Carbide spiral upcut bit diameter

[joe milana]

I am going to cut some circles out of 3/4" ply (24" & 36") with a plunge router and circle jig. What dia. bit would be "optimal" for this task? A 1/4" bit at about $25 or a 1/2" bit at $50+?

Thanks!

[Andy Sowers]

That 3/4" ply is going to be awfully tough on a little 1/4" router bit... I would be surprised if it didnt break unless you take several shallow passes to cut it. With a 1/2" bit your still removing a lot of material, so it will be slow going either way.

Can you cut them close first with a Jigsaw or similar and finish them up with a 1/2" router bit? That's what I'd suggest if you're making a lot of them...

--Andy

[pat warner]

Definitely 1/4".
Agree with solid carbide (your spiral) but not with the spiral design.
The web in a spiral is so skinny, that whilst routing diameter pathways, these cutters squggle, squirm and deflect.
2 flute solid carbide a better choice for this app., much stiffer. Stage cutting required either way.

[Myk Rian]

For plywood, I would use a 1/4" spiral compression bit.

[Anthony Whitesell]

Are you trying to cut 3/4" circles or holes?

If you're trying to cut holes. You could pre-drill with a 1/2" bit and then open them up with a 1/4" bit in a router. That would eliminate some of the load on the bit. I think the 1/2" bit would be better as it would provide more lateral strength against breaking. If you buy one 1/4" and it breaks you'll end up spending $50 on bits (two 1/4" bits at $25 each). MLCS has decent (I would say 3 of 5 stars) bits and free shipping. Their 1/2" bit is $35.

[Steve knight]

I have heard cnc router bits are too agressive for hand held routers. I have used a 1/4" downcut in a hand held but it was for a shallow cut.
I don't know why most of the spiral bits for hand helds are so thin in the middle. cnc router bits are more like endmills. I have used endmills often in my cnc router with no problems at all. they are very strong and cut well. though now I mostly use downcuts so I use cnc bits.

[Peter Quinn]

I would change strategies completely. I don't like to hog a lot of material with any router bit. Its messy, its noisy, and its hard on both tools and operator. First question, are the circles the keepers, or are you trying to make holes? Either way, I would let a saw do the cutting on multiples, either a band saw or a jig saw. I would make one perfect template in 1/4" to 1/2" material for each size hole using a router on a trammel with light passes and what ever bit you have available. Then it is a simple flush trimming application which can be done with a big pattern makers bit or a 1/2" spiral carbide, or any number of bits frankly.

[Alex Shanku]

Cant rough it on the bandsaw or scrollsaw?

Jigsaw?

Then use a trammel and router?

I have even mounted circles that were too thick for any of my router bits on the lathe and trued them that way.

[joe milana]

I'll be cutting circles to use, not holes. I figured cutting close with a jigsaw then finishing with router circle jig would be best, but eliminating the jigsawing would be a big time saver. I could just lay the plywood on a sheet of styrofoam insulation, set the bit to just penetrate, and cut away.

[Anthony Whitesell]

Now that we know you need circles. 3/4" diameter is small. Can you have a hole in the center or no?

[Lee Schierer]

The half inch bit will do the job easier than the 1/4" bit. I would still do it in at least two passes unless you are just cleaning up after a band saw or jig saw cut.

[joe milana]

Yes, each circle will have a 1" hole in the middle. It's looking like pre-cutting with the jigsaw is the way to go. Followed by cleaning up with the router.