Must forge thick and grind thin,"
may be carried out far more conveniently than in the case of whole tools which are generally filed into shape before tempering, and when worn down must go to the fire again and have the process repeated. But the detached cutter admits of being tempered evenly throughout its whole length and ground up afterwards as long as it lasts, without going to the forge again to the deterioration of the steel.
The patterns of tool-holders are innumerable, but very few are good for general service, because most of them are arranged so that the natural sides of the cutter are used for the face or faces of the edge. Thus either the plan angle of the point is limited to the angles presented by the transverse section of the cutter employed, or else the section angle is fixed by the position in which the cutter is clamped. Holtzapffel's arrangement is open to the first objection, Babbage's to the second. To obviate this inconvenience, Prof. Willis arranged a holder which clamps the cutter at an angle of 55° from the horizontal line. Thus no side can be used either for the lower or upper face of the edge, but any faces can be ground upon it; and the plan and section angle of the edge may be varied at pleasure within the whole range available for metal turning. Prof. Willis's holder for the cutter is almost a facsimile of his admirable tool-holder for the slide-rest, than which none is more convenient or can act more perfectly. But the arrangement is a little complicated for a cutter holder, and must be very carefully made with the knowledge of certain laws, if it is to insure a perfect grip of the cutter. It is also designed for the use of sound wire cutters which require filing flat on one side.
Adopting Willis's inclination for the cutter I have found that all its advantages may be secured with a simpler form of holder and common square for steel for the cutter. The holder is simply the modification of an old pattern to suit the inclination of 55°, and the sketch needs little explanation beyond saying that the nick in the solid part should be rather less than a square angle, and made perfectly true all the way down, or, if anything, rather hollowed in the middle, so as to insure the greatest amount of pressure at the top and bottom, as otherwise the cutter might not sit quite true and firm. The angle at the end of the strap against which the cutter bears should be rather more than square, both to allow for any want of exact truth in the squaring of the cutter and to avoid the wedging action which would be set up on tightening the screw if this angle were less than square, as this could of course create a risk of splitting the strap. The end of the screw and the cup in which it fits should be round, as this allows of a little play and insures a truer grip in the strap than a pointed screw working into a conical hole. A perspective sketch of a detached cutter is added, with dotted lines to show how exactly the arrangement of the faces can be accommodated to the positions which have been shown to be the best in solid tools for the slide-rest.
D. Haydon.
[New form of Rose Engine by E. Taylor.]
Seeing that the Editor of the above Articles has illustrated and described Holtzapffel and Co.'s Rose Cutter and two methods of executing rose cutting, the latter being the ordinary rose engine, I am induced to send you a description of a method that I have adopted whereby I can with considerable despatch execute this description of turning.
I will first preface my description by saying some thirty years ago I purchased Ibbetson's Book on eccentric turning, and I was so much taken with it and the illustrations, that I determined to make myself in accordance with his description and engravings an eccentric chuck; and although I was a long time about it, being at the time much otherwise engaged, I succeeded beyond my expectations, and was enabled to do some very fine work with it; and I have never regretted the time I spent over the chuck, as I became familiar with metal turning and screw cutting flying in the lathe, which latter I was surprised to find how easily I could execute. However, I was much disappointed in the usefulness of the chuck (Holtzapffel's eccentric cutter, which I purchased is far more useful), and also with the tediousness of using it (fancy stopping the lathe to alter the chuck 360 times or 180 times to cut a row of circles either distinct or overlaying each other), and there was also a certain vibration occasioned in using the chuck which I also disliked. I therefore determined to cut up some rosettes and convert my headstock into a rose engine, to effect which object I got Holtzapffel and Co. to return up with a new steel collar and make my mandrel traversing. I cut myself a rosette both ways with 16 waves, and I was much pleased with the variety of work I could perform with this one, but the rosette took me a long time to make, and disheartened me from cutting up a variety. It, however, occurred to me that if I added an extra mandrel by the side of and attached to my headstock, and on which extra mandrel, if I had an eccentric chuck connected with a rod to the wall of my room, I could get my headstock to oscillate, and by connecting and multiplying wheels cause as many waves on each revolution of my principal mandrel I pleased; this after much time and patience I succeeded in doing, and worked it with the hand motion often adopted for rose work. After between two and three years, I put the extra mandrel over my principal mandrel instead of by the side as before, to enable me to dispense with the hand motion and to work the upper mandrel with the slow motion on my lathe wheel, and which I found a very great improvement, and I now give the details of the plan I have adopted for the benefit of your numerous readers.
The drawings are to a two-inch scale, or one sixth of their full size.