plastic hinge out of alignment tolerances

[Muggnz]

hi,

I recently bought a supply of Monroe Plastic hinge.


with the aim of fitting it where the hatch meets the body







However as can be seen this isn't all that straight. There's about a 5mm difference between the center & the edges. I may be able to reduce the curve. But before I try & possibly break stuff. Do I actually need to change it, or can the hinge cope with with the current curve?

thanks
david

[parnold]

Sorry in advance if this is a dumb question, but wouldn't you want the hinge to lay flat on top of the trailer?

Also, how much did you buy and how much did it cost, I'm thinking of using it on my build #2?

[madjack]

...the hinge needs to lay flat, just like any other hinge would...otherwise, it would end up pilling loose, like any other hinge would....................
madjack

p.s. smaller pics would be appreciated as well...at a maximum 800x600 or preferably 640x480..........MJ

[Muggnz]

Sorry in advance if this is a dumb question, but wouldn't you want the hinge to lay flat on top of the trailer?

Also, how much did you buy and how much did it cost, I'm thinking of using it on my build #2?

I agree, but how "flat" is flat?

this is a copy & paste from the http://www.monroeengineering.com/ invoice
Our Part# Description Quantity Price
CPB2000-50 50' LENGHT 2" OPEN BLACK 1 53.00

[Muggnz]

...the hinge needs to lay flat, just like any other hinge would...otherwise, it would end up pilling loose, like any other hinge would....................
madjack

p.s. smaller pics would be appreciated as well...at a maximum 800x600 or preferably 640x480..........MJ

sorry about the picture size, I thought i'd made them small enough, yet still big enough to easily view.

[Steve_Cox]

I agree, but how "flat" is flat?

Muggnz,

If you use a butyl tape as a sealant under the hinge and a strip of aluminum on top of it to screw into, the butyl tape will fill some pretty wide gaps, the plastic hinge is pretty tolerant to misalignment stresses, the wider the hinge the less the surface imperfections will matter. 5mm gap seems reasonable.

[Muggnz]

thanks Steve

I've already bought some ali strips shaped like this
.. ___________
. /....................\

to cover the stiffer portion of the hinge. So I'll try to flatten the ali covering the body first, in the hope that it'll help.

I don't plan to use butyl tape. As others on this forum have mentioned that it deteriorates & cracks with age. I prefer a large dollop of local ( high uv proof ) focussed silicon sealant.

david

[eamarquardt]

I think long term your hinge would give you trouble. Maybe use two or more short sections of piano hinge or other other hinges (with the hinge pins in the same line-you could mount the hinges vertically to do this or mount them horizontally with a little shimming to get the pins reasonably in line) to allow the hatch to open without binding and then cover the whole opening with some flexible rubber held in place with your aluminum trim. Others have used flexible rubber held in place with trim to seal the joint. As was pointed out in an earlier string, you can hinge curved doors by using two hinges with their hinge pins in line. Boeing does it all the time!

Where there is a will, there is a way!

It looks like taking the bow out would be a major project.

Hope this helps.

Cheers,

Gus

[Steve_Cox]

I think long term your hinge would give you trouble.

Gus

Monroe Plastic Polymer Hinges aren't your old time poly hinges of yesteryear. I think the hinge will outlast what it's attached to Muggnz.

[eamarquardt]

I think long term your hinge would give you trouble.

Gus

Monroe Plastic Polymer Hinges aren't your old time poly hinges of yesteryear. I think the hinge will outlast what it's attached to Muggnz.

I agree the materials available today are not the materials of yesteryear or even last week. But when you open and close the hinge, and due the curve in the surface it is mounted to strech it 5mm which it is not designed/intended to do, long term your gonna have trouble. The hinge, in this case, is not being installed properly. I think that was the original question, not the quality of the hinge.

Cheers,

Gus

[parnold]

Doesn't that come under the rules of bending something on two separate axises? Unless the hinge is designed with a lot of elasticity in all directions it will fail prematurely.

[Steve_Cox]

So with all that being said here's a quote from Monroe "Monroe Living Hinges (plastic piano hinges) do not wear, fatigue, or deteriorate in the harshest conditions, including moist and corrosive applications. UV resistance is built in to our Living Hinge products providing protection from brutal effects of the sun. Our living hinges are manufactured from flexible alloyed polymers in standard colors: White & Black.

So if it wears out just a little short of "do not wear" that would probably be OK.

OK, time for a confession, Used the plastic hinge on my TD built in 2005, one end had a missalignment of 0.200" or about 5mm. and it was at one end of the hinge, it put what I considered at the time an extreme load on the the part of the hinge that folds. Well, 5 years and hundred of openings later, the hinge shows no sign of failure....

[eamarquardt]

OK, time for a confession, Used the plastic hinge on my TD built in 2005, one end had a missalignment of 0.200" or about 5mm. and it was at one end of the hinge, it put what I considered at the time an extreme load on the the part of the hinge that folds. Well, 5 years and hundred of openings later, the hinge shows no sign of failure....

Practical experience trumps conjecture every time!

One could still shim it a (as you've proved it doesn't have to be perfectly flat) to get it a bit straighter.

Why did you hold out on sharing what you know? Are you sure you measured the bow correctly. Not too many people would say .200"
they'd say 3/16" or so. It could have been .195" or .205" or maybe .1875".

Cheers,

Gus
Cheers,

Gus

[Steve_Cox]

OK, time for a confession, Used the plastic hinge on my TD built in 2005, one end had a missalignment of 0.200" or about 5mm. and it was at one end of the hinge, it put what I considered at the time an extreme load on the the part of the hinge that folds. Well, 5 years and hundred of openings later, the hinge shows no sign of failure....

Practical experience trumps conjecture every time!

One could still shim it a (as you've proved it doesn't have to be perfectly flat) to get it a bit straighter.

Why did you hold out on sharing what you know? Are you sure you measured the bow correctly. Not too many people would say .200"
they'd say 3/16" or so. It could have been .195" or .205" or maybe .1875".
Cheers,

Gus
Cheers,

Gus

Gus,

Old habits are hard to break, I do woodworking with dial calipers in hand to set my saws, rip fence and to measure thicknesses of materials, etc. It was 200 thousandths of an inch including several coats of epoxy. It is a number I have remembered these 5 years because I had many nay sayers here on the forum that were sure the plastic hinge wouldn't work, at the time only two others had come forward and told of using it for a galley hatch, they planted so much doubt I even added a couple of nylon web safety straps in the top corners of my hatch. End of story.




Some people know it all, but there is always someone that has done it all.

[kennyrayandersen]

Still, as a practical matter, when we have hinges that are installed on something with a bit of a wave we use a fiber-reinforced epoxy ‘shim’ that takes up the gap. I’m not doubting the hinge, and I’m actually leaning that way myself, but I think I’d be tempted to at least shim it straight before installing it as I think it could not only work the hinge (apparently no problem there) but it works the fasteners as well. It probably isn’t a big deal, but I’d do it anyway (but that’s just me).