I was trying to get back into playing guitar. I only took lessons for a few years with a nylon string guitar that was fairly cheap. When I pulled the guitar out of the attic it needed new strings so I purchased medium steel strings. I know regret not getting light strings. However, I am wondering if there is a difference between the fret board of a nylon guitar and a steel guitar. I know medium strings are harder to press down but I need to used a ridiculous amount of force to get a good sound and sometimes I feel like the frets seem lower on my guitar. Is the guitar only made to be used with nylon strings?
Remove the steel strings immediately. They will permanently damage your guitar.
Do not use light-gauge steel strings either. You should only use nylon strings on this guitar.
Steel strings put much more tension on the neck of a guitar compared to nylon strings.
Guitars designed for steel strings have very stiff, strong necks with a metal truss rod inside the neck designed to counteract the additional tension from the steel strings.
Classical guitars designed for nylon strings generally do not have a truss rod in the neck, and the neck is built only to withstand the lower tension of the nylon strings.
Furthermore, the top of the classical guitar and the bridge are braced underneath only to withstand the much lower tension of the nylon strings.
If you keep those steel strings on your guitar, the neck will permanently bend and warp, the top of the guitar will "belly up" and warp, and the bridge will eventually rip loose from where it is glued to the top of the guitar, taking a good deal of the wood of the top of the guitar with it. Your guitar will be ruined. It will not be feasible to repair the damage.
Never, never put steel strings on a classical guitar built for nylon strings.
I did the maths based on data from string sets at the D'Addario string company web site.
A typical set of regular-gauge steel acoustic guitar strings puts 179 lbs (81.3kg) of tension on a guitar.
A typical set of nylon strings puts 83.6 lbs (37.9kg) of tension on a guitar.
Therefore if you put steel strings on a classical guitar, you are more than doubling the amount of tension and strain that the classical guitar has been built to handle.
A classical guitar is built for the tension of nylon string guitars. I suspect, if you put steel strings on a nylon string guitar, it'd sound fantastic ...
Also, fret material for steel strings is harder, so you'd do damage to the frets, if the guitar lasts that long.
Seriously, classical strings on classical guitars.
If you are playing only classical music then nylon string guitar is the best as it is easier for fingers. Otherwise for all other styles of music opt steel string guitar. You feel a joy while playing a steel string guitar.