using boards to create a concave top for my mailbox - please advise - - Woodworking Talk - Woodworkers Forum
 
Thread Tools Display Modes
post #1 of 20 Old 08-06-2014, 10:21 PM Thread Starter
Member
 
Join Date: Nov 2013
Location: Los Angeles, CA
Posts: 47
View jousley's Photo Album My Photos
using boards to create a concave top for my mailbox - please advise -

Hey all - on my ever-growing project list - I want to make a mailbox for my home. I have it all completed in sketch-up. Attached is a sketchup screenshot.

It's all pretty straightforward for me, except the top of the mailbox - the concave piece. I know that you can cut indiv board down - miter the sides, glue together, and then sand away. I think that's the procedure.

But I'm not really sure how to do that - the math involved, and the best method. I don't want to bend - kerf cut, and want the material .75" thick.

I was hoping someone could enlighten me on how to measure the angle to cut the individual boards, how thick I should make them, and a good glue up and sand process.

If there is another way that I'm not aware of - all knowledge is appreciated.

thanks... as always -

J
Attached Images
 
jousley is offline  
Sponsored Links
Advertisement
 
post #2 of 20 Old 08-06-2014, 10:29 PM
Senior Member
 
Join Date: Sep 2011
Posts: 25,991
View Steve Neul's Photo Album My Photos
You just make a series of miters in the slats giving it the rough shape and then take a sander to round it. Before you get too far into it get approval from your local postmaster. Some of them are picky and will only allow factory made mail boxes. Sometimes to make a homemade one you have to build it around a postmaster approved mailbox. In my area I think you could just stick a cardboard box out there. A neighbor took a hollow log and just nailed it to a post. It has no back or door.
Steve Neul is offline  
post #3 of 20 Old 08-06-2014, 10:45 PM
John
 
Join Date: Mar 2010
Location: La Crosse, Kansas
Posts: 3,028
View jschaben's Photo Album My Photos
Quote:
Originally Posted by jousley View Post
Hey all - on my ever-growing project list - I want to make a mailbox for my home. I have it all completed in sketch-up. Attached is a sketchup screenshot.

It's all pretty straightforward for me, except the top of the mailbox - the concave piece. I know that you can cut indiv board down - miter the sides, glue together, and then sand away. I think that's the procedure.

But I'm not really sure how to do that - the math involved, and the best method. I don't want to bend - kerf cut, and want the material .75" thick.

I was hoping someone could enlighten me on how to measure the angle to cut the individual boards, how thick I should make them, and a good glue up and sand process.

If there is another way that I'm not aware of - all knowledge is appreciated.

thanks... as always -

J
Angle would depend on the number of pieces you want to use to make the top. Half circle is 180 so you would divide the number of pieces into the 180 to get the angle of each joint and, if you want the angles equal, divide that in half to get the angle on each edge of each stick..

IMO, a slick way of doing it would be to use a canoe bit set:
http://www.rockler.com/rockler-bead-...canoe-building

You just put the cove on one edge of each stick and the bead on the other and when you put them together they just roll to conform.
You can't really be married to the 3/4" stock requirement though, most of the reasonably priced sets work with 1/4, 3/8 or 1/2" stock.
The plus is, you don't need to work out the angles, just the widths and number of pieces.

John

If I strive for perfection, I can generally achieve good'nuff, If I strive for good'nuff, I generally achieve firewood
jschaben is offline  
Sponsored Links
Advertisement
 
post #4 of 20 Old 08-07-2014, 03:23 AM
Village Idiot
 
epicfail48's Avatar
 
Join Date: Mar 2014
Location: Springfield MO
Posts: 4,710
View epicfail48's Photo Album My Photos
What ischaben said, though remember, more sections make for a smoother curve but an infinitely trickier glueup. I recommend cutting the profile of the curve you plan on making in a few pieces of mdf to make a glueing template, just to make things easier
epicfail48 is online now  
post #5 of 20 Old 08-07-2014, 08:37 AM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 25,944
View woodnthings's Photo Album My Photos
other methods are ....

Kerfing the back side of a board to allow it to form a rounded top of any radius:
https://www.youtube.com/watch?v=TYfRyt6OQkY#t=24

you can also bend thin layers of plywood or veneer and glue them over a form like this:
https://www.youtube.com/watch?v=xaU8uc5OJBA

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
woodnthings is offline  
post #6 of 20 Old 08-07-2014, 09:31 AM
Old School
 
cabinetman's Avatar
 
Join Date: Jul 2007
Location: So. Florida
Posts: 24,062
View cabinetman's Photo Album My Photos
About The Other Methods

Curved tops to mailboxes can be made from segments of solid wood. Making them from plywood or MDF won't last long exposed to the elements. It would be best to start with lumber that fares well outside, like Cedar, Cypress, Redwood, White Oak, or Ipe.

