Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Apr 21, 2022 16:42:49 GMT
Gary S235 30mm x 50mm x 2.6mm thickness steel section as a simply supported point load has a max stress of 97MPa, which is well below the 235 Yield and deflection at mid span will be 6mm. The mass of each beam is 14.5 kg without any structure tying them together. This is essentially a stiffness issue as if you limit the deflection the stress takes care of itself. If we look at Aluminium, you have to remember that while a material like 6082-T6 is as strong as S235 steel, 255 MPa yield and a third the mass. It is only a third as stiff so the equivalent structure for the same deflection has to be more substantial. 25mm x 60mm x 3mm thickness box has stress at mid span of 73MPa and a deflection of 12mm and a mass of 6kg per beam. 75mm x 25mm x 3mm thickness has a deflection of 7mm and a mass of 8kg per beam. I can send you an excel spread sheet that works it all out if you want. Dave Thanks Dave that's most helpful, exactly the advice I needed! The 25 x 75 x 3 aluminium seems the most attractive in many ways, but a very quick look at the website of an illustrative supplier* indicates a material cost in the order of £153 before carriage, which calls for a hasty rethink... The 30 x 50 x 2.6 (actually 2.5 nominal) steel costs a lot less (around £54) but it will weigh 29kg before any cross bracing is added. This could be reduced a little by going down to 25 x 50 x 2.5. IIUC, reducing the width won't affect the deflection much if at all -? (The grade in this example is E220; at this sampled supplier E235 is only available galvanised, with not much choice of section.) Many thanks again for the calculations and the offer of a spreadsheet. As you'll gather I'm a complete duffer at proper mathematical engineering, so I'm not sure how much it would help Gary *Metals4U. Just happened to be the first I clicked on. I will shop around obvs, but at least it gives a ball-park figure.
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Apr 21, 2022 16:54:17 GMT
Hi Gary, I made a 5 feet long bridge for my Bagnall in steel angle. It is extremely heavy and one of the reasons i am struggling with engines of this size. I believe it is 3" x 2" angle so pretty robust. Pete. Ha! Yes indeed Pete, I must admit I am slightly overawed at the physical weight of my loco now it is all assembled! It is nice to look at big engines, and the weight isn't all that difficult to get a ball-park estimate for, but it is just numbers until you physically have to move the beast! If it derails for example, it will not be a simple matter of lifting it back on the tracks as it is with Bridget. It could be worse of course. I once tried to assist getting a NG loco back on the 7¼" track at the club, and it was impossible to move it at all without resorting to levers and (if I remember correctly) a jack. Heavy locos need heavy equipment to carry them, in my case a complete rethink of this bridge. I don't have to lift the loco, but I willhave to lift the bridge Gary
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Apr 21, 2022 17:06:49 GMT
Why not use 2 pieces of 2" x 1/4" angle iron as rails and the bridge at the same time. 200Kgs will be nothing to that section, and it can be made light enough to handle easily by using wood to join the 2 angles at the right gauge. I've use 1.1/2" x 1.1/2" x 1/4" angle for my 5" 9f and the angle handles it with hardly any deflection. Bob. Thanks Bob. 50 x 50 x 6 angle iron would be in a similar range of strength to the 30 x 50 x 2.6 box proposed by Dave, and rather more weighty, but it is reassuring to know that this is the right sort of size to go for. Angle iron is easier to build into a braced structure, short of welding; but less stiff in torsion I believe. I wonder if that would matter much in the sort of sizes we are considering? Gary
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Apr 21, 2022 17:52:45 GMT
Hi Gary I recently lifted a new lathe in my workshed using a pair of 40mm square x 3mm (nominal wall) hollow section beams to take the load. The lathe weighed somewhere between 150 and 200kg and the span of the beams was about 1500mm, so a bit less onerous than your problem, but everything went well at least in regard to supporting the load. These beams actually have a wall thickness closer to 2.8mm, which would make the moment of inertia 96638mm^4 and the bending stress 103MPa for each of two beams for a total central point load of 200kg and 2000mm span. The maximum deflection if 8.6mm (I think). So one beam could probably take the full weight, which gives some comfort. A bit of cross bracing between the beams would also help by giving a bit of torsional rigidity. Eric Thanks Eric that is also very helpful, and 40 x 40 x 2.8 is in the same ball-park as Dave's suggestion of 30 x 50 x 2.8. I think that clinches it, because a rectangular section will be stiffer in the vertical plane where it is needed, for a similar weight. Very little stiffness is needed in the horizontal plane, other than to resist twist, and with a pair of beams a little light bracing should make the structure adequately stiff in that direction. Actually it raises a further possibility that I hadn't thought of. If we consider a RHS beam of 50mm depth, and take away the horizontal webs altogether, we would have 2 solid thicknesses of 2.8mm thickness, or call it one of 6mm. A plate of that thickness would have the same vertical strength I think, save a certain amount of weight. The horizontal stiffening could be taken care of by cross-bracing. Would this be a suitable solution?? Plates are much easier to bolt together than RHS. Gary
