•

# Dome roof construction

3 replies to this topic

### #1 StarmanDan

StarmanDan

Aurora

• topic starter
• Posts: 4,791
• Joined: 27 Aug 2007
• Loc: Where the stars at night are big and bright...

Posted 13 October 2020 - 09:22 PM

I am in the final planning stages of my observatory and putting the finishing touches on my blue prints and had a question regarding building the roof transition for the dome.

I am planning on building a roof transition similar to what KennFromTX has built.  My question is how do I go about calculating the compund miter cuts needed for the roof rafter span between the corner of the octagon to the corner of the outer square?  I've never done compound miter cuts before and while I can figure out the angles needed mathematically based off the blue prints, I dont know which angles are relevant to the cut or how to set the angles on the saw to make the needed cuts. Any help or links would be appreciated.

### #2 darkcloud

darkcloud

Vostok 1

• Posts: 115
• Joined: 04 Feb 2006
• Loc: Central NC

Posted 14 October 2020 - 07:48 AM

Do a google search for "compound Miter cut calculator."  It should return several sites like this one:

http://jansson.us/jcompound.html

Maybe one of them will be what you need?

SG

### #3 kathyastro

kathyastro

Mercury-Atlas

• Posts: 2,652
• Joined: 23 Dec 2016
• Loc: Nova Scotia

Posted 14 October 2020 - 08:02 AM

You could do what carpenters do: hold a piece in its intended position and scribe the angle directly onto it.  With the pictured structure, you could attach the octagon to the square with the three straight rafters on each side.  Then scribe the cuts for each of the angled pieces, cut them and install them.

### #4 windowpane

windowpane

Explorer 1

• Posts: 88
• Joined: 03 Sep 2019
• Loc: Virginia

Posted 14 October 2020 - 08:41 AM

I once installed some very large and ornate cornice molding in a room that required both inside and outside corners.  After screwing up a few practice cuts, I made "sample" pieces of every cut, marked what they were, that I then used to set the saw blade angles.  It worked, and saved me from making some very expensive mistakes. Compound miters can be confusing! I like the looks of your building.

## Recent Topics

 Cloudy Nights LLC Cloudy Nights Sponsor: Astronomics