AmericanLongRifles Forums
General discussion => Contemporary Accoutrements => Topic started by: DougS on September 07, 2019, 03:33:20 PM
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Hello to all,
I have a couple of box compasses that need a little help.
Both needles could probably use re-magnetizing? I'm guessing? They sort of point north, however do not flow as freely as I think they should.
Has anyone done this before?
I will replace the glass from the larger compass once I get the needle right.
The larger compass (without the glass) has a nice "sharp" point on the nail underneath the compass arrow.
Has anyone had a similar situation, and or know how to fix these?
Also, when putting in the glass should I use any epoxy or something else to seat the glass?
Thank you much In advance.
Regards,
Doug
(https://i.ibb.co/dQn8Hc3/SN855439.jpg) (https://ibb.co/brpcG3y)
(https://i.ibb.co/B4LpdrT/SN855440.jpg) (https://ibb.co/0Bq78FY)
(https://i.ibb.co/qWVJqjn/SN855441.jpg) (https://ibb.co/k9vmbBy)
(https://i.ibb.co/DrpnfxT/SN855442.jpg) (https://ibb.co/MB6LkYQ)
(https://i.ibb.co/nnJVQcp/SN855435.jpg) (https://ibb.co/YysKfkg)
(https://i.ibb.co/1rT1wZk/SN855436.jpg) (https://ibb.co/Htq6k7j)
(https://i.ibb.co/2gYrSPb/SN855437.jpg) (https://ibb.co/nz8yBfW)
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Any idea when these were made?
Mike
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Hi Mike,
Not sure.
I got both of them off e-bay some time ago.
Regards,
Doug
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The reason I asked is that you said they "sort of point North."
I don't know a lot about compasses. But I do know that they don't really point towards true North... They point towards magnetic North and most modern compasses have markings that account for this... declination.
I also know magnetic North shifts over time. I just wondered how old the compasses might be... If they are very old it might be possible that enough magnetic shift has occurred that they may not be as accurate now than when they were first made and calibrated. I looked it up and magnetic north has shifted about 1200 miles in the last couple of centuries... Might be a factor.
Just a thought.
And it could be as simple as they were dropped too many times. Lol
Mike
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Thanks Mike,
They are slow to point in a northerly direction.
I wasn't sure if he needles could be "re-magnetized" or if by doing so, would they not work.
I suppose I could try it.
Thanks again,
Regards,
Doug
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Doug, you might try rubbing them repeatedly over a magnet. I have made "survival situation" compasses by rubbing a sewing needle on a piece of steel, then tying a length of thread so that it can swing freely.
Study up some on compasses, learn about variation, declination, E-W turning error and N-S acceleration. The "Airman's Handbook" published by the FAA had a pretty good chapter on compasses. Don't know if it is still put out or not. Seems like everyone wants to use a GPS for direction!
Compasses work when electricity fails.
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Minor correction to terminology......magnetic north is subject to "variation". Variation is different depending on where you are on the planet and it is the difference between magnetic north and true north. It can be plus or minus and a compass usually will not have any markings to tell you how much or which way the variation is....because it is different in different places on the surface of the earth. "Deviation" (not "declination") is error introduced by what surrounds the compass (like the steel hull of a ship or electrical equipment, cell phone, etc.) The compass, if working at all, will point to wherever magnetic north is today....it doesn't matter when it was made and where magnetic north was at the time.
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Minor correction to terminology......magnetic north is subject to "variation". Variation is different depending on where you are on the planet and it is the difference between magnetic north and true north. It can be plus or minus and a compass usually will not have any markings to tell you how much or which way the variation is....because it is different in different places on the surface of the earth. "Deviation" (not "declination") is error introduced by what surrounds the compass (like the steel hull of a ship or electrical equipment, cell phone, etc.) The compass, if working at all, will point to wherever magnetic north is today....it doesn't matter when it was made and where magnetic north was at the time.
Deviation would be "interference" like you mentioned... metallic ship's hull, electronic equipment, etc... Declination would be the actual variance between true North and magnetic North.
