I was reading an article published by The Home Shop Machinist today, and I was very surprised to see my name as the author.
I had submitted it to HSM several years ago, and had totally forgotten about it.
I had to read the article to remind myself how I achieved this neat little trick, of machining an exact 1.5 degree taper in a very thin workpiece.
Click on the link below to see the short article.
My expert friend Stuart Tankard suggested that I try a digital video camera to locate work on my milling machine.
I have various gadgets for finding edges and tool heights, and I find that the electronic edge and height finders are the most accurate. But, I have never been satisfied with accurately locating other points in workpieces.
So I purchased this small video camera which is attached to a shaft for attachment to a collet or chuck which is held in the spindle.
The camera on the left is as supplied. It needs to be adjusted so that the camera is pointing exactly to the centre under the spindle. The adjustment is made to the 3 grub screws in the metal disk shown. When the unit is inserted into the collet, the screws are inaccessible unless only a fraction of the shaft engages in the collet. Also, the setting which is eventually determined seems quite precarious and liable to be altered with a slight bump. A very unsatisfactory arrangement.
So Stuart came up with the modification on the right. A CNC’d perspex disk replaces the back of the camera case. The new camera back is attached to a larger, more solid, steel disk. The screws are now accessible when the shaft is fully engaged in the milling machine spindle collet. Altogether, a superior setup.
This is the computer screen view on Mach 3 showing the magnified scribed lines (thick white lines), the “smooth” workpiece surface, and the centered crosshairs. I have not worked out the degree of magnification. (note added 1/1/16: the centre circle is 1mm diameter so the scribed lines are about 0.2mm thick)
Lining up cross hairs with the centre of the spindle is still fiddly and time consuming, but with the new, more solid setup, it should need to be done only once. It is done by loosening the cap screws and nudging the camera laterally.
Any slight angulation in the camera lens, or the chip, or the steel backing plate or shaft is compensated by fixing the focal distance. This is accomplished by making a small sleeve to fit between the lens and the camera body. It is the brass bit in the photo.
The following photos show some of the steps in making the modifications.
Opening the original camera case. The security label needs to be removed.
Freeing the camera cable from the case without damaging the cable, using a Dremel.
The new camera back was CNC’d from perspex (thanks Stuart!)
Turning the backing plate. I chose to use a silver steel shaft 12mm dia, silver soldered to a disk, which I then turned in a collet chuck.
Testing the altered unit. Those scribed lines are probably 0.25 of a millimeter wide. They are shown on the pic of the computer screen earlier. The camera has LED’s which are not well aimed for close distances. In use the camera lens is only 5mm above the workpiece.
The camera is a TP-03 Machining Camera, purchased from Homann Designs. It cost $AUD88 plus postage plus GST.
The software to put the fine cross hairs on the screen was downloaded from http://www.kd-dietz.de and it is version 3.02 of “WebcamPlugin” for Mach3.
Check out the following link suggested by reader Hamish. It is a more complete discussion of the process and the technology. It is in the comments section below.
johnsmachines 