Using an ER40 as a spider in a G0709

M

mcdanlj

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I noticed that the outboard end of my spindle had the same M50x1.5 thread as an ER40 nut, which made me wonder if I could use an ER40 nut instead of a spider, as a self-indicating outboard stock support.

I used some 1 7/8" CRS stock and made an adapter to hold the ER40 collet inside the end of the tailstock. Because the thread doesn't run to the end of the spindle, this has less clamping range than a standard ER40, but it's good enough for most cases. And when it isn't, it's not hard to go back to the real spider.

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I freestyled this, measuring against nut and lathe as I went, but I reverse-engineered it afterward and made a drawing. (Sorry, as an amateur my drawings are very amateur.) All dimensions in mm because I do everything I can in metric.

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That neck has to be very narrow (about ⅓mm), and the brim thin, for the nut to engage the threads that aren't very close to the end.

Here are some more photos:

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That line about a third of a way from the brim is real and not a photographic artifact; there's clearly a slight taper inside the spindle, so I ended up with the inside end a thou narrower in diameter. That's a one thou step.

Here's the outboard end with no spider.

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Inserting the collar into the spindle end:

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With a nut and collet:

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That's using the old head, for something other than a hat rack. Mike
 
This idea can be adapted for lathes with larger spindle bores by making a custom nut. I'd start with a sacrificial nut and cut it down, then press fit or loctite it into an adapter to the thread for the larger spindle bore.

I might even want to do something like this for this my existing lathe in order to make it easier to use with the gear train cover installed. I could run the custom nut substantially further outboard to make it easier to tighten and loosen. It would also give me more clamping range, though I might need to re-make the adapter with a tighter taper to take advantage of it.
 
Great mod ! I dont think i can easily do this mod on my 9972z lathe. The outboard spindle lock nuts are M39x1.5. My spindle bore is only "very rough" machined to about 1.047". A traditional spider is going to work best for me.
 
This idea isn't for everyone. If there is anyone who is interested in this idea on a smaller lathe, you could consider smaller collets in the ER family, like ER32, and might have to make a custom nut as I highlighted above. If you, say, wanted to use ER40 on a lathe with a ~1" spindle bore in order to be able to grasp all stock that could fit through the bore, then you would need to make a different kind of adapter and it would put the collet further outboard so be usable only with slightly longer stock.
 
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