Will the gate sag?

[yves]

I have a gate to forge, 2 sections of 3' x 7'.

The frame I think about would be 1/4" x 2-1/2" riveted. The top, bottom and center horizontal parts would also be the hinges turning on pintles. The open top and bottom spaces would be "covered" by a grille like this one I am examining. The grille (riveted and not bolted like the exercise appearing in the pic)  would be riveted to the frame. The grille parts are 4" apart.

Question : will such a set-up sag? Do I need diagonal brace or an "X"?

I read the "Realy big gates" topic here on IFI where there is probably the answer I am looking for, but it is not realy clear to me. I enjoyed reading about the principles involved and how large gates were set up traditionaly but ... my gates ... what about my small heavy gates ...

Thank you.

 

[jeremy k]

Theoretically it should not sag due to the overlapped parts being riveted, as the design does not allow for the parts to move in a diamond shape. I would be more concerned with the strength of the post (if applicable) or the hinge mounts, as the weight of the gate being 7ft long can apply a good amount of pressure on the hinge mounts.

[ThomasPowers]

Is your 7' horizontal or vertical?  

[arftist]

Theoretically it should not sag due to the overlapped parts being riveted, as the design does not allow for the parts to move in a diamond shape. I would be more concerned with the strength of the post (if applicable) or the hinge mounts, as the weight of the gate being 7ft long can apply a good amount of pressure on the hinge mounts.

​Your answer assumes perfect fitup. The design is actually highly susceptible to sagging; the single rivets all act pivot points and the weight is massive considering the frame choice.

I would switch to heavier frame stock, say 1/2" and pre stress the gate about an inch upward, then hang the gate in the shop to check for sag, unless you are willing to add diagonal bracing. 

[Charles R. Stevens]

Square rivets, adjustable lower hing, a diaginal (far lower corner to above the top hinge and tie the posts firmy into the fence/wall. Sleepers extending90 to the fence and under the gate may also be necisary. The silty lome i live on moves a lot and cement is nearly usles as the ground still gives. Digging a "X" or "+" saped post hole with cement works tho.

[jeremy k]

​Your answer assumes perfect fitup. The design is actually highly susceptible to sagging; the single rivets all act pivot points and the weight is massive considering the frame choice.

I would switch to heavier frame stock, say 1/2" and pre stress the gate about an inch upward, then hang the gate in the shop to check for sag, unless you are willing to add diagonal bracing. 

​If the parts are made as in the sample picture and all the rivets are done correctly, I would bet that it will not sag - Yes it would sag if all parts are somewhat loose, but once you have many rivets set properly and the offsets like the picture - it wont move. I have done similar riveting projects like this and once everything is fully riveted - it's very solid. I would use no less than 3/8" diameter rivets.

[yves]

Is your 7' horizontal or vertical?  

​Vertical. Sorry, I should have mentioned.

It will look like some sort of prison door. It is to stop dogs, deers and humans from entering a cider (I do not know how to say this, une cidrerie) while letting the doors opened for air circulation.

 

​If the parts are made as in the sample picture and all the rivets are done correctly, I would bet that it will not sag - Yes it would sag if all parts are somewhat loose, but once you have many rivets set properly and the offsets like the picture - it wont move. I have done similar riveting projects like this and once everything is fully riveted - it's very solid. I would use no less than 3/8" diameter rivets.

​I was counting somewhat on the offsets to help. I would add 3/8" rivets as you suggest and square rivets as suggests Mr Stevens.

What say you Arftist now that you know the horizontal span is 3', that I would use 3/8" square rivets. I would like to stay away from a diagonal brace if at all possible. Is it possible?

Edited April 24, 2015 by yves

[Alan Evans]

If you ignore the friction grip of the rivets and shoulders of the joggled flat and think of them purely as pivot points it can only sag if all the rivets conform to a regular spaced grid. You can only achieve this with very accurate marking and drilling. Even a slight irregularity in the grid will cause it to lock. You can prove this easily with a few strips of card and drawing pins. It is very difficult to make anything other than a 4 pivot grid go lozenge shape, every extra pair of pivots increase your need for precision. The arcs described by the pivots have all got to be absolutely identical for the lattice system to be able to concertina.

You have a choice of either making it deliberately inaccurately!  Or even better vary the spacing of the grid deliberately. The more pronounced the variation the better the triangulation and locking effect.