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kipford
Statesman
Building a Don Young 5" Gauge Aspinall Class 27
Posts: 566
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Post by kipford on Apr 21, 2022 18:14:10 GMT
Gary Using a 6mm x 50mm plate vertically results in a stress of 196 MPA on a point load so it is still OK from a yield stress point of view in steel. Deflection is 12mm and mass is 5 kg per plate. if you go to 75 mm depth the deflection reduces to 4 mm but the mass increases to 7.4 kg. However using a simple plate you will need to ensure there are sufficient cross braces to prevent it failing in the transverse direction as Chris Vine pointed out earlier. I can look at the transverse direction loads and deflection, but cannot do it for a few days due to other commitments Regards Dave.
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Post by thumpersdad on Apr 21, 2022 20:47:49 GMT
Hello Gary
assuming that I understand correctly, then it is not really that simple. The horizontal parts provide the greatest contribution to the total moment of inertia for bending in the vertical plane, because they are furthest from the neutral axis of bending.
For the 40mm square box section mentioned above the horizontal bits contribute 77600mm^4 of the 96600mm^4 moment of inertia, which is why Dave is finding that you need more metal if you take away those bits.
Eric
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Apr 21, 2022 23:35:35 GMT
Hello Gary assuming that I understand correctly, then it is not really that simple. The horizontal parts provide the greatest contribution to the total moment of inertia for bending in the vertical plane, because they are furthest from the neutral axis of bending. For the 40mm square box section mentioned above the horizontal bits contribute 77600mm^4 of the 96600mm^4 moment of inertia, which is why Dave is finding that you need more metal if you take away those bits. Eric Hi Eric and Dave, and indeed everybody who has contributed to this enquiry No indeed Eric, it is me that is that simple! When it comes to moments of inertia and neutral axes etc you are talking to a total numpty as I'm sure you have already guessed. But at least I know I'm a numpty so I can ask advice from the right people, and MECH never fails in this. So plate is not such a great idea, and I'll forget that. It seems that the best-performing section out of those that you have kindly worked out between you is Dave's 30 x 50 x 2.6 in S235 steel RHS, so I'll do some sketches and start shopping around for a supplier tomorrow. I think I'll abandon the initially attractive idea of adding triangulated bracing to the existing aluminium bridge. It would need a lot of thought and effort to add enough strength to match the kind of steel sections we are talking about here, but there is also the matter of criticality. If I get it wrong and a steel bridge in RHS is overloaded, it will start to bend, and I will back off. If a single joint in a structure based on triangulation fails, there is the likelihood of progressive failures of other parts leading to total collapse. In (Greenglade) Pete's excellent lightweight stand there are intermediate supports, so the span is divided and a total failure is unlikely, but if I use my bridge with no intermediate struts (as I hope to) it is all or nothing- it stands or it fails, and I can't expect any bending phase to signal the structure is in distress. I really don't want to risk years of work crashing to the floor (and probably through it)! So thanks very much to all who given their time to help with this. I couldn't have got this far on my own, I really am most grateful. Gary
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Post by steamer5 on Apr 22, 2022 3:23:01 GMT
Hi Gary, I had a chat to dad about the link span we use. He made it from 1”x1” box with 1/8” wall, it’s 5 foot long, there is 4 cross members welded across flush, he then used an angle grinder to provide flange clearance on the cross members. At the middle he has a short bits sticking down with rods welded back to each sand to form the triangle to strength it. ( As a thought if the span was slightly bowed prior to welding in the rods might help, guess Dave will be able to tell us) Couplings each end depending on what you are coupling to. After an almost crash, he put an adjustable leg on the transport frame as it kicked up when the load went on the span, he did the same in the middle of the link span, it pivots out of the way when not required. Oh on the derail, rerail, we were away having fun playing trains, dad derailed & tried to put his loco back on the rail, the loco slipped & took 1/4” of the end of his thumb!! After that he built gear to lift & pivot the loco back on. The guys with bigger locos here have hydraulic jacks setup…….there’s nothing like getting 3 or 4 people around a loco in the dark to lift & 2 lying on the ground trying to get it sorted!
