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MessiToM
scholastic sledgehammer
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Reged: 12/21/09

Loc: Huntingdon PA
car valve springs in cell : )
      #5466034 - 10/11/12 09:35 PM

Can you have to stiff a spring on your collimation bolts? I ask because Iam using valve springs from a leftover engine head's valvetrain in my project. I thought it was a neat idea.

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Happy-Idiot
Stuck with it
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Reged: 04/06/06

Loc: 3rd Rock
Re: car valve springs in cell : ) new [Re: MessiToM]
      #5466038 - 10/11/12 09:41 PM

Would tightening the bolts be considered a valve lash adjustment or collimation? Let us know how it works, good idea.

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MessiToM
scholastic sledgehammer
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Reged: 12/21/09

Loc: Huntingdon PA
Re: car valve springs in cell : ) new [Re: Happy-Idiot]
      #5466039 - 10/11/12 09:44 PM



Works so far


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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: car valve springs in cell : ) new [Re: MessiToM]
      #5466069 - 10/11/12 10:12 PM

if you want to use springs on your collimation bolt, don't use them on the teeter totters.

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hottr6
Carpal Tunnel
*****

Reged: 06/28/09

Loc: 7,500', Magdalena Mtns, NM
Re: car valve springs in cell : ) new [Re: MessiToM]
      #5466120 - 10/11/12 11:02 PM

Quote:

Can you have to stiff a spring on your collimation bolts? I ask because Iam using valve springs from a leftover engine head's valvetrain in my project. I thought it was a neat idea.



My gut tells me it waaaaay overkill. Valve springs have rates measured in hundreds of lbs; Mirror cells need only rates measured in 10s of lbs.

You'll need really strong fingers to collimate.... made even tougher with cold fingers at night.


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MessiToM
scholastic sledgehammer
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Reged: 12/21/09

Loc: Huntingdon PA
Re: car valve springs in cell : ) new [Re: hottr6]
      #5466135 - 10/11/12 11:10 PM

O overkill for sure! I just wanted to tie in my other hoby (building engines) somehow in this scope build and thought it was clever.

Very good point about tuff collimation with cold fingers.


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cheapersleeper
Post Laureate
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Reged: 01/22/10

Loc: Sachse TX
Re: car valve springs in cell : ) new [Re: hottr6]
      #5466162 - 10/11/12 11:36 PM

Quote:

Quote:

Can you have to stiff a spring on your collimation bolts? I ask because Iam using valve springs from a leftover engine head's valvetrain in my project. I thought it was a neat idea.



My gut tells me it waaaaay overkill. Valve springs have rates measured in hundreds of lbs; Mirror cells need only rates measured in 10s of lbs.

You'll need really strong fingers to collimate.... made even tougher with cold fingers at night.




I agree that valve springs may be too much, but I do think that the stiffest springs that allow you to turn the knobs are the best way to go regardless of whether it is cold or not. Much better to have too much than too little tension. As mirrors get bigger and heavier we have to make sure that regardless of the orientation of the optical tube, the springs are strong enough not to compress. If it's hard to turn the collimation bolts, use a bolt with a bigger head.

Regards,
Brad


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ausastronomerModerator
Carpal Tunnel
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Reged: 06/30/03

Loc: Kiama NSW (Australia)
Re: car valve springs in cell : ) new [Re: cheapersleeper]
      #5466222 - 10/12/12 12:52 AM

This will be the only amateur scope, I know of, that you will need a torque wrench or rattle gun to collimate

Cheers


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John Carruthers
Skiprat
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Reged: 02/02/07

Loc: Kent, UK
Re: car valve springs in cell : ) new [Re: MessiToM]
      #5466314 - 10/12/12 04:02 AM

I've used bike valve springs in a cell, and old mower motor springs. The strongest I've used were the inner coils from Cooper S blue double valve springs (70 lb/inch)the red ones (90lb/inch) were just too much.

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JasonBurry
sage


Reged: 04/27/12

Loc: Cape Spencer, NB, Canada
Re: car valve springs in cell : ) new [Re: John Carruthers]
      #5466438 - 10/12/12 07:26 AM

A friend has Fiat valve springs on his 13.5" cell. Works well, but stiff to adjust.

I'd rather have too strong a spring installed than too weak.

J


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: car valve springs in cell : ) new [Re: JasonBurry]
      #5466517 - 10/12/12 08:57 AM

The springs in my 12.5 inch Novak cell are quite stiff and there is a pair each bolt. I suspect they are similar in stiffness to a valve spring. The main thing is that cell needs to be able to handle the springs..

