Author Topic: picked up a new used lightbridge , some questions  (Read 540 times)

Rick Nocturnum

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picked up a new used lightbridge , some questions
« on: December 28, 2017, 10:39:03 AM »
found a 12" at a good price.  mirror look like it needs recoating with some visible blotches and dark spots, but once cooled (thin mirror fortunately) it gives nice pinpoint stars, though I'm not knowledgeable enough on sstar testing for a thorough test.. visually its good though. I planto just wait until Isend it to a mirror company for analysis/fixing. eventually. 

noticed there's a little bit of flex/vibration in the trusses. I had this issue on my 16" Hubble and found that bungee cords or a snug cloth  strap mid way around the trusses can damp a lot of the flex and vibration. unfortunately with the LB design bungee cords cut into the light path a bit.

my base is old swollen particle board. I put some spacers above the lazy Susan as the top and bottom were touching affecting the motions.. I'm wondering if this added space is adding to vibrations? maybe the struts are worse because of this?  I have ordered a wood base from Dennis at dobstuff  if that is a vibration source the new wood should help. that will be in this week.

any other ideas too stiffen it up? I could add "strings" vertically I guess   that I could then use a strap or bungee. I'msurprised they flex.. its about as bad as my un modified hubble which uses much thinner trusses and are longer!

question #2: this model uses  felt on the altitude bearings. as is its a tad too much friction. but I do like the felt feel of the motions. Dennis's kit includes felt. is there a ration to how much felt to  how much weight? I've read there Is  such a ratio using ebony star and  Teflon. I was going to experiment and put on less felt to start, adding more as I determine needed. seems likea plan but not sure if tthere's a more precise method? I do want to stay with the felt.. at most elevations its quite nice movements!

the scope came with a gso focuser, two speed. on the course adjustment there's ever so little catching on something, a slight skipping when turning. usable, just annoying. I don't experience this on the micro adjustment knob.  is this fixable? worth the effort on a low cost focuser?

it had original collimation knobs, springs and locking bolts. I've upgraded the springs but they still weren't strong enough.. ordered springs and bobs knobs, also to be in this week. I have tto say even though its an old beater and needs some tuning, they are awesome scopes!  thanks for any tips on my issues!

 



incojukam

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Re: picked up a new used lightbridge , some questions
« Reply #1 on: December 31, 2017, 08:39:54 AM »
I have the 16" and also had problems with flex. Or at least, I thought I did. It turned out that my primary was moving about in the cell with altitude changes. My fix is pieces of paper pushed in between the edge of the mirror and the cell. Still a very small amount of movement is possible, but this cured the altitude/collimation shift effect.(and I just got my Dobstuff base from Dennis today, and will be giving it run in the weekend!).

Jacob Julian

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Re: picked up a new used lightbridge , some questions
« Reply #2 on: December 31, 2017, 09:14:55 PM »
Thanks! i don't know if ill get my base from Dennis before my local star party this friday. hope so  are you going to use the teflon/ebony star for your azimuth? i think I'm going to keep using the lazy susan but on the dobstuff base, i really like them after having owned a AD10. smooth and simple adjustability.my issue isn't so much movement in collimation at differing latitudes. it seems pretty good using the locking bolts.. once i get the new springs in we will see if the locking knobs are still necessary. currently, once locked down, my bar lowed primary donut shadow might move 1/16 to 1/8 of an inch. not sure how that is considered, but i find it acceptable... and its only at low altitudes which i use rarely anyhow. hopefully ill get the springs and bobs knobs in tomorrow. needing a screwdriver to collimate is ridiculous  my flex issue is more of a stiction issue i think, at lower altitudes i can feel the poles flex before the scope actually moves.. I'm going to try using less felt. I'm not sure why i don't noticed this much at higher altitudes though if its the stiction.  well guess i will see how it goes with less felt. i can always go to teflon if i can't narrow it down to the amount of felt. I'm surprised theres not more mention around here of the felt on these lightbridge scopes, they seem pretty popular.  theres a vendor at the star party I'm going to so i will likely just pickup a new focuser there if they have any (they did last year).

Zac Purvis

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Re: picked up a new used lightbridge , some questions
« Reply #3 on: January 01, 2018, 06:41:17 AM »
Ah, ok. Yes, my original lightbridge base used felt for altitude, and teflon for azimuth. The Dobstuff base does felt for altitude (I've yet to tinker and check azimuth). Both have nice, smooth movements in altitude. It is surprising that stiction is the cause--must be a LOT! Good luck and report back!

blasbunmena

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Re: picked up a new used lightbridge , some questions
« Reply #4 on: January 08, 2018, 02:03:29 AM »
I seem to recall reading on these forums about some Lightbridge scopes that have the truss clamp knobs were the threading goes into the ring being too long. The fix was to place a washer on the stud before threading it. I would check this, and check the tube ring screws as well for tightness.

laycacdownsell

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Re: picked up a new used lightbridge , some questions
« Reply #5 on: January 11, 2018, 03:57:11 AM »
Quote
though I'm not knowledgeable enough on sstar testing for a thorough test.