Cheers Kerrin
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Apr 22, 2022 20:26:09 GMT
Hi Gary, I had a chat to dad about the link span we use. He made it from 1”x1” box with 1/8” wall, it’s 5 foot long, there is 4 cross members welded across flush, he then used an angle grinder to provide flange clearance on the cross members. At the middle he has a short bits sticking down with rods welded back to each sand to form the triangle to strength it. ( As a thought if the span was slightly bowed prior to welding in the rods might help, guess Dave will be able to tell us) Couplings each end depending on what you are coupling to. After an almost crash, he put an adjustable leg on the transport frame as it kicked up when the load went on the span, he did the same in the middle of the link span, it pivots out of the way when not required. Oh on the derail, rerail, we were away having fun playing trains, dad derailed & tried to put his loco back on the rail, the loco slipped & took 1/4” of the end of his thumb!! After that he built gear to lift & pivot the loco back on. The guys with bigger locos here have hydraulic jacks setup…….there’s nothing like getting 3 or 4 people around a loco in the dark to lift & 2 lying on the ground trying to get it sorted! Cheers Kerrin Thanks Kerrin It is becoming increasingly clear to me that the issue causing the difficulty is the length of the span. I suspect that if I reduced the span just 1 ft to your 5ft, I could go down at least one section size, and possibly more, (though I doubt if 1" x 1" would carry this amount of weight, even then). The same is true if I abandon the idea of an unsupported span (which is more for convenience than anything) and put in one or more intermediate props. The convenience of not having intermediate supports is very much cancelled out by the weight that would be needed for a 6ft bridge without supports: 29kg before I add the cross-bracing. A long and heavy item like that can easily cause damage while it is being manhandled around (including to me!) and I'm not getting any younger. I'm beginning to think I must try to 'think outside the box'. One possibility is to have a 'transporter bridge' which doesn't span anything, just carries the loco across the gap on wheels. An off-the-peg lifting table would do that. It would be significantly more costly than a bridge, but it would also have other uses which might justify the outlay. And unlike a bridge, it will always have a certain resale value. Sorry to hear about your Dad's thumb. Not fun at all when accidents happen. Gary
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Post by steamer5 on Apr 23, 2022 5:42:30 GMT
Hi Gary, Yeah it took his thumb a while to heal & get feeling back in it, he found doing up nuts & bolts a bit of fun with no feeling ! Just had another thought, if the link span was pivoted from your existing rail, shown in your photo, & that was then hinged in the middle….. so it doesn’t hit the roof! …..then as you open it…put it down then the support leg swings down….hope that makes sense! I guess the lift table in the picture is the one you will put outside the door to run the loco on for transport to your vehicle?