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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: car valve springs in cell : ) new [Re: MessiToM]
      #5466561 - 10/12/12 09:34 AM

with the spring under the teeter totter/collimation bolt, you will always have collimation issues as you rotate thru the alt axis, from zenith to horizon.

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MessiToM
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Huntingdon PA
Re: car valve springs in cell : ) new [Re: Pinbout]
      #5466732 - 10/12/12 11:40 AM

Well that's unfortunate ^

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Gastrol
Pooh-Bah


Reged: 11/04/11

Loc: los angeles
Re: car valve springs in cell : ) new [Re: ausastronomer]
      #5466966 - 10/12/12 03:44 PM

Quote:

This will be the only amateur scope, I know of, that you will need a torque wrench or rattle gun to collimate

Cheers


...and a feeler gauge...

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jgraham
Postmaster
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Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: car valve springs in cell : ) new [Re: Gastrol]
      #5467061 - 10/12/12 04:43 PM

I think that I'd go with a push-pull system before using springs with this much force. But, to each their own...

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Ed Holland
Carpal Tunnel


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: car valve springs in cell : ) new [Re: jgraham]
      #5467184 - 10/12/12 05:58 PM

Surely, springs from a Nova would be most appropriate...



Edited by Ed Holland (10/12/12 06:00 PM)


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Binojunky
Carpal Tunnel
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Reged: 12/25/10

Re: car valve springs in cell : ) new [Re: Ed Holland]
      #5467227 - 10/12/12 06:28 PM

Not wishing to kill a scope builders jest for the hobby but just once in a while things get a bit silly, car valve springs of all things, not needed and a crazy way to go,JMPOV,DA.

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MessiToM
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Huntingdon PA
Re: car valve springs in cell : ) new [Re: Binojunky]
      #5467255 - 10/12/12 06:54 PM

What's it gona hurt? Other than my thumbs possibly ^

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MessiToM
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Huntingdon PA
Re: car valve springs in cell : ) new [Re: Ed Holland]
      #5467306 - 10/12/12 07:26 PM

Quote:

Surely, springs from a Nova would be most appropriate...






Nope, just mopar springs here lol


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kfrederick
Carpal Tunnel
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Reged: 02/01/08

Re: car valve springs in cell : ) new [Re: MessiToM]
      #5467310 - 10/12/12 07:31 PM

I used valve springs on my 20 newt. I built it in 1992. A 3/8 bolt compress them easy. It holds alignment very good the mirror weighs 50 lbs .A weaker spring I think would not be as good .I put them on a plate not on the cross bars of the cell.

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TxStars
Pooh-Bah
*****

Reged: 10/01/05

Loc: Lost In Space
Re: car valve springs in cell : ) new [Re: MessiToM]
      #5468755 - 10/13/12 06:45 PM

I see no problem with some grade 8 bolts & all metal parts to prevent wear.

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Jeff Porter
super member
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Reged: 09/03/10

Loc: Utah
Re: car valve springs in cell : ) new [Re: TxStars]
      #5469472 - 10/14/12 09:41 AM

I like it. You could then add an old Mercedes hood ornament as a finder.

-Jeff p


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MessiToM
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Huntingdon PA
Re: car valve springs in cell : ) new [Re: Jeff Porter]
      #5469804 - 10/14/12 01:25 PM

lol

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bremms
Carpal Tunnel
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Reged: 08/31/12

Loc: SC
Re: car valve springs in cell : ) new [Re: kfrederick]
      #5469850 - 10/14/12 01:52 PM

I still have some inner valve springs from a Fiat X1/9 they would work well with a fine thread bolt. It wouldn't take that much to compress them if you oil the threads and use a nice knob.

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careysub
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: car valve springs in cell : ) new [Re: JasonBurry]
      #5470425 - 10/14/12 07:58 PM

Quote:

A friend has Fiat valve springs on his 13.5" cell. Works well, but stiff to adjust.

I'd rather have too strong a spring installed than too weak.

J




Hmm... how strong does a spring to be so that is not too weak?

Lets say a mirror+cell weighs 30 lb and is supported by 3 springs. Pointed at the zenith, 10 lb of weight compresses each spring, then we want the collimation bolts to pull the spring down further, to create enough force to hold it securely against the bolt. I'm guessing that another 10 lb of force, the equivalent of 1 G holding it against the bolt would be more than adequate. If you treat that as the top of your collimation adjustment range, you will want to pull it down further, a quarter-inch maybe (and have a total 1/2 inch adjustment range)?