If 'twere me I would favour having the grid bars closer together at the base and hinge side in order that the visual weight lessens as you move upwards and away from the hinge side…basic growth lines however subtle. If each grid is based on 100mm (4") spaces you will be having 8 spaces across each leaf. You could vary those by say having the first two spaces near the hinge/back bar at 90mm (3 1/2") and then the next two at say 95mm (3 3/4") and the remaining four spaces at 100m (4") and divide up the vertical spacing the same way with the same three different spaces in your three different panels.

You are the only one that knows the setting for the piece and the way people will interact with it. That will determine whether you make the grid difference overt or more subtle.

The pragmatic way of course if you want to keep the grid regular and are able to make it sufficiently accurate to sag is just to do discrete welds along the bottom of some of the halving joints below eye level.

Alan

 

Edited April 24, 2015 by Alan Evans

[yves]

Alan Evans,

Thank you for the info. Thank you also for the inspiration. This evening, I will examine the possibility of spacing the components keeping the golden mean in mind. I'll see. I realy like the idea of crowding the hinge side and the bottom. 

[Glenn]

If you use rivets think square or rectangular rivets and still have a round head. It should resist movement better than round.

Another suggestion would be to add L shaped braces at each corner. They could be decorative as well as structural and if placed on the inside, would not show.

As suggested, discrete welds would strengthen thing a lot. They could be part of the rivet, that is to say weld the rivet then form the head over the weld. A hole could be drilled into one piece of overlapping metal and then the two pieces of metal welded together, the hole filled with weld and ground flush.

Build it strong enough so that one or more children can use it as a swing without damage. It can happen. (grin)

 

Edited April 24, 2015 by Glenn

[jeremy k]

What Alan Evans said is why I believe it will not sag - I think there is no need to go through the extra effort to use square rivets.

[Alan Evans]

I think the round rivet square / rivet choice is best resolved by thinking in terms of the length of leverage generated by the geometry of the structure as a whole.

If you are hoping that the 10mm (3/8") side of a square rivet will make a 3' by 7' frame rigid, think how much more rigid the frame will be held by the length of the lattice construction +/- 100mm (4") sides which are rendered immovable because all the other linked rectangles are trying to move through a 90mm (3 1/2") or 95mm (3 3/4") arcs.

With an irregular grid you could have roller bearings on the rivets and it still would not move!

Alan

[ThomasPowers]

rather than sq rivets I would just use two per crossing and off set them---a lot easier than messing with sq rivets.

(eg one in the top left quadrant of the crossing and another in the bottom right quadrant)

[Alan Evans]

My apologies, I got carried away by my notion of irregularity, and my favouring of the movement of the visual weight.

 I fell asleep in the chair, woke up, went to bed, and just as I was trying to get to sleep played my last post through in my mind again and wished to emphasise that it is the irregularity of pivot centre within the grid that creates the lock, not the space shapes. If all the the pivot points on the grid remain in perfectly parallel lines it can of course collapse. 

So here I am at 4:20 am making my correction!

If you are able to get all 150 joints to conform to a precisely parallel grid (unlikely with forged joggles) there could be movement until the shoulders of the joggles bite if the rivets are not tight. If the single round rivet holes are drilled slightly off the parallel centres even 3mm (1/8") left and right alternately the lock would be robust, and together with the friction grip of the rivets and your joggle shoulders the 150 odd joints will be very good.

As a fail safe...make it, drop it on one corner, if it moves drop it on the other corner to get it back to square and weld along the bottom of some below-eye-level joints and the top of the above-eye-level ones!

I must remember to engage brain before typing when tired...

Alan

 

[Charles R. Stevens]

And persisly what would be the fun in that, Alan?!

[Alan Evans]

And persisly what would be the fun in that, Alan?!

​

@ Yves, one thing that may save you many fitting headaches given the number of joggles you will be doing is to just joggle one bar on each joint…so maybe just all the horizontals or all the verticals. Or the bottom section horizontals and top section verticals and etc. Not so important if you can jig up and joggle under a press, preferably all the joggles in one go!

If the gates will usually only be seen from one side then the articulation is slightly wasted on the unseen side. By joggling just the one bar you can increase the articulation / 3D quality on the show side.

You have probably already considered it, but you can also can also play with alternating the joggles to give you a woven structure.

