Quorn Tool and Cutter grinder

A 40 TPI thread with a typical micrometer barrel of about say 1/2" diameter with 25 divisions around it gives a precision of one thou per graduation and is easily enough used to measure/move half or quarter of a thou by eye on the graduations. Should be enough for most home shop applications. After all, it works on micrometers, even the tenths mikes with the vernier scale added.

On an application such as the Quorn though, you could, say, double the diameter of the micrometer barrel, or even triple it, to make the graduations further apart around the increased circumference and thus easier to use for fractions of a thou.

BTW we are assuming the geometry ensures distance moved by the arm equals distance moved by the tool. Otherwise we are back to 'a tad' and one could make small adjustments by inserting bits of paper under the screw contact point. What is the thickness of MEW pages?

I am pretty sure that the movement of the arm bears no relationship to the movement of the tool. No doubt someone more proficient in CAD will offer us a drawing to prove or disprove my thoughts.

I think I recall checking this and the length of the moment arm equals the height of the axis of the tool holder - not sure though.

If this were so there would be some advantage in a measurable displacement of the arm. This DHC photo gives some idea of the relative positions of the parts:

I think it is clear that the movement at the arm will be magnified at the tool holder but given the various adjustments inherent in the design it may be hard to be precise about by how much.

Hemingway Kits get a good many mentions here and it is a shame that they do not follow Ketan's example in engaging with members.

Just looked at my Quorn, built long ago. The rocking lever screw is 32tpi, (not 40tpi as I suggested earlier ). I've divided the screw-head into 12 divisions each marked 4 thou. (0.004" ), ie 0.048" per turn. I can't remember how I decided on this calibration, I seem to remember the ME build notes referring to it but I can't find that reference now. A problem with this adjuster is that there is no fixed index mark to refer the scale to and, as ega says, it's a variable figure anyway.

For most of the grinding that I do, the actual cut is controlled by the front bar micrometer, with the rocking lever used as a movement stop, so usually not too critical.

True, with all the possible configurations there isn't any absolute numbers. But judging the CAD drawings I think it will be somewhere between 1:2 and 2:1. Maybe there is a point to this super fine adjustment, but I think I will keep it as a future upgrade.

When this post was opened I couldn't see any advantage of a 30 TPI screw for adjustment of the rocking lever, I was not aware of the dual thread rate of the design.

However I now see the advantage of the dual rate threads on the arm adjuster if grinding the flutes of milling cutters or machine reamers on the face of a wheel at 90 dgreees to the tool,

Emgee