# Creating 4" to 6" round concave depressions in a wood plank.



## Nick Ivancovich (Jan 13, 2012)

I'm trying to figure out how to make shallow concave bowls in the middle of a board. Any ideas?


----------



## bobj3 (Jan 17, 2006)

hi


----------



## jlord (Nov 16, 2009)

Do you have a lathe?


----------



## DaninVan (Jan 1, 2012)

Hey, Nick; greetings! Do you have Lee Valley Tool access down there?
Kutzall Sanding/Carving Disc - Lee Valley Tools
Pg 87 0f their 2011 online catalogue has a few other options for high speed grinders.
The chain saw circlet looks interesting. I've been meaning to get one...just haven't found a good enough excuse. 
Cheers,
-Dan


----------



## gav (Oct 12, 2009)

Hi Nick, you might get some ideas from this previous thread on a similar topic.
http://www.routerforums.com/router-bits-types-usage/31492-what-dishing-bits-there.html

By the way, is your surname Croatian ?


----------



## Nick Ivancovich (Jan 13, 2012)

This looks interesting. I was thinking more along the lines of large router bit that would plunge cut this shape. Doesn't look like theres anything like this out there. The tool you referred would definately work but would be a freehand operation and I need to replicate this cut multiple times with accuracy. I might give it a try. Thanks for the input.


----------



## Nick Ivancovich (Jan 13, 2012)

Yes. Second generation American. Grandparents immigrated just after WW1.


----------



## CharleyL (Feb 28, 2009)

How about giving us some dimensions.

What size is the board - Length, width, thickness?
What size and depth will the "shallow concave bowls" be? 
What is the position of these bowls in the board?
How accurate does the shape of the bowls need to be?

A lot of what we suggest will depend on this information.

Charley


----------



## DaninVan (Jan 1, 2012)

Nick; this may be exactly what you're looking for...
Building the 3-D pantograph - YouTube
Of course you still need the first one as a pattern.


----------



## DaninVan (Jan 1, 2012)

Coincidentally, there's another thread running with a lot more info!
http://www.routerforums.com/jigs-fixtures/29165-pantograph.html


----------



## allthunbs (Jun 22, 2008)

Nick Ivancovich said:


> I'm trying to figure out how to make shallow concave bowls in the middle of a board. Any ideas?


Hi Nick:

There are three methods that will meet your requirements: the pendulum, the saddle and the pivot frame. Depending on how many you have to do, I would suggest taking the time to make the saddle. It will meet your requirements perfectly and the results will be predictable.

The pendulum will work for you but you'll have to be careful with the chain. It may have a tendency to bounce, depending on length.

The pivot frame is the preferred method for a one-off. Practice with this one first to get repeat-ability down pat.

All of these methods will require more setup time than actual production time.

As a last resort, you can take a series of circular templates, each smaller than the next and use a guide bushing and progressively deeper cuts. It will then be a simple matter to sand or scrape out the finished shape.


----------



## Nick Ivancovich (Jan 13, 2012)

Thanks for the input. Could you explain the saddle option mentioned?


----------



## allthunbs (Jun 22, 2008)

Nick Ivancovich said:


> Thanks for the input. Could you explain the saddle option mentioned?


Hi Nick:

Take a close look at this picture. You'll see that there are two rails on the bottom, in this instance they're curved downward, and attached to the router are two "skis" that match the curve of the rails. The craftsman was creating a curved face for a speaker.










Your jig will require a circular base, two concave rails and two convex "sabot" attached to the router, like skis. The circular base will allow the rails to be rotated around one centre so you can carve all facets. Mount your workpiece(s) inside the circular base.

You will need to use a rounded bottom cleaning bit. I've attached a picture of Lee Valley's "dish carving bit" If you can, find a bit that has a complete round bottom instead of the flat bottom of this one. The size in this picture ain't bad. Some of the "ball" bits have too pointed a bottom and core box bits share the same problem.

Next, you'll need a good curved scraper. The second picture is of LeeValley's "super-hard curved scraper sets." If you have access to good hard thin steel, you can grind your own to match your specific profile.

This is method #24 of 25 methods for router usage.

I hope this helps.


----------



## gav (Oct 12, 2009)

Hi Nick,
In the other thread on this topic I posted this picture for what Allthunbs is calling a saddle jig.









You'd obviously have to change the diameter to suit your needs.

Having said that, I have been making dished recesses in boards lately with my arbortech wood grinding attachment for the angle grinder, and I don't think the router will be able to do the job quicker. Perhaps with a more consistent result though.


----------



## allthunbs (Jun 22, 2008)

Hi Nick:

Gav is bang on with his graphic. It just occurred to me that if you had access to a radial arm saw, you could just drop and spin the blade. Alternatively, it would be a pain but possible with an "L" fence to do it on a table saw (I think ;-})


----------

