ARISTO Rod Compass for Circles up to 1280mm Diameter with Accessories AH59000

Product Information

You are pushing the trammel at [B] while it is fairly snug on the beam. Lubricating helps here. To lubricate this design; tighten [B], screw the radius adjustment screw [C] off completely. Loosen [B] while holding the trammel point. It is under spring tension. It will slide off of the beam and it can be cleaned and lubricated with beeswax or hard paraffin. Lubricate the thread with the same. Under the two trays is a space for set squares, protractors and French curves. Apart from two large (45 and 60 degree) celluloid set squares that could be original (although they were catalogued as Vulcanite) the original items are all lost. There are two celluloid protractors and an angle template, all from different vendors, that are later additions. Works great! Infinitely adjustable within its range and very easy to make and use. It’s already a valuable addition to the shop and I expect it’ll be used often, assuming I can find it. I’ll probably paint the beam a bright colour, yellow, for example, to make it more visible. With the beam finished, I made the pivot pin. It’s a 1/4″ bolt, cut to length and sharpened to a point:

The needle point is located on the steady leg, and serves as the center point of the circle that is about to be drawn.I have this set up as you usually find them, steel point is adjusted. I actually find it easier to control the point while I adjust if I reverse the points so that I am holding the compass at the lead point as I adjust it; I hold the steel point on center with one hand and adjust with the other. Personal choice. Loose leg wing dividers [4] are made of all forged steel. The pencil holder, thumb screws, brass pivot and branches are all well built. They are used for scribing circles and stepping off repetitive measurements [5] with some accuracy. To get started, I cut two strips of hardwood, leaving them long. I then cut them to length and kept the off-cut ends. These pieces were then glued in at each end of the “beam”: It got broke! Such is the state of modern manufacturing when a flimsy cast part is used and can’t stand up to just a few hundred pounds of wood and shop tools piled on it. If you prefer an easy to print pdf version, Jay Bates took the time to make this one from the SketchUp file available above:

Compasses-and-straightedge constructions are used to illustrate principles of plane geometry. Although a real pair of compasses is used to draft visible illustrations, the ideal compass used in proofs is an abstract creator of perfect circles. The most rigorous definition of this abstract tool is the "collapsing compass"; having drawn a circle from a given point with a given radius, it disappears; it cannot simply be moved to another point and used to draw another circle of equal radius (unlike a real pair of compasses). Euclid showed in his second proposition (Book I of the Elements) that such a collapsing compass could be used to transfer a distance, proving that a collapsing compass could do anything a real compass can do. There are two views of the second tray, the second being with the solid electrum rolling parallel rule and some spurious items removed. The case was offered by Stanley (Catalogue number K2202 in the 1912 catalogue) with either six chain scales and six offsets or six mechanical engineer’s/architect’s scales. There are three, possibly four, of the original scales remaining. They are ivory and for mechanical engineers/architects. Three are signed Stanley. The fourth is signed Reynolds but faintly discernible under is an erased Stanley signature! All are stamped with the original owner’s name. The fifth scale in the illustration is a boxwood scale by J Archbutt that dates from 1838 - 64 and is clearly not original to this case. There are also two later boxwood scales, one by Stanley and one by Reynolds. Two offsets by Gray & Selby of Nottingham are additions and irrelevant as there are no matching scales. The ivory sector and the four line ivory protractor are unsigned and possibly replacements for the originals. The eight line ivory protractor is signed Elliott Bros London and clearly an addition. Some of the electrum drawing pins and the horn centres are probably original items in the case. The handle, a small knurled rod above the hinge, is usually about half an inch long. Users can grip it between their pointer finger and thumb. The pencil lead draws the circle on a particular paper or material. Alternatively, an ink nib or attachment with a technical pen may be used. The better quality compass, made of metal, has its piece of pencil lead specially sharpened to a "chisel edge" shape, rather than to a point. Circles can be made by pushing one leg of the compasses into the paper with the spike, putting the pencil on the paper, and moving the pencil around while keeping the legs at the same angle. Some people who find this action difficult often hold the compasses still and move the paper round instead. The radius of the intended circle can be changed by adjusting the initial angle between the two legs.

Occasionally I need to draw circles or arcs of a specific size, usually smaller ones. In the past I’ve used various ways to do this, often searching for the right size round thing in my shop or surrounding area. Much time can be burned up that way and after looking high and low, I still might not find the diameter I need. sharp point used to score a fine line in the birch plywood connected to each other by a piece of 3/4" × 3/8" mahogany