Morning!
Apologies if your offended drtsfc, your later posts have clarified the circumstances.
However, I bet I wrote what a lot of others were thinking!
My advice is to sharpen with a file not a grinder. You can get a far sharper chain with a file by hand.
Once you've taken a grinder to a chain it heats up the cutters too much and then they are hard to file by hand afterwards.
If you are cutting a lot of dirty wood and are repeatly having to sharpen, buy a carbide tipped chain and use it for that purpose only.
You will find that it will save you endless time in the future if you spend some time now with your groundman and teach him how to sharpen chains properly. Like anything else it'll only come with practice.
On the other side of the coin, these people presumably have got certs and will have been passed as competent to maintain a saw. If they can't then they deserve to struggle until they make the effort to be able to do the job your paying them for.
If they are no hopers then get some other staff.
I am of the opinion that if some one can't sharpen a saw to at least a reasonable dgeree of usability they should not be any where near one in the workplace.
They will only have an accident and cut their leg or boot when they are trying to force a blunt chain to cut and keep the job going when the pressures on.
Why not send the lad home with a saw and some of the blunt chains and let him have a go in his own time?
He'll be pleased as punch if he brings them back and you tell him he's made a good job.
If he ruins them, so what? You say they are cheap anyway?
It was my junior staff members job to sharpen any of the medium sized ground use saws in a vice whenever they required it. In this way he was getting as much practice as possible. Now he's not bad and we let him sharpen anything.
As regards hitting nails etc and keeping the job going on site we always take a couple of spare saws onto every job in case of nails/breakdowns whatever. That is a lot quicker than sharpening or changing a chain.
Change chains or sharpen during a lull in the work.
Thats my bit of advice, others may do it differently and tell you otherwise.
All the best.