Cutting perfect disc in 1/2 lexan?

[bobby_m]

I need to cut out a perfect 4" diameter disc in 1/2" thick lexan. Obviously a hole saw won't work because I can't have a pilot hole in the center. Here's how I first thought to do it.

1. Measure my router base's outside edge to the far side of a 1/4" straight cut bit (I guess I'd call that base radius + bit radius)

2. Add that measurement to the finished disc radius and reate a circle jig with that exact radius.

3. Cut the circle out of 1/2" MDF and clamp it to the bench.

4. Affix lexan inside the circle and fix to bench with double sided tape.

5. Use hardboard as a guide and run the router around.


However, now that I have a bit kit that includes panel trimming bits with both a top or bottom bearing, I suppose I can now use a wood disc as my pattern and it won't matter if I have a pilot hole in it. Is there any other method i'm not thinking of?

Bobby

[John Hunter]

I think I would just use a circle cutting jig I made for my bandsaw. If I removed the center pin and replaced it with a short one that set in a center punch dimple it should work.

[Tequila]

The way you suggest has the possibility of ruining the piece if the router slips, since it would cut into the disc. I think your best bet is to use a wood disc and a top bearing pattern bit. That way if you slip, you'll slip outside of the disc, and the lexan won't get ruined.

You can attach the disc to the lexan with double sided tape and a clamp for extra security. You'll need to move the clamp once or twice during the process, but the tape should hold the template in place when you do.

If you have a bandsaw or scrollsaw, you might want to use it to trim the lexan down to size & shape, and leave just a little extra to trim off with the router. That will make the job much easier.

[scorrpio]

Option: if you have a drill press and a 4 1/4" hole saw, get a machine bolt which exactly fits the hole on the saw. Secure the saw on the bolt with a lock washer and a nut, and chuck the bolt in the DP. You now have a holesaw without the center bit. Make sure to secure the lexan on the DP table before cutting. That saw size might be hard to come by, though.

Option: cut a rough piece of lexan, cut a circle out of hardboard, using some sort of circle jig. Attach lexan preferrably still with protective film on) to hardboard with DS tape, chuck a flush trim bit into router table, and trim lexan to template. To make things easier, attach a piece of wood on top of hardboard to act as a handle.

Option: DS- tape that rough cut lexan piece to a chunk of wood and chuck it into a lathe.

Option: Attach a rough-cut lexan piece to a rough-cut piece of plywood, and cut it on a bandsaw using a circle cutter jig - the center pin will be in plywood, not lexan. You can also do it on a router table.

I am sure more ways can be found.

[onedash]

What is it for??? I just cut a 4" hole in lexan with a Jig Saw. I just took the blade out every 5-10 seconds to blow on it with the compressor because if I didnt the blade would get to hat and it started to melt.
It turned out almost perfect. Just some very light sanding and I was done.

[linear]

On a similar project I did a few years ago, I tried just removing the pilot drill from the holesaw arbor, it seemed like a good idea. It really really wasn't. The amount of force at the edge of the holesaw was slightly imbalanced and that imbalance was enough to take the chuck off my drill press. I was real surprised to find a spinning holesaw in my lap.


pic taken right before the lesson was learned.

As someone who's tried this, I'll offer you the following trick passed on to me by a guy that worked on solid surface countertops a lot:

With the pilot bit in, make a cut through a 3/4" scrap of plywood or whatever you have lying around. Then you place that as a holesaw guide on top of your workpiece, remove the pilot drill from the holesaw arbor and cut the workpiece on the drill press. The cutout will not have the center hole that way, and the holesaw won't fly into your lap.

And best of all, you don't have to buy anything to do it.

[jhart]

If you or a friend has the Roto Zip with the circle cutter, it would be a breeze.
I also second John Hunter's suggestion of using a circle cutter with your router. They are easy to make or inexpensive to buy.