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Unusual counterweight shaft thread problem

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#1 eklf

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Posted 08 April 2013 - 08:52 AM

Greetings,

I have a vixen custom D alt-az mount which, unfortunately, is missing the counterweight shaft. I was using the mount with a short tube 80mm and it worked fine without the shaft. I have now upgraded the OTA to a 127mm F6.5 refractor..and cant use the mount anymore.

I have looked and adverstised for a counterweight shaft for it but was unsuccesful.

I think I can easily fashion a workable counterweight shaft with a long 1/2 inch bolt and barbell weights etc. But the problem is the threading. The bore threading is m12x1.25. The longest M12X1.25 bolt I could find at my local hardware stores was 75mm, which is not long enough. I thought of using it and fashining a wood adapter that could accept larger/longer bolts, but the presence of knobs etc demands that the M12 bolt be atleast 8 inches.

One meter long threaded bolts are available online but costs $88 ..a little too much for my pocket book.

Is it possible to buy adapters that would convert m12x1.25 threads to standard 1/2 threads (I can buy 1/2 bolts of 8 inches easily)?

Has anybody faced a similar situation?

Many thanks in advance for your thoughts.

Kumar

#2 Sean Cunneen

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Posted 08 April 2013 - 09:51 AM

You can retap the threads.

#3 stmguy

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Posted 08 April 2013 - 10:29 AM

Or cut off the metric bolt and weld on an extension shaft
Norm

#4 nitegeezer

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Posted 08 April 2013 - 10:41 AM

If you do not want to retap the threads but are willing to do a little custom work I went looking for hardware. I am including a couple of links, you would need to go to the hardware store and get a bolt and coupler . Now cut the hex end off the bolt, and drill half the thread of the coupler out to be 12mm. This will not remove all the thread in the coupler but should allow it to slide onto the cut end of the 12mm bolt. Use some good metal epoxy and glue these two together. I think this would be fine to now use a standard half inch bolt for your shaft, but if you want to play it safe you could drill a small hole through the side of the coupler and 12mm bolt and insert and glue a keeper pin so there is no way it would come apart.

Good Luck

#5 John Carruthers

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Posted 08 April 2013 - 11:12 AM

you can buy lengths of 'studding' (threaded rod) in metre lengths. M12 studding can be found in 1m and 2m, galvanised or stainless.
http://www.amazon.co...m/dp/B0082HDLWM

or

http://www.ebay.co.u...TUDDING-200m...

#6 nitegeezer

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Posted 08 April 2013 - 01:54 PM

After having trouble of my own I have found that the availability of metric hardware here is the USA is a bit limited. I went out looking at local sources for 12mm threaded rod and I was able to find it but it was the wrong thread pitch 1.75 rather than the posted need of 1.25.

#7 m. allan noah

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Posted 08 April 2013 - 06:28 PM

You want a M12x1.25 thread on the end of a 1/2 inch shaft? Make some friends in your local astro club, someone has a lathe. If not, I can do it for you, for the cost of materials and shipping.

allan

#8 mconnelley

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Posted 10 April 2013 - 03:14 AM

Hello:

Why not get a length of aluminum rod stock, find someone with a metric die set, and cut threads into the metal rod? I'm assuming that the M12 metric thread is a standard thread. I have a Takahashi mount that uses a 1/2"-12 bolt. Yup. Not metric. Not 1/2"-13 (which is the standard thread for 1/2" screws). I made by first custom bolt on a lathe that day.

Cheers
Mike

#9 terraclarke

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Posted 11 April 2013 - 01:34 PM

Here you go. 1/2 inch diameter round stainless steel bar stock should do it. You should be able to find a metric die at Harbor Freight.

http://www.metalsdep...html?page=round

I had a Custom D years ago and sold it. I hated the way that the simulated stacked counterweights (really just one) were fixed to the bar, with just one smaller adjustable weight at the end. I considered replacing the bar and putting on adjustable weights myself but wound up seling the mount instead. It was fine with my 4 inch Vixen Fluorite but my Vixen 102NA was too much for it. Wound up selling both of those scopes too.

#10 Geo.

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Posted 11 April 2013 - 01:44 PM

Stainless is pretty hard to work with hand dies. If you want to try it I'd get something of better quality than HF.

By the time you tool up may as well slip a $20 to those auto geeks.

#11 Jon Isaacs

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Posted 11 April 2013 - 02:07 PM

Mcmaster-Carr has 12mm x 1.25 inch pitch threaded rod, 300mm for about $20...

Metric Threaded Rod

12mm x 1.25 x 300mm threaded rod

They also have a 1 meter length for about $25. They probably more choices, this is the first one I found.

