Looking for a router bit...

[EightFingers]

...spiral, at least 1 3/4” cutting length, either 1/4 or 3/8” diameter.

Googled around haven’t had much luck. 

Any ideas?

[Lucky Irish]

If you can move up to 1/2" one of these may work for you.

https://www.mscdirect.com/browse/tn/Mill...4288056343

[fredhargis]

No help with the bit, but I'm wondering if the volcano is causing you any problems?

[SceneryMaker]

...spiral, at least 1 3/4” cutting length, either 1/4 or 3/8” diameter.

Googled around haven’t had much luck. 

Any ideas?

Have you tried Holbren.com? I've had good luck with Brian.

[Cooler]

A  spiral end mill in 1/2" diameter is about $50.00.  You will have to decide on upcutting or down cutting varieties.  

I don't know how well it will cut in wood.  It is designed for metals.

Up cut will splinter plywood.  Down cut should be cleaner.

[BloomingtonMike]

https://www.mutualscrew.com/product/end-...-82328.cfm

Something like that?

Search for long endmills

[Brian in sunny FL]

I have never seen one, would probably break too easily too.

[Cooler]

We have a milling machine at work.  The end mills are generally the same size as the shank.  So unless you have some special collet for your router you will have to probably stick with 1/2" or 1/4" end mills.

A down cutting bit will cause less tearout on the top surface of wood. 

Milling bits are designed to cut metal.  I asked our lead tool and die maker if it will work on wood and he said that it will cut wood, but he didn't know how clean a cut it would be.  He said the grinding geometry is likely different for wood.

[Timberwolf]

We have a milling machine at work.  The end mills are generally the same size as the shank.  So unless you have some special collet for your router you will have to probably stick with 1/2" or 1/4" end mills.

A down cutting bit will cause less tearout on the top surface of wood. 

Milling bits are designed to cut metal.  I asked our lead tool and die maker if it will work on wood and he said that it will cut wood, but he didn't know how clean a cut it would be.  He said the grinding geometry is likely different for wood.

..............
Milling bits will work on wood but not as efficiently ..The clearance angle is not large enough to eject the chips very well...and they are available in plunge cutting and non plunge cutting designs.

[EightFingers]

Thanks for the leads and ideas, I may have to make a design change.

Fredhargis, the volcano is pretty far from us as well is the eruption in lower Puna, so no effects here.
Did feel the 6.9 earthquake tho’!