Mount counterweight

[Gorr_77]

Hi All,

What material would you use : Stainless Steel Grade 304 or Grade 316 if you are on the budget? 

Best Regards

 

[johninderby]

Would you be machining the weights yorself?

304 is easier to machine than 316 but 303 is much easier than either 304 or 316 but not as strong but not a problem for a counterweight. 303 has added sulphur to make it easier to machine which means it can develop surface corrosion and pitting if exposed to water for long periods. However it’s ease of machining makes it ideal for counterweights.

Rowan Astronomy uses 303 for their counterweights.

Edited May 14, 2020 by johninderby

[MarkAR]

I would consider cast iron, hell of a lot cheaper, easy to machine. Just slap on some paint.

[tomato]

Gym barbell weights make cheap and cheerful counter weights with minimal machining. They’re  round, painted and already have a hole in the middle. You can buy the required weight also.

[Gorr_77]

Thank you all.

really thinking on a paint scheme...

I've been quoted for the below: £300 in SS316. but no chamfered edges or locking holes, What do you think?

120.65MM DIA with 32MM HOLE DOWN CENTER

2x 150mm length 

1x 75mm length 

1x40mm length 

1x20mm length 

 

Edited May 14, 2020 by Gorr_77

[MarkAR]

Decent price I would say, locking bolt holes would be a massive benefit but will up the price plus the knobs.

That's a set of big weights.

[newbie alert]

316 is marine grade ss 

[MarkAR]

No need for paint on that stuff. 

[Gorr_77]

I am just thinking to get a bench drill for £90 and drill it in my shed..

But that might be a cost to do side holes in the same workshop I will find out.

[Gorr_77]

8 hours ago, MarkAR said:

Decent price I would say, locking bolt holes would be a massive benefit but will up the price plus the knobs.

That's a set of big weights.

I have only one quote, so not sure about price - i do remember that old day it will only cost few bobs... Aiming for 30kg on approx 350mm long bar...

[TerryMcK]

30KG is a big lump of counterweight. What are you swinging on it and what sort of mount is it going on?

Edited May 15, 2020 by TerryMcK

[MarkAR]

3 hours ago, Gorr_77 said:

I am just thinking to get a bench drill for £90 and drill it in my shed..

That will be harder than you think, over heat the stainless and it'll work harden and burn out your drill bits.

[Gorr_77]

1 hour ago, TerryMcK said:

30KG is a big lump of counterweight

It is going on gemini E.fric with C11 on it / 120-140 Apo + 5kg the rest +10% for the future use...Also it is cheaper to do all at once with extra one....

[tooth_dr]

1 hour ago, MarkAR said:

That will be harder than you think, over heat the stainless and it'll work harden and burn out your drill bits.

Agreed, I wouldn’t contemplate drilling that depth of steel at home.  I do work with aluminium often for little brackets for telescope parts, but steel is a different ball game.  I try to do as much work as possible but I recently got my own CWs made up by someone else, for the Mesu. I converted EQ6 weights to fit the mesu shaft, with chamfered edges on the plastic liners. 

Edited May 15, 2020 by tooth_dr

[Gorr_77]

I have an answer back:

£400 for Grade 304, and side holes for locking nuts - i will have to tap it.

[Gorr_77]

... i could try tap it  5mm or so not too much so there is no strain on the tap bit....use a bolt to the end of the thread and the rest a pin, .

[Gorr_77]

... small works keep adding on and on to the finale price..

[johninderby]

Most of the better brands of mounts that supply stainless counterweights use 303 stainless as it’s better for machining than 304 or 316. Should reduce the machining costs.

[MarkAR]

Don't use a 5mm, you need 8mm minimum.  I suggest 10mm. To do the threaded side holes will take a long reach tap, even if you counter bore the hole the risk of breaking a tap in stainless is high. The suggested drill for 10mm is 8.5mm and clearance is 10.2mm. 

Use a good high pressure tapping fluid.

 

[Gorr_77]

2 minutes ago, johninderby said:

Most of the better brands of mounts that supply stainless counterweights use 303 stainless as it’s better for machining than 304 or 316. Should reduce the machining costs.

I'snt Geoptik doing 303? - problem with rust?

[johninderby]

No problem with suface corrosion with 303 unless used in a marine enviroment and constantly exposed to water. Not something that is going to happen with a telescope and mount anyway. There is a reason high end mount manufactures use 303 when the could easily afford 304 or 316. It just machines better.

Edited May 15, 2020 by johninderby

[Gorr_77]

That might change the prices as well. Let me ask "the" man again.

[TerryMcK]

Yes I agree with Mark the bigger the tap the better in stainless. I used to work with it a lot and have pinged a few taps in stainless. The trouble is it doesn't let you know and then all of a sudden you have a broken tap. Make sure you use a lot of cutting fluid or lube too.

[david_taurus83]

£400 for a lump of steel! I'd be looking for threaded steel bar for a shaft and use nuts to hold weights in place!

[MarkAR]

2 minutes ago, TerryMcK said:

Yes I agree with Mark the bigger the tap the better in stainless. I used to work with it a lot and have pinged a few taps in stainless. The trouble is it doesn't let you know and then all of a sudden you have a broken tap. Make sure you use a lot of cutting fluid or lube too.

It's is scary, recently made up a couple of extra long c/w bars for Star Adventurers, watching the 6mm tap twist as you get to the bottom is a sweat inducing moment.