Cheers Kerrin
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Apr 23, 2022 15:42:38 GMT
Hi Gary, Yeah it took his thumb a while to heal & get feeling back in it, he found doing up nuts & bolts a bit of fun with no feeling ! Just had another thought, if the link span was pivoted from your existing rail, shown in your photo, & that was then hinged in the middle….. so it doesn’t hit the roof! …..then as you open it…put it down then the support leg swings down….hope that makes sense! I guess the lift table in the picture is the one you will put outside the door to run the loco on for transport to your vehicle? Cheers Kerrin Hi Kerrin Yes, the green lift is the one that does the actual movement to the car. It is getting on for 20 years old, built from a kit, and an indispensable machine. Sadly the kits are no longer available, or I would be thinking of building another! Thanks for the idea about the pivoting/hinged bridge. Rather like an old-fashioned carpenters rule? Yes, it would work well in the right hands/right place. But I couldn't obstruct the end of the fixed rail, because that is where the lifting table connects for movement around the workshop. But my other problem is more mundane... I'm no welder, so I need to keep it simple. In fact that is part of the reason I'm getting cold feet about building it with RHS, which is not easy to make decent joints with unless they are welded. Angle iron (Bob's suggestion) is much easier, so I think it will end up as a choice between that (with an intermediate support) and a wheeled lifting table. The latter of course is much more costly, but quicker and less bother and also a lot more versatile. Professional construction of a RHS bridge is an option (which is how the fixed track was built), but that would take time (probably) and meanwhile the loco is stuck in the workshop waiting for me to bridge the gap! Life's never simple, is it! Gary
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on May 29, 2022 23:49:00 GMT
Hi folks Many thanks to all those who gave advice and information to help extract the heavyweight Paddington from my workshop. This posting is just to wind it up and let you all know about the eventual result. I was coming to the conclusion that a bridge across the threshold (the main obstacle) was going to need to be quite heavy and somewhat expensive, but more important, the design would be critical (200kg dumped on the floor from a broken bridge metre or so high would not be enjoyable) and the structure would be quite restricted in what it could do. Thus it was that I came to the conclusion that the best solution would not be bridge at all, but a second hydraulic lifting table for the 'outside' movements. This would have the benefit that the loco lift proper would not need to leave the workshop, and in itself it is a heavy lump to manoeuvre down the step. Not requiring it to trundle a heavy payload along a brick path would extend its life too. The new lift table is a bog-standard off-the-peg item, the cheapest least expensive I could find that was specified for a SWL over 200kg: It is shorter than ideal, so the loco overhangs each end, and care has to be taken not to collide with the fixed handle. It is less manoeverable than the loco lift, because (as is normal with lift tables, and unlike my loco lift) only two of the wheels are swivelling casters, the other two are fixed. The mechanism is massive, but an unexpected omission is that it lacks a strut to retain it at full height. All hydraulic jacks are prone to sinking slowly under load, so this was a pity, but I have improvised temporarily with a baulk of timber (not shown in the photo). Rails are not needed (which makes accurate alignment unnecessary) but loco brakes (or an end stop) are essential. Here's a view from inside the workshop: I'm happy to say that the setup works fine, and I have confidence in it because a catastrophic breakage or bending is scarcely likely, and stability is good. Moreover, when the second lifting table is not being used for the transfer from loco to car, it is available for any other lifting or support task that might be needed. So it's 'case closed' as far as Paddington's Flyover is concerned. There will be updates on steaming the loco in due course, but for the time being other commitments have intervened, so rectifying the defects standing in the way of passing the steam test is proceeding at a glacial pace, and lately not at all. Many thanks to all, and see you later! Gary
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Post by steamer5 on May 30, 2022 8:18:52 GMT
Hi Gary, Looks very ship shape! Can I make one small suggestion? Please fit a pair of chains between the trolleys at deck level, I can see you outside trolley has brakes, but a belts & braces approach yes, but cheep insurance .
Cheers Kerrin
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on May 30, 2022 17:26:25 GMT
Hi Gary, Looks very ship shape! Can I make one small suggestion? Please fit a pair of chains between the trolleys at deck level, I can see you outside trolley has brakes, but a belts & braces approach yes, but cheep insurance . Cheers Kerrin Thanks Kerrin Good point. The loco trolley has brakes on all wheels and the 'outside' lift table has them on two wheels, though they are slightly awkwardly placed. But I agree, linking the tables together would give an extra level of security when the loco is being transferred from one to the other. I'll put it on the (growing) rectifications list! Gary
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Post by steamer5 on May 31, 2022 6:36:05 GMT
Hi Gary, I forgot to add Dad was transferring his loco between its storage trolley & his trailer……… he was very fortunate not to drop the loco…….I mean 150 plus kgs on your toe makes it hard to jump around!
Cheers Kerrin
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Post by doubletop on May 31, 2022 9:16:22 GMT
Hi Gary, Looks very ship shape! Can I make one small suggestion? Please fit a pair of chains between the trolleys at deck level, I can see you outside trolley has brakes, but a belts & braces approach yes, but cheep insurance . Cheers Kerrin I had considered saying something similar. But I would suggest having the tie at the bottom of the trolleys. It may not be such an issue in Garry's case as the link rail is very short. Were it to be longer there is a risk that the outside trolley could jacknife in the vertical plane as the load goes onto the link rail. tieing the bottom of the trolleys prevents that happening. Pete
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on May 31, 2022 22:39:56 GMT
Another very good point, thanks Pete Gary
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