lightbridge 16

qld · #1 12-08-2008, 08:27 PM

the collimation springs on the 16 lightbridge seem very flimsy,telescope makers i have spoken to have used heavier springs they have salvaged from motor car clutches or tappets as springs for their telescopes as they were firmer in the compressed state due to their original design purpose.The benefit of such a spring is that it holds the telescopes collimation better.The springs on the meade 16 seem to be made of wire and on compression seem to fold over resulting in the collimation being easily disturbed if the scope is mooved .My question to the ether specialists is have any of you experienced this problem,and have any of you replaced the springs as supplied by meade.If you have what did you replace the springs with.or was there another solution? I await with great interest any views on the matter qld

PCH (Paul) · #2 12-08-2008, 08:40 PM

Hi Qld,

it's a well known fact that the primary springs supplied with the 12 and 16" LBs are insufficient to hold the mirror steady. Most people (myself included) purchase a set of stronger springs (made by Bob's Knobs) available from Bintel and probably others.

Hope this helps !

Cheers,

qld · #3 12-08-2008, 08:50 PM

Quote:

Originally Posted by PCH

Hi Qld,

it's a well known fact that the primary springs supplied with the 12 and 16" LBs are insufficient to hold the mirror steady. Most people (myself included) purchase a set of stronger springs (made by Bob's Knobs) available from Bintel and probably others.

Hope this helps !

Cheers,

hi went to bintel but no knobs from bob for this one as meade provides the knobs as standard on the 16(which are very good) as a consequence no springs are available from bob ,hence my enquiry of the members

JethroB76 (Jeff) · #4 12-08-2008, 09:27 PM

Plenty of others have visited Bunnings or similar with an example of the original and bought suitably beefed up versions..odd that this problem still hasn't been addressed

CoombellKid · #5 12-08-2008, 09:43 PM

IMO, which probably doesn't count for much is, a 16" LB is a rather expensive
way to buy a 16" GSO mirror set.

regards,CS

Ian Robinson · #6 12-08-2008, 11:26 PM

I would be might pissed off if I bought a professionally made scope and found out when I used it that it would not stay collimated because of a poorly designed / engineered mirror cell .... this is something the manufacturers have to get right else their reputation for quality will go around the S-bend with the next flush.

Why should the customer have to modify a scope (at their cost) to fix a problem the manufacturer should have sorted out in the first place ?

tnott · #7 13-08-2008, 09:22 PM

The main problem with the 16" Lightbridge is that the design has just been scaled up from the smaller models to keep the cost down - same parts, design, materials etc.

The problem is that when you double the length of components you get 8 times the flexure - and that's without any increase in weight, which is proportional to the cube of the aperture. In other words, if you double the aperture of a scope (without changing the design) you can end up with 8 times the weight combined with 1/8 the rigidity.

That is why some modifications (like replacing the springs, shimming the center bolt, reinforcing the tall skinny rocker etc.) may be required to get the scope to work it's best.

Quark (Trevor) · #8 13-08-2008, 10:13 PM

Hi qld,
Look at the difference in price between the 16" Lightbridge, !6" Bintel and compare them with the most excellent SDM's and other quality scopes such as the Obsessions.

For the considerably smaller purchase price you get quite good optics, but these scopes are mass produced to a price. For anyone willing and able to make suitable modifications, these are excellent propositions to get a reasonable aperture.

When I purchased my 16" Meade 13 yrs ago all I wanted were the mirrors but Meade, at that stage would only sell scopes as a complete unit. Because of that I purchase the scope as a Dob and then designed and built a German Eq mount to put it on.

I then designed and built my own 27 point primary mirror cell and secondary mirror mount and made significant modifications to how the focuser mounted on the tube. It took about 6 mths to sort it out but everyone that has visited my observatory since would vouch for the quality of the images the modified scope produces.

Regards
Trevor

erick (Eric) · #9 13-08-2008, 10:50 PM

Quote:

Originally Posted by tnott

The problem is that when you double the length of components you get 8 times the flexure - and that's without any increase in weight, which is proportional to the cube of the aperture. In other words, if you double the aperture of a scope (without changing the design) you can end up with 8 times the weight combined with 1/8 the rigidity.

