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Eyepiece undercut.

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Could someone please tell me what an undercut is on an eyepiece. Am I right in assuming it is the ridge around the barrel.

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An undercut is a royal pain in my opinion, but sadly something I live with as I like TeleVue kit.

The images from John do explain visually rather well.
Supposedly the undercut ensures the item does not slip from the telescope.

I disagree as the undercut catches when taking items on off the scope and move the scope position. 
The only time something fell from my scope was an undercut that caught as I removed an EP.
But each to our own favours of course, some love them, many loathe them. 

Edited by Alan White
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I think undercuts may have had a purpose in the days before compression rings when screws were used to lock the eyepiece in place but now are just an anoying anachronism. 🙁

Edited by johninderby
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14 minutes ago, johninderby said:

I think undercuts may have had a purpose in the days before compression rings when screws were used to lock the eyepiece in place but now are just an anoying anachronism. 🙁

Exactly in this day and age they are not needed and actually problematic as allot of the time it can just end up tilting adaptors etc as the compression ring closes on the cut. 

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Thank you all very much for your clear and precise explanation, even I can understand it.  😀

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I don't have a problem with bevelled undercuts, to be honest.  They seem like a very reasonable compromise.  I've even machined them into various bits and pieces I've made myself.

James

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They are the work of the Devil!

 

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Just now, Merlin66 said:

They are the work of the Devil!

No, I think that's Marmite :D

James

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23 minutes ago, JamesF said:

No, I think that's Marmite :D

James

Or Vegemite.  😁

Edited by johninderby
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1 minute ago, johninderby said:

Or Vegemite.  😁

I couldn't say, to be honest.  Having smelled Marmite once and nearly lost a perfectly good breakfast, I now make it policy not to eat anything with a name that ends "...mite".

James

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 Vegemite is the equivelent of Marmite in the land down under.

Still I suppose it’s one use for the sludge scraped out of old engine oil pans, or at least that’s what it smells like. 🤮

Edited by johninderby
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Oooh, now, this is way off-topic, but John's post just tickled a memory that I've had hidden away for far more years than I care to consider.

Who else remembers home oil changes with the old engine oil being drained out into a metal oil can with one side cut out of it?  Has to be a metal can, mind.  Bonus points if the sump plug was accidentally dropped into the can and you had to fish around in the filthy (and probably quite warm) engine oil with your hand to find it again.

James

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I was more posh. Had a proper oil drain container made for the purpose. I know it’s somewhere in the garage. 🤔

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ahh memories James, and of dropping the slippery oil filter and of course it falls into the drained oil and covers you

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Oh god, now I'm off...  Large screwdriver and a hammer used as a filter wrench...

James

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While working in Canada, I took some Vegemite with me....why not!

Showing it to friends....looked at it....looked at me....looked at it and said " Do you really take that stuff internally????"

 

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1 minute ago, johninderby said:

And yet another SGL thread goes wildly off course. 🤣🤣🤣

I blame DaveL59.  He seems to have spilt oil everywhere.

James

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Oh dear looks like DaveL59 has been changing his oil in his driveway again. 

649B719B-7126-4FA5-859B-17DDA8EFA969.png

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4 hours ago, Alan White said:

An undercut is a royal pain in my opinion, but sadly something I live with as I live TeleVue kit.

The images from John do explain visually rather well.
Supposedly the undercut ensures the item does doe slip from the telescope.

I disagree as the undercut catches when taking items on off the scope and move the scope position and
the only time something fell from my scope was an undercut that caught as I removed an EP.
But each to our own favours of course, some love them, many loathe them. 

I'm in the loathe camp!        😡

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I seem to recall that the undercuts could be filled using metal tape ?

They don't bother me personally but I know quite a few people really don't like them.

 

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Tried many different solutions - metal tape, epoxy, etc etc etc none of them worked really successfully - just canvass the suppliers to drop the  (un)"safety recess".

 

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has to be remembered too that not all of us are using more modern compression ring fitted gear so I guess the undercuts could be around for a while yet.

as for hammer and screwdriver to the oil filter, yeah I tried that one time on a stubborn one, wouldn't shift. so chain filter wrench and the old-style torque wrench and... at an off the scale 140+ lbs/ft the filter moved... just as the chain broke! Never let an ovlov garage service an alfa is all I can say (by the PO not me).

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I have a “collection” of four old eyepieces - no undercut. On the diagonal there are two screws (bolts) with v. fine threads. New OTA and a new EP with an undercut. At first I thought this would be a problem but I realised that it takes 9 half turns to fully undo the screws but 2 half turns to retract the screws so that the screw is retracted into the mount and the EP slips out. So I settled on 3 half turns is all that’s needed to retract the screws.. So two screws and an undercut looks to be a simple solution but also a more reliable one.

I haven’t handled a twist to lock or compression style fixing but the size of these doesn’t seem to be standardised. Since some of them push a ring sideways the EP isn’t held as securely as the two screw method. I can see this style being difficult to release because the mechanism eventualy sticks/twists.

So the old method of two screws doesn’t seem to be bettered? It doesn’t look sophisticated but it doesn’t seems to cause problems either?

Simon

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