ShawnR - are you still looking to upgrade your hydraulics? For a few bucks more than PA this would give you all the hardware for mounting the ram, a gauge and other stuff.
And it's on sale!
And it's on sale!
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Shop press build
- Thread starter ShawnR
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Ancient GM show demo: 6ft length of 6”x6” steel I-beam, flat side up, supported at each end on a knife edge coming up from a concrete floor. Tenths Starrett dial gauge placed on a separate stand, at the middle of the beam, zeroed to the top face of the beam.
Six year old pushes down on the beam, the gauge dial moves about 30*. Six year old is amazed.
Everything moves or flexes under load.
Six year old pushes down on the beam, the gauge dial moves about 30*. Six year old is amazed.
Everything moves or flexes under load.
All this stuff? lol....no but I get the concepts. Putting real numbers on things is the hard part and it becomes a question of am I learning fast enough to maintain my interest and justify my time or will I decide that the theory is not necessary to get the project done? The bearing came off yesterday but I don't know at what hydraulic pressure or if deflection occurred in my table. I would like to know but no other reason than putting numbers on something. And then, a whole multitude of thoughts to keep me awake....The fact that @ShawnR knows what a strain gauge is, would indicate he knows all this stuff already
If one press deflected the table say 0.010" at peak pressure, would a 1x2x0.125 tubing recover to zero or maintain a very slight curve? If 10 bearings required the exact same force, would the table then maintain a percentage of total deflection? and on .....as mentioned, another rabbit hole for me to trip into. 
I do enjoy these threads with many members chiming in (and a few leading the learning) . There is a vast amount of knowledge in the members here.
Thanks all!
Thanks @YotaBota I did see that before I built my press. I suppose I could take everything off of it and transfer it but now that I am this far, if I fall into a great deal on components, I will switch to a Ram system but for now, just going to beef it up a bit and hope something comes along that needs pressing..
A load cell makes a Ram set look real cheap!
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All this stuff? lol....no but I get the concepts. Putting real numbers on things is the hard part and it becomes a question of am I learning fast enough to maintain my interest and justify my time or will I decide that the theory is not necessary to get the project done? The bearing came off yesterday but I don't know at what hydraulic pressure or if deflection occurred in my table. I would like to know but no other reason than putting numbers on something. And then, a whole multitude of thoughts to keep me awake....
I do enjoy these threads with many members chiming in (and a few leading the learning) . There is a vast amount of knowledge in the members here.
Thanks all!
I love the members here. I particularly love their collective experience, wisdom, and witt.
Yes, putting real numbers on this stuff is the hard part. Even when you know the theory inside out, putting real numbers on it is still the hard part. That's why safety factors are used and that's why I could be out by so much on the numbers I gave you, and that's why @Dabbler was out on his. Too many variables. Too many unknowns. The best we can hope for is to be in the ballpark and apply a safety factor to keep us out of trouble.
Does it really matter? Probably not. A basic understanding of the curve that @YYCHM provided and some thinking around how that affects a part that is being subjected to loads is enough for most of us. I really only crunched the numbers because it was apparent to me (on the basis of the experience we all get) that your design might be marginal. Adding two more cross beams above or below the others is easy and doubles the cross-section which MORE than doubles the stiffness and strength.
I think a cruise through an introductory text book on "Strength of Materials" would be useful to you and perhaps others here too. I often read text books and manuals when I go to bed. It's a great way to learn new things and it's a sure fire way to put me to sleep too!
Based on your questions, it might help to add a few thoughts:
Deflection is not a bad thing. In fact, as @whydontu & @YYCHM & @Dabbler & I have all illustrated, it is unavoidable. Any force that is applied to any beam - no matter how big - will bend it. It's not if, it's just how much! That beam is basicly a big leaf spring. The key is usually to design and build the system such that it will not permanently deform. Bigger and stronger never hurts. Too small a beam (too weak) or too big a cylinder (too much force) and it deforms and buckles when overloaded. A little spring like deflection is harmless and unavoidable. A permanently bent beam is usually not.
10 thou over 22" is absolutely nothing. It will recover back to zero. But you should measure it! In fact, put another reference beam across the frame (a simple plate held on with Clamps will do) and then mount an indicator on it and play with it. Have some fun! I'll resist the temptation to spoil the surprise!
Nope, the force is additive. The beam sees the sum of the forces and deflects "roughly" 10 times as much. Look at the curve that @YYCHM provided. The left half of the curve is linear. But interestingly, if you stack these identical bearings of yours, the force will stay constant. Each bearing will simply pass its force to the next. But the stroke required to compress all of them will be 10x greater!
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Just thinking, a plate across the frame probably won't work all that well because the frame flexes too. You will have to mount the plate to both ends of the beam so you can measure the curve as it changes. Even figuring out how to do that without measuring a lot of other things unintentionally will be a great learning exercise!
I hope you are joking. If so, I am having a good laugh with you. But if not, I am just enjoying the moment knowing that you are going to have a lot of fun and you will learn a lot real fast! Go for it! And please keep us in the loop!
