what's the correct way of scribing the logs?

[Michael34]

I'm going to build a log cabin and I haven't done that before. I want to use dovetail. according to one manual when joining logs with saddle notch the long groove is scribed more (3/8") than the notch itself (1/8") and extensions are scribed 1/4"; this means that we create a slot of 1/4" between each of the logs and 1/8" between outside extensions; when using a round notch it says that the same scribe setting should be used for both of them; as to dovetail joinery over scribing was not mentioned there. it was also said that weight distribution in case of over scribing at length would be 75% on corners against 25% on the long groove. please check if I understand this correctly. when wood dries it decreases in size, so those slots in between would only be getting bigger, more weight would be on the corners and less at length; on the other hand they say that in scribefit woodwork these slots are so small that a piece of paper would not get there. so what's the purpose of over scribing logs at length? what would happen in an opposite case if I under scribe logs at length, with all the weight resting on the long grooves and none in the notches? and finally in my case of dovetail joinery which scribe settings should I use for the notches and long grooves?

[beenthere]

Welcome to the Forestry Forum.

Over the years there have been threads and pics showing the scribing methods used. Browsing through this timber framing forum will bring up some interesting reading, as well as putting in some key words in the Forum search function.

But also, there are members who have done the scribing and will chime in with their advice.

You have some very interesting questions. Have you done any of this before, or just getting started ??

[Magicman]

Welcome to the Forestry Forum, Michael34.  I have building a log cabin on my mind, so I am interested in your questions too.

[jander3]

If you are new to log building and want a general idea of how to approach log consturction, I suggest that you obtain Allan B. Mackie's book Building with Logs.  This book is a great starting point.

Discussion below is related to round notches or saddle notches:

Full scribed log building is designed to be applied to green logs.  If used properly, the building will get much tighter with time.

The terms underscribe and overscribe are often mixed up; they generally are trying to communicate the same thing.   The weight of the log should be on the notch, not on the lateral groove. As the building settles and the logs shrink, the notched logs slide down and tightens up.  If you cut saddles for the notches, this improves the fit.    When you drop the lower log on the building the lateral groove might be 1/8" off the log below. Provided you have no hangups in your work, by the time you have the top log installed on your building, the lower groove will be tight to the log below. As you work your way  up the building the amount of overscribe is decreased as there will be less weight  the notches.

If you cut the log such that when you install the log, the weight is on the lateral grooves. As the logs settle, shrink and dry, the notches will get floppy and sloppy and mouse holes will open up at the notches.

For setting your scriber, find the widest gap with the rough notched log sitting on the building.  Use this setting for the notches.  Add about 3/8" to scribe the lateral groove (overscribe), add an additional 1/8" or so to scribe the flyways.  As you put more logs on the building, you decrease the amount that you overscribe.

Dovetail:

When I think of dovetail, geneally I am a fan of dovetail with chinking (works for round logs or square logs).   The gap is determined by the size of the template you use to cut the dovetail. A beginner can pick this up.

You can full scribe round logs (lateral grooves) and use a dovetail notch.  This is more advanced and for a first building, I would not attempt.  I would start with a saddle notch.

Some related cabin building topics
https://forestryforum.com/board/index.php/topic,33283.0.html
https://forestryforum.com/board/index.php/topic,74685.msg1131615.html#msg1131615
https://forestryforum.com/board/index.php/topic,81229.msg1236623.html#msg1236623




  

 

[Michael34]

im going to use square hewn timbers, half dovetail notch ( i think the fit is tighter compared to full dovetail because the slope is more steep, am i right?) cant use saddle notch because log length is limited. logs are natural moisture content, not dried. so im going to build with lets say 3/8" (10 mm)  gap with installation of jute chinking in it of the same thickness. from your experience how much of a gap will remain there after drying and settling, will it be practically the same size, half of it or close to zero?