Primary Collimation spring question

[peter_4059 (Peter)]

I'm looking into replacement of the primary collimation springs on my LXD55 SN10 to something a bit firmer. I've got the approximate dimensions of the existing springs however I'm looking for ideas on how rigid a replacement spring to select.

The existing springs are 14.5mm OD 1.5mm wire and in the collimated (compressed) position they are approx. 19mm long with 7 coils. The mirror is 254mm OD/26mm thick and I estimate the mass is approximately 3.5 kg's so about 32N total force.

I've previously purchased some Bob's Knobs springs for my Newt and these are 14.2mm OD, 1.6mm wire stainless steel. Comparing these dimensions to what's available at Small Parts I reckon they are rated around 112N, giving a capacity of three springs about 10x the actual force from the mirror.

Bunnings has some CSC springs (C-712) in suitable dimensions however these are rated at 198N. Small parts has a much larger selection however the price is a lot higher. I assume making the spring too rigid will make it difficult to turn the collimation knobs.

Does 100-200N sound like a reasonable range to target?

Cheers,

Peter

[blexxx1769 (Ian)]

G'day Peter, A few thoughts on springs etc. I reckon you'll find the Bob's springs to be in the ballpark, but the adjuster screws require some attention to get the best from them. I have found that carefully rounding off the threaded ends of both the primary & secondary screws stops them from biting into and misaligning the engagement surfaces resulting in much more consistent & stable alignments. You can carefully ease the knobs off the bigger screws then grip them in a drill chuck & round over with your trusty Dremel tool or file, polish some & push the screws back into the knobs. Done!
Regards, Ian.

[peter_4059 (Peter)]

I picked up some C-712 springs today - they sure are firm. I'll give them a try next time I remove the mirror cell.

[troypiggo (Troy)]

They the 200N ones?

[peter_4059 (Peter)]

yep - 198N I think.

[dave brock]

I think they'll be fine. Springs that feel very firm between the fingers are still easily compressed when placed over a bolt. There's alot of leverage action involved (if that's the right way to explain it).

Dave