I have just read with interest Richard Jones's article on backlapping in the current edition of Grassbox and while not wishing to start a controversy on the subject I feel that there is one important omission in his text. While it is undoubtedly true that the majority of professional users will perform in-season backlapping he omits to say that their machines will probably have been single blade relief ground at their annual service and not spin ground (spun ground?!) as is now the norm for domestic machines. Relief grinding not only presents a "thin" cutting edge to the bottom blade rather than wiping the whole width of the moving blade across it but also, by virtue of the relief angle, offers a reservoir to hold the grinding paste rather than have it all wiped off during the first rotations.
I will stick my neck out and say that while backlapping definitely has its place as an in-season maintenance operation for well maintained fine turf machines it is not a practicable substitute for grinding as a stand alone operation for the average domestic cylinder mower in "everyday" use which will more than likely be presented with rusted, rounded and "dinged" blades.
Backlapping is never a replacement for grinding, spin or relief, it is a maintenace item to keep a sharp edge on all the blades. If the blades are damaged in any way, backlapping will never bring back the required sharp edges, only grinding will get them back.
As for relief versus spin grinding, some people swear by one, others swear by the other, my feeling is that only the thicker cylinder blades require relief grinding.
The problem with spin grinding is that most operators let the cylinder run out until there is very little contact between the grindstone and the cylinder, wrong! At this point the stone should be wound on slightly to give a firm contact between stone and cylinder and then pass the stone down the cylinder again about 4-6 times, this removes metal from the back of the cylinder cutter blades and gives something similar to relief grinding.
As for backlapping domestic machine, yes you can do this, but again, only if the cylinder etc is fairly sharp to begin with.
Backlapping is never an alternative to spin grinding, and relief grinding is a process done once the cylinder has been spin ground. The reason cylinders are relief ground is to reduce the friction between the cylinder and bottom blade, which will...
- Improve the life of the cylinder
- Reduce heat on the bottom blade, which can sometimes distort the bottom blade.
- Demand a lower power requirement.
It's nessicary on some blades, but not on others, it's a modern process and probably wouldn't have been done on a lot of older machines, it's not something I'd bother with if I could get away with it. Unfortuntatley, some mowers are impossible to set up properly without first being relief ground.
Backlapping is just a process used to maintain a good cutting edge during the season, if the blade or cylinder has been damaged by a forgein object (stone), then it's got to be reground properly. Regarding a previous comment about the grinding paste building up and forming a resovoir in the relief cut on the cylinder blades, you ideally want to pressure wash the cylinders while they're rotating to remove all the grinding paste left on the blades.
You want to spin grind the cylinder before relief grinding for this reason; the spin grind creates the sharp edge on the cylinder, the relief grind cuts the back face off the cylinder to reduce the contact the cylinder has with the bottom blade.
Relief grinding is done to reduce the contact area of the cylinder blades to the bottom blades, this will as has been said reduce heat, it will not improve the life of the cylinder or require less power.
From my experience, relief grinding is only really required on thick cylinder blades and is not a modern process. If you cannot set up a cutter unit without relief grinding, you are not doing it right.
You do not have to spin grind a cylinder first before relief grinding it, it just makes it easier by trueing up the cylinder, you can just relief grind the cylinder and leave it at that, but it is usual to give it a quick spin grind after.
I enjoy going back and reading all these older topics and replies, in my job as an assistant greenkeeper I often had my packed lunch with Bob, who'd been an engineer all his life, he looked after the club's machinery etc and did a good job, my first ever job my first wet Monday morning was to help clean the cylinders on the Ransomes Hahn LTD 500 rider used for cutting the greens, Bob told me it wasn't easy to get the blades exactly as he'd like them and did wonder about a fault on the ancient flat belt driven Broom I believe cylinder grinder. I later used the Ransomes myself as the greens mower operative.
One year we had a day off at a machinery 'convention' or show at Shirley in Warwickshire open to only trade, Bob came and spoke with the makers of his machine, and was told "you've simply had the cylinder on too long"!
Bob has long gone, he was of retiring age in 1980 when I met him, but he just would not have it, he believed in the 'spark out' theory, but if the blade and grinder are no longer touching, you have no way of knowing exactly where the measurements are? Coupled with the heat and warpage of cylinder too etc. I find it hard to see how he could have been so narrow about it all.
He told me of many experiences he'd had, one was about a train load of Atco lawn mowers arriving whilst he was in the army, they were to go to the married quarters for the staff, he was slightly tickled about how the sergeants for instance had only a hand push mower but as the ranks progressed upwards, so did their lawn mower entitlement! A field marshal probably had a servant to go with his 36" machine, thought Bob.