The "grinding stones" or "culm crushers" were erected principally for the purpose of tempering culm and yellow clay to make culm balls or bombs, which were generally pronounced as "bums". The other uses to which they were put were of an ancillary nature. Whether the culm crushers were 'company' stones or privately owned they were used to temper the culm and clay as follows. The farmer or non- farmer alike took some culm, usually a couple of beds of culm, on a horse and car, jennet and car or ass and car to the culm stone together with enough yellow clay for the mix. Very often the yellow clay could be obtained close to the grinding stone. As well as the culm and clay, they had to take, according to Tom McDonald of Johnduff's Wood, six other items to the grinding stone: a shovel, bucket, brush, swingle, dronlain and a pair of draught chains. Sometimes an S-hook was necessary in order to hook the swingle to the drawbar of the culm crusher.                                      

When James O'Brien (1913-1998) of Raheendoran, Carlow,brought home the horse -load of culm from the colliery, he heeled it in the yard overnight and the next morning he went up the road to the grinding stone near Whelan's Cross. There was a day's work in tempering a whole car-load of culm according to James. He got the yellow clay in the adjacent townland of "Craanlusky" where there was a marvellous vein of the finest clay which he dug out like butter with a spade and brought home in a sack. He used about two buckets of that clay to the 14- 15 cwt. load of culm. He dumped the load of culm on one side, unyoked the horse, put the swing or swingle on the bar, placed the chains and dromain on the horse before yoking the chains to the swingle. It was important to have a quiet, seasoned horse for the job. He threw a bed of culm on the base under the stone, and gave the culm a few dry runs with the grinding stone, before he chopped in the moist clay and gave it a few more runs with the stone, and began to wet it gradually until it was tempered. All this time he was turning the culm back in under the grinding stone with the shovel. It was properly tempered when it no longer stuck to the stone. That bed of tempered culm was then taken out and replaced with a fresh bed of culm. When the whole load of culm was done it was loaded up on the car, taken home and heaped in the yard or house until there was time to make the "culm balls". This part of the operation was done by hand in the early years and in later years with the bomb-maker made by the local blacksmith or handyman, It was usually called a "bummer".  

Tempering the culm at the culm crusher was generally a 'wet-day job' according to Michael Whitely who often saw half a dozen people waiting their turn at the grinding stone in Coorleagh, on a day that wasn't suitable for other  work on the farm. It was important not to put too much water in the culm, especially on a wettish day, as the culm could flow out over the end board of the car on the way home if the road was any bit hilly.

In the normal situation where the culm and yellow clay were mixed together by dancing the culm with the feet and turning it with the shovel, the ratio of culm to yellow clay was generally six, seven or eight to one. If the culm was coarse it gave a better fire but it was very difficult to temper it properly, and it took a lot of yellow clay to stick it together . The more clay that was used the duller the fire burned. In the old days the culm at the older pits, such as The Rock, Vera, Monteen or Ridge pits, could be quite coarse. This was where the real great advantages of the culm crusher. 

      The grinding of the coarse culm at the grinding stone made it easier to temper the culm. Much less clay was required. It was easier on the hands to make the culm balls and the culm balls burned better in the fire. Some people would even riddle the very course material out of the culm before they went to the culm crusher because it gave great heat when put on top of the culm fire. The Tynans of Muckalee, Co. Kilkenny usually tempered the "culm" in the normal way by dancing it with their feet. But according to Richard, when they had "coarse culm" they took it to the Muckalee "culm crusher" to temper it. The ratio of culm to yellow clay used by James O'Brien was probably in the order of twenty or thirty to one. According to Paddy Clarke of Graiguenaspiddoge, clay was not required if the culm was ground fine enough. There was sufficient dirt or clay in the Rossmore culm to make it into culm balls without using any yellow clay as experienced by the Lawlors of Coon when they ground the culm at the culm stone at Tyndall's Lane.

      It was important to have a quiet, seasoned horse or cob when grinding the culm at the culm crusher but in most cases it could be done also with a jennet, pony or good ass. It was a heavy job on an ass and a small ass was generally too light for the job. It was generally considered a job for a horse and in the words of John Dooley of Wolfhill "a man without a horse was out". When Michael Farrell of Tomard knew that someone was grinding at the stone at Whelan's Cross he'd throw a jog of culm on the ass and car and slip down with his load in the hope that the farmer would take pity on the little ass and temper the bed of culm for Michael with his horse before he unyoked him from the stone.

A horse was generally the most suitable animal for grinding the culm, especially at the larger culm stones. The big stone at Cody's Lane, near the Ridge Cross Stones was "a savage stone to pull" according to John Meaney of the Ridge, and "you needed a good horse" to pull it around. This was not only because the stone itself was large but because the base stones consisted of roughish granite stones. According to Hugh Carpenter, of Raheen, when  Jim Meaney went to the Raheenwood culm stone up above the village of Old Leighlin he took two horses with him, one to draw the stone around and the other followed behind trampling the culm. The Harpers in Uskerty, Castlecomer, often used two horses when grinding the culm at their own stone but in this case they traced one in front of the other and used both horses to pull the huge grinding stone.

 In the 1960's and later, the Harpers ground the culm at the stone with a Ferguson tractor. Ned Byrne of Old Leighlin did the same thing at the Raheenwood Stone and the tractor kept going on its own by tying the steering wheel to the body of the tractor. Michael Purcell of Lacken who was born in 1953, saw the Lakes of Old Leighlin using the grinding stone at Walsh's Quarry, known as Lakes grinding stone, with a horse when he was going to school in the early 1960s but in later years he saw them using a Ferguson tractor.  

Most people traveled relatively short distances to grind culm at the culm crushers. Even people living near the stones didn't always go to them, especially when they were tempering only small amounts, due to the trouble.