Jump to content

Length of Rafter/Joists/Valley...etc


ccw

Recommended Posts

Good question ... answer = trig. In this case angle = 28.44?, or 6.5/12 pitch.

1) 92"/104.625" = 0.8793

2) On calculator use cos^-1 ( reciprocal function of cosine=arccos) to determine the angle.

3) and, cos^-1 (28.44?) = 1.137 * run=92" to get rafter length = 104.625"

4) Pitch is determined by the tangent using base 12, tan28.44?=0.54, 0.54*12=6.49,

therefore, pitch = 6.49:12

Download a PDF ( upper right ):

http://www.fractalnet.org/gallery2/v/CAD/CAD_RoofPitchMath.pdf.html

Link to comment

actually I have the pitch at 8:12 or 33.69 degrees. Isn't there a way in VW 2008 to tell the length of a rafter? If I select one it give me a lot of information. I just don't get how to tell the actual length from that information.

Link to comment

Assuming you are using the roof framer, when a rafter is selected the OIP has a field Nominal:. For a 1 1/2" x 9 1/4" x 9'6" rafter it is showing 4"x10"x10' in the nominal field. I'm not sure where the 4" is from but the last number (10') shows the length rounded up to the nearest 2' increments.

Link to comment

ccw:

You say you've got your rafters developed in 3d. Why not simply cut a Cut 2D* section down the centerline of your hip or valley and measure directly? This only takes a few seconds (action creates a new layer), but also provides a clear look at what you've built.

*Cut 2D and Cut 3D have, unfortunately, been moved to the Legacy folder within the Workspace Editor and so will require a bit of work to add back to your workspace.

Link to comment

ccw,

We use the VW framing tools every day, so I'm hoping I might help.

First of all, what are you trying to accomplish?

If you need to show a building section, with the rafter length dimensioned, you can use tguy's approach. But creating a Section Viewport will get you there quicker and it will be "dynamic" (if the model changes for any reason, so will the Section). Then, in Viewport Annotations, apply whatever dimensions you need.

If you want a framing materials or cut list, you'll need to get fairly familiar with VW's reporting capabilities. But be assured, you can present an accurate list on your plans. I'd encourage you to search these discussion boards for excellent pointers; use the Create Reports menu item; and post here with more questions.

If you want to insert a Call-out note, say on a roof framing plan, with the rafter's actual length (not the span length, or even the nominal length) originally mentioned, you'll either have to "do the math" or go to an elevation view to get an accurate measurement. However, I can't think of a time when we would have used this approach.

As you've already noticed, while the OIP (Object Info Pallet) gives you some useful feedback, it doesn't show the actual cut length. But the nominal length (rounded up to the next 2'-increment, on the Imperial system) may be what you'd want anyway; especially if you're trying to create a materials list. If you'd like to correct the Nominal Size problem that Ray observes, please repost and I can walk you through that process.

Ray: It's a simple data table problem that has never been resolved in any shipping version of VW, yet. I've given up complaining: we just replace the data table with each new issue.

Good luck,

Link to comment

Ok, so what are the nominal measurements that ray is talking about. Is the 10' the lenght rounded up? What I am trying to show is a roofing framing plan showing the purlins/rafters and ridges. I want to be able to tell the framers a what these measurements are. I could hand measure each of these but I just feel like there is an easier way. Say wanted to do the math, what would be the formula for figuring this out? It has been a while since I have had to do any trig.

Link to comment

As a builder or framer (myself), I'd appreciate the info but wouldn't necessarily use it in the field. And I'd feel a little like you were stepping into my 'territory'.

I draw pretty complete roof framing plans, but don't call out specific lengths, etc; odds are, those numbers won't work in the real world, anyway. I'd concentrate on making your framing plans clear and legible and include 3d iso's to help in visualization.

DonB

Link to comment

As aptly pointed out above, job site technique and direct measurement in CAD sections usually remove the need for this kind of DoTheMath. But just for fun, the 3d extension of Pythagoras' formula can be applied:

For a box (or as my high school math teacher would call it, a right rectangular parallelepiped - that's pronounced pear-ah-lella-pie'-ped) with dimension xyz, the interior diagonal length, for instance the distance from bottom left corner to upper right corner = sq root(xx+yy+zz)

And to add my mantra, this is another example of the need in VectorWorks for 3d measurement and dimensioning tools! Put it in the Wish List, everyone!!

-B

Link to comment
If you'd like to correct the Nominal Size problem that Ray observes, please repost and I can walk you through that process.

Ray: It's a simple data table problem that has never been resolved in any shipping version of VW, yet. I've given up complaining: we just replace the data table with each new issue.

Travis,

I'd be interested in knowing how to resolve this as I've run across it too and I find it irritating.

I'd imagine this would be exceedingly easy for NNA to resolve if a user can resolve it. What could possibly be keeping them from correcting it?

Link to comment

Travis said:

"If you need to show a building section, with the rafter length dimensioned, you can use tguy's approach. But creating a Section Viewport will get you there quicker and it will be "dynamic" (if the model changes for any reason, so will the Section). Then, in Viewport Annotations, apply whatever dimensions you need."

I have to respectfully disagree with Travis that Viewport Sections are quicker. To cut and measure, using the Cut 2D Section or Cut 3D Section tool, takes exactly two actions--cut--measure.

Most of my sections are used to develop--figure out--drawings and only later are sections created for purposes of display.

Link to comment

tguy,

I thought my leading statement "need to show a building section" would have implied a "section created for purposes of display". My apologies if that was unclear. If all one needs is a quick measurement, it can be got directly from the model layer by switching to an elevation view. If the model is complex and a measurement is needed somewhere in the "middle", one could certainly use the old Cut Section tool. But don't forget to count the "delete" step, if it's only a temporary item.

boxjoint,

In the VW application folder go to Plug-Ins>VW_Arch>Data and open Lumber Sizes.txt. Under Units\Actual\Nominal, change the actual to 1.01", 2.01", etc. (Since we frequently use 3x material, we've even added a full line that reads 3.01"/3") Then scroll down and update Length increments (Imperial) to 24.01"

It seems the nominal calculation in the PIO is set to round at the numbers in the "Actual" column. We want 2" to NOT round up, since we frequently work in full-dimension timber. And, since milled lumber typically comes slightly longer than specified dimension, we would rather not have a 12'-length rounded up to 14'. By "upping" the rounding point to .01" beyond, we now get the expected Nominal dimension. Which we then flow to a materials list.

I realize the above looks only to Imperial measurements, but the logic works just as well for Metric.

If something's not clear, please repost.

Good luck,

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...