Thread: 55t press

In a nutshell:

If you have narrow end posts and your PFC's running straight across the ram mount to the end posts, then the forces are all captured in a single line.

If you want to push the end posts apart, you aren't transferring load in a line any longer, you are transferring load from the centre of an X to the corners of the X where the posts are. This can require a very different design.
An alternative to the X design is to still run PFC's close to the ram and toes out, but have them meet another cross beam at each end (PFC should work there too) which takes the load out to the corner posts.

Originally Posted by Dougal

In a nutshell:

If you have narrow end posts and your PFC's running straight across the ram mount to the end posts, then the forces are all captured in a single line.

Are you talking theoretical design of the PFC's touching back to back, because it would be impossible to do this unless the ram was mounted underneath the head beams, pushing up aginst the bottom of it....

If you want to push the end posts apart, you aren't transferring load in a line any longer, you are transferring load from the centre of an X to the corners of the X where the posts are.

Are we looking at this X in plan, end or side view (or all) ??


This can require a very different design.

???


An alternative to the X design is to still run PFC's close to the ram and toes out, but have them meet another cross beam at each end (PFC should work there too) which takes the load out to the corner posts.

I thought you were saying that the X is whats happening, not the design??? Remember I did say that the ends are tied together. This, say, by welding 100x12 FB into the ends of the PFC, from top to bottom flange, then using 250x12, across the 340mm plate to bolt these together (like Dave's)

With the example given in my post before yours, I have changed nothing except the direction of "toes". So PFC are still spaced the same distance apart, but it does change the distance between webs and the FB uprights

Is their any +'s with having more seperation of the PFCs? kinda like a beam with more vertical seperation, except now we have more horizontal seperation?

The message you have entered is too short. Please insert atleast three characters.........

Originally Posted by Bush65

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Your proposal has other ramifications that I don't have time to go into now. I will scribble something later but won't have a chance to post until Thursday or Friday.

There are certain rules of nature/physics that must be satisfied, and an important one here is that if the press is to remain static, i.e. fixed in space (no translation in any direction or rotation about any axis), while it is in operation, then every force and every moment must be in equilibrium. This can be simply stated, as Isaac Newton told us, “every action has an equal and opposite reaction”. Any force not in equilibrium will result in translation (Force = mass x acceleration) - moments result in rotation about some axis.

When the ram is used to press parts together, or apart, or deform a part into some other desired shape, the reaction from the work piece, against the ram is equal, but opposite to the force created by the ram. As we analyse the other load carrying members, these forces and reactions are distributed between them in the one and only way that satisfies the test for static equilibrium.

The threaded section of the ram body exerts an upward force on the threaded section of the 400 x 400 x 40 plate, which is in equilibrium with the downward reaction between the underside of the pair of 250 PFC's and the plate. Given the ram is centred between the pair of PFC's, then the plate will subject each PFC to halve of the ram force in the upward direction, but here is where it starts to become murky.

Where on the underside of the PFC is the upward force applied? We know the reactions to this force must be downward, as tension in the ties fabricated from 100 x 16 FB + 75 x 10 FB, but how/where is each reaction distributed between the flat bars?

Because PFC's are asymmetrical in one direction their shear centre is outside the section and forces offset from at the shear centre will cause twisting. Also if the force from the plate at the underside of the PFC is not in the same plane as the reactions from the ties this will also create a twisting moment in the PFC.

We might assume that the plate contacts the flange of the PFC over most if not all of the 90 mm width of the flange, but under load as the plate and flange deflect the contact pressure (load / area) will not be uniform. The plate deflects upward at the ram and downward at the PFC's (it is said to “hog”, which is the opposite of “sag”). If the PFC's have the toes in, i.e. [ ] this would cause pressure to increase toward the toes of the PFC and reduce toward the heel.

That is not the end of the story – assuming no flange stiffeners welded into the PFC in this area, the contact pressure will deflect the toe upward. The flange will bend at the point where the 8 mm thick web meets the 15 mm thick flange. Compared to the 40 mm thick plate the web is not very stiff when it comes to bending the flange like this. So the contact pressure will increase toward the heel and the position of the resultant force will most likely be close to inline with the inside surface of the web (how close is anyone’s guess – it could be modelled with non-linear FEA software at some $$$). If the PFC has flange stiffeners to reduce/prevent them bending, then the resultant would be close to the toe (undesirable). The PFC is still subjected to gross section twisting due to torsion and the offset of the shear centre, which will distribute pressure toward the heel. We would like the resultant to be close to the shear centre of the PFC and close to where the reaction occurs in the flat bar ties.

The other affect of having the toes in, is that it increases the bending moment in the 40 mm thick plate. Increased BM results in increased stress and deflection in the plate. Although I don't expect this to be critical, I just don't like doing that if it is not justified – there could have been material weight and $$ savings for example.

Now if the toes of the pair of PFC's were out, i.e. ] [ the reaction between the 40 mm plate and the flange of the 250 PFC will be located at the heel. The flange will not be bent, the vertical load will be distributed into the web where it is stiffest and best able to carry the load (the action, along with bending, that the section was designed for). In addition, this location is as close to the shear centre as we can hope to achieve simply and is going to be minimise the out of plane offset (twisting moment) to the 100 x 16 FB ties, assuming the FB is attached to the web of the PFC.

In either case the PFC's will need to be restrained to reduce the twisting, but it will be easier or more effective if the toes are out.

Originally Posted by uninformed

Are you talking theoretical design of the PFC's touching back to back, because it would be impossible to do this unless the ram was mounted underneath the head beams, pushing up aginst the bottom of it....

Not touching, keep the ram between them, but have them orientated toes out.

The X is looking down from above.

