Screw in end grain

[steelnz2003]

thread337-163298
Hi
We sell balustrade glass and I saw lot of odd fixing
Try to figure out the best screw in end grain.
I read almost all data I find for this topic in the internet.
There is not enough guidance and the way I see it to do some testing which I am planning to.
What I am looking for is the pilot hole size and the best thread profile also the pull out capacity in end grain if I used some inserts

 

[hokie66]

You won't find much about screwing into end grain of wood, because almost all engineers will avoid it like the plague. Wood is just not designed to take structural fasteners in the end grain.

 

[dhengr]

Steelnz2003:
‘Lag screw into end grain of a 2x8…?,’ you better watch out for splitting of the 2x8. Most bldg. codes, IBC and NDS do not allow structural loads of any value on fasteners in end grain application. They are notoriously weak and subject to thread stripping, least affective frictional interaction with fasteners, lumber splitting, etc. There are several advantages of inserts, one is that multiple applications of the screw, bolt or lag screw does not strip the wooden thread on reapplication, and the other is that you have a .5 or .75” course threaded insert into the wood and its cap’y., never to be moved again, for a .25 or .375” screw and its pull out cap’y. When you do your testing, try a few inserts and/or lag screws with a dollop of epoxy in the pilot hole. The pilot hole is generally slightly smaller than the inner thread dia., shank dia., of the screw, and slightly shorter. You want the screw to slightly expand the hole while it is forming the thread in the wood. Some of the newer structural screws are self-drilling, and longer is better, but still watch out for splitting into thin members.

 

[berkshire]

As you know by now screwing into end grain is not a good idea , however when you absolutely have to do it, I have had good results by pilot drilling the holes , then using a screw 4 times the length of a screw you would use for cross grain to compensate for the poor holding power i.e. cross grain 2" long end grain 8" long . remember for a 3/8" lag screw you will have a withdrawal force of 216Lbs per inch in white pine across the grain, you will only have 54Lbs per inch in the end grain.
I hope this helps.

You are judged not by what you know, but by what you can do.

 

[msquared48]

But if you use plate attached to the sides instead of end plates, you will be dealing with shear values on the screws, not tension.

Mike McCann, PE, SE (WA)

 

[steelnz2003]

dhengr
We are trying to place a steel insert in a 4 inch or 100mm timber from the bottom and then have the screw to it so the pulling load will be taken by bearing of this insert.
We going to test it the only way to know how it will perform.

 

[hokie66]

steelnz2003,
Short term testing may not tell you much, as timber had a tendency to split, and the hole you make for the insert will provide the stress riser needed for a potential split to occur on that plane.

 

[Compositepro]

If the connection is critical put a steel band or box over the end of the wood, as is done with wooden tool handles.

 

[dhengr]

Steelnz2003:
And, under what conditions is the pull out (tension) on the screw/bolt not pull out on the insert? In the first case it is metal to metal thread contact as the tension btwn. a nut and a bolt, and a higher cap’y. While, in the second case the insert has a larger o.d. and generally a courser thread than the screw/bolt so it has higher cap’y. w.r.t. the wood member than the screw into the wood. But, because of the issues mentioned above these end grain connections still deserve a fairly high FoS.