1948 SB-9C: Info Please, Back Gear SPRING (Under Square Head Set Screw)

Metal-Masher · Jan 20, 2019

Hi everyone,

I'm disassembling my lathe headstock. I removed the set screws that secure the back gear, but I found that the small spring under the square head set screw is missing.

I'm hoping someone can give me some key dimensions of the spring so that I can find another spring that comes fairly close.

If possible, could you please provide the following:
- Wire diameter
- Number of coils
- Free height
- Solid height
- Outside diameter

I assume its made from music wire, not stainless

A photo would be great.

Many thanks for your help!
Alex

iwananew10K · Jan 21, 2019

doesn't really answer your question but i just went the hardware store(ACE)
and got the stiffest one that fit in the hole and seems like it was about 3/8"ish long.

could be ignorance is bliss, but i never had an issue with it.

is the little shoe that goes under the spring there?

Metal-Masher · Jan 21, 2019

iwananew10K said:
doesn't really answer your question but i just went the hardware store(ACE)
and got the stiffest one that fit in the hole and seems like it was about 3/8"ish long.

could be ignorance is bliss, but i never had an issue with it.

is the little shoe that goes under the spring there?

Yes, the shoe is there. I was surprised it was there, since the spring was gone.

I know I could empirically test several springs to get the right "feel" of the back gear movement action, but I was hoping to somewhat match SB's original design intent.

kitno455 · Jan 21, 2019

I thought I had one of these, so I went out and looked in the scrap parts bin. What I found surprised me- the spring is short, perhaps only 5/16 long, and the wire is an odd square cross section. It looks a lot like a section of a helicoil. The ends are ground flat. I'm not sure this thing is original, but it is quite stiff, which makes sense given the potential for vibration.

allan

Metal-Masher · Jan 21, 2019

kitno455 said:
I thought I had one of these, so I went out and looked in the scrap parts bin. What I found surprised me- the spring is short, perhaps only 5/16 long, and the wire is an odd square cross section. It looks a lot like a section of a helicoil. The ends are ground flat. I'm not sure this thing is original, but it is quite stiff, which makes sense given the potential for vibration.

allan

Yeah, that does sound like an odd spring. There must be a reason SB went through the effort to make it from square wire...perhaps for vibration issues, as you said.

Maybe its because a square cross section has more area than a round section of the same given size, so more area equals more material, and more material equals stiffer wire. If that's the case, it sounds like SB was having a problem getting a high (enough) spring rate spring into the available real estate of the back gear casting. Did we just find a design flaw?

Yan Wo · Jan 21, 2019

kitno455 said:
I thought I had one of these, so I went out and looked in the scrap parts bin. What I found surprised me- the spring is short, perhaps only 5/16 long, and the wire is an odd square cross section. It looks a lot like a section of a helicoil. The ends are ground flat. I'm not sure this thing is original, but it is quite stiff, which makes sense given the potential for vibration.

allan

That description matches the spring from my 1948 9A. However, I don't have the shoe. It was missing when I first disassembled the lathe -- or that's my story, anyway.

kitno455 · Jan 22, 2019

I have a small brass round which I assume is the shoe. Chad gave these parts to me, so I'll pass them along. Yan Wo and Metal-Masher, send me a private message with your mailing addresses, and I'll send the shoe and the spring out to you guys.

allan

Metal-Masher · Jan 22, 2019

kitno455 said:
I have a small brass round which I assume is the shoe. Chad gave these parts to me, so I'll pass them along. Yan Wo and Metal-Masher, send me a private message with your mailing addresses, and I'll send the shoe and the spring out to you guys.

allan

Many thanks for your generosity Allen! :Ithankyou:

A private message has been sent.
Alex

Yan Wo · Jan 23, 2019

kitno455 said:
I have a small brass round which I assume is the shoe. Chad gave these parts to me, so I'll pass them along. Yan Wo and Metal-Masher, send me a private message with your mailing addresses, and I'll send the shoe and the spring out to you guys.

allan

PM sent -- I think. Thanks!

CC984 · Mar 16, 2023

Did anyone have the specs of this little spring? I am also missing the spring, I have the shoe and bolt but some how the spring has ran away.

Thanks,
Chad

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1948 SB-9C: Info Please, Back Gear SPRING (Under Square Head Set Screw)

Metal-Masher

Plastic

iwananew10K

Diamond

Metal-Masher

Plastic

kitno455

Titanium

Metal-Masher

Plastic

Yan Wo

Stainless

kitno455

Titanium

Metal-Masher

Plastic

Yan Wo

Stainless

CC984

Plastic

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