If you plan on kerfing solid wood, plan to glue the segments, and/or cover with a weather resistant veneer. I haven't run into any USPS requirements regarding mailboxes other than they should be placed to be accessible.






.
cabinetman is offline  
post #7 of 20 Old 08-07-2014, 09:50 AM
Wood machinist
 
difalkner's Avatar
 
Join Date: Nov 2011
Location: NW Louisiana
Posts: 3,630
View difalkner's Photo Album My Photos
Here are the requirements per USPS - https://www.usps.com/manage/know-mailbox-guidelines.htm

You can check out sites related to making barrel staves, coopering, to get some info on cutting the joints if necessary. You won't be making a barrel shape but there's always something to be learned by checking out similar builds and construction techniques.

David

Curly Wood Shop on Etsy
David Falkner - Woodworking YouTube channel
Our music at church - current videos Airline Baptist BC Facebook Live
Romans 3:23
difalkner is offline  
post #8 of 20 Old 08-07-2014, 11:17 AM
Senior Member
 
Join Date: Jun 2012
Location: Belden, Mississippi
Posts: 629
View Bill White's Photo Album My Photos
Uhhh??? Don't ya mean "convex"?
Bill
Bill White is offline  
post #9 of 20 Old 08-07-2014, 08:44 PM
Village Idiot
 
epicfail48's Avatar
 
Join Date: Mar 2014
Location: Springfield MO
Posts: 4,710
View epicfail48's Photo Album My Photos
Quote:
Originally Posted by Bill White View Post
Uhhh??? Don't ya mean "convex"?
Bill
Depends which side of the curve you're looking at :P
epicfail48 is online now  
The Following User Says Thank You to epicfail48 For This Useful Post:
jschaben (08-07-2014)
post #10 of 20 Old 08-07-2014, 09:33 PM Thread Starter
Member
 
Join Date: Nov 2013
Location: Los Angeles, CA
Posts: 47
View jousley's Photo Album My Photos
I am thinking of making shorter pieces, beveling them at a certain angle, gluing and sanding. Was hoping for how to figure out the math.
J
jousley is offline  
post #11 of 20 Old 08-07-2014, 10:13 PM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 25,944
View woodnthings's Photo Album My Photos
boat hulls.....

Quote:
Originally Posted by cabinetman View Post
. Making them from plywood ..... won't last long exposed to the elements. .
A proper finish would be required of course.....

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
woodnthings is offline  
post #12 of 20 Old 08-07-2014, 10:16 PM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 25,944
View woodnthings's Photo Album My Photos
you want us to do the math?

Quote:
Originally Posted by jousley View Post
I am thinking of making shorter pieces, beveling them at a certain angle, gluing and sanding. Was hoping for how to figure out the math.
J

Ok determine the arc.
Then determine rise from the chord to the radius.
Then divide the arc into equal segments....


The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
woodnthings is offline  
post #13 of 20 Old 08-07-2014, 10:16 PM
Senior Member
 
Join Date: Sep 2011
Posts: 25,991
View Steve Neul's Photo Album My Photos
Quote:
Originally Posted by jousley View Post
I am thinking of making shorter pieces, beveling them at a certain angle, gluing and sanding. Was hoping for how to figure out the math.
J
How many pieces would you use to make the radius? Divide 180 degrees by the number of joints and divide that by two because it takes two pieces to make that joint.
Steve Neul is offline  
post #14 of 20 Old 08-07-2014, 11:49 PM
Old School
 
cabinetman's Avatar
 
Join Date: Jul 2007
Location: So. Florida
Posts: 24,062
View cabinetman's Photo Album My Photos
Quote:
Originally Posted by woodnthings View Post
A proper finish would be required of course.....
That wasn't my exact statement that you quoted. I never mentioned boat hulls. You just indiscriminately added that.






.
cabinetman is offline  
post #15 of 20 Old 08-08-2014, 12:02 AM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 25,944
View woodnthings's Photo Album My Photos
not indiscrimate at all....

Quote:
Originally Posted by cabinetman View Post
That wasn't my exact statement that you quoted. I never mentioned boat hulls. You just indiscriminately added that.






.

