Alan Marshall at Lyon was interested in acquiring a full-sized replica of the Franklin press and in 2006 invited me to build one. This turned out to be quite a learning curve. My first mistake was in ordering the wood. I specified air dried oak. This turned out to be very un-dry and full of cracks and some of it had to be returned. To be fair I think this grade of timber is normally used on things like gateposts where the wood is cut with the heart of the tree in the centre of the log so that over time it remains reasonably straight but not crack free. The wood yard pointed out that using kiln-dried oak would have been preferable but at that time (2006) it was only available here up to 75mm in thickness. I believe this is no longer the case as I have since had some excellent dry oak from the same wood-yard up to 150mm thick. I think it comes from Southern Europe.
After completion the Lyon press was dismantled, loaded into a camping trailer and transported down through France to the museum, where we found that its planned location was up two flights of a spiral staircase. This meant that we had to carry everything up by hand including a large Carrara marble press stone which the two of us took upstairs in a blanket!
The renaissance building in which the museum was housed was extremely hot and without any air conditioning, and I was concerned that the likely variation in temperature would over time, cause problems. This proved to be the case. The press worked well in the first few months but subsequently became very stiff to operate. The following Summer again at the invitation of Alan Marshall, my wife and I went down to Lyon to service the press and to fit braces to the ceiling. We found when we arrived that the press had been moved into a much more impressive room with very high ceilings.
The location was lovely but the ceiling was both high and of a quality which made attaching braces to it, problematical. With the help of the museum staff we managed it. The problem with stiffness when using the press was that the wood of the hose was rubbing on the spindle. This was solved by sanding away wood from the interior of the hose using a flap disc mounted on an electric drill. I have had this same problem with another of my presses. Getting the conical hole in the centre of the hose just right, so that it fits closely to the spindle, calls for nice judgement.
For me the metalwork of the common press was much more of a challenge than the woodwork. In particular the spindle and its thread really do need to be made in a well equipped engineering shop. In the past this part will have been forged in wrought iron and then trued up on a lathe. The thread will then have been marked out on the forging and cut by hand using cold chisels and files. Moxon describes the process in ‘Mechanick Exercises or the Doctrine of Handy-Works’3 in the section on Smithing, sub-section ‘The Rules and manner of Cutting Worms upon great Screws’. I attempted this procedure on a cylinder of mild steel but found that its toughness relative to wrought iron was such as to make it virtually impossible.
Moxon fails to describe how the nut for this thread was made but it is probable that as the nuts on common presses are normally in brass or bronze, they were cast around the hand-made thread. The following description of such a method appears in C. Holtzapffel ‘Turning & Mechanical Manipulation’ Vol. 2 pp 6684.
……. but for nuts of brass and gunmetal, sand moulds were formed. The screw was always warmed, to avoid chilling the metal and for brass it was sometimes heated to redness and allowed to cool, so as to slightly oxidize the surface and lessen the disposition of a union or natural soldering of the screw to the nut. It is commonly necessary to stretch the brass by hammering, to counteract the shrinkage of the metal in the act of cooling and to assist in the releasing of the screw, from the nut cast in this manner. The mode is by no means desirable, as the screw is exposed to being bent from the rough treatment, and to being ground by particles of sand adhering to the brass.
On the Lyon press I had the spindle made on a CNC lathe but because the machine shop were unable to make the screw I had that part of the spindle reduced to about 25mm. A separately turned screw with a hole through its centre such that it was an interference fit with the reduced section of the spindle was then heated and shrunk on. This arrangement worked well but be aware that the thread when cooling does not just contract centrally, it shortens slightly making it necessary to drive it down whilst it is cooling in order to avoid a hairline space between the thread and the shoulder of the spindle. I was fortunate in finding an engineering shop with a lathe capable of making the thread. Lathes which can cut a thread of such an extreme pitch (about 65mm) are not common.