Posted: 4/21/2010 5:39:28 PM EDT
|
Anyone know of a manufacturer that can make a lensatic compass that does NOT develop incapacitating air bubbles?
I have 2 now that will definitely get me lost. |
|
Man I have a compass that I paid $3 for over 25 years go that I have kept in my tackle box that still doesn't have air bubbles.
None of my brand name compasses do. I tend to buy brand names even their cheaper models. In the manufacturing process, its really typically a simple matter of degasifying the liquid. That's basically just putting it under a partial vaccum for a while till all the gas comes out, which is typically simply heat it up some. Its a pretty simple process. Now most compasses, almost all hand compasses, will develop a vaccum void. If they don't cool the liquid before sealing it, some compasses can be more susceptible to voids than other. That's from a combination of temperature and barametric pressure (elevation) and a simple volume shift. Now that's not really a bubble and has no impact on compass performance. It will impact the dampening effect of the liquid a little but that's all the liquid does anyway which doesn't have anything to do with the needle pointing north. Typically vaccum voids go away when you heat the compass up a little or move it to a lower altitude. Most compasses re assembled at room temperature. You get them cold enough, they will develop a void. Now if you are getting a leak, that's in handling typically. Compasses are not typically vented. If handling is your problem then the more robust the compass or better its protected, the more it will last. Typically if you have broken the seal, you probably have scratched it up some in the process. If you are truly getting air bubbles then looking at what type you buy is as important as who makes it. Unless its some volumetric compensating unit like a gyroscope on an aircraft with a metal bellows that increases or decreases volume with pressure, then its going to get vaccum voids depending on the conditions. I hope that helps. Tj |
|
First of all, true Cammenga's are not liquid filled –– they're magnetically dampened. So a genuine Cammenga will never have an air bubble.
Second, I own Silva, Brunton, Suunto, High Gear and other generic liquid-filled compasses and every one of them, even my prized Suunto MC-2G "ranger type," has had a bubble at some point (and yes, the bubbles chap my hide). Usually they come and go –– they're more prevalent in cold weather it seems. For some reason my Brunton's developed bubbles that never went away. It's a shame because they have the most innovative designs! They're pretty much still usable. I'm a bit dubious about the claims that bubbles don't affect navigation. I've definitely had them big enough that you can watch them push the needle depending on how you hold it. Usually if they're small enough, you can hold the compass so the bubble is out of the way as you're taking a reading. I have one of those little "high gear" all in one tools and its compass is completely hosed by a bubble that literally fills half the capsule. Also I'm less trusting of bubbles in the Brunton "circle over circle" disk-type needles since there's no way to position it with the bubble completely out of the way. BTW, thanks to TJ for the scientific explanation –– that's very interesting and I never knew how they were formed. I'm gonna read that again! |
|
I'll have to look again (at work now) but I think they were Ozark something or others.
Not very expensive, I'm looking for a decent replacement. Have a Brunton, small bubble but is OK. Will reliably point NORTH. What I'm dealing with is just impossible to get a "positive" NORTH when I know where it should be. Can you imagine being in a close pine forest, over-cast day, with a compass you know has trouble? No thankyou. Thanks guys, I'll see if I can get my hands on some of those makes to see which I'm comfortable with. |
|
Quoted:
I'll have to look again (at work now) but I think they were Ozark something or others. Probably Ozark Trail –– WalMart's house brand. Yeah, their stuff ain't exactly made to last (and I confess to buying OT stuff from time to time). You should be generally ok with Suunto, Silva, Brunton, and of course Cammenga. All three of the first ones have basic models for less than $12. |