Question... Were older instruments built with knowledge of that variance? Or were the compass points laid out with the needle pointing at magnetic North?
Mike
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Variation (also known as "declination" and / or "inclination" in some circles) has been apparent for a couple of centuries. And yes, when magnetic compases were built, at least for the last couple of hundred years, the makers and users were aware that geographical (i.e. "true") north and magnetic north did not always coincide. It is easy, in the northern hemisphere at any rate, to take a magnetic compass bearing of the north star (Polaris) and see the difference (variation). (Note: While not exact, Polaris is observable "true north" for all practical purposes). The 32 points of the compass were laid out precisely around the compass line marked as "north". There was no attempt to skew the bearing markings to make a magnetic compass read true bearings because, as I noted in the previous post, variation (or declination if you prefer to call it that) changes considerably depending on where you are geographically located on the earth. For example, here in California, true north and magnetic north are fairly close to being the same. In other areas of the country, magnetic north and true north can be 15 degrees or more different. And, again depending on where you are, sometimes the variation is added to magnetic north to get true north and sometimes it is subtracted. At sea in the US Navy, it was part of the navigator's daily tasks to keep track of magnetic variation as we sailed from point A to point B. It was also his responsibility to check and correct compass deviation.....not an inconsequential effect on a steel ship full of high power electronic equipment and with a huge set of magnetic coils inside the hull that reduced the hull's magnetic signature to defeat magnetically detonated mines..... :) Of course, our magnetic compass was only a back up to the primary master gyro compass that did read directly true north.
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Thanks to all.
Some good stuff.
Will also further my research..
Regards,
Doug
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Variation (also known as "declination" and / or "inclination" in some circles) has been apparent for a couple of centuries. And yes, when magnetic compases were built, at least for the last couple of hundred years, the makers and users were aware that geographical (i.e. "true") north and magnetic north did not always coincide. It is easy, in the northern hemisphere at any rate, to take a magnetic compass bearing of the north star (Polaris) and see the difference (variation). (Note: While not exact, Polaris is observable "true north" for all practical purposes). The 32 points of the compass were laid out precisely around the compass line marked as "north". There was no attempt to skew the bearing markings to make a magnetic compass read true bearings because, as I noted in the previous post, variation (or declination if you prefer to call it that) changes considerably depending on where you are geographically located on the earth. For example, here in California, true north and magnetic north are fairly close to being the same. In other areas of the country, magnetic north and true north can be 15 degrees or more different. And, again depending on where you are, sometimes the variation is added to magnetic north to get true north and sometimes it is subtracted. At sea in the US Navy, it was part of the navigator's daily tasks to keep track of magnetic variation as we sailed from point A to point B. It was also his responsibility to check and correct compass deviation.....not an inconsequential effect on a steel ship full of high power electronic equipment and with a huge set of magnetic coils inside the hull that reduced the hull's magnetic signature to defeat magnetically detonated mines..... :) Of course, our magnetic compass was only a back up to the primary master gyro compass that did read directly true north.
Thanks Dave. Kind of what I believed to be the case... If an instrument was made in Spain, or Greece, or wherever was assembled with the North point aligning with the needle... Then any appreciable distance traveled would cause the compass to not be true to that North point anymore.
And from the little bits and pieces I've picked up over the years there are spots across the globe where the rules break down completely... Once when I was in grade school I checked out a book about the Bermuda triangle. One of the first passages in a book was an entry from a sailor's log. That particular day the ship was crossing a specific area of water and it was noted that the compass began behaving erratically and would just spin... The sailor was Christopher Columbus and it was during his voyage to the New World that this occurred.
Fascinating stuff.
Mike
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Topographic maps here have the true north and magnetic north variance indicated in degrees. Also there is enough uranium bearing rock here that some places are just not compass friendly.
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Topographic maps here have the true north and magnetic north variance indicated in degrees. Also there is enough uranium bearing rock here that some places are just not compass friendly.
Pretty wild Bob.
Mike