https://www.youtube....h?v=MFmFpuST67M

also you can null test it with a bright star. find a bright star with a widefield eyepiece. take out the eyepiece. then lay a piece piece of electrical tape across half of the focuser hole. place your eye close to the tape and run the focuser thru intra and extra focus. you will see the star fill the the mirror and use the edge of the tape to cut into the light. at focus it should totally grey out. if there is any spherical abberation you'll see something that looks like a classic parabolic donut foucault test.

opalytun

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Re: picked up a new used lightbridge , some questions
« Reply #6 on: January 12, 2018, 04:47:55 AM »
Standard LightBridge mods:1) add fender washers unterneath the spider attachment nuts and tighten the spider more.2) add star washers under the heads of every screw by which any tube "ring" is held to the end of a tube segment.  Otherwise, the rings slide in the holes.3) make sure the plastic holder for the secondary isn't pinching the secondary mirror4) place grip tape under the pressure plates that hold the poles at the bottom.  Or, knurl the flat ends of the aluminum poles.  Whatever increase the "bite" of the plates on the poles.  Otherwise, they slip.5) add additional felt to the ends of the felt bearing materials to become tighter on the aluminum trunnions.  otherwise, the scope tends to rock in the slightly over-sized cutout in the wood and "bounce back" when you let go of the UTA.  Don't use teflon or furniture glides for bearings to run directly on the aluminum--too little friction and it makes the scope incredibly sensitive to balance.6) rough the felt up with a stiff toothbrush.  it acts better when the felt is not flattened down.7) replace the springs behind the mirror cell so that they are stiff enough to hold collimation without the locking screws.8) Unglue the primary mirror, clean off any glue until the mirror slides freely.Then add two bottom edge support screws or plastic nuts at the center of gravity of the mirror, 90 degrees apart so the mirror rests on the bottom two edge screws and is not held by glue.9) powdercoat the poles black or add pipe insulation to them.10) add a light shield on the top opposite the focuser.  The UTA is too short and light enters the bottom of the eyepiece directly.11) flock the inside of the UTA opposite the focuser12) Add a shroud from top to bottom in which hoops have been sewn to keep the shroud round and not let it fall into the light path (there are a couple commercial makers who do this for LBs)13) Make the end rings black if they are not already--that includes the mirror cell backing.  When you look down into the tube, you should not see white around the primary mirror.14) remove the locking screw from the focuser (the one nearest the tube) and adjust the pressure screw until the focuser moves smoothly, yet supports your heaviest eyepiece and accessory without slipping.15) Loosen the two setscrews in the base plate and rotate the focuser to a 45 degree angle so that coarse and fine adjustment knobs are available easily no matter where the scope points.16) add a stop screw to the altitude trunnions so the scope cannot go below the horizontal.  This will prevent mirror movement and prevent the poles from impacting the front panel of the rocker box.17) Make sure the mirror clips do not touch the primary mirror but are a hair above it.18) add buttresses to the sides of the rocker box to prevent lateral shake in the vertical side boards.  This really damps vibration.19) replace the rubber feet on the groundboard with hard pucks of plastic or wood.  A lot of wiggle takes place at this point.20) replace the tiny center marker on the primary with a larger one.  Use a white reflective material if you can, as the small one in the scope appears black otherwise, and it makes collimation difficult.21) Add a steel fender washer between the secondary holder's top and the 3 collimation screws.  This will prevent dimpling of the secondary holder and make rotation of the secondary easier in collimation.22) replace the secondary collimation screws with longer thumbscrews so no-tool collimation is possible.I've seen a lot more mods done, of course, including turning the base into a collapsible one, but the above should keep you busy for a while.

coreanoguf

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Re: picked up a new used lightbridge , some questions
« Reply #7 on: January 18, 2018, 12:27:53 AM »
Hey Starman1. I've noticed that my LB sometimes gets too sticky in altitude-adjustment if it is very humid out. I had an idea of "waterproofing" the felt bearings with some WD-40. Do you think this is a good idea or would it make them too slick?

lodbelimfo

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Re: picked up a new used lightbridge , some questions
« Reply #8 on: January 18, 2018, 08:07:43 AM »
Quote
Hey Starman1. I've noticed that my LB sometimes gets too sticky in altitude-adjustment if it is very humid out. I had an idea of "waterproofing" the felt bearings with some WD-40. Do you think this is a good idea or would it make them too slick?
Good question.  I don't know.  Perhaps it would make the felt too slick.
I'd say try it, but have some replacement felt handy.

Jason Pederes

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Re: picked up a new used lightbridge , some questions
« Reply #9 on: January 18, 2018, 09:51:21 AM »
How about using paraffin to waterproof the felt bearings?

