304 Grade Stainless Steel for Counterweight Shaft

[SnakeyJ]

I managed to source some 32mm diameter 304 grade SS at a sensible price for another project, but have enough left to make an extended counterweight shaft for my cge pro.

 

Looks great and machines nicely - pretty sure it will do the job and stay shiny in my obs, but just wanted a second opinion.

 

The original is 15.5" X 1.25" including turned down externally threaded end at 1" X 16tpi  but thinking I might add 7-8" and reduce the number of weights (currently 25kg, original Celestron 10kg, 2 X SW 5kg and 2 X 2.5 iron gym weights).

 

(BTW - I'm still looking for some cheap/free 8" SS billet bar - about 10" should suffice and a powered hacksaw/ bandsaw.... )

[fozzybear]

we use 316 at work but would cost a fortune to ship an offcut to you we waste a lot.... but recycle it... anyway, how about a steel billet and then cold glavanise it (spraycan) cheaper?

[SnakeyJ]

Just now, fozzybear said:

we use 316 at work but would cost a fortune to ship an offcut to you we waste a lot.... but recycle it... anyway, how about a steel billet and then cold glavanise it (spraycan) cheaper?

316 is good, but much more expensive and harder to machine, though a few inserts or taking lighter cuts makes little real difference to me at home.

 

Cold galvanise, paint or electro plate all good enough for me, but it would be nice to do stainless if I could find a bit.  

[Ben the Ignorant]

Right in front of where I sit now is a sodium street lamp with cable holders and clamps and stuff. Some parts are regular steel, other newer ones are A-2 stainless. I know because I've often looked at it at night to check for scatter and monochromatic aberrations in optics, and in the daytime to check for chromatic aberration and resolution. The fine spider threads in all manners of thicknesses make for good estimations.

While the ordinary steel in some components is deeply rusted (and dangerously so in my opinion), the prominent A-2 bolt shines, a bit dull because of dust but not rusted at all, not after at least twenty years under the rain, and not even where regular rusted steel could have contaminated it.

The screws and bolts I've bought commercially are all A-2, and I was very pleased to see that some high-grade mount maker (maybe Avalon if I remember correctly) was using A-2 to built tripods. Not that I want to buy one but knowing good stuff is in astro gear makes me feel okay about the hobby.

[JamesF]

Not seen you posting for some time, Jake.  Good to know you're still here :)

My gut feeling is that it's better to have more weight closer to the mount than less weight further out in order to reduce the moment of inertia (which varies with the square of the distance from the axis of rotation, IIRC).  You've got a lot of weight there though.  What's on the business end of the mount?  The OO 250?

James

[SnakeyJ]

On 12/07/2019 at 00:16, JamesF said:

Not seen you posting for some time, Jake.  Good to know you're still here

My gut feeling is that it's better to have more weight closer to the mount than less weight further out in order to reduce the moment of inertia (which varies with the square of the distance from the axis of rotation, IIRC).  You've got a lot of weight there though.  What's on the business end of the mount?  The OO 250?

James

Hi James, and thanks for your response - I do still dip in and follow the forum and progress on your obs, but have been busy with my daughter and very little time and energy for astronomy.   I have managed to sort my bijou 8x8' workshop and trying to get my new planetary setup running.

 

My rig is quite unweildy, with an OO 14" swinging on old style CGE Pro, within a 2.2m pulsar dome.   To shift the OTA CoB forward sufficiently to operate in the dome, I had to add almost 5kg of lead flashing wrapped around the front of the OTA.   This is held in steel rings between two 14" losmandy dovetails.   All up with camera, ADC and Barlow's, just under 30kg.

 

I'm hoping the OO ultra grade optics, smaller CO and open tube will give the C14's a run for the money and have a couple of years yet to tweak before Jupiter, Mars and Saturn become decent UK targets. 

 

Certainly not expecting this to perform for LX imaging, but with CMOS sensitivity improving, exposure rates commonly over 100fps at f15-f20 and the rig reasonably sheltered from the wind, it should be stable enough.

Edited July 13, 2019 by SnakeyJ
Remove duplicate content

[Chriske]

Very hard to machine indeed SS.
That's why I rarely use it. I use brass instead. Polished it looks awesome.

[SnakeyJ]

2 hours ago, Chriske said:

Very hard to machine indeed SS.
That's why I rarely use it. I use brass instead. Polished it looks awesome.

 

It certainly would look awesome, but a fair amount of polishing to keep it gleaming - would look great for that cyber punk effect (like the Great Weatherall Refractor below) and a little denser than SS, but also fair bit more expensive to buy.

 

The stainless surfaces up nicely with Carbide tooling on my lathe and no problems so far with drilling, boring and tapping ops - though I did use the feed and suds pump for the finishing cuts.

[Chriske]

21 minutes ago, SnakeyJ said:

 

 

The stainless surfaces up nicely with Carbide tooling on my lathe and no problems so far with drilling, boring and tapping ops - though I did use the feed and suds pump for the finishing cuts.

AWESOME..!!

