Engineers drawings of a cut / join .....

[ynneb]

In the engineers drawings he has sketched to make a join as shown in the attached drawing.
Does it actually mean this, or is it a symbol?
How do you tackle this cut?
Is it acceptable to do just a diagnal cut?
The beam is 240 wide.

Benny

[prozac]

There are others here with a greater knowledge of this than I , but I'll give it a shot.
1. It is called a scarfed joint. Used when it is not possible to source a piece of timber long enough to do the job, and so 2 pieces are needed and require joining.
2. Diagonal cut or truncated cut? If you went ahead and made a diagonal cut then the pieces could slide over one another. By truncating the apex of the pointy bit you are providing a landing to locate one piece against the other. In compression the joint will be stable.
3. The diagonal part of the cut will need to be less than the width of the beam or rafter that it covers. I won't guess the depth of the cross-cut, but will leave that to greater minds. Is the size of cut specified in the drawing?

[ynneb]

Thanks for reponding.
The engineer does not specify the cross cut depth nor the angle of the cut.
I was presuming the angle would be 45 degrees?
The beam is to be used for a suspended floor, and spans between to posts 4m apart. ( If that adds anything)

[prozac]

I think that the angle of the diagonal will depend on the depth of the cross cuts, which appear to be around 1/4 the width of the beam, or 60mm each.

[fletty]

Hi Benny,
Prozac has hit the nail on the head (no pun intended) about the importance of the the 'flats' as they stop any compression loading from allowing the beam to compress by the 2 parts sliding over each other. As you can see from the engineers drawing, at the centre line of the supporting bearer, the the thickness of the beam is halved and that gives the maximum ammount of timber around both bolts. 'Tradition' has the flats a maximum of 25% of the thickness and I have seen them considerable less but the angle is much shallower than 45deg. It is not necessary for the flats to be within the width of the bearer. If I was making it and the beam was100mm thick I would cut flats of about 20mm and the final joint would have the 2 flats about 250mm apart. If the beam is not a design feature, that allows plenty of 'meat' to put 2 bolts through the joint to clamp it together. If you have any doubts, get the engineer to clarify.
Fletty

[Malcolm Eaton]

Benny I agree that the engineer needs to provide more information on the construction of the joint. It appears also that from the detail that the beam is relying solely on the bolts fosupport, I would have thought that it would be preferable to check out the post so that the load is fully supported and not relying on direct load on bolts ( what happens if the bolt shears or rusts through).
Scarf joints are usually determined by a set formula which I have shown in the attached sketch. I would also suggest to check out the following web site-
www.sawdustmaking.com/woodjoints/scarf.htm refer to fig 213.
Do a search on Google under "scarf joints in carpentry" as there is quite a lot on this subject


This scarf joint is used when the beam is subject to a transverse stress, its top is in compression and the underside is in tension. Usually the joint is bolted vertical with a steel plate on the underside to hold it together.
In the case where the beam is in tensile stress the joint is constructed in a similar fashion but fox wedges are included in the centre to tighten the joint and is further strengthened by steel plates fitted top and bottom of the beam.
Regards.
Mac

[ynneb]

Thank for all the feedback guys. What a great forum. Who would have thought a forum dedicated to timber.

I cannot contact the engineer any more. Since he has been vauge with his drawings, I guess the buiding inspector cant give me a hard time. I will use the sugestion of 25% cross cuts, and I will do the diagnal as 45 degrees.

My drawing doesnt show it as checked in, but it is checked in on the engineers drawings.

He has specified double thickness, nail laminated. How many nails per meter, and where they go, I do not know. :(

I guess you guys can see I am a amature owner builder here :)

The posts that the beams are to be bolted into are 250mm diameter treateted pine.
Do you think I should apply a preservative chemical to the checks?

You guys are a great help.

Benny

BTW How should I go about the process of doing the diagnal cut without cutting into the cross cuts?

[Malcolm Eaton]

Thank for all the feedback guys. What a great forum. Who would have thought a forum dedicated to timber.

I cannot contact the engineer any more. Since he has been vauge with his drawings, I guess the buiding inspector cant give me a hard time. I will use the sugestion of 25% cross cuts, and I will do the diagnal as 45 degrees.

My drawing doesnt show it as checked in, but it is checked in on the engineers drawings.

He has specified double thickness, nail laminated. How many nails per meter, and where they go, I do not know. :(

I guess you guys can see I am a amature owner builder here :)
The posts that the beams are to be bolted into are 250mm diameter treateted pine.
Do you think I should apply a preservative chemical to the checks?

You guys are a great help.

Benny

BTW How should I go about the process of doing the diagnal cut without cutting into the cross cuts?

Benny what do you mean by double thickness lamination? do you mean that the 240 beam is made up by laminating in depth by 2 pieces 120 mm thich or are you referring in the actual thickness to the beam ie 250 x 50 or 250 x 75 or what ever.

The cutting of the diagnal you need to get a good hand saw or a power saw and carefully cut to the shape. If you know someone or a joinery company who has a heavy duty band saw pass it on to them, once again I suggest you check out the detail of my previous post on calculation of the angle and the shape to cut paticular the top and the bottom of the splays. Have you checked out the purchase of a gluelam beam in the full length without a joint? This could save you some work in joining and lamination.
Mac
Mac

[ynneb]

Mac, the beams are 240 wide x 4m long and have to connect over 6 posts in line with each other. The total distance is 20m divided by the 6 upright posts.
There are to be two beams per span. The beams are 45mm thick. once nail laminated they will be 90mm thick x 240mm wide x 4m long.
Maybe I should try and scan the drawings and upload them here?

