PST Etalon removal woes

[spaceboy]

I am aware that some PST modders have encountered etalon assemblies "welded" to their PST body (black box) and that some have had to throw in the towel and others that eventually freed the thread weld. 

With the intension to do away with the pathetic focuser on the PST and move to a stage 2 mod I set about removing the etalon from the black box. As splitting all parts of the eyepiece holder was relatively easy and the previous owner had already split the gold tube from the front of the etalon with success I figured I was going to be one of the lucky ones and started off with a simple rubber jar opening strap. This failed miserably so I moved on to a heavy duty oil filter remover which too eventually gave up grip and just slips. I tried various rubbery things between the etalon (tuning ring removed) and tool in the hope of a better grip but to no avail.  I threw caution to the wind and clamped the etalon rather tightly in a metal working vice with V blocks getting full wrath of spaceboy twisting the black box itself yet still it ended up slipping rather than breaking the bond. On this occasion when I say slipping I mean stripping metal from the body of the etalon (thankfully this is hidden from view when the tuning ring is installed) where gripped in the jaws of the vice.

The stage 2 had been intended to be done on the cheap really only to do away with the short comings of the PST body,  like the weight, prism, focuser. I had not intended to do a complete stage 2 with BF10 filter so bearing in mind that there are indeed optical elements within the etalon it was at this point I figured I was doing more harm than good and called it a day. I have read varying reports that stage 2 mods offer any significant visual gains over a stage 1 when sticking with a BF5. Some say it offers for better clarity and others suggest its negligible at best. Personally I just can't get on with the focuser but if it offered significant improvements visually that would also be desirable to have another go at splitting the etalon.

I really cant see what else I can do to split the etalon with out risking damage to either the thread, the box or etalon itself. I had considered making c blocks from wood and sticking this around the etalon to then put it in the vice so it is less likely to start binding / stripping the ally and also grip better than metal would. I do though believe there has been so much lock tight used that I have more chance of stripping the actual thread than I have breaking the thread lock bond.

I guess I have 4 questions:-

1) Is a stage 2 with BF5 (possibly BF10 at later date???) worth risking another try at splitting the etalon from the black box ??? If it is worth going down a stage 2 route should I just go all out with the wooden c blocks and hope the thread on the black box/ etalon is stronger than the lock tight ??

2) Is there a retaining bolt/ screw I'm missing or is the etalon a left handed thread ????

3) Any suggestions other than contoured wooden blocks a vice and a 12 stone man hanging of the PST for splitting the bond ?? I'm a little dubious of using hot or cold on the thread when optics are near by, but I guess this is an option ???

4) Just make do and enjoy what I have ? This is not without its advantages as the PST can still be used as a 40mm stand alone if need be.

 

 

[xtreemchaos]

don't know if this would work but I find warming the metal up with a hair dryer can help with stuff stuck with locktight, don't know if it would be safe as ive no idea how a pst works or is put together, just a thought , charl.

[Peter Drew]

Always a tricky situation and one I've faced a few times myself. A couple of things to clear up, there is just the one screw to remove, the etalon is a right hand thread and applying heat as Charl suggests can help to unstick locktite, heat shouldn't be a problem compared to its working temperature. I would overall prefer an etalon housing stuck in the black box rather than on the end of the "gold" tube as it allows the fitting of the PST to 2" adaptor to be used. If you can't manage with the PST focuser you can always use a standard focuser ahead of the etalon although this will probably require shortening of the donor OTA, a much safer option!. My experience with PST modding has shown me that provided there was no problem with the original PST regarding focusing or astigmatism then there is no significant optical benefit from a stage2 conversion, I've tried several of each. A good time for a reminder regarding blocking filters and PST mods. Changing up from a 5mm to a 10mm gives a wider field which is useful for imaging but it does not increase the sweetspot size, this remains the same regardless. The main point of a mod is to improve the resolution and permit higher magnification, using a 2x Barlow and binoviewers in conjunction with a BF5 gives a full field of on band tuning and a respectable size FOV bright and detailed. Finally, PST's are mass produced with a spec that is 1A or better so if you are lucky your etalon could be nearer 0.7A. My personal mod includes one at the best end of the scale and gives outstanding performance.

My advice in your situation? give the stage1 a try in the first instance and change to stage2 eventually if it offers you any further advantage. 

[Moonshane]

I can honestly say that the views through Stu's stage one created by Peter were truly stunning.

An advantage of stage twos is that in e.g. mine can get full disk views with my original bf5 at 68x with binoviewers which seems impossible but it works. I can then use standard pairs of eyepieces to get more magnification if the seeing allows.

[spaceboy]

Thanks for the replies. I've now decided to stick with the stage 1. It would have been nice to have the option of a stage 2 but I don't think it's worth the risks damaging the etalon. I know I'm not the first and probably won't be the last to have had to give up on the idea. I did though spend a little time on the lath making an oversized knob to try and aid better focusing with the PST. Probably won't add any real advantage but it at least kept me out of trouble for an Hr or so

[Moonshane]

Nice idea. could you extend this further and make a longish lever to focus? Making it removable with a thumbscrew would be a good idea naturally.

[spaceboy]

Good idea mate ...I LIKE IT! I guess I could drop a small hole in the side of the knob where I could insert a match. I could experiment with varying lengths and plus if I was unfortunate to catch the lever in anyway the match would be the weak link and hopefully snap before anything else. I could just push the match in and out as needed and replacements are easy to find should I loose it.  

[moriniboy]

I found this stuff was good at dissolving the thread locker, takes a bit of time though (days) apply copiously with a q-tip

[Solar B]

I

 

I now use one of these an oil filter wrench it's pretty heavy duty 

 

Brian 

[spaceboy]

On ‎05‎/‎05‎/‎2017 at 11:10, moriniboy said:

I found this stuff was good at dissolving the thread locker, takes a bit of time though (days) apply copiously with a q-tip

The trouble is with using WD40 or Gasket remover is there are optics very near by and the threads are not really accessible to spray anything on them.

[spaceboy]

20 hours ago, Solar B said:

I

 

I now use one of these an oil filter wrench it's pretty heavy duty 

 

Brian 

I've already tried one of these  with a grippy rubber material for grip wrapped around the etalon with no success

I appreciate the ideas being posted guys but TBH I have given up on the stage 2 for now at least. For what I will gain from a stage 2 modification now simply isn't worth the potential damage I may inflict on the etalon or pst black box.

[moriniboy]

51 minutes ago, spaceboy said:

The trouble is with using WD40 or Gasket remover is there are optics very near by and the threads are not really accessible to spray anything on them.

Agreed, that's why I said use a q tip to apply