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Equipment Discussions >> Equipment

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ChrisMax
member


Reged: 12/28/13

Crayford Focuser Cracked
      #6449228 - 04/05/14 03:48 PM Attachment (48 downloads)

I just discovered a crack in the Crayford Dual Speed Focuser on my Orion Astrograph 8 f/4. As you can see it's in the plastic cover. I'm wondering if it should be replaced. Any opinions?

Thanks


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Kim K
member
*****

Reged: 08/31/10

Loc: Eastern NM
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6449404 - 04/05/14 05:23 PM

Assuming the plastic cannot be glued and that Orion will not sell a replacement then I would make a plate out of 1/16" aluminum that covers the bolt holes. Get longer bolts from your hardware store. I would not glue the plastic since the crack is separating which indicates stress.

Hope this helps...


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obin robinson
Carpal Tunnel
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Reged: 10/25/12

Loc: League City, TX
Re: Crayford Focuser Cracked new [Re: Kim K]
      #6449576 - 04/05/14 06:59 PM

Quote:

I would make a plate out of 1/16" aluminum that covers the bolt holes.




Ditto. I would get some aluminum and use the plastic part as a template for the shape and the hole placement. You don't need super thick aluminum. Even 1/8" thick would be much stronger than the plastic.

obin


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ChrisMax
member


Reged: 12/28/13

Re: Crayford Focuser Cracked new [Re: obin robinson]
      #6449687 - 04/05/14 08:19 PM

Thanks for the helpful suggestions! I'm wondering though if the plastic is just a cover.

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Geo.
Carpal Tunnel
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Reged: 10/01/08

Loc: Upstate NY
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6450624 - 04/06/14 11:06 AM

No, the part is bearing the thrust of the set screw and not very well. It was either a bad molding or bad design. I laugh every time I read of plastic as an engineering material.

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ChrisMax
member


Reged: 12/28/13

Re: Crayford Focuser Cracked new [Re: Geo.]
      #6450757 - 04/06/14 12:41 PM Attachment (28 downloads)

I've taken the focuser apart and this is the part I need. Anyone know where to buy one?

Thanks George yeah now that I see the part it is indeed a really bad design. Maybe I should just upgrade to a moonlite focuser and be done.

Edited by ChrisMax (04/06/14 12:42 PM)


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gdd
Pooh-Bah


Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6450813 - 04/06/14 01:15 PM

Quote:

Thanks for the helpful suggestions! I'm wondering though if the plastic is just a cover.





My brand new AT8IN does not have a plastic cover over that part, I think it is probably not needed. It does not look like it would even keep dust out.

Gale


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hottr6
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Reged: 06/28/09

Loc: 7,500', Magdalena Mtns, NM
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6450822 - 04/06/14 01:19 PM

I *think* that focuser is made by Kunming Optical. Try calling Lunt as they are distributing a lot of Kunming products and parts.

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ChrisMax
member


Reged: 12/28/13

Re: Crayford Focuser Cracked new [Re: hottr6]
      #6450982 - 04/06/14 02:41 PM

Hi Gale

Unfortunately George is right about the plastic cover. It does bear the thrust of the set screw which is why it cracked. I will post a photo of the repair when it is done.

Thanks Shane I'll check it out.


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SteveG
Post Laureate
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Reged: 09/27/06

Loc: Seattle, WA
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6451111 - 04/06/14 03:59 PM

Have you called Orion? They've sent me replacement parts on many occasions.

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tedbnh
scholastic sledgehammer


Reged: 11/14/07

Loc: New Hampshire
Re: Crayford Focuser Cracked new [Re: SteveG]
      #6451486 - 04/06/14 07:21 PM

With nothing to lose, I'd try clamping it tight, milling out a hole the size of a double-hole washer (the kind for hanging pictures) that looks like a figure-8. Then drop in the washer with some JB-weld and let it dry. The washer will take up the stress.

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ChrisMax
member


Reged: 12/28/13

Re: Crayford Focuser Cracked new [Re: tedbnh]
      #6451557 - 04/06/14 07:59 PM

Hi Ted

It's pretty thin plastic to mill out. Orion must be saving a lot of money using such thin plastic in such an important part of the focuser.


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gdd
Pooh-Bah


Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6451830 - 04/06/14 11:07 PM

Are you sure that plastic was supporting anything? Maybe the holes were not aligned correctly causing the pinion to cut into the plastic. What held the plastic in place? On my AT8IN focuser that that part looks like yours with the plastic removed. The pinion with the knob just sticks out with nothing supporting it.

Is that second picture of a plastic part, or a metal part with the plastic cover removed?

Gale

Edited by gdd (04/06/14 11:12 PM)


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ChrisMax
member


Reged: 12/28/13

Re: Crayford Focuser Cracked new [Re: gdd]
      #6452128 - 04/07/14 05:52 AM

Hi Gale

The part is a piece of molded plastic and the tension screw nut is embedded in it. When the screw is tightened the plastic bears the tension. Over tighten the screw and the plastic cracks which is not really all that hard to do as the plastic is thin. It should have been made of metal. If you look at the focuser on the latest Orion Astrograph it has been redesigned and has eight screws in this part not four as shown in my photo. So they must have had many of these focusers fail in the same way.


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gene 4181
Pooh-Bah


Reged: 11/12/13

Loc: n.e. ohio
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6452655 - 04/07/14 12:18 PM

Quote:

I've taken the focuser apart and this is the part I need. Anyone know where to buy one?

Thanks George yeah now that I see the part it is indeed a really bad design. Maybe I should just upgrade to a moonlite focuser and be done.


+ 1 on that thought

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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6452884 - 04/07/14 02:14 PM

Quote:

I've taken the focuser apart and this is the part I need. Anyone know where to buy one?

Thanks George yeah now that I see the part it is indeed a really bad design. Maybe I should just upgrade to a moonlite focuser and be done.




Is it really plastic? I would think that particular part would be aluminum. I can only see a tiny glimpse of the bore but it appears to be aluminum.

Jon

Edited by Jon Isaacs (04/07/14 02:15 PM)


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hottr6
Carpal Tunnel
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Reged: 06/28/09

Loc: 7,500', Magdalena Mtns, NM
Re: Crayford Focuser Cracked new [Re: Jon Isaacs]
      #6453016 - 04/07/14 03:25 PM

Quote:


Is it really plastic? I would think that particular part would be aluminum. I can only see a tiny glimpse of the bore but it appears to be aluminum.



If it were aluminium, there would be no need for the threaded insert.


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ChrisMax
member


Reged: 12/28/13

Re: Crayford Focuser Cracked new [Re: hottr6]
      #6453054 - 04/07/14 03:40 PM

Hi Jon

Yes it is really plastic and thin. I'm almost finished with the repair I've done and will post a picture. Hope it works!


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ChrisMax
member


Reged: 12/28/13

Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6453097 - 04/07/14 04:04 PM Attachment (9 downloads)

I've taken the suggestions above but used 26 gauge (0.016) sheet metal. It seems to be working fine in fact feels stronger. Well at least it may save me $200+ on a new focuser!

Edited by ChrisMax (04/07/14 04:06 PM)


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T1R2
Carpal Tunnel


Reged: 06/11/13

Loc: NeverWhere, 35*N
Re: Crayford Focuser Cracked new [Re: ChrisMax]
      #6453122 - 04/07/14 04:14 PM

my aluminum lens cell has threaded inserts

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