Alan

[bigfootnampa]

I am surprised that no one has yet mentioned the option of keying the rivets!  It seems much easier than using square rivets.  The simple way would be to use a star drill to nick the edges of the holes.  A grid like this, with many rivet connections, would have tremendous resistance to racking forces owing to the natural variation of the rivet placements, friction from tight rivet heads and the locking keys!  

[Charles R. Stevens]

Thats why we keep you around, BFN! 

[yves]

It never ceases to amaze me the quantity and quality of knowledge and the generosity or is it passion ... probably both ... of the people here on IFI.

When I first posted my query, I had read some about gates here on IFI and Peter Parkinson's "Forged Architectural Metalwork" but I still had this worry about the possible sagging of the gates.

The square rivets or the keyed ones by BFN as Mr Stevens calls him, the corner braces proposed by Glenn and all the analysis of grid resistance to sagging by Alan and his proposal for joggling the bars (not counting the lost sleep about all this), Thomas Powers' suggestion to cut down work time and complications, all these are on the table. Today I do soft work (design for a coming commission, writing down procedures so that I do not have to reinvent the wheel when something comes up again, etc. all these things that are not hammering but part of the job) and I will make decisions as to how I design and put the grilles together.

Of course I thank you all and I will come back with a report. I owe you that ... at least. Thanks again.

Yves

[ThomasPowers]

Hmm what if you decreased the spacing between vertical bars (and or Horizontal) as they progressed across the gate so you could not get even racking.  I't put them wide toward the side farthest from the hinges and tightest towards the side nearest the hinges for weight reasons.  Then it would look like a design choice (and they should pay extra as it's "fancy")

[arftist]

 

What say you Arftist now that you know the horizontal span is 3', that I would use 3/8" square rivets. I would like to stay away from a diagonal brace if at all possible. Is it possible?

​I say that using 1/4"x 2.5" is too light and if I were doing it, the frame would be 1/2" thick but 3/8" will work. Too much weight for a 1/4" thick frame. Not only physically but aesthetically as well. At least make the side the hinges attached to thicker, plus I will add that I always hang gates in the shop. It is extra work but it saves a lot of field time. 

As an aside, a diagonal tension bar is not a cop out or a cheap way out. They actually serve aesthetic purposes as well, however, in the case of your design it would not integrate well nor are those other purposes desired since the grid itself provides plenty of visual appeal and is not a plain field. 

 

You can't imagine the wasted time and cost of making gates designed by architects of weaker and or softer metals who insist upon not having diagonal bracing. They ALL sag and the cure is building them enough out of square that they sag to square. 3 foot wide gates are not too much of an issue though. 

Edited April 25, 2015 by arftist

[ThomasPowers]

I once was talking smithing with some old timers and they told me of a fellow during the great depression that was building a steel frame building who calculated the sag of the cross members then went out into the field and dug a whopping big trench forge and heated the beams and pre-bent them so they would sag straight.

[jeremy k]

I will agree with Arftist - using the 1/4" stock is a bit light - mainly in my eyes the possibility of twisting as a panel. A square tube type frame will defeat that easily but not sure it would render itself use full with the design tho, only you will know that as we do not know of the final full design.

[ianinsa]

While I agree with Alan and a slight discrepancy in the regular pattern will create a 'lock' you can also 'hide' a weld in plain sight . Just drill a hole   through one bar and 'plug-weld' grind smooth and texture.

The profile on the flat bar will have a ridgidising effect and if you use them alternately your gate will develop an 'eggbox' effect.

Edited April 26, 2015 by ianinsa

[Alan Evans]

While I agree with Alan and a slight discrepancy in the regular pattern will create a 'lock' you can also 'hide' a weld in plain sight . Just drill a hole   through one bar and 'plug-weld' grind smooth and texture.

The profile on the flat bar will have a ridgidising effect and if you use them alternately your gate will develop an 'eggbox' effect.

​Fit of the joggle will be a bit of a juggle ( ) between tight fit to aid rigidity, and loose fit /tolerance to enable ease of assembling. To get 150 or so forged joggles to both fit tight enough to lock and still go together easily would be some feat. 300 shoulders if single joggles and 600 shoulders if both elements joggled…some precision joggling called for.

I would definitely go for a bit of tolerance on the shoulders and rely on a slightly eccentric riveting position and system, and possible plug or other discreet welding for rigidity.

Alan

p.s.  Sorry Ian, couldn't get the word eggsactly in…guess the yolks on me...