Grindstone Shafts

[Guest dig6]

I have 2 old grindstones - both are a similar sort of size diameter 16 -18 " width 12 - 14 " ( Ipresume this was a minimum useable size as you see many around Sheffiels of this size). They both appear to be a similar type of stone. However one has a round centre hole - I got this one from a site on the East of the city, the other is from the South West side of the city centre (I dug it up recently in my garden), this one has a square centre hole.

Does anyone know why there should be a difference in centre hole? - is it age?, location?, different use? or just at the whim of the maker?

Thanks

[Bayleaf]

Table knife grinders use stones approximately 4ft to 4ft 6in diameter and 9in wide. They use them until they're worn down to around 21in diameter, which is about 28 weeks use.

It would then be sold to a pocket knife grinder who will use it down to about 15 in diameter.

Your stones are much wider. Possibly scythe grinding? Stones for grinding scythes were about 6ft in diameter, but I don't know the width.

Sorry can't be more help. You could try a visit to Shepherd Wheel one weekend. There's always a SIMT engineer there and they're extremely knowledgeable.

( Every Sat & Sun 10-4, or 11-3 when the clocks change)

[Bayleaf]

Called in at the wheel today and asked Keith the engineer about your grindstones. Apparently the one with the circular hole is earlier than the one with the square hole. Both were fitted to the shaft in a similar way, but the square ones gradually replaced the round ones, giving a better grip.

[hilldweller]

Called in at the wheel today and asked Keith the engineer about your grindstones. Apparently the one with the circular hole is earlier than the one with the square hole. Both were fitted to the shaft in a similar way, but the square ones gradually replaced the round ones, giving a better grip.

One explanation I've heard is that the stones with the square hole enabled the wheel to be easily trued by driving wooden wedges into the gaps between axle tree and stone. By using four tapered wedges from each side the wheel could be trued. An off-centred wheel would vibrate at speed and be dangerous. It would be much more difficult to drive wedges into the annular gap between a round hole and a round axle tree.

HD

[Bayleaf]

One explanation I've heard is that the stones with the square hole enabled the wheel to be easily trued by driving wooden wedges into the gaps between axle tree and stone. By using four tapered wedges from each side the wheel could be trued. An off-centred wheel would vibrate at speed and be dangerous. It would be much more difficult to drive wedges into the annular gap between a round hole and a round axle tree.

HD

That's what I understood, but the engineer said they were both fixed with cones driven in from both sides and tightened with huge spanners. I'm still not sure, I'll seek a second opinion!

[hilldweller]

That's what I understood, but the engineer said they were both fixed with cones driven in from both sides and tightened with huge spanners. I'm still not sure, I'll seek a second opinion!

I think that ideas a big no-no.

Imagine the effect of forcing round cones into the square hole of a natural stone grinding wheel. I wouldn't like to be on the premises if that engineer was resposible for mounting grinding wheels. The pressure would be very unevenly applied to the centre of the wheel and it wouldn't be possible to true the rotation of the wheel.

In illustrations in books I have seen, the wooden wedges are used but I can't post them because they are copyright.

HD

Further to the above modern synthetic grindstones are mounted between circular steel flanges.

The faces of the flanges that touch the stone are recessed slightly on the inner diameters so that the pressure is applied well away from the central hole. To further equalise the pressure soft paper discs called blotters (they feel like blotting paper) are used between the flanges and the wheel.

Only specially trained persons are certificated to change and dress grinding wheels.

Looking at the photos on Picture Sheffield of Shepherd Wheel, the wheels seem to be mounted between flanges but by the time the pictures were taken they would be using man-made wheels with round holes.