Jayarajan Mcloven

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Re: picked up a new used lightbridge , some questions
« Reply #10 on: January 26, 2018, 05:05:15 AM »
Quote
How about using paraffin to waterproof the felt bearings?
Could work, but might be too sticky.
Or, conversely, reduce friction too much.
If you have multiple replacement felt strips available, it wouldn't hurt to experiment.
Some felt is fairly smooth and some is coarse.  That difference could also be exploited.

Alex Miller

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Re: picked up a new used lightbridge , some questions
« Reply #11 on: January 30, 2018, 06:44:15 AM »
I have been using parrafin on velcro batting for my 16 Lightbridge.  A guy I know used the batting as a substitute for the original felt on his 12 Lightbridge.  Paraffin is sticky, but doesn't seem to have much stiction.  I can pull out a Nagler type 2 20mm eyepiece without any change in altitude.

adviconno

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Re: picked up a new used lightbridge , some questions
« Reply #12 on: January 31, 2018, 10:22:23 AM »
Lots of good info for me, thanks. still haveta go through most of it. I've been clear coating/sanding my dobstuff lightbridge base "kit" the last two days. Two coats of helmsman crystal clear. Going to assemble and then give a third coat before use. Later I plan to paint the lightbridge logo on it in white letters. I'll see how that helps vibrations or not first.

i received and installed the bobs knobs primary knobs and springs, installed and used them last night: BIG difference. Holds collimation accurately at all elevations, barely need the locking knobs. Replaced the secondary collimation knobs with bolts from the hardware store, works fine.

Will ill be going through this list of items, thanks again!

Btw- I noticed on Rob Teeters scopes last week he uses a small metal piece to protect the corners. Anyone know where I can get some of those? I now have two dobstuff bases and those corners do get bumped a lot unfortunately.

Ralph Sonberg

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Re: picked up a new used lightbridge , some questions
« Reply #13 on: February 03, 2018, 01:09:38 PM »
Quote
Lots of good info for me, thanks. still haveta go through most of it. I've been clear coating/sanding my dobstuff lightbridge base "kit" the last two days. Two coats of helmsman crystal clear. Going to assemble and then give a third coat before use. Later I plan to paint the lightbridge logo on it in white letters. I'll see how that helps vibrations or not first.

i received and installed the bobs knobs primary knobs and springs, installed and used them last night: BIG difference. Holds collimation accurately at all elevations, barely need the locking knobs. Replaced the secondary collimation knobs with bolts from the hardware store, works fine.

Will ill be going through this list of items, thanks again!

Btw- I noticed on Rob Teeters scopes last week he uses a small metal piece to protect the corners. Anyone know where I can get some of those? I now have two dobstuff bases and those corners do get bumped a lot unfortunately.

OSH, Home Depot, Lowes.

Johnny Jeep

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Re: picked up a new used lightbridge , some questions
« Reply #14 on: February 08, 2018, 01:16:21 AM »
I've had the scope out a few times now with the new base Dennis made me at dobstuff. My LB had a lazy Susan, and having experience with them on my past apertura dob I really like them for azimuth so I reused that on the birch ply base instead of the included teflon. Since I have to do some hand lettering and then a third final coat of clear, I don't consider it done.. But wanted to use it so I pulled off the felt of the old base and stuck that on the new one before applying the new felt which I'll do after the finish coat. In the meantime I'm using it every night for a fortunate string of clear nights around this new moon. I'm pretty shot from lack of sleep

The new base solved the vibration problem and the supposed truss flex.. That wasn't it, It was the base! With the new springs from bobs knobs I used them tightened enough last night to not need the locking bolts. Holds collimation perfect. I did have to tighten the spider and center the secondary using washers.. All the poles are attaching and staying very snug, maybe the previous owner did some mods.

Regarding #5 in the list above from Don: I have noticed a slight bounce back at certain elevations. Before reusing the old felt I experimented with various smaller pieces of felt I picked up at the hardware store, in 1" square pieces which I tried.. and no matter what configuration, how few or where placed, the scope was unusable sticky in altitude.. It needs the weight spread out over as much of the bearing as possible it seems, thus needing the single long stretches of felt. It seems the dobstuff base cutout is virtually identical to the LB original and it too could fit tighter, so that your # 5 re adding additional felt looks still appropriate with a dobstuff rebuild. I'm going to try that tonight with a little extra felt on the outer ends of the existing.Has has anyone tried any felt lubrication ideas? I was considering waxing the aluminum trunnions but I don't know if theyd get sticky in moisture as it definitely does with teflon/ebony star. (Learned the hard way). I did try scuffing up the felt with a toothbrush idea. didn't notice much differences maybe i should try before each use? It is moderately sensitive to balance without the break installed but the counterweight system it came with works good with occasional help from some stick on magnet pucks if pointing low. I've noticed with these felt bearings that moving down is the absolute perfect amount of stiction and smoothness. but moving up can have that bounce back issue at some elevations. I haven't figured out yet what can improve just the upward motion. I haven't tried the added felt discussed above yet. Tonight.

Regarding tube rings to support a shroud, haven't gotten that far, as is the case with a few other things on the list of ideas above. Thanks!