Benny

[ynneb]

I have attached the drawings as the engineer gave to me.
I hopen this helps.

[Malcolm Eaton]

I have attached the drawings as the engineer gave to me.
I hopen this helps.

Thanks for the drawing Benny, I will give it a bit of thought during the day. With nail laminating of timber beams there is a formula for the no of nails and spacing, unfortunately I have had no experience in a large application like yours, CSIRO had some publication on the subject some time ago, it may pay to check the timber engineering division out of that organization.
The attached web site my help in the mean time.
Mac

[prozac]

Thanks also Mac and Fletty, it has been an education for me as well.

Good luck Benny...I'll keep checking in as this is interesting.

BTW Benny, regarding the 45 deg cut. Mac points out an important detail about the formula used to determine the length of the diagonal cut and the depth of the "flats" (thanks fletty). You will need a diagonal cut LESS than 45 deg. The flats will stop the cuts sliding against each other. The low angle of diagonal cut ensures that the forces along the beam are transmitted as evenly as possible to the other side of the scarf.

Imagine a scarf cut at 90 deg (yes I know it's not a scarf) so that the ends of the beam butt each other. As soon as you apply a compressive force to the ends of the beams they will want to buckle at the butt join. This tendency to buckle will decrease with a decrease in the angle of the diagonal cut. Try this, get 2 pieces of 4x2 say 18" long each. Square cut the ends and butt them up together. Now push the ends toward each other. They should buckle!

[Malcolm Eaton]

Benny I have attached another sketch of the scarf joint showing a slightly more acute angle as on my previous sketch, the splay joint to be spread in width from 450 to 500 wide, The square cut at the top to be 60mm deep and the angle cut on the bottom to be also 60mm deep and at around 70 deg. The purpose of the angle cut is to lock the joint together under load.
If the beams were solid sections and not laminated the beam should be bolted together with vertical bolts as shown on my previous detail. In your case I guess the engineers detail of bolts bolting each section to the post would tie them together and stop them spreading longitudinal, but if it was me I would add a say 3mm thick galvanized face plate to resist any side ways twisting at the joint. The beams being laminated is going to make the cutting and fitting of the joints quite difficult and a close fitting joint is essential in your case.

In regard to the nail lamination of the beams my thoughts on this are I would only ever use this method if the beam was in a concealed application, in your case the face of the beam is fully exposed , the nails would be visable and hard to conceal, nether less I think I would investigate using stainless steel nails if available. Another option would be to do the rounds of the demolishion yards and see if you could pick up suitable oregon beams of around 250 x 75 mm or even hardwood beams , it may save you a lot of trouble.
I look forward to hear what you finaly decide.
Regards .
Mac

[artme]

Just came across this interesting discussion.

Some years ago I made a beam that was meant to span about 4metres and carry a mezzanine floor. Where I had a joint I laminated over the joint by gluing ,clamping and screwing a length of timber each side of the join.

I wonder if something similar could be done here?

[ynneb]

I Know you guys will be dissapointed in me but Ill tell you what I finally did, and more importantly, why.

The beams are 240 wide so I meaured 240 back from the ends and drew a line.
I cut down the line 6cm and then did the diagnal cut to 6cm from the opposite corner.

The angle cut is not as long as has been suggested in this thread, but I made the mistake of ordering the timber the distance from the outer extreme of each pole. I didnt consider the long diagnal cut when I ordered.

The way I figure it, there is a chance that the inspecter might not notice it, espaecially if I put a metal plate across the two bolt as has been suggested in this thread.

My house is an existing pole house build high on the posts. I am building under the house. If you see the joins I have done, it is obvious that its all rock solid.

I will post some pictures tomorrow, and I will also let you know if it passes inspection in about a week.

Thanks for all the input guys. I have used assorted bits of your information, as well as adjust to the materials and conditions I have.

Fingers crossed for next week.

Benny

EDIT: I might keep this thread running for my entire project, as I have stairs to build, windows to install, etc. As well as this, I'll start posting lots of pics, so its more obvious what I'm talking about.

EDIT: AS far as nail laminating, I couldnt drive the nails deep enough into 90mm of HW without bending them, so i have used 5mm screws, that are driven in by a low gear drill. (I'm not sure what they are called) The beams were I little bowed once bolted so I had to use some serious G Clamps to bring them down 5mm in the center, before I bolted them.
Maybe you guys can call me Butcher Benny instead :)

[prozac]

Thanks fopr the lesson Mac. I like the little locking flat at the base of the joint. You're not a boat builder?

[Malcolm Eaton]

Thanks fopr the lesson Mac. I like the little locking flat at the base of the joint. You're not a boat builder?

Hi Prizac.
No I am not a boat builder but I have dabbled in it in a small way. I have also been involved in some serious refit work on a Tall Ship ( Sail training ship The Leeuwin 11 that sails along the west coast of WA). Most of the info on scarf joints was taught at TECH way back in early 50ies .
Mac