*
Thanks to the ever helpful souls on the CN Observatory forum I have overcome my "Sidewinder" larch, hatch inertia. The sideways opening hatch always had problems. Not least its weight!
A forum member suggested a forward opening hatch worked well for him so I had another try myself.
I needed a deep foothold at the top tread. I also needed the hatch to be flush with the obs. floor level when closed.
The answer was to pull the ladder back by 10cm [4"] and lower it by 1" to bring the top tread down by the obs. floor thickness. By fixing a 2"x4" beyond the ladder top it now had something really solid to rest against. The handrails had flexed somewhat when the ladder was in use. The 2x4 also provided my vital deeper landing at top tread height.
The 1" difference from obs. floor level didn't seem to matter, in practice. It was much easier to use the top step going both up and down the ladder. Previously I would step up from the next tread down and move bodily sideways and upwards at the same time. Even with lots of practice it never felt very natural. Particularly as I was also avoiding the handrail with my feet at floor level. Now I can comfortably use the top tread for the lateral transition to obs. floor from much closer to the same level. There is no simultaneous, upward body movement required.
The 1" difference from obs. floor level didn't seem to matter, in practice. It was much easier to use the top step going both up and down the ladder. Previously I would step up from the next tread down and move bodily sideways and upwards at the same time. Even with lots of practice it never felt very natural. Particularly as I was also avoiding the handrail with my feet at floor level. Now I can comfortably use the top tread for the lateral transition to obs. floor from much closer to the same level. There is no simultaneous, upward body movement required.
The new hatch can now be laid on the top tread [when closed] without it becoming a nuisance or danger when open. It will be hinged at the edge of the existing larch boards as shown. The mock-up in the image uses a smaller scrap of 18mm ply. In practice the new hatch will be the full width between the handrails at 50cm wide. Though there is room for 53cm the hatch might strike the handrails as it rises and falls.
The new hatch can also be made much longer so that it fits inside the pier's "kennel opening." This will provide a much greater level of safety when the hatch is closed. With a greatly reduced danger of my falling through the opening. A foot bumper rail is now easily possible without it lifting the hatch off the floor when open.
The new hatch can also be made much longer so that it fits inside the pier's "kennel opening." This will provide a much greater level of safety when the hatch is closed. With a greatly reduced danger of my falling through the opening. A foot bumper rail is now easily possible without it lifting the hatch off the floor when open.
When opened, the new hatch will lean safely against the inside of the observatory wall between and beyond the ladder handrail extensions. Where it can be latched for extra security if so desired. I get to keep my full height handrails and close off more obs. floor gaps in one go. Now I just need a much lighter hatch material than the heavy larch floorboards. The hatch can be braced with stiffening strips on the hatch underside where it clears the top ladder tread. The foot bumper will provide lateral stiffness.
I have some 12mm [½"] plywood to make a trial hatch. If I shorten one length to clear the ladder's top step I can have 3 layers for 1.5". Perhaps it doesn't need to be that thick? The weight is a serious issue even if it is easier to lift it forwards. Since the ladder will support the hatch right up to the change in thickness two layers of plywood might do. The larch was only just over an inch thick but weighed a ton. With noticeably wide variations between samples.
There is the possibility of using spring hinges, gas struts or counterweights to aid lifting the new hatch. Since it the angle of rotation [around the hinges] from fully closed[horizontal] to fully open exceeds 90° simple levers and attached weights won't help. Ropes might get in the way when the hatch is closed.
Weights or levers could pass through the unused floor area beyond the top of the ladder. Either through slots or holes for rope. I'll have to give this some thought. Levers attached to the hatch with secondary weight levers passing through slots might work.
Here I have shown the hatch rotating around the hinges with fixed [primary] lever[s] attached at an angle of 135°. Ropes or a second set of freely pivoted levers carry counterweights to almost balance the hatch. The primary levers must be able to pass through slots in the floor beyond the hinges or they will strike the floor. Easily arranged simply by separating the larch boards as required.
Black is hatch closed. Red is hatch lifting. Green is hatch fully open and parked against the obs.wall.