Aah! The wonders of scaling. Linear versus area versus volume. Strength proportional to cross section etc. Hence why an elephant looks proportionately so different to a gazelle. And the impossibility that Gulliver and the inhabitants of Lilliput could look the same.

qld · #10 14-08-2008, 10:56 PM

Quote:

Originally Posted by erick

Aah! The wonders of scaling. Linear versus area versus volume. Strength proportional to cross section etc. Hence why an elephant looks proportionately so different to a gazelle. And the impossibility that Gulliver and the inhabitants of Lilliput could look the same.

i concur withall views expressed so far ,however the main question remains unanswered....that is what size spring do you buy to replace the one issued by meade,and where do you buy it

qld

erick (Eric) · #11 14-08-2008, 11:06 PM

I don't know since my 8" springs were satisfactory and the previous owner had already done the "Bob's knobs" spring change on the 12" I bought from him.

But I do know that Bunnings stores here have a large selection of springs of two types - compression and expansion. It's the compression springs you want. They come in all weights and sizes, so you probably want to carefully pull out one of the collimation bolts and its spring and carry them with you when you go searching. Now it may be that a spring of the right weight and diameter is too long - so that might mean taking the hacksaw to it. I suspect that will require a little thinking since they are finished, as manufactured, with two flat ends perpendicular to the spring axis. The hacksawed end may need some grinding work to return it to a fairly flat end?

However, one suggestion is to see whether the existing springs will do. It could be that the mirror has been set some considerable (in mm!) travel up the tube unit and all three screws can be adjusted to pull the mirror back closer to the end of the scope, hence compressing the springs further to the stage where they work more effectively? Again, this is all theory - I'm sure some folks who have got their hands "dirty" on this end of the scope can advise.

marki · #12 14-08-2008, 11:34 PM

Another option might be to put a smaller diameter spring inside the standard one to increase the pre-load against the mirror cell. This is often a good way to keep a constant pressure over a longer distance when a single spring has the tendency to collapse at some point in its travel. To much pre-load would make it a pain to collimate though and it would just be a case of trial and error.

Mark

Quark (Trevor) · #13 15-08-2008, 09:05 PM

Quote:

Originally Posted by qld

i concur withall views expressed so far ,however the main question remains unanswered....that is what size spring do you buy to replace the one issued by meade,and where do you buy it

qld

Looking at the springs that are supplied in the 16" scopes I have see I would suggest, as a starting point, springs with diameters about half as much again and of a heavier gauge. I would suggest taking an original spring along with you when looking for replacements. Think about how much further up the tube your primary mirror can move before causing problems with the available movement of the focuser.

It is a good idea, as a starting point to measure the movement required of the focuser to bring all of your eyepieces to focus, so that you have some idea about how much longer the springs can be. Measure the fully compressed length of the original springs.

Knowing the fully compressed length of the original springs and the amount of travel of the focuser required for your range of eyepieces provides the info you need to fit heavier springs

Stores such as Repco generally carry compression and extension spring kits, these kits have a range of springs in them. When you take out one of the original springs I am sure you would be amazed at just how easily compressed they are. You should be looking for something larger in diameter that is harder to compress.

Because of the vastly different grades and quality of steel used in springs it is very hard to specify a specific diameter or gauge. I suggest that such springs are better sourced from a reputable engineering supplier rather than a hardware store. It is better to pay more for higher quality springs that will do the job for the life of the scope.

If the only springs that you can source are too long then have then cut to size. Personally I do this with my bench grinder but I am a fitter & machinist by trade. It can be very dangerous to cut springs with a grinder and if your not confident it is best left to someone with the right gear and personal safety equipment.

The end that is cut can be quite successfully cleaned up with a grinder, again this can be a dangerous job especially if you don't have appropriate safety equipment.

Using two springs is not a good idea, better to use one spring that is up to the job. With two springs, the inner spring can jam between the coils of the outer spring resulting in a total loss of adjustment.

Hope this helps regarding the selection of appropriate springs.

Regards
Trevor

kinetic (Steve) · #14 15-08-2008, 09:38 PM

Trev,

I think you are missing the point re: spring pressure on a mirror cell.
Sure the GSOs etc have got it wrong with the springs.
But all that is needed is a spring that holds the mirror firm at the setting
of the collimation adjustment. A very firm spring.
Any typical four stroke valve spring does the job.

Zero movement due to mirror weight.
I don't know what eyepiece and focuser have to do with any of that?
Surely that is an issue of what you intend the telescope to do...planetary
(barlows, EP) or deep sky ( focal reducers etc) , each requiring a
completely different focuser range.

regards,
Steve B.

Quark (Trevor) · #15 15-08-2008, 10:27 PM

Quote:

Originally Posted by kinetic

Trev,

I think you are missing the point re: spring pressure on a mirror cell.
Sure the GSOs etc have got it wrong with the springs.
But all that is needed is a spring that holds the mirror firm at the setting
of the collimation adjustment. A very firm spring.
Any typical four stroke valve spring does the job.

