In my very personal opinion, purchase another router that accepts 1/2" bits. You can use it for 1/4" bits with the adaptor. But, not from a 1/4 to a 1/2. Ohhh Noooo.

 

Your Craftsman router has a 1/4" collet and will not accept a 1/2" collet. Also, it has a fixed, no-load speed of 25,000 RPMs which is way too fast for rail & stile router bits. I agree with John in that you need to acquire another router. It needs to have 1/2" shaft capability and be variable speed so that you can slow down the RPMs for larger bits. I have a Milwaukee variable speed router that came with the 1/2" collet installed, but the 1/4" collet was available direct from Milwaukee for that specific router. So I can use both 1/4" & 1/2" shaft sized router bits without an adapter. Other manufacturers may also have that capability. I just wanted let you know what to look for in a new router.

 

No, for 2 reasons.

This router only accepts 1/4" shank cutters, and I would not try and change that configuration. Cheaper, and safer, to buy a newer, safer router that takes 1/2" shank cutters.

Also, this router is, IMO, not powerful enough to handle rail and stye and panel raising cutters, for continuous use.

 

The router is limited to quarter inch shanks. Totally under powered for the larger diameter bits. I'm afraid you'll have to bite the bullet for one with a half inch collet. Bosch 1617 is my choice because it's much stronger, and unlike Craftsman, you can get parts and accessories galore. It is also strong enough to go in a table, which is required for the large bits. Large diameter bits must turn at a slower speed, 10,000 to 12,000 rpm.

A large bit on a quarter inch shank will have so much torque that it can easily break and fly off, tearing up anything and anyone it hits. Also you should cut rail and stile profiles on a table. If you don't have a table, they are really easy to make, for you, that would likely be a 4-8 hour project. One nice thing about the Bosch is that they have a base with a key so you can make height adjustments from above the table Last time I looked, it was only$60 or so. Or just use the existing base and adjust the height from below, using the mounting base clamp to tighten it in place.

If you decide to buy some profiling bit sets, get them matched. These sets have shanks of exactly the same length, so if you don't move the router height, the rest of the set automatically lines up properly. This becomes a big deal if you're going to make something complicated like a glass or wood panel door.

I have a couple of Sommerfeld brand matched sets, but you can also find Freud matched bit sets These are pricey, but so much easier to use. Sommerfeld has a star shaped device called the Easy Set, It is set up for matched sets of their bits (yellow color) or similar sets from Freud. What makes them wonderful is that they have an adjustment for the exact thickness of your wood stock. A touch of genius.

If you want a really good way of working with a router table, check YouTube for videos by Marc Sommerfeld. He passed away some time ago, but his methods are simple and terrific. One thing that is great in them is how he used squares of cheap 3/4 inch MDF (Medium Density Fiberboard) to push the stile ends through the bit. This allows you to work face down and mill the ends of the stiles without changing the bit height. Without going into detail, this will save you a lot of frustrating trial and error, especially with matched bit sets.

One hint I picked up from him is to drop a half inch grommet into the bottom of the collet so the bottom of the shank is always consistent. Tiny idea that will save frustration.

This is the base with key for the Bosch. If you make your own table I suggest you pop for a router mounting plate. You attach the adjustable base to the plate. Then you can remove the router for hand work, or you can just use your craftsman with quarter inch shanks for things like roundovers and using small profile bits. Here's the 1617 and the RA1165 base with key

I have also attached a pdf on making your own router table. I think it is your first priority, given the kinds of stuff I think you're making. Just out of curiosity what region of the country are you living in? Don't be too specific please.

 

Here's a shot of that router motor. The shaft is likely little more than 1/2" diameter so what others have said, that is a lightweight router capable of only accepting bits with a 1/4" shank.

 

Usually, routers that can handle both come with interchangeable collets. If the collet did not come with it or is not available from the maker, it is not a good idea to use a bigger collet. The router probably can't handle it, too low a power or weak mechanics.