# Need help with determing thread size for a mini-lathe spider?



## RMS (Jan 27, 2013)

I need to make a spider for my 7x14 mini-lathe. The spindle has male threads and two spanner nuts. I am by no means a machinist so I need some help determining how to select the correct gears but I don't even know what the thread size this is. I took some basic measurements. Does anyone know what thread type this is?

Thanks.


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## bb218 (Jan 27, 2013)

Assuming that it is a Metric I would guess it is a 38mm x 1.5 thread.  Usually you can subtract the Pitch from the Major Dia and that would be the " Tap drill size" which would be 36.5mm or 1.437"  That does not match with the 1.006" you have on your sketch.  Where did the 1.006 dim come from?  I also and not sure what a " spider " is ?  Mike


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## RMS (Jan 27, 2013)

Hey Mike,

The 1.006" was the measurement I took from the inside of the spanner nut, so I am guessing this would be the [SIZE=-1]Minor Diameter [SIZE=-1]of the [/SIZE]Female Th[SIZE=-1]read[SIZE=-1]??

[SIZE=-1]Robert[/SIZE]
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## chucketn (Jan 27, 2013)

RMS said:


> I need to make a spider for my 7x14 mini-lathe. The spindle has male threads and two spanner nuts. I am by no means a machinist so I need some help determining how to select the correct gears but I don't even know what the thread size this is. I took some basic measurements. Does anyone know what thread type this is?
> 
> Thanks.


 
Here's a drawing of the mini lathe spindle at LMS:

_www.littlemachineshop.com/products/*drawings*/1341*Spindle*7x12.pdf_

_It says the thread you are looking for is M27 x 1.5. I have made a spider to that thread and it fits my Micromark 7x14._

_Chuck_


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## RMS (Jan 27, 2013)

Thanks Chuck!

@bb218 Mike I did your formula subtracting 1.094" Maj. Dia. (a calculated guess) from .058" and got 26.3mm and a 26.25mm tap drill equals an M27 x 1.5" so thanks to both you guys -Rob


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## RMS (Jan 27, 2013)

Update:

I set up my gears to cut at 18 TPI and so far so good. It goes on easy at half way then starts to get really snug with about another 3/16" to go; so I think it will work and its made from aluminum so if the threads are not perfect it should deform and be OK if not I will have to make a 1/8" thick washer.


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## chucketn (Jan 27, 2013)

RMS, Little Machine Shop website also has a reference area that has a gear selection app. It will show you what gears you need for what thread you want to turn.
Why would you turn an 18tpi thread for the spider if the spindle has a metric M27 x 1.5 thread? What brand lathe do you have? As you state it's 7 x 14, I asume it's a MicroMark.

Chuck


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## RMS (Jan 27, 2013)

Well not knowing much about machining I just put a rule over the top of the spindle and counted the threads per inch; looked like it was 18 TPI to me. I will look at the link, thanks.


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## robcas631 (Jan 27, 2013)

What make is your lathe?


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## RMS (Jan 27, 2013)

MicroLux tru-inch the older red model 7x14


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## robcas631 (Jan 27, 2013)

Nice machine! Are you replacing a part or refurbishing one? The spindle that is.


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## RMS (Jan 27, 2013)

Thanks! Its an OK lathe for the average Joe like me. I am making an accessory part called a "spider" use to hold up a long shaft that extends out the back side of the spindle hole. I next have to drill and tap 4 holes that will be used to center the shaft and keep it from wobbling around.


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## bazmak (Jan 27, 2013)

Hi,if the 1.006 and 0.058 are correct then the 1.480 must be incorrect
To obtain the thread size,you must know the OD,the PITCH and the thread form
Regards barry


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## Tin Falcon (Jan 28, 2013)

to do metric threads on   a true inch lathe you need a transposition gear IIRC 9 tooth LMS or MM sells them.
Tin


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