So a spring that has 1/2 inch of travel left with a 20 lb load would be about right, wouldn't it? Say a rate of 20 lb/inch and 1.5 inches of working length, or a 40 lb/in rate and a 1 inch working length.

Why would a spring need to be stiffer than that (adjusting for the mirror weight)?


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bremms
Carpal Tunnel
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Reged: 08/31/12

Loc: SC
Re: car valve springs in cell : ) new [Re: careysub]
      #5470444 - 10/14/12 08:08 PM

The cell shifting is the problem. I use push pull screws on the periphery for my cells. I would want at least 10 times the preload on the springs compared to the weight on the spring. springs are just not a positive way to locate a mirror. I have one PP cell that has locating goves for the push of the push pull screw. The unit came from an industrial laser.

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careysub
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: car valve springs in cell : ) new [Re: bremms]
      #5471168 - 10/15/12 09:50 AM

Quote:

The cell shifting is the problem. I use push pull screws on the periphery for my cells. I would want at least 10 times the preload on the springs compared to the weight on the spring. springs are just not a positive way to locate a mirror. I have one PP cell that has locating goves for the push of the push pull screw. The unit came from an industrial laser.




That explains some of the comments I have seen over time that has puzzled me about collimation springs. That is - some cell designs are using the springs to hold the cell in position by gross pressure when the scope is tilted, in addition to their role in holding the cell against the collimation bolt stop.

If the cell is kept in position by having it "travel" vertically in the mirror box by some sort of guide rail, then the demand put on the spring is reduced to simply holding the mirror cell against the collimation bolt stop.

For example a spring mounted on a guide rod with the cell sliding up and down on this for collimation through a sleeve bearing, or simply a hole drilled in the cell, with the collimation bolt a separate component (a linear bearing would be over-engineering I think).

Other possibilities are slots cut in the cell which ride on a flat rails created by aluminum angle pieces, or a "Dobsonian bearing" approach where there are teflon bearing surfaces on the inside front and back of the mirror box with the cell having sledge extensions that slide on these perhaps similar to a simple vertical drawer slide.

These all fit under the umbrella of "kinematic design" (which mechanical engineer Benach on this forum turned me on to), where the position of the mechanism is completely deterministic. That is, the degrees of freedom are locked down, so that it can be in only one state at any one time, and is also not over- constrained creating an "elastic design" that warps in unpredictable ways. Although jiggling the mirror box can make the cell bounce against the collimation stop it would immediately settle into exactly the same position without affecting collimation or allowing the mirror to shift (it would take pretty severe jiggling to overcome a one-gee-plus load against the stop though - you wouldn't see this at all during an observing session).

Poster "Pinbout" on this thread commented about the problems of trying to combine multiple roles with one structural element - the Kriege and Berry design having the teeter bar support also being the collimation bolt, and adding spring loading on top of that. Separating these roles probably makes for more predictably behaving designs, a few more parts perhaps, but in some sense still a "simpler" design.


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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: car valve springs in cell : ) new [Re: careysub]
      #5471250 - 10/15/12 10:42 AM

Quote:

That explains some of the comments I have seen over time that has puzzled me about collimation springs. That is - some cell designs are using the springs to hold the cell in position by gross pressure when the scope is tilted, in addition to their role in holding the cell against the collimation bolt stop.






in my 8in stellafane dob, I have a common cell where I have springs on the bolts. I only have three support pads, not floating.

I have to seriously torque those bolts to compress the springs enough so that I won't get a cell shift. and it does start to inflict pain...

and I test it everytime running the tube thru alt axis from horizon to zenith and the laser collimation will not change.

if I don't compress the &(*$%^ out of the springs I will see the laser collimator light move as I rotate the scope.



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JasonBurry
sage


Reged: 04/27/12

Loc: Cape Spencer, NB, Canada
Re: car valve springs in cell : ) new [Re: Pinbout]
      #5471283 - 10/15/12 10:59 AM

Agreed, Danny. My 8" cell is similar to yours, basically a plate with 3 collimation bolts, and 3 fixed support pads. The springs surround the col. bolts and the spring/bolt tension is all that holds the cell in position. My springs need about 20# of preload before col. stays stable.

J


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