Gluing the diagonal -Help!

[GReilly]

I am in the final stages of assembling a homebuilt 8" F6. I want to glue the diagonal to the (pvc) diagonal holder but am unsure of the best adhesive to use. The hardware store stocks "Glass ******" - I think they use it for fish tanks....
Is this what I should use?
Greg

[leon]

Araldite, the 5mins drying type, is probably your best option, Greg

Leon

[bojan]

Do not use 5 min araldite, it tends to soften and even let loose after some time. (couple od years).
24 hour version is much better, especially if you allow to it cure under sunlight (UV light) and/or at elevated temperature (60C or higher, it cures after 15-30 minutes under those conditions).
However, the best option in my opinion is non-acidic (or non-corosive) silicone rubber.
But before you do anything, just make sure the rubber will cure - with one particular syringe I had a bad experience with, it would not cure at all even after 5 days, and I had to try to use it on my own diagonal!!! The other tube was OK (12 hours and the job was done)

[Karls48]

Don’t know what will work best, but do not use Superglue. As it dries its vapours deposited cloudy coat on my prism diagonal.

[cristian abarca]

Hi Greg I use this stuff available at Bunnings or big hardware store. It works well and is easy to use. I have stuck several secondaries with this and have not had any problems.

Regards Cristian

[rmcpb]

To stop distortion of the secondary you need a flexible, gap filling glue so the silicone types are perfect. Make sure you leave a gap between the mirror and the holder, I use some 3/32 drills but thin nails would work. Use three small dobs of glue then remove the spacers when the glue is cured.

Cheers

[Garyh]

Like Rob and Cristian say...use a silcone product not a glue? I used similar to what Cristian shows but was a translucent type...I only left maybe 1mm between the stalk and mirror back.it won`t come off very easy. Make sure the surfaces are very clean before stacking down.

[GReilly]

My thanks to all of you with your responses. I will proceed with a silicon sealant/glue with a lot more peace of mind now.

[Sharnbrook]

I would strongly recommend using a neutral cure sealant, rather than an acidic cure type. Little or no difference in cost, but there would be no possibility of corrosion, whereas the acetic acid types can cause corrosion. If I was doing it myself, I would use a polyurethane sealant such as Sikaflex. It'll cost about twice as much as the silicon sealant, but is an excellent product. Bojan mentions that you must be sure that it will cure properly, and that is a major consideration, use only a fresh tube, and do a test first. If you buy from a major store, you will be pretty sure of getting a fresh tube, as there will be a high turnover, whereas a corner store may have old stock, and that could lead to problems, as it will only have a shelf life (in the tube) of 9-12 months, or less if it hasn't been kept at reasonable temperatures.