Zero movement due to mirror weight.
I don't know what eyepiece and focuser have to do with any of that?
Surely that is an issue of what you intend the telescope to do...planetary
(barlows, EP) or deep sky ( focal reducers etc) , each requiring a
completely different focuser range.

regards,
Steve B.

Hi Steve,

Don't know about you but I have always setup the mirror cells in my telescopes so that the springs are close to being fully compressed.

Well, almost always the three springs will require different amounts of compression, so I try to have the spring under the most compression close to being fully compressed. I have had success with this methodology over the years. It seems to provide consistency of movement.

If using springs of a heavier gauge than the originals, that still provide a similar amount of overall travel, then such springs will be longer when fully compressed.

That is why you need to know at what point of the focuser's travel, focus is achieved for whatever eyepieces, cameras whatever will be used in said focuser.

If the heavier springs result in the primary moving farther up the tube when collimated, then obviously there will be ramifications relating to the amount of travel that will be required of the focuser, to focus whatever equipment that is normally used in it.

Whether or not the use of heavier springs my require the use of a spacer to move out to the point where focus will now be achieved due to the use of heavier gauge, hence intrinsically longer springs.

There is no point whatsoever in ending up with a truly bonza mirror cell that maintains collimation perfectly if none of your equipment can be brought to focus, due to the point of focus moving outside the range of travel of the focuser.

Hope that clears up my point.

Regards
Trevor

kinetic (Steve) · #16 15-08-2008, 10:39 PM

Quote:

Originally Posted by Quark

Hi Steve,

Don't know about you but I have always setup the mirror cells in my telescopes so that the springs are close to being fully compressed.

Well, almost always the three springs will require different amounts of compression, so I try to have the spring under the most compression close to being fully compressed. I have had success with this methodology over the years. It seems to provide consistency of movement.

If using springs of a heavier gauge than the originals, that still provide a similar amount of overall travel, then such springs will be longer when fully compressed.

That is why you need to know at what point of the focuser's travel, focus is achieved for whatever eyepieces, cameras whatever will be used in said focuser.

If the heavier springs result in the primary moving farther up the tube when collimated, then obviously there will be ramifications relating to the amount of travel that will be required of the focuser, to focus whatever equipment that is normally used in it.

Whether or not the use of heavier springs my require the use of a spacer to move out to the point where focus will now be achieved due to the use of heavier gauge, hence intrinsically longer springs.

There is no point whatsoever in ending up with a truly bonza mirror cell that maintains collimation perfectly if none of your equipment can be brought to focus, due to the point of focus moving outside the range of travel of the focuser.

Hope that clears up my point.

Regards
Trevor

Errr not really...
Did you read my post Trev?

regards,
Steve B.

Quark (Trevor) · #17 15-08-2008, 11:07 PM

Quote:

Originally Posted by kinetic

Errr not really...
Did you read my post Trev?

regards,
Steve B.

Yes Steve I did read your post.

Obviously, from your reply, I have missed the thrust of the point you are trying to make and equally you have not understood what I am on about.

My advice is based on the trials and tribulations I experienced when designing the mirror cell for my 16 and on the modifications made to the scopes in my astronomy group.

Not sure I can add any more.

Is your new GSO a dob or have you put it on a eq mount and do you still have the 8" Newt

Regards
Trevor

kinetic (Steve) · #18 15-08-2008, 11:26 PM

I'm not sure I can add any more either....

regards,
Steve B

Jeff · #19 16-08-2008, 12:13 AM

I agree with Trevor's approach below...

Quote:

I try to have the spring under the most compression close to being fully compressed. I have had success with this methodology over the years. It seems to provide consistency of movement.

From a quick Google search & check on Bob's Knobs site, primary springs on the LB16 should be fine.

When collimating my newts (10" ligtbridge, 8" skywatcher) I start with fully compressed springs, then adjust from there. This gives maximum stability, since the rebound force of each spring would be directly proportional to its compression.

This might be obvious, but I thought I would mention anyway ... to be sure.

Is the scope loosing collimation in normal use?
Are you sure that the LB16 primary mirror is moving (as opposed to the truss points)?

Cheers,
Jeff

bananarama (Deb) · #20 16-08-2008, 03:26 PM

Hi qld

Mayo Hardware are the Australian distributors of Century Springs. Go to their website which has a list of all springs and their specs. They will also be able to direct you to your nearest supplier. Hope this helps.

http://www.mayohardware.com.au/produ...ges.htm#ranges

Regards
Deb