Meade AR6 drawtube modification

[John]

I have a nice Meade AR6 6" F/8 optical tube and I want to use a Chromacor corrector with it.

The Chromacor is a 2" accessory that screws into the 2" thread on the bottom of a diagonal and projects into the drawtube about 10cm.

Two adaptations are needed to facilitate this:

i) removal of the last baffle from the drawtube as it would contact the end of the Chromacor when inserted. This was easy to achieve so I can tick that off

ii) the removal of the small screw / nut that holds the focus rack onto the bottom of the drawtube and projects around 3mm into the drawtube bore. To accommodate the Chromacor, the inside of the drawtube bore (which is a snug 2" fit) needs to be entirely smooth so I figure that I need to cut a fine thread into the 2mm hole that the screw passes through in the drawtube wall and replace the screw / nut with a slightly larger screw that will screw into the newly threaded hole while not projecting into the drawtube bore at all.

Can some kind soul, with a more practical / technical mind than mine, offer any advice on how I might do this ?. The drawtube on the Meade has walls around 1.5mm thick so not much to play with. I have wondered whether there is some form of small self-tapping screw that might do the trick ? - the drawtube is aluminum so not too hard. The arrangement at the other end of the rack can stay as it is as it's way down the drawtube and nowhere near the Chromacor.

All suggestions considered ! - I've even thought of strong glue as a possibility but possibly not

I'll try and post a picture of the issue but my son has nicked the batteries from our digicam for his XBox controllers

Thanks

[Maltese Falcon]

Any chance of a picture? How far up the inside of the drawtube does Chromacor corrector intrude?

[John]

Any chance of a picture? How far up the inside of the drawtube does Chromacor corrector intrude?

This is a pic of the Chromacor on my old diagonal. This time around I'll be using a Tele Vue Everbright but the dimensions are much the same. The extension ring here (between the Chromacor and the diagonal barrel) is the Hyperion 28mm fine tuning ring which is the longest I'll need to use. This gives some idea of the depth of clear drawtube bore that I'll need. The intrusive screw / nut that I'm looking to remove are beyond the end of the diagonal barrel but not the extension that is required to get the Chromacor the correct distance from the eyepiece focal plane (161mm +/- 1mm) or the widest part of the Chromacor itself:

[Maltese Falcon]

Ok with no picture I have made some asumptions.

Fig A is how I assume it is at present.

Fig B is a method WITHOUT a nut just thread the hole the size of the new screw and thread the inside of the drawtube to accomatate the Chromacor corrector.

Fig C retains the nut but moves it to the outside of the drawtube and is fixed with either epoxy resin or is welded or soldered to the outside of the drawtube and a section of the rack is removed to accomadate the nut.

Two words of caution with fig. C 1 if you use epoxy then you might as well just use epoxy to attack this end of the rack. 2 It is not easy to either weld or solder steel to aluminum. Staneless steel is even worse but it can be done with specialst kit/flux.

img020.pdf

[Maltese Falcon]

Sorry that didn't work right I'll save it as an JEPG and see if it works:iamwithstupid:

[John]

Thanks for your thoughts on this Maltese Falcon

Ideally I'd like to achieve your option B although the inside of the drawtube does not need threading to accommodate the Chromacor - it just slides in connected to the 48mm thread on the bottom end of either the diagonal or the extension tube.

Interesting to see your option C - that could be a "fall back" position if B can't be achieved.

Thanks again for going to the trouble of drawing and posting your thoughts - much appreciated

I'll try and post a pic of the drawtube and protruding screw / nut today sometime.

[dweller25]

It would be easier to buy a big Newt

Hang on you already have one - LOL

You must be one of those refractor lovers

[John]

You must be one of those refractor lovers

Yep

Nothing quite like the views through a large aperture refractor