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Home made CW bar for AzGTI - choice of material?


vlaiv
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I already made one out of threaded rod and some washers - but it seems that such approach has enough weight for DSLR and not for more intricate setup involving side by side lens + guider.

Since I can't get 12mm cw bar with M12 thread (I can order EQ1/EQ2 weights and that should fit fine on such rod) - I decided to fabricate one myself.

Question is - what material?

I'll be hand cutting the thread with die and I have choice of two materials : brass and aluminum.

Brass is Ms58 while for Aluminum I can choose between AlCuMgPb D5 Dural and AlMgSi1.

Which one to go for? I'll be using single weight of 1.8Kg and limit length of CW bar to say 35-40cm?

Edited by vlaiv
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  • vlaiv changed the title to Home made CW bar for AzGTI - choice of material?

Maybe @Tomatobro will comment on this, as he has a lot more experience than me of working with these different materials, but I would suggest given the relatively undemanding duty,  whichever is easier to cut the thread,. Do you have to thread it just enough to screw the bar into the mount?

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30 minutes ago, tomato said:

Maybe @Tomatobro will comment on this, as he has a lot more experience than me of working with these different materials, but I would suggest given the relatively undemanding duty,  whichever is easier to cut the thread,. Do you have to thread it just enough to screw the bar into the mount?

Yes, I think that half an inch will be enough - maybe even less.

I don't think it will be too much of a problem to do it by hand

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I would go with the Dural if you can machine it well. Both would be good, but the brass can be susceptible to stress corrosion cracking long term. Dural is benign for the most part in humidity and as strong as low carbon steels. Dural can corrode a little long term because of the copper inside, but easier to combat with a surface aluminium coating if it ever became likely. I dont have any idea how each compares for ease of threading/machining though.

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8 hours ago, Elp said:

Are you looking to add more counterweight with limited room on the bar?

I'm actually thinking of just adding counterweight bar to my setup to replace current - one that is capable of holding a bit more weight - like regular mount weights (those for EQ1/EQ2).

This is the one I have so far:

image.png.aad2c16e3dd2658b2f42a3b78b24bfba.png

It was simple DIY solution enough to balance out DSLR + lens:

image.png.8cf4392a4d8b19afd74a7c4cf0f9740d.png

I now have more complex / bulky setup that I want to use to image:

setup.jpg.62a96c0998be94a4baa5f5312de1798b.jpg

And this small counter weight is simply not heavy enough to balance out the scope. I think I still have piece of threaded M12 rod that I used, and I could make longer CW bar, but that was temporary solution anyway and it's time to move on to "real deal".

I have couple of options. I could purchase Star Adventurer counterweight kit - but that is M8 and I'd need to get M8/M12 adapter - which I would need to order from abroad. With current postage prices - that is just silly. It would cost me like 40e or similar to get that and I'd have to wait some time.

Another option is just to order shaft with M12 thread - but same thing - it would end up costing silly money.

Solution is to purchase 12mm metal rod (either aluminum or brass - that is why I asked which is better) and tap it myself - that way whole thing would cost me like 40 - 45 euro total and I'd have some additional tools for later use (die / die handle - I might even go for a set taps+dies)

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2 hours ago, GalaxyGael said:

I would go with the Dural if you can machine it well.

That was the part of the question :D

I saw a youtube video where guy hand cuts cold rolled steel with larger diameter and coarser thread - 3 inches long. There is a bit of hard work involved - but nothing that can't be done.

My reasoning was that both aluminum and brass would be easier to work with than cold rolled steel. My thread will be much shorter as well - maybe 10-12 turns of the die.

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Starting the die square to the bar is a challenge by hand for larger diameters but for a CW bar its not really critical. I have made bar extensions for EQ5's out of brass with no issues.  I would thread both ends so that a safety nut can be added after the CW is on.

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Just now, Tomatobro said:

I would thread both ends so that a safety nut can be added after the CW is on.