 

[Ben the Ignorant]

I might as well show what I am talking about.

This is one of the A2 bolts that's been enduring the weather for at least twenty-two years, that lamp was already converted to sodium when I moved into this neighborhood. No one to clean it up but shiny after all those years. Note that there is some lateral color because the photo was taken through a Baader Hyperion 10mm, which are notorious for that, but the Sun's reflection on the bolt at the center causes no fringing, thanks to the very good correction of the FPL-51 80mm f/7 doublet.

The clamp is either aluminum or stainless, too, and didn't suffer any corrosion either.

[SnakeyJ]

15 hours ago, Ben the Ignorant said:

This is one of the A2 bolts that's been enduring the weather for at least twenty-two years, that lamp was already converted to sodium when I moved into this neighborhood. No one to clean it up but shiny after all those years. Note that there is some lateral color because the photo was taken through a Baader Hyperion 10mm, which are notorious for that, but the Sun's reflection on the bolt at the center causes no fringing, thanks to the very good correction of the FPL-51 80mm f/7 doublet.

The clamp is either aluminum or stainless, too, and didn't suffer any corrosion either.

Thanks Ben - amazing condition given 20 years exposure to British weather.   I'm sure that 20 years will see me through.

 

Interesting that the street light, a traditional bane of  UK astronomers, can prove to be such a useful tool.   In my area we changed over to LED some 4-5 years ago, I expect the contractors will have scrimped on fittings, but will take a closer look now!

[Ben the Ignorant]

2 hours ago, SnakeyJ said:

Thanks Ben - amazing condition given 20 years exposure to British weather

I am on the continent but rain is the same. 🙄

[Peter Drew]

Any chance of encapsulating a mild steel billet inside some stainless steel tubing?. The large polar disc of my 8.5" refractor was prone to rust until I wrapped some ss strip round it.  😀 

[Rusted]

Pedant mode/

a) Making the declination shaft longer may help to reduce the required mass but the actual "moment" wont change. 
I prefer a short, thick shaft and more weights rather than a longer one: Less spring and takes up much less room in the observatory.
b) Brass doesn't last long in a shiny condition when exposed to the atmosphere. Soon ugly when not polished.
c) Bare aluminium soon becomes spotted and ugly unless regularly polished.
d) White Hammerite paint is the cheapest form of stainless steel.  <Arrowed.>

\ Pedant mode

[Davey-T]

14 minutes ago, Rusted said:

Brass doesn't last long in a shiny condition when exposed to the atmosphere. Soon ugly when not polished.

Surely you mean it acquires a nice patina 😂

Dave

[JamesF]

52 minutes ago, Rusted said:

a) Making the declination shaft longer may help to reduce the required mass but the actual "moment" wont change.

The moment won't change assuming everything is still in balance, but the moment of inertia will as far as I'm aware, as if I recall my schoolboy physics correctly the moment of inertia varies as the square of the distance from the axis.

So, you might balance the kit with a mass m at a distance d from the axis of rotation or a mass m/2 at a distance 2d from the axis and the moment will be the same in both cases.  However the moment of inertia will be mdd in the first case and m/2 x 4dd = 2mdd in the second.  As the moment of inertia is "resistance to change in motion", the former may be preferable to the latter, particularly where guiding is concerned.  Perhaps (and I'm guessing here) it is also kinder to the drive train for the mount to have a configuration with a lower moment of inertia.

At least, that's what I remember.  I may be wrong.  I asked my son, but he says they didn't cover moments of inertia for his GCSE this year.

James

[Gina]

I think that's right.

[Rusted]

2 hours ago, Davey-T said:

Surely you mean it acquires a nice patina 😂

Dave

I'm far too "lacquered" to respond to this barb. 

"Where there's brass there's muck."

 

[Rusted]

1 hour ago, JamesF said:

The moment won't change assuming everything is still in balance, but the moment of inertia will as far as I'm aware, as if I recall my schoolboy physics correctly the moment of inertia varies as the square of the distance from the axis.

So, you might balance the kit with a mass m at a distance d from the axis of rotation or a mass m/2 at a distance 2d from the axis and the moment will be the same in both cases.  However the moment of inertia will be mdd in the first case and m/2 x 4dd = 2mdd in the second.  As the moment of inertia is "resistance to change in motion", the former may be preferable to the latter, particularly where guiding is concerned.  Perhaps (and I'm guessing here) it is also kinder to the drive train for the mount to have a configuration with a lower moment of inertia.

At least, that's what I remember.  I may be wrong.  I asked my son, but he says they didn't cover moments of inertia for his GCSE this year.

James

We didn't do physics in my day. It was all alchemy to me.

Balance in all things. Ohhmmm.

Don't forget to add the increased moment of the extended shaft.

If you can lift it. 

 

 

[SnakeyJ]

16 hours ago, Rusted said:

d) White Hammerite paint is the cheapest form of stainless steel.  <Arrowed.>

Excellent point Rusted - I have a lot of assorted cast iron weights of various makes and colours and will invest in some white smooth hamerite and a few cheap brushes