Thread: 55t press

You've got the internal forces sorted.

For the PFC's, you want them as close together as possible/practical to minimise bending on your mounting plate. By putting them toes-out you'll get the web of the PFC's (which carry the shear load) closer to the ram and further minimise bending of the mount.

John had mentioned that he felt that the PFC's being so short wouldnt bend much, but want to shear. Im thinking that, and along with the bottom plate being 400x400x40, the top plate being 400x300x25 and bolting them together AND locking in the top and bottom flanges (im looking at only max 0.5mm gap between the flanges and mounted fb's) that A this will help resist twisting and B, be bloody hard to bend all that locked together

The table being of slightly different design will be toe out, but they will require more fabrication for where they mount to the FB uprights

Excuse my drawing of what I think this head beam arrangement is going to look like.

If we consider the thing in the center of both elevations to be the ram, the blue circles/rectangles to be bearings to allow the ram to be slid/rolled along the head beam, where the head beam is made up of the two PFC with toes in. Which tabs/blocks red or green will be most beneficial in assisting with the prevention of the PFC twisting?

Thanks Slug, I really need a basic computer programme to allow me to draw that stuff.

There are a few corrections though:

The bearings will NOT be mounted to the top plate. There is another way to do it so, when the ram is in use, they do not touch, and the top and bottom plates are firmly tightend together so they are in contact with the PFCs, . This I believe will add to stopping diflection.

The red blocks of flat bar should be one peice left to right in your end elevation. This being more of a direct transfer from one PFC to the other. These FB will be either 75mm or 100mm in contact with the PFC flanges. There is also no room for them to run across the mounting plates as they are on the outside, given that there is only 160mm between PFCs and the ram is 127mm dia.

The green blocks should be, top and bottom, the same as you have drawn the bottom mounting plate in your end elevation, but running the full length, that is: 400mm for the bottom and 300mm for the top. The top plate over hangs the PFC the same as the bottom plate.

There is no mounting collar on the ram under the bottom plate, and the top and bottom flanges are not tapered

I can't see practical benefits of what you are intending. I strongly suggest what Dougal suggested - toes out, with webs as close as practical to the ram. BTW where Dougal spoke of bending, I read that he was referring to the 40 (ex 50) plate. And yes the 100 x 16 FB should be attached to the web of the PFC.

I did say I think shear and not bending of the PFC's will be what determines their capacity. Remember when I stated that I said the toes should be out.

Open sections like PFC's perform badly when subjected to torsion. The pics below are screen grabs that show some section properties. Note the columns for Torsion Constant J. J for a 250 PFC (J = 238 x 10^3 mm^4) is between a 60.3 x 2.3 CHS (353 x 10^3 mm^4) and 48.3 x 2.9 CHS (214 x 10^3 mm^4). Also CHS doesn't warp when twisted so no Warping Constant Iw (RHS and SHS do warp). Open sections resist twisting moments (torsion) by edgewise bending of the flanges, the web contributes next to nothing - for your 250 PFC's the bottom flanges (90 x 15 mm) bend in the 90 mm direction toward the ram and the top flanges bend in the 90 mm direction away from the ram.

Open sections should be avoided where there is torsion. Box them or eliminate or reduce the torsion to a minimal value. Normally for a press, there is no requirement to be able to shift the ram to the side. This allows the pair of beams to be simply tied together and eliminate the twisting (the clockwise twisting moment in the RH (looking on end view) beam is apposed by the anti-clockwise moment in the LH beam).

Your going to a lot of trouble to achieve a not so effective method to tie them together, treating the symptom of twisting but ignoring/exagerating the cause.

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.

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...)

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

Ok, flanges aren't tapered.

I thought that you were modelling your press on this one



that is why I placed the bearings at the top.

I went back and had at look at your ram and there is no collar as I have drawn and I now understand why you are having to tie your top and bottom plates together. You are suggesting to clamp the top and bottom plates onto the PFC. This is not as simple to move the ram as that in the photo above. Still adjustable just takes a bit longer.

I am having trouble keeping up with the textual description. I thought that I would put up a straw-man for people to pick at.

From what John has said I think that the answer to my question is that you need the green blocks on the top and the red ones on the bottom of the PFCs. But as John says that would just be treating the symptoms. I think that I can say I have learned as to which way the PFC will want to twist when loaded, if I have interpreted the moments described correctly.

As far as drawing packages. Nothing flash just the Microsoft Paint software that comes with Windows and is in the Accessories folder access from the "Start Menu" and visible when you select "All programs". CAD would be great but I'd have to learn how to drive it as well as having to buy it.

Originally Posted by slug_burner

Ok, flanges aren't tapered.


Was a joke, nit picking insignifigent stuff, hence the poking tounge

I thought that you were modelling your press on this one......that is why I placed the bearings at the top.

I am, if you read Dave's artical AND look at his pictures, you will see that his bearings are not fixed to the top plate that also clamps to his PFCs. When he has his ram in postion, top and bottom plates are clamped. To move he simply loosens the 4 mounting rods, then winds the 2, 3 armed handles that lowers the bearings, when they touch the top of PFC the continueal winding will lift the top plate off and weight is bearing on the bearings. So now top and bottom are clear to tram ram left or right.......

I went back and had at look at your ram and there is no collar as I have drawn and I now understand why you are having to tie your top and bottom plates together. You are suggesting to clamp the top and bottom plates onto the PFC. This is not as simple to move the ram as that in the photo above. Still adjustable just takes a bit longer.

Again, see above......

I am having trouble keeping up with the textual description. I thought that I would put up a straw-man for people to pick at.

I do appreciate your time and help.

From what John has said I think that the answer to my question is that you need the green blocks on the top and the red ones on the bottom of the PFCs. But as John says that would just be treating the symptoms. I think that I can say I have learned as to which way the PFC will want to twist when loaded, if I have interpreted the moments described correctly.

How is treating the symptoms any different to welding ties form PFC to PFC??? In my mind Im still trying to deal with that particular problem.

TO ALL:


I am greatful for the help by all so far, But, If you can take the time to read Dave's artical, which I have posted links to and said more than once.......it will probably save some time and effort on all counts.

I have said my ram will not be height adjustable. I have also said my head and table will not cantilever at any end

I could just build a stock press with no ram travel and weld it all together......BUT again, if you have been following from the begining you will know my reasons for choosing to not go down that path.

Please dont think I am ignoring the information given, or that I think I know better...HELL NO!!

The compromisies are comming from budget, material already bought, usage of press and ability to assemble/disassemble/move the press.

Simply putting the PFCs toe out and on the outside of the uprights changes the whole concept of the press. That is to have a good usable distance between uprights for work objects to pass through

Welding ties between the PFC will not allow ram travel

Welding the 75x12 FB to the 100x16 FB at anything other than a flush angle is not possible due to the mounting of table and head beams....

cheers
Serg