Originally Posted by uninformed

I thought you were saying that the X is whats happening, not the design??? Remember I did say that the ends are tied together. This, say, by welding 100x12 FB into the ends of the PFC, from top to bottom flange, then using 250x12, across the 340mm plate to bolt these together (like Dave's)

With the example given in my post before yours, I have changed nothing except the direction of "toes". So PFC are still spaced the same distance apart, but it does change the distance between webs and the FB uprights

Is their any +'s with having more seperation of the PFCs? kinda like a beam with more vertical seperation, except now we have more horizontal seperation?

The X is showing where the force is acting and where the load needs transferred to. You can use an endless number of different shaped designs to transfer load from the centre to the points, but some are clearly better than others.

Having the PFC's closer together means less bending load in the mounting plate transferring load from the ram to the PFC's.

Originally Posted by uninformed

I have seen may presses available to buy with rams that can travel left to right. This can be of benefit. Think not only of pressing a simple bearing off/on a shaft, but rather something larger, longer odd shaped. Which also brings us to toe in or out. If I go toe out, and fasten the web to the 100x16 FB, that means that I wll only have approx 185mm between uprights. If I do it the way I have suggested/copied it will give me 340mm between uprights. This can allow for jobs to fit between the uprights. Again this with less cross ties between uprights allows for those odd jobs. Normally you would just have the flat bar and cross ties welded. With cross ties at bottom, table and head there is much more clear area. This is why the 75x12 has been added perpendicular to the 100x16, to make its stiffer.

If the bottom flanges are bowing inwards and the top flanges outwards, wouldnt the flat bar fastend to the top and bottom plates help resist this? The 2 PFCs would be fighting each other??? I would have also thought that the friction from the top and bottom plates to the top and bottom flanges helped some as I cant see the top and bottom flange JUST bending in and out, wouldnt they be trying to move some what vertically as well, ie twist.??? If only trying the top and bottom flanges together as above may induce buckling of the web, then as you have already mentioned, web stiffeners can be welded in PFCs.

Lets also not forget that the ends of the PFC's are bolted to each other. But I guess that these arent helping where the twisting is going on, ie at the ram postion....This is why that if I can control the twisting where the ram is, no matter the position, it seems like not a bad Idea?

Regarding boxing in the PFCs. I have already been giving this some thought. And even though the calcs show the 8mm web to be ok. I figured more wouldnt hurt. I was thinking along the lines of getting some 250mm plate, 8 or 10mm thick, cutting and bending to suit. Bending it so, say, 120mm on the ends are hard against the web, then it bends at 45 degrees so it comes out to within 15mm of the edge of the flanges,bends back 45 degree and runs right along the length of PFC to the other end, where it bends back in to be hard against the web.

so plate would look a little like this in plan view (above) and be the same overall length as the PFCs: (ignore the @, I had to use them as spaces dont work...)

@@_________
__/@@@@@@ \__

I can see that there may be times where shifting the ram could be the only way to get a job under the ram.

I have great difficulty accepting that there would be no work around for something needing to be fed in through the side, unless the press is located in a position that confines access from front and back.

John, I need to read and digest your info more. But I AM hearing you.

Dougal, with the PFCs at 340mm outside to outside, and a 127mm dia ram, I only have 16.5mm clearance between ram and each PFC.....regardless of toe in or out..... im just spinning them around.

Im getting that closer together is mostly the Web distance?

John, Even if I place PFCs toe out and on the OUTSIDE of FB uprights. How do I go about restraining the 2 PFCs togther with out welding them, so I can still travel the ram left to right.

One example I can think of regarding placing work peice through the uprights is pressing an axle housing. If it goes through the uprights, parrallel with the table, it is much easier to sort out support points. If it passes perpendicular to the table then now support points have to be sorted from the floor....

Originally Posted by uninformed

John, I need to read and digest your info more. But I AM hearing you.

Dougal, with the PFCs at 340mm outside to outside, and a 127mm dia ram, I only have 16.5mm clearance between ram and each PFC.....regardless of toe in or out..... im just spinning them around.

Im getting that closer together is mostly the Web distance?

John, Even if I place PFCs toe out and on the OUTSIDE of FB uprights. How do I go about restraining the 2 PFCs togther with out welding them, so I can still travel the ram left to right.

I thought that you could use the top and bottom plates with the appropriate placement of cleats, that was what I was trying to get across with the use of the red and green blocks. I don't know how much the PFCs will twist though. If the movement is not that much then you could not allow much of a gap to allow the plates to tram across the PFCs!

One example I can think of regarding placing work peice through the uprights is pressing an axle housing. If it goes through the uprights, parrallel with the table, it is much easier to sort out support points. If it passes perpendicular to the table then now support points have to be sorted from the floor....

....

whoops sorry if there was any confusion:

Bush65 = John
Slug Burner = Johnk
Dougal = chooice brew

JohnK, what you drew with the red and green blocks, IS along the lines of what I was getting at....my previous post and photo showed this.

But, as John has said, its not just one thing, not just the top and bottom flanges moving laterally (end view). The bottom plate will not be pulling dead flat against the bottom flange, The PFC will not be "loaded" ideally for how it is designed. Basicly, keep the strength as close to possible to the "load/force"

Problem is, on advice from a mate that built his own presses (rams and all) he has 200mm between the uprights, and has said dont go less, even he gets caught out when having to pass things through them.


I would still like to know ideas for cross tying the PFCs so the Ram can travel left/right. I am open to the idea of boxing in the PFCs, If I understand correctly, this would change the shear center....and then the "reaction" of the modified PFCs

I could get a touch more between the uprights, mounting the PFC outboard, toe out, IF I was to fix the cleats to the ends of the top and bottom plates, not the faces. I didnt like this as the cleats bolts would be pulling on the threads, rather than in shear.