HD

[Edmund]

Pages 43 -53 of The Cutlery Trades (1913) answer every question possible about grinding (with the exception of the current question):

http://books.google.co.uk/books?id=9oHEctlB3psC&printsec=frontcover&dq=The+cutlery+trade&source=bl&ots=JBDxmLTmQ5&sig=ezOnZnSaA0FE8XStmAsD89vpgoQ&hl=en&sa=X&ei=3SlDUO2ANqKU0QWBsoCAAQ&ved=0CDsQ6AEwAA#v=onepage&q=The%20cutlery%20trade&f=false

[Guest dig6]

Thanks to all who are on the case - I suppose Hilldweller's wedge explanation raises another question - Is the shaft round or square ? (or different for the appropriate hole)

perhaps when I get time an experiment would be possible

I would also imagine that care would be needed in selection of the wedges - if they were too dry, or too tight when dry, the expansion when the stone was wet could burst the stone

[hilldweller]

Thanks to all who are on the case - I suppose Hilldweller's wedge explanation raises another question - Is the shaft round or square ? (or different for the appropriate hole)

perhaps when I get time an experiment would be possible

I would also imagine that care would be needed in selection of the wedges - if they were too dry, or too tight when dry, the expansion when the stone was wet could burst the stone

I've just been ferreting around on the t'internet and found a link to a document by a French cutler circa 1771.

In it he mentions in great detail the method of securing small grindstones on to their arbors.

It mentions multiple wooden wedges made of hardwood.

I don't know if English practice was similar but I gather that French artisans came to England at times.

The link is:- www.knife-expert.com/p05-shar.txt

HD

[Edmund]

The answer may be here. In 1856 James Wilson of Sheffield read a paper "On the Manufacture of Articles from Steel, particularly Cutlery" before the Society of Arts in London. It was reprinted in full in the Sheffield Independent. An extract below:

[Guest dig6]

That is interesting and tells us about improvements, but still leaves the question - round or square?, particularly if the iron plates held the side of the stone transmission of torque would be less of an issue.

I was wondering if the timber for the shaft was a possible reason? information from Sheppard Wheel is that the round holes were older stones.

It would be important to have a straight shaft (otherwise the stones would vibrate and not run true however well mounted). Before the introduction of mechanised sawing of timber in about 1850 it would be easier to select a naturally straight tree trunk for the shaft, rather than use cut timber that would have been produced by hand in a saw pit. Hand sawn timber was often sawn green and by rack of eye . The introduction of machine saws would make square cut seasoned timber, cut from heartwood (stronger and less prone to rot), available

Just my theory - what do you think?

[Edmund]

Not relevant to the shaft question, but shows that improvements continued being made. The technology we see, at for example, Shepherd Wheel, may represent a quite undeveloped grinding era?

[Edmund]

The patent for the improved mounting of grindstones dates from 1810 (John Slater) and a summary was published in the Retrospect of Philosophical, Mechanical, Chemical and Agricultural Discoveries:

[Bayleaf]

Right, took a second opinion this morning. In fairness the person I spoke to last time is an engineer, more usually seen at Kelham running the big engine.

The person I spoke to today is a cutler and penknife maker and grinder.

According to him, the stone with a square hole is the older of the two. These were in use as far back as the 1200's, and lasted until the mid to late 1600's. The shaft on which they were mounted was square, with the ends turned to fit the bearings. The stone was mounted on the square shaft and packed with iron wedges.

They were eventually superceded when they perfected turning a circular shaft with a thread on it. The stone had a circular hole, and was fitted with a plate either side. A large nut was then screwed up on either side to hold the stone in place.

Since dig6 found both together, it may be they were brought from elsewhere separately, or if they were in situ on the site of a wheel, then they could mark the period, in the 1600's when the changeover took place. Square shafts remained in use throughout the 1600's before being finally phased out.

[Guest dig6]

Thank you Bayleaf

That seems like a comprehensive answer. Both stones have been imported to their current site (my garden). The round hole one by me, the square hole one was buried in a wall butress, built I would guess in the early C20 (black mortar). Incidently the butress comprised of quite a lot of interesting flag-stones and dressed stones including some stone gulleys about 6" wide and 3" depth.