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Thread size on focuser?

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#1 tnranger

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Posted 06 February 2013 - 03:17 PM

I have an Orion XT10i with the stock single speed Crayford focuser. I would like to replace the stock metal thumbscrew on the 1.25" barrel with a nylon one to keep from marring my eyepieces. I took the thumbscrew to the big orange box store to match the threads, and it is smaller than the smallest threads on the thread checking board. (Say that 3 times fast)

Anybody know what the threads are, or where I could get a nylon replacement thumbscrew?

#2 p1taylor

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Posted 07 February 2013 - 05:14 AM

Hi Just measured my one it is a standard 4mm, OD 3.9mm x 0.7mm Pitch, hope this helps.

peter

#3 tnranger

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Posted 07 February 2013 - 06:35 AM

Thanks Peter. That helps a lot.

Other metric threads I have seen are classified M4, M6, etc. Does this mean these threads are M3.9?

#4 ausastronomer

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Posted 07 February 2013 - 07:09 AM

No its a standard M4 thread, which is 4.00mm x .7mm pitch.

Cheers

#5 tnranger

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Posted 07 February 2013 - 07:37 AM

Not to disagree, but it is smaller than the M4 thread tester at the hardware store. It actually fit inside without threading it. I wonder if Peter has the same thumbscrew as I do.

#6 tnranger

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Posted 08 February 2013 - 05:44 PM

Does anybody else have any ideas?

#7 don clement

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Posted 08 February 2013 - 07:13 PM

Does anybody else have any ideas?


If the screw size is indeed about M3 (OD 0.118”) then one could run a 4-40 or 6-32 tap thru and use available 4-40 or 6-32 nylon thumbscrews available from McMaster-Carr. http://www.mcmaster....-screws/=le83wj

Don Clement

#8 StarStuff1

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Posted 10 February 2013 - 04:02 AM

I would recommend as large a nylon thumb screw as possible for the material being worked with, the 1 1/4-in focuser.In my experience 6-32 would be better than 4-40, 10-32 even better yet.

Also, larger thumbscrews are easier to find in the grass in the dark. :lol:

#9 don clement

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Posted 10 February 2013 - 04:25 AM

I would recommend as large a nylon thumb screw as possible for the material being worked with, the 1 1/4-in focuser.In my experience 6-32 would be better than 4-40, 10-32 even better yet.


I agree. I use a McMaster-Carr P/N 90291A826 10-32 x 3/16 length nylon tipped SS set screw in 2" to 1-1/4" adapter rings. Each of my 1-1/4" eyepieces has it's own adapter ring. This way I can parafocalize all my 1-1/4" eyepieces with a 2" focuser. Shear-Loc http://www.shear-loc.com/ press-on thumbscrew knobs work very well pressed onto nylon SHCSs. BTW I also dye white nylon SHCS with black Rit dye with excellent results.

Don Clement

IIR nite eyes (?) used to sell glow in the dark Shear-Loc type press-on thumb screw knobs.

#10 don clement

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Posted 10 February 2013 - 04:30 AM

Also, larger thumbscrews are easier to find in the grass in the dark. :lol:


Would that be around 4:20 AM?

#11 Gene7

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Posted 10 February 2013 - 09:48 AM

Please, please get a digital caliper. Thread sizes are on line. NO,you do not want nylon, too soft. Get brass, just right. What a problem...

#12 psi_chemie

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Posted 10 February 2013 - 09:59 AM

I have 97 M4x.7 40mm long (you cut to length) nylon hex heads. If anyone wants a few I can stick some in an envelope and send it ur way. PM me

#13 StarStuff1

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Posted 10 February 2013 - 04:37 PM

NO,you do not want nylon, too soft. Get brass, just right. What a problem...


Sorry, I have to differ. Sure brass is harder but is more likely to mar the barrel of an eyepiece. Nylon is still very tough and in a 1 1/4-in focuser should be fine... no multi-lb Ethos or Naglers being used. With about 25 years of use with nylon thumbscrews only one has deformed and one broke. Both were due to a drop on a concrete basement floor. This would also have happened with brass or aluminum thumbscrews. On a 2-inch focuser I would recommend two nylon thumbscrews. Again, the largest size appropriate for the job.

Here are two mounts with shopmade Vixen style dovetails. The smaller mount has two 1/4x20 thumbscrews that have held OTAs up to 5 lbs for 15 years. The other mount has three nylon 1/4x20s that has held scopes up to 20 lbs for almost 8 years. No problem with any OTA slipping. It is like the nylon threads will compress slightly, keeping the dovetail bar secure and without marring the bar.

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#14 don clement

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Posted 10 February 2013 - 10:58 PM

Please, please get a digital caliper. Thread sizes are on line. NO,you do not want nylon, too soft. Get brass, just right. What a problem...


In my experience and IMO Nylon works just great.
BTW a digital caliper has no greater accuracy than a dial caliper or vernier caliper.

Don Clement

#15 TxStars

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Posted 10 February 2013 - 11:23 PM

Digital would be easier to read for people who have not used one before.

#16 p1taylor

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Posted 11 February 2013 - 05:52 AM

All 3 types of callipers are easy to use, to get back to original post after a good look round, moonlight focusers are M4, others are M3 and M2.5, nylon not really strong info, Bras or SS Steel.

peter

#17 don clement

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Posted 11 February 2013 - 12:00 PM

Why use a thumbscrew at all? Cut four slots in the tube about 3/8" down the drawtube (two slots across the diameter at right angles using a hacksaw). Use a hoseclamp around slotted drawtube to clamp 1-1/4" eyepieces like a collet. Better yet get a bike seat lever clamp to quickly clamp the eyepiece.
http://tinyurl.com/a86jvqn

Don Clement






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