.Stick you plasticene with the pin in it on the bottom of your drill chuck.Start your machine on medium speed.With your 6inch steel rule(which every machinist should have on his person,or right handy)use the edge of your rule to manouver the pin untill the point spins with no wobble.Use your X and Y axis hand wheels to manouver the point of your sticky pin over  the midlle of you scribe marks,and you have quickly located your centre point.

                                                                 Back then,wind up gramaphones were still around,and you could still get gramaphone needles for them,these were much sought after,as we found they made the best needles for a sticky pin.I had tried using a sewing pin,and found it no good,it was'nt substantial enough.the ideal pin should be about one sixteenth of an inch in diameter.You can use this device on the bottom of an end mill,but I found it did'nt work well on the bottom of a twist drill. 

Tyler said:

I've heard of this before, but I've never seen it done. I'll check YouTube to see if anyone has made a video of the process. I understand the process, but it would still be useful to see a video of the process in action for others who might have trouble visualizing it. 

I was thinking a regular straight pen (found in the wife's sewing drawer) would work just fine, but you said you'd need something more substantial. Why exactly doesn't a straight pen (the kind with the round plastic head) work? It's just to flexible?

Tyler,it's a similar principle to a 'wobbler'.The old gramaphone needles were more substantial in the shank to a pin,When I tried using a pin,I found the length of it,and  the insubstantiality of the shank to affect how it works.obviously,when the pin is in the plasticene,it extremely unlikely that the point will spin concentrically,that is where the 6ins. rule comes in.With the machine on,you touch the edge of the rule to the spinning pin,about a quarter inch fron the tip,and gently manouver the tip untill it spins concentrically. it is easy to see when the pin is spinning absolutely concentrically,once it is,it can be set so that it is really close to the work.When the point is set as described,it is easy to locate centre punch marks,and crossed scribe lines accurately,you don't need to measure,you don't need to memorise settings,it's simply  a matter of positioning the point over the marked positions,using the londitudinal and latitudinal traverse wheels.As the   pin is attached to the endmill,or drill chuck,and spinning concentrically,wherever the pin tip points to,will be the centre of the spinning cutter,or chuck.As the saying goes'a picture is worth a thousand words',it is not easy to describe an action with words,especially to someone who has never carried out that action,I hope this description has clarified this procedure somewhat.To set up the pin,start the mill slow,and increase the speed untill you can see that the pin is spinning fast enough to be set with the rule,a simple matter for a mill with electronic speed control.

                                                                                                                      Swarfie(Tony)

Jerry said:

I'll make a vid for this, it's a way I use. One important thing is the stuff used to stick the pin is best if it's not elastic, i.e. chewing gum would be less good, Plasticene is ideal.

One thing I found with plasticene,it did'nt seem to be much affected by any oil,or cutting lubricants that were around,other materials tended to disintegrate.