That is actually great idea :D

I was thinking of the best way to do it and I only came up with drilling a hole on opposite end / tapping it and then using screw and washer.

This is much better idea - I can thread both ends and see which one is more square with the shaft - and use that on mount side and put nut on the other.

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6 minutes ago, Tomatobro said:

Starting the die square to the bar is a challenge by hand for larger diameters but for a CW bar its not really critical. I have made bar extensions for EQ5's out of brass with no issues.  I would thread both ends so that a safety nut can be added after the CW is on.

Just a quick question - what would be better then, aluminum or brass?

I have feeling that brass would be better (easier) as far as machining goes. I'm just wandering about mechanical side - will it bend in use (It should not, I mean it is 12mm thick shaft and weight is not going to be substantial).

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13 minutes ago, vlaiv said:

I'm just wandering about mechanical side - will it bend in use (It should not, I mean it is 12mm thick shaft and weight is not going to be substantial).

Young's Modulus ( stress/strain) is a measure of bending strength. In round numbers brass is about 1/2 the strength of mild steel. Dural is about 1/3 the strength of mild steel. I would go with brass which is heavier ( good for a counterweight bar) and the threads should be harder wearing.

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I just used a 12" long M12 Bolt, an iOptron 1.35kg weight and 3D printed insert. Depends of course what weight you needed?

The insert doesn't last too long and would be better out of a more resiliant material but was a cheap solution for me.

Not sure what size bore the weights you are hoping to use are but if you could get a threaded sleeve / connector to suit them you might be able to use your original threaded bar.

IMG_20211119_110829781_opt.jpg

Edited by Len1257
added sleeve bit
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16 minutes ago, Len1257 said:

I just used a 12" long M12 Bolt, an iOptron 1.35kg weight and 3D printed insert. Depends of course what weight you needed?

That was an option too - using DIN 931 type bolt. Problem is with imports again. Shipping and import duties cost much more than such single bolt.

Longest one that I have access here is less than 200mm long (180mm I think). That is not long enough. I would be happy with 300mm version like you have in the image there - but that I need to order from abroad.

 

Edited by vlaiv
typo ...
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My workaround:

M12 threaded bar (all thread) - the longer it is the less counterweight you'd need - I use 30cm,

Get some M12 serrated flanged nuts,

Get some M12 X 50mm flat steel washers,

Get some weightlifting cast iron weights which are cheap (or other material) - try to get the smallest hole diameter type.

The combination of the large diameter washers and flanged nuts clamp the weights securely onto the bar at any position.

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1 minute ago, Elp said:

My workaround:

M12 threaded bar (all thread) - the longer it is the less counterweight you'd need - I use 30cm,

Get some M12 serrated flanged nuts,

Get some M12 X 50mm flat steel washers,

Get some weightlifting cast iron weights which are cheap (or other material) - try to get the smallest hole diameter type.

The combination of the large diameter washers and flanged nuts clamp the weights securely onto the bar at any position.

That is good temporary solution I think.

I do have 1.25Kg weight which I can clamp with washers I already have.

It take some fiddling to get right position - but once done - I can mark bolt position for when I need weight for other stuff.

I just hope weight won't interfere with tripod or anything since it is quite flat and large diameter. Will need to test that.

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new_weight.jpg.7f8fcf022accb8edc062f2f8c4b760cb.jpg

This sort of balances fine :D

I can't really tell as my AzGti is a bit stiff in RA axis but it is much better than without it. I need to open it up and adjust tension on bearing so it moves more freely when clutch is disengaged.

Now just need to go and find actual weight that I'll use (above one has 30mm center bore and is needed for exercise so I need to get another for astronomy purposes - possibly smaller center bore).

 

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I would use brass as a first choice as its heavy and stiff but it would be harder to run the die down. Less likely to mark up from the CW clamp. If the hole in the CW is a good fit on the bar it could end up sticking where the CW clamp screw has marked the bar.

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