Note how the balancing force increases rapidly as the hatch starts to rise. Then steadily falls again as the hatch nears the vertical. [Where least effort is required.] Since the [counter]weight remains constant only the moment changes. [Mass x distance from the pivot.] The moment of force is measured as the horizontal distance between the hinge and the perpendicular of the hanging weight.
The angle between hatch and fixed primary lever[s] can be adjusted to maximize the lifting force from first opening. The limitation being the primary lever[s] becoming vertical in a downward position and providing zero balancing force on the hatch. Perhaps even blocking it from further movement. The advantage of this simple system is that it is foolproof and easily adjustable. There is nothing to go wrong provided the rope doesn't break. The weight, on its rope, can hang inside the observatory wall, under the ladder, well out of the way. If it is arranged to hang near the floor the weight can rest on the ground at its lowest point. Taking a well earned rest when it isn't needed to balance the weight of the hatch. 😉
I feel much happier about the safety and comfort of the new hatch arrangement. While I could lift and lower the old hatch it was an unnatural movement, sideways at arms length. Particularly if I was not to simply drop the hatch onto the obs. floor with a loud crash. Hardly sensible, when it could be happening in the middle of the night!
I have some 12mm [½"] plywood to make a trial hatch. If I shorten one length to clear the ladder's top step I can have 3 layers for 1.5". Perhaps it doesn't need to be that thick? The weight is a serious issue even if it is easier to lift it forwards. Since the ladder will support the hatch right up to the change in thickness two layers of plywood might do. The larch was only just over an inch thick but weighed a ton. With noticeably wide variations between samples.
There is the possibility of using spring hinges, gas struts or counterweights to aid lifting the new hatch. Since it the angle of rotation [around the hinges] from fully closed[horizontal] to fully open exceeds 90° simple levers and attached weights won't help. Ropes might get in the way when the hatch is closed.
Weights or levers could pass through the unused floor area beyond the top of the ladder. Either through slots or holes for rope. I'll have to give this some thought. Levers attached to the hatch with secondary weight levers passing through slots might work.
Here I have shown the hatch rotating around the hinges with fixed [primary] lever[s] attached at an angle of 135°. Ropes or a second set of freely pivoted levers carry counterweights to almost balance the hatch. The primary levers must be able to pass through slots in the floor beyond the hinges or they will strike the floor. Easily arranged simply by separating the larch boards as required.Black is hatch closed. Red is hatch lifting. Green is hatch fully open and parked against the obs.wall.
Note how the balancing force increases rapidly as the hatch starts to rise. Then steadily falls again as the hatch nears the vertical. [Where least effort is required.] Since the [counter]weight remains constant only the moment changes. [Mass x distance from the pivot.] The moment of force is measured as the horizontal distance between the hinge and the perpendicular of the hanging weight.
The angle between hatch and fixed primary lever[s] can be adjusted to maximize the lifting force from first opening. The limitation being the primary lever[s] becoming vertical in a downward position and providing zero balancing force on the hatch. Perhaps even blocking it from further movement. The advantage of this simple system is that it is foolproof and easily adjustable. There is nothing to go wrong provided the rope doesn't break. The weight, on its rope, can hang inside the observatory wall, under the ladder, well out of the way. If it is arranged to hang near the floor the weight can rest on the ground at its lowest point. Taking a well earned rest when it isn't needed to balance the weight of the hatch. 😉
I feel much happier about the safety and comfort of the new hatch arrangement. While I could lift and lower the old hatch it was an unnatural movement, sideways at arms length. Particularly if I was not to simply drop the hatch onto the obs. floor with a loud crash. Hardly sensible, when it could be happening in the middle of the night!
My search for a 135° angle bracket was fruitless. I scoured two large, DIY outlets in vain. Ideally I would find 1" wide strips, like a normal 90° corner brace, but with a 135° angle instead. These could be screwed to the outside edges of the hatch to project at 45° upwards and away from the hatch hinges. Steel would be best for stiffness under load but aluminium might work if thick enough to resist twisting sideways. Arm lengths of 10"-11" would be ideal.
Sudden screech of brakes!! A suggestion from another member of CN forums brings a new an potentially superior method of lifting the hatch. See the next exciting episode: Pt.61? Really?
Click on any image for an enlargement.
*
No comments:
Post a Comment