Angus Ross-Thomson's pantographAngus writes:
Your recent article on wooden rings has finally persuaded me that I might have something useful to contribute to the wonderful world of Woodgears.ca. Some of your readers' projects are so elegant and well made that I hesitated to draw attention to my ham fisted efforts. However, I have produced a circle fixture for my pantograph jig which may be of interest.
I always have enjoyed making stuff in a small way, mostly concentrating on electronics, PIC chips, software and low level mechanical engineering. My proudest products were a portable aircraft instrumentation system for flight testing (I was a test pilot in the Royal Air Force back when I had to work for a living) and a radar warning receiver for use on boats to warn of the approach of ships.
In 2005, my wife and I set off on an nine year circumnavigation on our sailing yacht which was a great experience but I really missed my small workshop and the facilities for making the dozens of widgets one needs around a live-aboard boat. However, during our time away I came across your website which was a complete inspiration and opened up a whole new way of approaching projects. I whiled away many a night watch under the stars imagining the creations I would make on my return, and watching your videos whenever I could find an internet cafe that could manage more than 5kbps (it was often a slow and painful process).
We returned to the UK last year and having got the house habitable, I placed an order on your website for five plans, including the screw advance box joint jig, the pantorouter and the pantograph. I completed the BJJ first, then the pantorouter and finally the pantograph. I have made a widget to help projects constructed with the pantograph, so I shall describe that first, and if you think it may be of interest and you have the time, I shall describe my experiences in constructing and using the BJJ and pantorouter in another email.
The fixture rotates on a short stainless steel pin located in the piece of chipboard and the pantograph follower rotates in the hole in the moveable block. There is a pencil scale on one side of the slot, and to help repeatability, I put a piece of masking tape on the other with the critical positions marked. The adjustments are made by turning the M6 bolt with a socket.
I produce the initial circular groove with a straight router bit, I then use a round nosed bit to round the bottom of the groove, then wind the cutter inwards to undercut the knob. Finally, I use a roundover bit for the top edge of the knob and the outer rim of the hole. I can now produce the knobs reasonably consistently and accurately in about 10 minutes including bit changes.
Download radius widget SketchUp model
Thanks for your inspiration and guidance.
All the best.