Calculateur Rapide “Système Bloch”

This is a french mechanical nomograph, which allows to mechanically connect values on several scales in order to give a result. The topic is cutting time for lathes, mills and shapers. There are three versions of the instructions, because of course Bloch wanted a tool that was as versatile as humanly possible ... that does make things little more unclear though.

First - let’s consider a lathe. The inputs consist of or the diameter of the workpiece (slider I, scale d) and the number of revolutions per minute of the lathe (Slider III, scale n). These can both be set, and are connected linearly to the scale in the middle, which gives a readout of the cutting speed. Setting the length of the workpiece with slider V while holding slider III fixed, allows to twist the arm on scale IV and show the relation between the advance of the cross-slide (i.e. depth of cut per revolution) and the total time needed to finish the cut. Sliders III, IV and V are also linearly connected.

Secondly, this is also useful for a mill or drill. In this case, on scale d, the diameter of the drill or milling cutter is entered. Scale n gives the revolutions per minute of the drill or mill, and scale l (slider V) either the drill depth or the distance to be milled. he butterfly shaped slider in the middle then gives the advance per revolution in relation to the total length of the job.

Finally, it can also be used for shapers. In that case, scale h is the single length of the cut, and scale n double the number of cuts per minute. This gives the cutting speed on II/s. Scale V/l is now the width of the piece to be worked, and scale IV/v gives the width of a single cut. THe butterfly can be turned to obtain the total job duration.

Bloch in his manual also warns that numbers in red on scales h, d, n, and z should only be read in conjunction to each other, never in comparison to the black numbers on these scales.

There are plenty of examples given in this manual on the website of Reinhard Atzbach. He also gives a very useful animation and explanation of this nomogram, if you would like to try it out for yourself.

The one I obtained is a french example of the “Schnellkalkulator “System Bloch”, s/n 112. The wood was broken, all sliders were stuck and all steel parts were heavily corroded. Enough penetrating oil allowed to start moving the sliders again in order to clean off the corrosion, and right now it is not exactly smooth, but at least everything moves and it can be demonstrated. Finally, new blocks of wood were glued into the hollow base in such a way as to not interfere with the momevement of the levers, and the brass plate (which has a steel plate of substantial thickness underneath and is riveted to that) was nailed back into place with brass nails.

Some pictures:

Bloch Calculateur Rapide

Bloch Calculateur Rapide

Bloch Calculateur Rapide