Glulam Press- Will these work?

[ApeNatural]

Hey guys, after doing some research, I am thinking that a wood press is the way to go for me. I was looking into doing a cordura style press with glulam beams, and I came across these on my local craigslist. Price seems good, but I have a couple concerns.

6 3/4 x 18 x 25 feet long glulam beams...............................$213.95 each

He has two of them, and I was thinking of going two sections wide (so 13 1/2 wide) by 8 feet long. If I buy both beams, I will have 4 8 foot beams, plus two 1 foot sections leftover.

I have two questions, will 18" be enough beam to be 1) safe, and 2) rigid enough to not allow too much deflection. To me 18 inches seems plenty thick, especially if I run some angle irons and threaded rod across the span. What do you guys think? Also, I was thinking, with the two 1 foot long sections I have left over, instead of making a cordura style press, can I use the leftover sections to make two end supports (think Iggy style but with wood). I will be left with 1 1/2 inches of overhang width-wise but I think it will work, providing this material is even strong enough in the first place. Thanks.


PS- I think I explained what I mean well, but if this doesn't make any sense to you i can draw it up quickly to help out my explanation. Thanks.

EDIT: Oh yeah, I forgot to mention that they are made from douglas fir. Don't know if that makes a difference but whatever.

[skidesmond]

First off I'm not an engineer. But there are quite a few in the forum so maybe they'll chime in.

I have a wood press where I made my beams from 3/4 OSB bolted together. They are 8 high x 12 wide x 96 long bolted every 12 in using 1/2 threaded rod. I have the beams framed by 4 inch steel U channel to keep it from exploding. I press at 35-40psi and I get about 1/8 deflection. I was surprised at first that it deflected at all since they are so heavy but it just goes to show the amount of force at play.

I would think 18inch engineered beam would be adequate but it all depends at the pressure you'll be using and how you fasten the beams to each other. But I would definitely reinforce w/ steel.

My press:

[ApeNatural]

Okay, so I am no engineer, and the extent on my knowledge of forces and pressure is my high school physics class last year. That being said, I ran some calculations (I could be totally off not even doing the right calcs) but if I was right, at 13 1/2 inches by 8 feet (96 inches), assuming a 100,000 pound gross pressure from the bladder (this is a total guess, but I have seen that figure thrown around on this site a couple times, maybe based off of a 50 psi bladder pressure?) there is roughly 78 psi exerted on the top part of the press. (I don't know if you have to divide this in half for the top section and the bottom section, but I did not) According to a stress test chart I found, the average rupture strength of a 8" tall x 6" wide and 10 feet long glu-lam beam is >8000 PSI. So I don't know if my logic is even in the right ballpark, but if it is it seems that the 18" tall x 6 1/4 wide by 8 foot long beam should be well more than enough? Someone correct me...

[skidesmond]

I believe the calc for total force is done this way:

Assume you're pressing at 50 psi and over a 13.5 x 96 total area of contact. Then the total force is 13.5 x 96 x 2 (for top and bottom) x 50psi = 129,600

Twizz or some other engineer, is this correct?

[ApeNatural]

So based off of that formula, that still only puts the stress on the material at 100 PSI, which is way under the rupture pressure... that is going by my off the wall calcs.

[Alex13]

For a very simple calc you convert the pressure into a uniform load along the beam. Imperial units confuse me so I'll use metric as an example.

350kPa (approx 50PSI) is 350,000N/m^2. Say you have a 2.2m x 0.4m gap (86.5" x 15.5" approx) that gives you a uniform load of 350 x 0.4 = 140kN/m = 140N/mm equivalent load.

Disclaimer at this point: This figure is likely to be high, as a) pressure is in the hoses, so not over an area equal to the space of the beam and b) this is a very basic load calc.

This site gives a rough idea. http://www.engineeringtoolbox.com/beam- ... _1312.html where R1 and R2 are the reaction forces (at the end points).

You can find moment of inertia and young's modulus for most I beams online. I'll take mine as an example... from here http://sketchup.engineeringtoolbox.com/ ... s-c_6.html mine is UB 305 x 165 x 46.

E = 210GPA = 210000N/mm^2(young's modulus of steel)
I = 9899cm^4 = 98990000mm^4.
Y = 1/2 height of beam = 152.5mm, therefore from that calc deflection is about 2mm. In actual fact it's lower (around 1mm), due to the errors mentioned above, but it gives an idea and builds in a factor of safety.

For deflection, use a central support at the bottom (i.e. wheels in the middle of the bottom beam). This will reduce your max deflection by 16 times. The top beam doesn't matter so much in deflection as the hose conforms to the shape.

[Alex13]

Dunno where my second post went. http://www.gltaa.com/product.htm has the young's modulus for various grades of glulam.

Basically though, with 6 3/4 x 18 glulam beams you should be right if it's fairly thorougly wrapped in cordura. Heavy for a fabric press though.

[ApeNatural]

Yeah, these bad boys are gonna be heavy as hell. I don't know if I am going to use cordura just because of the sheer size of my beams. I think I just may do an Iggy style press with the beams, and add some steel reinforcement. (Angle irons running the length of it, angle iron and threaded rod supports going around it, etc.)

[skidesmond]

Yeah I was thinking about the weight. Do you know how much they weigh? My 2 wood beams weigh about 525lbs. I didn't have fun attaching the beams to the steel frames. I had to use 6 ton bottle jacks to lift them, along with cribbing, pry bars and a few prayers.... probably what screwed my back up (herniated disc) ..... Be careful!

[ApeNatural]

Well, after a quick google search I found that 5" x 18" glulam made from pine weighs 22.4 pounds per square foot. So with my plan of doing 4 eight foot long sections, my whole press will weigh in the neighborhood of 700 lbs. Add in the steel reinforcement and I'm guessing it will be about 850lbs total, not including molds or cat track.

EDIT: On a completely non-related note: The spellchecker still doesn't recognize google as a real word? Weird, I thought this was 2010...

[MontuckyMadman]

proper name Google.

[skidesmond]

My wood beams 525lbs + the steel at 180 lbs = 705 lbs. Add in the top/bottom forms, catrack, hardware, it's around 850lbs+. It's on casters and still takes some muscle to move around.... which luckily I don't have to move very often.

[ApeNatural]

proper name Google.

Ah, that makes sense....


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