The Spindle Depth Stop

I had a small run of parts on the lathe that needed to be the same length.  There are a couple of ways to do this, such as :

1. After creating the part (and making sure both ends are faced, but a wee bit long), measure the length of the part.
2. Calculate the amount you need to remove by subtracting the final length of the part from your previous measurement.
3. Re-insert the part into the chuck (or collet), and measure the length of the stick-out from a known reference point.
4. Subtract the distance you need to remove from this stick out measurement.
5. Face the part until you reach that distance calculated in step 4. 

However, I'm lazy, and that's a little too much effort.  I'd rather do that only once, and on a single-run part, I'd have to do that, anyway.  The micrometer stop does a bang up job of getting it right on once you've gone through that.  But if I have four parts?  Uh-huh.  I'm too lazy, since I could insert the parts into a depth, while leaving the carriage/cross-slide in the one position.

It's time to make a spindle depth stop - something that locks into the spindle so you have a consistent reference point on all the parts.

Mind you, my spindle has either a collet closer attachment installed, or it has the big fat gear used by the collet, so I can't just throw a standard one in place.  But, just in case, my South Bend Heavy 10L (large spindle bore) regular, non-gear depth-stop was also designed.  This spindle depth stop can fit all three, just by making the locking spider for all three.  That's only two extra parts, allowing this to fit three different configurations.  I also wanted to use as many parts that I didn't have to make.  Because, again, I'm lazy.

Okay, okay, enough blab.  Let's get to it.  Grab the materials (I'm going to use CR1018/cold rolled steel).

 

First, let's get the stainless-steel 3/8"-16 all thread cut to length.  I used a 36" bar, and cut it at the 24" mark.  No precision necessary here, I just have two variations in case I don't like too much sticking out the back for an extra long part.

Next, I already had the nuts in hand (that's not what I meant, and you know it) for the 3/8"-16 all thread, and a 5/8"-11 nut for the locking lug.

First part to "really" make was the locking lug.  Really, it was a simple turning job for the most part.  Turning to 0.625" for the threaded end, threading to 11 TPI to match the nut, and then getting the main body set, the internals bored for clearance for the threaded rod (and one end threaded to 3/8"-16 of that internal bore.  The hardest part was the "cone" on the end.  What I had drawn up in the plans had a 17.615 degree angle, and to be honest, you just need it "close".  Using the compound, you can set the angle, then lock that in.  Do not change that angle until you have completed your locking spider(s)!

This was my first taper turning, and I went with a standard 17 degree.  I don't care how close I am to 17 - it's not moving until I've made the entire thing.

Next up was the washer.  It was coming from the same large stock as the spiders, so it's easy to slap in there and turn, face, and bore.

You just might notice that the proportions aren't lining up with the drawing.  I actually opted to make this 1/2" thick instead of 1/4" thick, and I bored out 1/4" of the internal bore to match the larger diameter on the locking lug I've finished.  This will give me a little more expansion room, and allow me to use less material on the spiders.

Now I just need at least one spider. I'll do the gear-based spider first :

Then, I'll do the collet attachment spider :

Now, I'm not making this next spider, because I have that fat gear that sticks out for the spindle attachment.  It means I can't really use it.  However, I drew the plans up anyway, just in case someone needed them.

So, I started out creating my two spider blanks.  I chucked up the material, faced one end and the diameter in order to get the base set up.  I also rough-turned one to get it not quite to dimension (I'm 0.050" oversized on the outside).  I did not go all the way to dimension yet because I needed the bore set up so that as stresses are relieved, the outside will then be truly concentric to the bore.

Once I had a close-but-no-cigar dimension on the outside, I turned (pun is not intended) to the inside for the boring process.  First, I used drill bits to get it to 0.5" (needed to get to 0.810"), and then I could use the boring bar.

Once the inside bore was complete, it was time to also turn the taper.  This is the exact reason why the compound was not moved - it already has the matching taper from the internal part, so I knew it would be a match made in heaven (or at least on the lathe).

With the spider's internal bore/taper and the locking lug fitting as they should, I went back and turned the outside down to the final dimension, and then turned the 0.125" circular relief groove using a rounded insert (could only find metric, and it was close enough).  Yes, in the following photo, the lathe is OFF.  I refuse to lose a hand.  But, I did it to provide a visual on the groove.

After the groove, I removed the chuck from the lathe and ensured I had a snug slip fit into the targeted location.  At that point, I could pull it out of the chuck and do a test fit up.  It definitely locks in there, but without the expansion slots, it won't truly lock.

I do know that I need to remove more on the outer end (largest diameter face), because I didn't get it short enough to fit on the locking lug.  So, into the chuck it will go with some brass shim stock to protect the finish, and then I can face it down to size until I have a perfect arrangement.

It's not often you hit the target width so closely.  I thought it was close enough, and assembled everything (not usable until the slots are cut).

Now, the remaining task is to cut the slots into the surface.  There are six slots, but using a band saw (my slitting saws are not large enough), it's only three cuts.  So, next I need to build a jig to keep it perpendicular to the saw blade, mark the three cuts, and then start slicing.  This had my anxiety running high, because there is no way I'm willing to lose a finger.  And, with two separate spiders for different dimensions, I need something adjustable for that smaller diameter.  I need it to be at least close to parallel to the axis.  So, after thinking on it for a month, one morning, I needed to get out of the house, and I ran out and grabbed some 2"x1/2" aluminum flat bar, and simply marked out a few parts.  Cut, drilled, tapped for M3 screws (because I didn't want to wake my wife early in the morning), and I had this little thing.

I can thread those two screws in or out, depending on the diameter of the spider end, so there is the adjustability that I needed for the two spiders.  It allows me to adjust those two screws until I have a parallel setup, and I can then feed that into the bandsaw blade without fear of something catastrophic.  It does fit like I hope.
 

The next task was the actual cutting of the slots.  The jig held up quite nicely, though I should have adjusted the screws part way through.  While there, I also drilled relief holes where those slots ended so that there wasn't a hard corner or edge to start cracking on.

I used a triangular (bastard) needle file to deburr the slots (outside and inside), and a round needle file to remove the burr on the inside where the drill bit broke through.  But, once that was done, I had a relatively decent part.  A quick test fit of everything together....

Now, it's time to try it out.

It locked in there without much of a tightening on that large nut (it could still slip, so I'd likely use a wrench when I really need it).  Functioned pretty well!

The second one can now be chucked up and replicated to the dimensions of the first (with the smaller diameter for the collet attachment tube).