Switch collet from 1/4 to 1/2 inch?

If it has ONLY a 1/4 inch collet, time to buy a new router. My fave is the Bosch 1617, which has both a half and quarter inch collet. In other words, you can drop down a size, but not step up to larger. Beside that, the Bosch has the ability to mount under the table and be adjusted through the top. Sorry for the bad news. Don't drill your plate because not all bolt patterns are the same.

One more thing, when mounting your present router, did you remove the plastic base plate before mounting it? That will give you a quarter inch or so more. Also what size is your opening in the plate. It should be large enough for your largest bit. You use an insert to fit the opening to the bit, which is pretty tricky to make work yourself. That's why most of us just bite the bullet and buy a pre-fitted plate. The pix is of the Woodpecker plate which has a twist lock insert. Kreg also makes plates with twist lock inserts (Blue plate pix), much cheaper that the woodpecker BTW.

Thanks for all the responses and great info guys (and so quick, too). I had no idea this was such an active forum! Nick, I did indeed remove the base plate before measuring, and there are no spacers, and thank you much for the warm welcome.
No worries Dan - 1) apparently this model comes in 3 different variations: 1/2, 1, and 1 and 1/2 HP, and I can't for the life of me find any distinguishing marks on mine (other than 25,000 RPM). 2) my router being hella heavy, I was worried about sagging/warping with a thinner sheet (although, in hindsight, maybe I could have gone thinner. 3) Bummer. 4) I didn't know that the router design (other than its own collet) dictated how thick a collet could safely/comfortably be used.
Tom, I've actually been looking at that model, and, if I can scrape the money together, is the one I'm leaning towards. Luckily I've not yet drilled my plate, but I do have those Bosch insert rings in my Amazon cart - I was going to use a hole saw in my drill press for the bit opening (I'm told to liberally use/apply machine oil when drilling) and rout the step for the insert rings (my machinist friends at the Banjo Hangout - which is where I've been getting my advice until now - say it should work fine).
Heya John, the Bosch is 2 1/4 HP - is that skirting the line regarding enough power? It does include 1/2 and 1/4 inch collet chucks, and a fixed base in addition to a plunge base.
Phil, it does indeed come with only the 1/4 collet and, even without the base plate installed, does not extend far enough, thanks.
Herb, I'm gonna be scrounging and scraping as is to upgrade my router, so I'm not sure I can drop 70 bucks on a chuck, thanks for the heads-up though.

That's about as good as first questions get. I suggest you pop for a commercial plate, pre drilled for the Bosch. It is much easier to fit a plate to your table than mill aluminum. I've seen them in the $30 price range.

And don't dismiss making your own router table instead of resurecting an old one. It requires a really flat chunk of plywood, 2x3 feet or so, a really flat 2x4 or 6 and a couple of clamps to hold the fence down. You can use your new router to cut an opening for the plate by using some scrap wood wrapped around the plate (as shown), then use a one inch long bit with a top mounted bearing (shown) to hog out the opening.

IF you want to get fancy, glue on a second layer and make a smaller hole in it so you form a lip so the plate won't fall through. In that lip, you can put in some screws to adjust the plate height so it's level with the top. It's really pretty simple and a lot of folks here swear by their shop made tables. You could even find an old table in a thrift shop and use it, if the top is flat, or lay your shop made top on it after cutting an opening for the router.

The last drawing is of how to drill a hole slightly oversized in the plate, using a flat head bolt, so the head is below the top of the plat. It allows you make fine adjustments to the bottom or plate position so it's perfectly centered using the positioning cone mentioned above. The other drawing suggests how to cut a rabbet for the plate to sit on. The graw arrow represents a height adjustment screw. Be sure you pre drill the hole for this screw so it doesn't split the edge of the layer it goes through

This is an excellent learning project, BTW. You will be doing this kind of technique again and again as you do more projects.