Making a spider for a Craftsman 12x36

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Making a spider for a Craftsman 12x36

Post by bennypapa » Tue Mar 18, 2008 8:08 pm

I'd like to make a spider for my craftsman 12x36 and the only place I see that it will attach is in place of the collar that adjusts the headstock bearings.

Has anyone been down this road before? I'd love some input.



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Post by gzig5 » Wed Mar 19, 2008 3:47 pm

Mine had one on it when I got the lathe. Nothing special, just a longer version of the original collar. I would use thread wires to measure the the thread on the back of the spindle (which I have done but can't find my numbers), and make a dummy male thread to use to check the internal thread on the spider. Material for the dummy can be whatever, but aluminum cuts the nicest. The spider should probably be steel, brass, or 7075 aluminum. 6061 would probably work fine, but I would only use if I had nothing else available.

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Post by bennypapa » Wed Mar 19, 2008 5:07 pm

I read that the thread is 1.25" x 20 tpi. Where can I find the diameter data for that?

What kind of steel would you use? I have a hard time getting anything quality locally. The last time I tried to get 1018 they sold me some stuff that was hard as nails and didn't turn worth a damn. As small a piece as I will need I'll be getting it from onlinemetals this time.

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Post by AlphaGeek » Wed Mar 19, 2008 9:34 pm

Stupid question time:

This is the second time this week I've seen the term 'spider' mentioned in a lathe-related discussion. Are you folks talking about the support used for a long workpiece which projects through the spindle? Google gave me a wide range of possible answers to this question...


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Post by mechanicalmagic » Wed Mar 19, 2008 10:32 pm

Yep, a spider is like a four jaw chuck. Typically four support screws that hold a part in the center.
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Post by BadDog » Thu Mar 20, 2008 2:43 am

Yeah, imagine a 1/4-1/2" aluminum bar hanging out the back of a 1-3/8 spindle bore. Now that's going to want to spin about 2k rpm or more, depending on what your doing. At best it's going to be rattling around, more like making an "L" if there is much hanging out at all. But now mount a collar on the back of the spindle, and put 3 or 4 screws arranged equi-distant around the perimeter. Run those in to hold the rear of the rod centered, and you are much better off. If it hangs out more than a few more inches, you're going to need a tube setup as feeder and such, but the spider keeps it somewhat axially aligned with the spindle.

I need to build one for my lathe. A few weeks back I had to take some scrap and make a bushing to go back there for similar purpose. Random 4* (or so) taper on the outside, bore inside for light slip fit on small bar, "thonk" it into the back side with a smallish dead-blow, and slide bar through. When I was done, back into the semi-tooling random-bits-of-aluminum-I-may-use-again box and on with my day...
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Post by BadDog » Fri Mar 21, 2008 2:57 am

I just saw this clear example of a spider in use and thought about this post. So here it is for anyone who has not seen one before.
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Post by Skeeter5000 » Sat Mar 22, 2008 10:38 pm

Here are shots of one I made for a 12 x 36. ... pider2.jpg ... pider1.jpg

This was out of stainless.

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Post by bennypapa » Fri Mar 28, 2008 5:54 am

Great pictures, Thanks

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Post by Greg_Lewis » Sat Mar 29, 2008 10:28 pm

Reminds me of the time I was turning a piece of quarter inch rod that was a little too long (well, a lot too long) for the spindle. Suddenly the butt end of the rod decided to take a 90° turn and whip around the back end of the headstock like a helicopter rotor. The bigger problem was that the switch for the lathe motor is mounted right there on the left-hand edge of the bench and the rod was whacking it with each revolution without the benefit of knocking it to the off position. I couldn't get to the switch without risking hefty whack on the back of my hand so my only alternative was to run around the outside of the shop and trip the breaker.
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Post by gangel99 » Sat Mar 29, 2008 11:06 pm

Dumb question #2. Can't you use a spider on the other side of the spindle; e.g. held by a 3 jaw chuck? Thought I read somewhere it was a handy way of holding a small piece in a 3 jaw - or holding a square piece of stock without needing to change to a 3 jaw chuck.

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Post by GlennW » Sun Mar 30, 2008 4:25 pm

bennypapa wrote:I read that the thread is 1.25" x 20 tpi. Where can I find the diameter data for that?
Assuming it will be internal threads.....
A good starting point might be a:

Minor Dia of 1.201 (65% threads)
Major dia of 1.255
Compound movement of around .032" at 29.5° should get you close. Too many variables such as tool geometry etc. to get exact numbers.

Best way would be to make a plug threaded to match the external thread you're trying to match usig thread wires and use it to check the fit of the internal threaded part you're making.


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