I have been interested timber framing for ages and i'm ready for my first project. It will be an introduction to the techniques involved but more importantly an introduction to the engineering of timber frames.

To this end I want to build a timber frame press. My friends and I have over the last three years made around 600L of cider. This year I don't just wasn't to do cider but also to pasture some juice so that we can have juice throughout the year. This means that the equipment that we have been using is a little undersized.

The current press is a shop press run by a 20t (20, 000kg) bottle jack and, with the current arrangement we can do about 30L of pomace per pressing. The plan is to build a press capable of handling 200L of pomace in one pressing run by the bottle jack from the existing press. The footprint of the pomace cheese stack will be about 9 times bigger and this will mean that the pressure that the pomace will be subjected to will be about a ninth of what we have previously done. Based on our observations of the existing press I believe (hope) that this will not effect the yeild too much.

I want to hew all the main members (posts, beams, braces) but the alll the bits involved in the press floor and ceiling will be sawn. I have access to reasonable quantities monterey pine and monterey cypress but they can be prone to large numbers of knots (in particular the pine) as they are generally from windbreaks on farms or from around houses. I can also get occasional logs from a range of australian natives but these are harder to source.

Naturally there are a number of members that need to be sized appropriately. The first being the top and bottom beams to contain the load grom the jack.

I'm new to all this but.....

The press frame consists of two posts joined by two beams one above the other. The bottom beam will support the press floor, while the top beam will contain the bottle jack. The top beam will be subjected to a point load from the bottle jack.When the press is loaded it must be able to handle the load fron the bottle jack of 20t or 44,000lbs.

The beam has a free span of 1.2m or 47.25" therefore w=931lbs/inch.

As a starting point i'll consider a beam 8" by 10" in pine(P. radiata, E=1,146,000psi), cypress (C. macrocapa, E=1,146,000) and yellow box (Eucalyptus melliodora, E=1,600,000).

Deflection =5wL^4/(384EI)

Pine and cypress deflection is 0.08".
Box deflection is 0.06".

To this point I havn't had any problems. Its when looking at shear that I'm out of my depth.

Actually reviewing my working through "sizing rough sawn joists and beams" by ed levin, I notice that it is at bending that I get lost.

I can calculate the extreme fiber stress, 3897psi, but what do I check that against? The example has 1500psi for red oak but I don't know where that value came from. I'm guessing that it comes from a table which means that at a guess that a 8x10 beam is not going to be big enough even in box. The E of green yellow box (11mpa) is 28% greater than green american white oak (8.6mpa I don't have a figure for red oak). Therefore if I add 28% to 1500psi gives me a figure of 1918psi. Is this reasonable?

That would then mean i'd need a box beam 12"x12" (f=1804psi). Yes?

Or in softwood (f<1343) 12" x 14".

Sorry I can't help with the numbers. But I would be interested in how it is all fitted together, joinery, bolts, steal? In the end the timber will be large enough but what about the joining members? Do you have a sketch or pictures?

I'll be doing sketches shortly as it gets too complicated to explain. I figured every one could get their heads around simple beams.

The engineering on the post/beam joint is next as that will be needed in order to size the post.

Article goes on to say to check for shear (h).

h=3V/2bd

V=wL/2=931 x 47.25 / 2 = 21,994lbs

h=3 x 21994 / (2 x 12 x 14) = 196psi

Which is way over the recommended value of 125psi for red oak. For EW Pine the Fv value is meant to be less than 65psi. If P. Radiata is comparable then the beam would need to be 23" square giving, h=62.4psi!

Green that sucker is going to way around 500kg!

My conclusions are that either:

- I'm doing something wrong;
- the safety factors, are overly conservative ie there is no need for a continous loading safety factor or wet service safety factor;
- traditonal screw presses, ie pre industrial revolution, didn't develop any where near 20t of force.

Where are you located?

Are you using wood that you can find the Fv Fb and E values for?

I'm in Victoria, Australia about an hour wnw of Melbourne.

I have the E values for a large number of species but my values for Fb and Fv come from approximations from the F grades or from the "Timber frame joinery and design workbook". The latter source doesn't have values for any of the Australian species (naturally) and the pine that I have access to is P. radiata and I don't know where that fits in the species groupings. The only values I have for the cypress I can get is from a web site that sells f5 and f7 grade cypress of the same species, ie C. macrocapa.

Shoot, I was going to tell you if you lived nearby me, to come and view an interesting cider press.
About an hour from me in the town of Berne, Indiana, is the world's largest cider press. It was built by a Swiss immigrant in the 1800's who decided upon coming to America to be a cider producer. He built this press entirely from memory of presses back home.
But I doubt you'd want to come so far for that...

I'd love photos though, website?