Perforated tape and sprocket pulleys?

That sounds like a prescription for fatigue failure, if I understand you correctly. A lot depends on how big the pulleys are and how long they're expected to last. Bandsaw blades are made to take it, but the wheel size has to be large enough to keep the flexing within bounds.

Have you worked that into your design?

Its actually very very slow action. Trying to get some insight into a failure mode of this type and model of tide gauge, this pic and the original in a 1920s publication is other wise the only info.

The relevant pair of pulleys are the wide ones , one under the mainframe and one with the brass cogs. But resolution in that pic , or the original book , not up to seeing the sprocket spacing. The plotter drum records 24x1inch paper for 1 days record, so circumference of 24 inches, for overall sizing. The band may well have been bronze as a marine context. There is surviving plot of when this machine "broke" in service as well as another one. Both subjected to an extreme tide surge. The traverse pen mechanism hit the designed-in endstop . The perforated tape jumped some sprockets and resettled , neatly still drawing , but displaced downwards. What was the surge level that in a sense , it recorded. One insight would be the spacing of the teeth, if only we knew, as it could only be an integre number of the spacing , for the jump slippage. It was of the order 2 inches to 2.5 inches from meteorological data etc.

I forgot to say , note the fusee compensator cone on the axis of the lower pulley. This takes/supplies the perforated tape, winding around that pulley. The fusee offesetting the varying weight of the suspension band. Also the large float about 2ft 6 in diameter is shown on the floor. The suspension must cope with the possibility of that float puncturing, filling with water, and jamming unsupported by seawater. Other models of the same make used a simple wire suspension and returning the counterweight down the sampling well, which then transfered silt and slime onot the recorder, not the case with the type pictured.

2 inches on the traverse represents 2 foot of water level change, 1 in to 1 foot scaling in the gear train.

The instrument appears custom made on general-purpose machine tools, in which case the hole spacing could be whatever the maker's rotary indexing machinery permitted, and the tape then punched or drilled to match. The number of pins has to be an integer but the arc length between them doesn't.

Can you reconstruct the circumference of the wheels?

-jsw

Aha. Now I see what it's about. That's an interesting old recording machine.

The thing on the right is probably an "Aga" stove. Not for cooking purposes but for some warmth. There was notorious problems of condensation freezing in the and jamming the mechanism. Not just that, but the lubrication gummed up , and close to frictionless operation is required for accurate recording.

Other than this pic, the only dimensional data is the recording drum is

24/Pi inches in diameter, the axial lengths varied . I only roughly scaled the dimensions to arrive at 12 inch diameter puppey wheels. I'll have another go as because of non factorable Pi, it cannot be exactly 12 inches diameter. Only the upper pulley is spoked, the lower has the end of the tape anchored to it , and rolls up the excess, can be 20 foot of tape plus the standing length for the overall length.

Hmmm ... sprockets for 35mm film -- two rows of square holes near both edges of the film.

Well ... 35mm film is flexible enough to wrap around about 1/2" diameter sprockets -- but obviously likely not strong enough for your purposes. But the sprockets themselves may be more readily available than other sizes. Then comes the trick of finding the steel tape to do what you want.

At 1 foot diameter sprocket, at a total guess, (no calculation, not sure where to start) I think that you could get away with perhaps

0.050" thick steel tape. You can look up the dimensions of 35mm film and sprocket holes, figure out how much area a cross-section of the film or steep tape would leave, and calculate the tensile strength. With that much hub (assuming a 180 degree wrap), you probably would have enough sprocket teeth engaging so the tensile strength of the unsupported tape would be the limiting factor.

Or -- look at suppliers like PIC, who make steel cable with cross pins, and paired gear teeth to go on either side of the cable and engage the pins. If that format, instead of flat tape, would work for your purposes, they can provide lots of calculation data for your application.

Good Luck, DoN.

Most of these systems now use beaded float line.

Multi-strand stainless wire has brass beads peened on every 6" or so. The pulleys have holes that line up with the beads.

I suspect the strength of the engagement between the tape and sprocket wasn't a primary consideration, as the sprocket drove only the plotting mechanism. Does an easy-to-index factor of 360 such as 12, 24 or 36 make sense as the number of sprocket pins?

A sprocket of 11.459" diameter would revolve once per 3' of band travel. It might have 24 pins spaced 1.500" apart, or 36 at 1.000". A

7.639" diameter sprocket would correspond to 2'.

The fusee and the frame suggest that a tower (turret) clock maker built it, so a 30 tooth sprocket is possible.

This shows a clock built on a similar frame:

-jsw

He's in England, so it may be metric with a one meter circumference which would make the diameter closer to 12.5"

[ ... ]

Hmm ... O.K. 35mm film has the sprocket holes on 0.1875" centers. You can get lots of details from the following WikiPedia page:

You can calculate the possible sprocket wheel sizes based on that. The sprocket wheels in 35mm hand held cameras (not movie) actually skip every other hole, but they only have to pull the film out of the cassette, which does not take much force.