Quite intentional on my part.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
woodnthings is offline  
post #16 of 20 Old 08-08-2014, 10:16 AM
Senior Member
 
Join Date: Mar 2012
Location: SE Michigan
Posts: 1,733
View bauerbach's Photo Album My Photos
the number of pieces would be dictated by how much you want to sand off, or how much you CAN sand off while maintaining enough material for a strong joint.

too many unknowns to really give a simple answer though. the simple calculation of the angle has been given, but you really need to decide how many pieces of wood you intend to use. Since you appear to be capable enough in sketchup, I would sketch out the shape with 5-15 pieces, then set a curve to it and see just how much material your removing/remaining. Somewhere should be a sweet spot between the number of joints and the amount of sanding..

with that said... laminating sheets together or kierf cutting certainly seems like superior options to me... Its going to be a real challenge to sand this thing into an arc, and get a consistent form all the way down the length.
bauerbach is offline  
post #17 of 20 Old 08-08-2014, 10:46 AM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 25,944
View woodnthings's Photo Album My Photos
I used the beveled board approach here



Keepsake Box Step by step

I made this arch top Keepsake Box using about 5 or 6 beveled boards, gluing them together in segments and then in a final glue up. Lot of planing on the "convex" top side and lots of scraping and sanding on the "convex" bottom surface.

I beveled the board on the jointer, setting the fence over at an angle.... pretty much eyeball guessing what it was, no math involved. A table saw would have worked just as well, maybe better. I don't remember if this curve is a true radius or just a pleasing curve which may not be consistent all across creating "math" issues to compensate. If it's a true radius, that makes it a lot easier. If you are dealing with a semi-circular form like a mailbox roof, your chord is also the interior diameter/outside of the box, plus a little extra for clearance.

Layout your semi-circle and strike lines to the center point giving you the angles, depending on the number of segments ...

180 divided by 8 segments is 22.5 degrees, a good place to start. 10 segments is 18 degrees. etc.

The bottom boards do not get beveled and are 90 degrees to connect to the sides.

You might be able to use the mail box itself as a clamping form, using bicycle inner tubes or small strap clamps. Just put a thin layer of strips to space off your wood leaving the gap needed.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 08-08-2014 at 10:53 AM.
woodnthings is offline  
post #18 of 20 Old 08-09-2014, 12:56 AM
The Man
 
Masterofnone's Avatar
 
Join Date: Aug 2010
Location: Kansas
Posts: 758
View Masterofnone's Photo Album My Photos
Quote:
Originally Posted by cabinetman View Post
If you plan on kerfing solid wood, plan to glue the segments, and/or cover with a weather resistant veneer. I haven't run into any USPS requirements regarding mailboxes other than they should be placed to be accessible.
There are guidelines on how tall the post is and far from the curb/road side the box must be. Other than that size isn't regulated. I would err on the side of "oversized" as the mailman may like to stuff things in the box.
Masterofnone is offline  
post #19 of 20 Old 08-09-2014, 12:58 AM
The Man
 
Masterofnone's Avatar
 
Join Date: Aug 2010
Location: Kansas
Posts: 758
View Masterofnone's Photo Album My Photos
Quote:
Originally Posted by woodnthings View Post

Keepsake Box Step by step

You might be able to use the mail box itself as a clamping form, using bicycle inner tubes or small strap clamps. Just put a thin layer of strips to space off your wood leaving the gap needed.
Wouldn't a several strips of masking tape do the same thing?
Masterofnone is offline  
post #20 of 20 Old 08-09-2014, 05:30 AM
Junior Member
 
Join Date: Oct 2013
Location: wheatland ca
Posts: 23
View chipslinger's Photo Album My Photos
I've ran into this on a couple projects. I'm having trouble posting pics but as a self taught craftsman I've developed a process. I draw it out as large scale as possible and lay out my pieces and angles. I trace my stock (end view) over the initial drawing of the finished product (stock needs to be scaled to drawing) shouldn't have a problem drawing a end view of your mailbox full scale. Then use a straightedge/ruler to extend the lines and figure angles with a protractor. The narrower your slats are the smoother the convex side will be. Its hard to explain I'll work on pics of my last one.
chipslinger is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Woodworking Talk - Woodworkers Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
How to cut a concave piece out of a 2x4-2x6 chargersrool General Woodworking Discussion 29 08-13-2014 10:53 PM
Bend/concave cabinet top wobblywood General Woodworking Discussion 7 03-24-2013 04:52 PM
Concave headed nails sailingjlw66 Design & Plans 2 07-02-2012 11:19 PM
How do I rip a concave surface? Sleeper General Woodworking Discussion 12 05-20-2012 04:47 PM
circular concave depression joesuper General Woodworking Discussion 3 02-20-2012 03:58 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome