I was wondering if it possible to put nylon strings on a steel string guitar.
Is it possible? If not why?
In theory, you could. In practice, however, not necessarily - at least not without some problems.
Steel and nylon strings are mounted differently. Nylon strings are simply tied around the bridge, while steel strings have ball-ends that are pulled up against the bridge by string tension.
In most steel string acoustics, the strings are held in place by tapered friction pins that push the ball-end beneath the soundboard, thus securing the bridge end of the string in place. Putting nylon strings on such a bridge might be very difficult (simply tying strings around the pins might not work, since friction is the only thing that holds the pins in place).
If your guitar has a tailpiece of some sort that the strings pass through, you might be able to tie the nylon strings around that, although it may not be as easy as with a dedicated classical bridge.
On the headstock end, steel string capstans are generally shorter and narrower, accounting for both the lesser thickness and better grip of steel strings. You might be able to secure nylon strings onto the tuning pegs nevertheless, but you might experience string slippage and associated tuning problems.
Of course, there are other issues involved as well - such as those mentioned by @Dr Mayhem and @Judv. Steel-string acoustic guitars are constructed to deal with higher string tension and thus may not respond to nylon strings like a classical guitar.
All things considered, it's generally a good idea to stick with the purpose the guitar was designed for.
Yes, you can. Not so much the other way round, as steel strings on a guitar built for nylon strings may snap the neck entirely due to the increased tension, but popping nylon strings on a guitar built for steel strings will work.
It may not sound as good as you would like, as the build will have been optimised for that higher tension etc, but go for it.
Aside from looking at how to attach the strings on the bridge side of things (nylon strings are almost always traditionally tied on to a pass-through of the bridge), the real problem may be binding in the nut. Nylon strings are significantly larger than steel strings and the nut slot on a steel string guitar may not compensate for this drastic difference in string size.
Also, nylon string guitars are usually not radius'd on the fretboard to compensate for these larger strings and their increased path of vibration, unlike a steel-string guitar which has a slight radius to compensate for hand comfort (which goes along with the added pressure of pushing down the string). The radius and saddle setup may come into play when getting a nylon string to sit just right on the neck.
As said before, it's best to use a purpose-built guitar for nylon strings. I was just at Guitar Center the other day and played some cheap classical guitars in their classical room. Some sounded much better than the ones costing 3x+. If you're serious about classical guitar, and not just looking to relieve pressure on your fingers that nylon strings may provide, it would be a worthy investment to get yourself a good classical guitar.
If you were to go and get yourself a good, affordable classical guitar, one wedding gig and it will pay for itself.
If you were to convert a steel string to nylon, some very possible problems would be:
Changing of the bridge, or completely re-engineering the pre-existing bridge pins and slots.
Possible adjustment at the bridge saddle for intonation and pre-existing break points that would burr into the string.
Necessary nut adjustment, which wouldn't allow you to go back to steel strings easily without a replacement nut.
String slots in tuning pegs may need to be more rounded because of any inherent sharpness in the metal that would compromise the nylon string.
Different types of guitars use different bracings, and the X-Bracing may be a bit too strong for nylon strings and cause a noticeable decrease in sound output since the top can't freely vibrate as well with steel strings which naturally pull harder on the top.
Can't speak for every combination, but found success with the following nylon string installation on a steel-string acoustic guitar. Love the sound, worth the time.
Most Modern guitars have a truss rod in the neck which means that tention or lack thereof is not an issue for bending or snapping - especially if applying nylon strings to a steel string guitar. Neither is the attachment of strings because ball end nylon folk strings are available. The real difficulty is the with of the neck and the depth of the string grooves at the nut end of the guitar. Nylon strings because of their lower tension tend to vibrate and flex more than steel strings and generally need a slighter wider neck to accommodate this - this is why nylon string guitars tend to have wider necks(besides the type of playing that also occurs). The nylon higher strings (G, B, E) are also thicker than their steel string counterparts and wont fit in as snugly to the nut string grooves resulting in a higher and uneven action which will affect playability. You could widen these with a nail file but thats a very permanent solution and one you might regret. The woods and bracing are also different between both guitars although this might not be such a big deal if playing through a pickup.
You did not explain why you would want to put nylon strings on a steel string guitar. But one reason to do so might be to make the guitar strings more "finger friendly" and less painful to play than standard steel strings.
For the reasons stated in all the answers posted so far, trying to put nylon strings on a guitar designed for steel strings is not really a viable thing to do. However, if it's playing comfort you seek, a set of Silk and Steel strings - such as the Martin M130 or M1400, is the next best thing to nylon strings as far as comfort.
The wound strings have a thin layer of nylon fiber that acts as a padding or cushion around the steel core – making these strings much more forgiving to play. Also, because they have less metal per string (nylon filament as part of the core) they tune to pitch with less tension making them easier to fret with less pressure.
Silk and Steel strings have the same ball end as regular steel strings and the diameter's are the same so they should fit in the nut slots of your guitar with no problem.
**For more on how to create a custom finger friendly more comfortable to play set of strings for acoustic guitar click here - Comfort Play Custom String Set for Steel String Guitars
There is a type of nylon string set that is designed to be installed on a guitar with the kind of bridge with bridge pins that you find on a steel-string guitar. Look for "folk guitar nylon strings with ball ends".
But if you use them, you'll certainly need professional work done to adjust your truss rod and to modify your nut and possibly your bridge saddle also.