Ways to eliminate undercuts on barrels ?

[Wavytone]

I have two particular eyepieces I quite like but the darn things have undercuts on the barrels which mean it's virtually impossible to get them to stay in a TEC turret - they fall out when rotated.

I'm at the point where either I sell these for something else (without undercuts) or cannibalise the barrels off something else, if I can find some that fit.

Apart from adhesive tapes, anyone have creative ideas on filling these annoying gaps ? One idea I have is to cut rings from plastic pill bottles but I know the lock screws on the turret tend to work loose on plastics.

[glend]

I have used aluminium flashing material ( from Bunnings) to fill the gap. I had some in the shed and it was the perfect thickness and can of course be bent in a perfect circle. You don't want it falling into a scope so securing it needs to be considered. I found some thin pvc tape worked well to secure the flashing, cut to notch width so it doesn't overlap the barrel, it worked fine for a short term fix.
I have also considered using heat shrink tubing of the right diametre, just cut a short section to match the notch width and heat it in situ, it would fill the gap, or you might need two layers. Heat shrink is easily removed and does not leave a sticky residue.

[Tinderboxsky]

Perhaps a fine brass sleeve with a small cut in it that allows you to expand it slightly to push it down the barrel and it then contracts into place in the cut out. The brass sleeves used in eyepiece holders would be close in size.
If the eyepieces were keepers, I would fire up the lathe and make new barrels.

[ausastronomer]

What are the 2 eyepieces you are referring to? I assume they are 1.25" eyepieces

Most 1.25" eyepieces use the industry standard 1.125" x 42 tpi right along the eyepiece barrel. Which means you can unscrew the barrel turn it upside down and screw it back on the other way round. Depending on the positioning of the undercut relative to the end of the barrel, this might even solve your problem. If it doesn't you should be able to source any old 1.125" x 42 tpi barrel (without undercut) off another eye piece and screw it straight on.

1.125" x 42 tpi is the standard thread size for 1.25" filters / eyepieces. A few eyepieces, notably Brandons/Questar use something different. FWIW the standard 2" eyepiece / filter thread size is 48mm x .75mm pitch.

Cheers
John B

[Kunama]

I use a bit of heat shrink tubing and a hairdryer to shrink it onto the barrel....

[LewisM]

Or fill the gap with a GOOD epoxy like JB Weld or Devcon. Be sure to tape off around it to avoid smears and also stop scratching the barrel when you sand it down.

[ZeroID]

I'd be trying the Shrink Sleeve idea first. I use it quite a bit and when shrunk down it will be quite firm but easy to remove if it's not suitable.

Get a few diameters so you can find one that shrinks the right amount to give an almost flush finish. It may not be the smallest diameter that is most suitable as it thickens as it shrinks of course.

Also cheap ..... :thumbsup: $5- $10 per meter at Jaycar !

[iborg]

Hi

If you want to try heat shrink tubing, I have some large diameter material that I can send you a small piece of, no charge. If interested, PM me details. I can't do anything about until Monday at the earliest.

It is part of what my work was throwing out.

Philip

[Wavytone]

Ok...

Tried the heat shrink. Works sort-of but I think it's still a bit on the soft side. Positive aspect is the extra friction it produces is good.

One is a vixen SSW. Will try a ring cut from pill-bottle over a layer of heat shrink or vice versa. The barrel unscrews but that's not much help as it's not reversible and it's a unique diameter.

The other is a 2" ProStar with a beveled undercut, deepest at the top and tapers to nothing 20mm down. The entire barrel is a one piece assembly ie the bit with the undercut doesn't unscrew. Looks like this one will have to be epoxied using a plastic pill-bottle as a cast and sculpted with a sharp blade. Also it matte anodised so epoxy should adhere well enough.

Third for fixing is a bintel 2" star diagonal which has a similar tapered undercut as the ProStar and a very glossy epoxy paint job. I'll try heat shrink on the first before resorting to sanding the paint off and using epoxy.