Jon

#12 bremms

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Posted 11 April 2013 - 02:49 PM

He's right Terra, 304 SS would tear up a HF die. you do need a good one and go SSSLLLOW with lots of lube. When 304 work hardens. Well, think diamonds. I've worked a lot of 304 ss.

#13 Tom and Beth

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Posted 11 April 2013 - 03:31 PM

OK, let's say you have a little bit of cash, you don't know any machinists and you don't feel like being socialble (I doubt these are all true so just play along)

I would find a piece of material from this guy, ask him for a quote to cut some threads, let's say one inch long, on one end of a 15 inch piece of Stainless and drill a hole in the other end you can thread a safety bolt in.

I didn't have him make me a counterweight but he DID respond a few times. My favorite source for RAW material.

BTW, note these are called "Drops" the ends may not be square and you might have to add a bit of elbow grease, deburr...

Ebay Dude

#14 m. allan noah

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Posted 12 April 2013 - 07:29 AM

You will have trouble forcing a 12mm die over 1/2 inch stock. But, here's a question- do you have any counterweights? If not, you might consider something other than 1/2 inch material.

Look for 12mm TGP shafting, maybe 1144 SP so the die will cut easily. You really don't need stainless as much with polished shafts, they don't rust as easily.

allan

#15 Jon Isaacs

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Posted 12 April 2013 - 07:34 AM

You will have trouble forcing a 12mm die over 1/2 inch stock. But, here's a question- do you have any counterweights? If not, you might consider something other than 1/2 inch material.

Look for 12mm TGP shafting, maybe 1144 SP so the die will cut easily. You really don't need stainless as much with polished shafts, they don't rust as easily.

allan


I guess I just don't understand the problem here. McMaster-Carr has the correct 12mm x 1.25 pitch threaded rod at an affordable price in lengths up to 1 meter. Vixen mounts like the Polaris, use threaded rod rather than a partially threaded shaft.

What is wrong with just using threaded rod and a few nuts?

Jon

#16 terraclarke

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Posted 12 April 2013 - 08:59 AM

Sorry, never had to buy any taps and dies myself. I know about Harbor Freight because my step son just bought a set of taps and dies from them for working on his motorcycles. My machinist friend has a fully stocked shop with everything for cutting and threading brass and aluminum all the way up to tool steel. He's totally spoiled me. He just looks at the material we will be working on with the lathe or mill, goes to a drawer and pulls out the right tool. The other day I said I needed an M3 metric tap for aluminum and he sent me home a pocket full of all sizes up to nearly a cm. :)

#17 terraclarke

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Posted 12 April 2013 - 09:06 AM

The counterweight bar on my Vixen Custom-D was a totally different animal from my Vixen GP. As far as I remember, the two were not interchangeable. It's been nearly 10 years ago that I had them both at the same time, but it seems I remember trying that and it didn't work.

Here is the Custom-D:

http://www.cloudynig...php?item_id=610

Those weights are really one solid weight that looks segmented and are threaded at the top into the bar, they don't move. The bottom of the counterweight that you see is actually drilled and tapped for an additional shorter bar (not shown), and that bar has a sliding counterweight on it. Depending on the load, it can be adjusted or not used at all.

It was a really neat mount with the exception of its counterweight system. I never liked it and wished that it had the same bar and weight as the GP. In retrospect I width I would have kept my Custom-D mount. They are hard to find. It was very steady yet quite portable. One thing I whisked it had at the time was a handle. The slow motions were nice but that was also a problem as I remember because it seems it only allowed around 120 degrees of movement without readjustment, not a full 360.

#18 Jon Isaacs

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Posted 12 April 2013 - 10:01 AM

The counterweight bar on my Vixen Custom-D was a totally different animal from my Vixen GP.



I understand that.

Reading the original post, it seems that:

"I thought of using it and fashining a wood adapter that could accept larger/longer bolts, but the presence of knobs etc demands that the M12 bolt be atleast 8 inches."

It seems to me the availability of affordable M12 x 1.25 threaded rod in lengths up to 1 meter, ($25 + Shipping) should resolve this issue and in fact, a single threaded rod might well resolve the issue.

If I am not mistaken, the Polaris mount uses a single threaded rod for it's counterweight shaft though I believe it is probably a 16mm course thread.

Jon

#19 eklf

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Posted 20 May 2013 - 08:34 PM

Hello All,

Thank you all so very much for all your very helpful comments. I am sorry I am only now getting a change to post here (Life has been particulary busy lately). I very much appreciate your time and help. I will post an update as soon as I have had a chance to improve the mount.






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