FILENAMES: Spiral1.jpg Spiral2.jpg DESCRIPTION: These are pictures of illustrating the machining of a spiral. Posted by Bill Darby . Bill provided the following description: ================================================================= Help with Machining Spiral Hi All Well, things were slow at my place so I set to work to see if I could cut a spiral as I suggested in the recent "Help with Machining Spiral" thread. I tried to do it exactly as I suggested but I failed because the method was damaging the work. The idea seemed right but the method was wrong. So I set about adjusting the method and I came up setup as shown in spiral1.jpg and spiral2.jpg. The pictures pretty much show how it works If you don't quite see what's going on in the pictures the following description may assist: Spiral1.jpg shows a fairly steep taper having been cut on a one inch Al rod. For the purpose of this exercise it is assumed that the required taper is steeper then the taper attachment could negotiate if such is available. Also note the shape of the form cutter (the shank end of a 3/16ths carbide end mill ) The idea was to cut a spiral path that a rope could follow. Spiral2.jpg shows the completed spiral which was cut under power with the threading levers set to 4 TPI and the 3/16th formed cutter having cut, in successive passes, to a depth of about a single radius. The cutting was accomplished by providing a fixed point against which the side of the compound would ride against as the carriage was advanced The fixed point was provided by first building a suitable block that could be bolted to the bed, between the carriage and the chuck. (like the base of a steady rest) A half inch thick triangular plate was then anchored to the top of the block in such a way as to project out over the carriage and house a 1/4" 20 adjusting screw that would come in contact with the flat side of the compound. Prior to turning, the formed cutter was positioned to start the first cut, with the half nuts engaged and motor off. The cross feed nut was then disconnected and the gibs freed up somewhat for ease of travel. The adjusting screw was positioned such that it was snug to the side of the compound with enough thread showing to allow the required in-feed as cutting progressed. When all was set as above, a steady manual pressure was exerted on the tool-post and the motor switched on. As the threading began the compound was forced progressively rearward as the side of compound advanced past the adjusting screw, thus tracking the taper of the work being cut At the end of the cut the motor was reversed and the cutter was returned to the start position. Once there the adjustment screw could be backed off slightly (.050" per full rotation) and the process repeated again and again until a suitable depth was reached. (Never once disengaging the half nuts.) The method described works well enough but the quick and dirty 1/4" adjuster bolt dug into my compound a bit (if you look close you can see where it dug in) But for a test of concept it went well enough, and if I were going to do this a lot I would attach a rubbing block on the end of the 1/4" adjuster bolt.