A thought about the intended purpose of the application suggests that instead of having the fusee to counter the weight of tape above, you could use the mylar film base used on modern films (movie and still camera), and make it a complete loop over two identical sprocket wheels. This would have an equal weight of film between the wheels, no matter what the position of the float happens to be, thus no need for correction.

Of course the film is not strong enough to support the worst-case situation of a flooded float, but the float could be allowed to slide up and down on fixed guide rods, with a link to the side coupling it to the film to transfer the position.

I would enclose the film within a U-shaped housing to keep the wave forces from tugging at the film.

With the 35mm sprocket, I calculate 192 pins for a 36" (3') length. Of course, you could skip every other pin as the 35mm still cameras do. Or using one out of four pins, you get 48 pins. And with Mylar film, it should be strong enough to last a reasonable while under water. And I would suggest making the sprocket wheels via 3D printing, so it would be similarly waterproof and corrosion proof.

No fusee needed if you have a complete loop with wheels at top and bottom.

O.K.

Enjoy, DoN.

Associated pages to that pic of the gauge

Looks like an exploration of the background to the Cary & Porter company as to any clockmaking connection.

Same company tide gauges , but the models using the troublesome counterbalance going down the stilling well, and no metal tape (ignore what I was saying on there about slippage in the traverse area, moved on from that)

going by the B&W graphic , the original model, not the one in coloured pic , was one of these earlier fusee, and perforated tape suspension models

Busy today, but i'll try pixel counting on those "trigtools " " images. The pulleys ,rather than gear wheels, have a reinforcement flange on the inside of torque/tension bearing flange, so the tape is quite recessed into those pulley rims .

Is it possible to determine from records whether the transient that caused the skip was due to a brief nearby ship launching or a longer lasting storm surge?

-jsw

More interesting than the other stuff i should have been doing.

From 24 inch circumference of the recording drum I make the key data for that top image 0.0868 inches per pixel, vertical and horizontal, as circular wheels. The clocks were 10 day , allowing 7 days of continuous recording on one sheet of paper, much overlapping of about 19 tide cycles, before having to change paper and re-synching. Hence accurately inferred diameter dimension there. I reckon, from 20 foot of tide range, 7 turns of tape ,then from the following, 1 1/3 inches wide and 0.083 inches ,probably 5/64 inch, thick tape. The spigotted pulley , the measurement-active bearing face , between

11.08 in and 11.13 in diameter. So for a jump between 2 and 2.5 inches, if perforations spacing 0.75 in between centres, then 46 spigots and jumped 3, 2.25 inches, pulley diameter 10.98 in. If 1 inch spacing, 35 spigots, jumped 2 , or 2 inches, pulley diam 11.14 in If 1.25 in spacing ,28 spigots, jumped 2 or 2.5 inches, diam 11.14 in If 4/3 inch spacing , 26 spigots, jump of 1 or 2 is outside the 2 to 2.5 inch range, but if so, then pulley 11.03 in diam .

For the tape width appearing to the left wide side on, from the lower image , ratioed pixels to the diameter of the suspension band counterweight and then used the upper image to get 1.33 inches. The lower image shows the recess in the rim of the upper spigotted pulley, assumed to have one thickness of tape on it. From the twisty looking appearance the tape band is broken or cut, and just draped through near and to the rear of the lower pulley,not wound on it , same diameter as the upper one ,same recess , but no spigots on that one.

The failure mechanism , prior to jump, as a band suspension.

12:1 gearing stops, so spigotted pulley stops rotating, the float continues rising. Band disengages from pulley, counterweight takes up the slack 1 ,2 or 3 times, until the float goes back down again.

The background is the anomaly surrounding the surge of 26/27 Nov 1924 on my page (an update should go there today or tomorrow)

The official record did not agree with contemporaneous press reports, nor the meteorology of the day. I should say I'm involved with a couple of a couple of academics at the Southampton National Oceanography Centre . Trying to get to the bottom of this 1924 event, and then the GIGO business of "return periods" for marine surge flooding events ,ie inadvertently downplaying the risk in effect.

A connection may not be apparent. I studied watch and clock precision machining techniques while I was involved in developing GPS-related electronics for the US Air Force. At microwave frequencies signals interact with nearby metal and being able to machine custom enclosures as needed rather than draw them up and contract them out was extremely useful.

-jsw

It's easier to space the holes in the tape at some arbitrary non-integer distance than to divide the wheel by an odd number, unless the maker already has the correct index plate. 24 is particularly easy.

This is a modern example of a classic design. I have an indexer that may date from the 1880's.

-jsw