Dabbler
ersatz engineer
For an engineering rule of thumb it is common to accept 1/600 of the width of the supports as acceptable deflection IF the member is an I beam, and the load is a simple one. (this comes from some basic crane design stuff I took in school)
Because you are using a welded together set of tubes you should be looking for less deflection
If you were to find a 30" I beam for your table, and your supports were 25" apart, your acceptable deflection under load would be 25/600 or 42 thou
The things is, very heavy loads over very short intervals doesn't scale very well. The 'farmers rule of thumb' may very well work out for you.
Frankly if you are in a big city, look up 'metal fabricators' and ask if they have a short I beam they can sell you out of their boneyard. You will also need an equally strong beam at the top of your press, so double the length you need...
I have a PA 20 ton press I picked up on sale more than 25 years ago. It lives outside, as My shop is too small. It is very similar to this:
from experience, we regularly get around 50 thou deflection under use, but it springs back, as I have a double U table with an additional stiffener to prevent local deflection. You have to use these offshore presses very carefully (including the CanTire one) The bottle jack can easily permanently deform the table they provide. My personal rule is that if you can see the table bending it is time to reconsider the push.
Because you are using a welded together set of tubes you should be looking for less deflection
If you were to find a 30" I beam for your table, and your supports were 25" apart, your acceptable deflection under load would be 25/600 or 42 thou
The things is, very heavy loads over very short intervals doesn't scale very well. The 'farmers rule of thumb' may very well work out for you.
Frankly if you are in a big city, look up 'metal fabricators' and ask if they have a short I beam they can sell you out of their boneyard. You will also need an equally strong beam at the top of your press, so double the length you need...
I have a PA 20 ton press I picked up on sale more than 25 years ago. It lives outside, as My shop is too small. It is very similar to this:
from experience, we regularly get around 50 thou deflection under use, but it springs back, as I have a double U table with an additional stiffener to prevent local deflection. You have to use these offshore presses very carefully (including the CanTire one) The bottle jack can easily permanently deform the table they provide. My personal rule is that if you can see the table bending it is time to reconsider the push.
I was not joking but perhaps there is a miscommunication. Good you had a laugh.
I was thinking we just wanted to note or measure deflection in the table under some load. Unfortunately, with a bottle jack, hard to quantify the actual pressure. Rather than attempting to compensate for relative stresses in the rest of the press, why not just measure the beam deflection with a source independent of the press. Maybe I misunderstood.
As mentioned above, I barely contacted the table and the dial indicator started moving.
I was thinking we just wanted to note or measure deflection in the table under some load. Unfortunately, with a bottle jack, hard to quantify the actual pressure. Rather than attempting to compensate for relative stresses in the rest of the press, why not just measure the beam deflection with a source independent of the press. Maybe I misunderstood.
As mentioned above, I barely contacted the table and the dial indicator started moving.
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Well ok then. You were serious. In that case you will learn something so it's all good.
Unfortunately, you cannot hope to measure the beam deflection if you try to measure it relative to an independent location. All you will be measuring is the collective sum of relative movements in the entire press. You MUST measure the bending relative to the plates anchored ends. I suppose you could do it your way, but you would need 3 independent indicators. One at each end of the beam and one at the center and then do some fancy vector math to subtract out the ends. But even then, there will be unaccounted for movements outside the plane of the plates bending. If you doubt this, use your same setup to measure movement at the pins. You will find that they moved too. But there are lots of ways to skin the cat. Put a bar across the plate from side to side on v-blocks. Put another block in the center but with a small gap. Use an indicator to measure the gap change. Make sure that you use pins or vblocks at the ends so the reference bar itself does not bend.
But either way, the plate will start bending the moment the ram makes contact with it so that result is indeed correct.
Further down the hole we goooooo....
I like this. I might make one! But I won't waste a perfectly good bar of aluminium. I'll just cut the caliper apart and use it. It already has the oil hole. And the bore is already the right size for the piston. I don't believe a big stroke is needed. Maybe it could even be turned to "look pretty"! Just fill the piston cavity with oil (or even brake fluid), and install a very high pressure gauge the area of the piston and pressure reading can be used as I described earlier to measure the force. Psi x area = force.
Edit - I found two old brake calipers in my scrap pile. They might prove to be too rusty to pull apart, but I'm gunna give this a try. Ive also got a few 4000 psi pressure gauges that I use when I'm working on tractor hydraulics. I've always wanted a load cell!
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Yep, I know nothing. But I see what you are talking about now. The true deflection is relative to the ends. I will experiment tomorrow.
Another site I found just used the short ram common in the frame porta power kits, the one like a hockey puck and installed a gauge where the hose fitting is. Of course, fill with oil and bleed (somehow). I have big chunks of aluminum from melting last winter so that part is easy (although I might question the quality of it. )
I contemplated a warning about pressurized gas VS oil earlier in this thread, but decided against it. But if you are thinking about making your own cylinder out of cast aluminium, I have changed my mind. Pressurized oil (or other liquids relieve the pressure instantly when something breaks because they are incompressable. Gas can be compressed and therefore it can explode sending shrapnel everywhere at high velocity if something breaks. So if you decide to use your own castings, then make sure you bleed all the air/gas out of the system before building any pressure. This is VERY IMPORTANT.