A draw type collet with a stop will not work. If the stock diameter varies the collet position, when closed, will vary.

I would use a backstop n the spindle. The work would be held in a 3-jaw chuck. I would saw the blanks to approximate length. Face, machine shoulder, drill & tap one end. Do all pieces. Do the same to the other end.

How the lathe carriage stop is used is key. I have a 4 position carriage stop so I can set up all 4 stop positions in advance using a test part.

If using a fixed stop, make a spacer equal in thickness to the length of the spigot. Hold the spacer against the fixed stop when facing off. The stop without the spacer will control the length of the spigot. Reset he fixed stop to get the correct shoulder to shoulder length. Do the second end of the part in the same manner as the first.

For more consistent results a tubular backstop contacting only the shoulder could be used

12 pcs may not justify the method below, but for lg qty here's how I would do it on a home shop lathe. The method assumes you have a 4 or 6 position QC toolholder.

1. Make a two tool cutter with the HSS cutters mounted in a block 15 mm (plus or minus X within your tolerance) apart, and wide enough to cut the end dia's plus partoff tool width at headstock end.

2. set up above two tool cutter in toolholder, and set up a parting tool for next indexed op.

3. set up a work stop on the tailstock (could be just a rod in the drill chuck, and a removeable spacer so the stock doesn't rub on the stop) and arrange stock to feed through spindle hole up to spacer on stop. The stop and spacer should be set relative to the two tool cutter so cut is in correct place relative to stock end. Lock tailstock.

after setting up as above, ops as follows:

1. feed stock through spindle, through chuck or collet , to the spacer on the stop rod. Tighten chuck or collet.

2. remove spacer from stop rod.

3. make cuts to depth on ends with the two tool cutter, using cross slide (carriage locked).

4. index toolholder to the parting tool, to part off cleanly (no pip ideally)

5. replace spacer on stop rod. Index toolholder back to two tool cutter

6. repeat for next part.

Just my $0.02 worth. Done many like it. Standing by for the flaming. Just trying to offer simple practical methods.

Edited By Jeff Dayman on 23/01/2019 00:53:35

A backstop in the spindle is very useful to turn parts to dead length, easy to make at minimal cost. Mine is just a piece of threaded rod with its end bored and carefully faced, the bored hole means that any pip or slight bulge in the part face will not change the length. Just remember its there if you are working with a small diameter part that would fall into the hole.

On bigger lathes you may need a version for long and a version for short parts to avoid too much stick out of the threaded rod from the headstock, not safe and it can vibrate.

You will need to make some sort of split expanding collet to hold the stop securely in the spindle bore not hard to make it does not have to be super accurate. keep it short so that you have more capacity to hold longer parts.

Depending on the length of the spindle bore you may need to support the free end of the threaded rod in the bore, On my setup I did and made one from a piece of nylon cutting board a running not tight fit in the bore mounted between nuts and washers on the threaded rod, it does not rattle and keeps the rod centered.

Regards
John

Edited By John McNamara on 23/01/2019 01:20:48

As others have mentioned, you'll find a spindle backstop invaluable for repetitive work. Combined with a DRO, you can machine parts consistently accurately.

• Make a batch of parts but only one with the final shoulder not cut.
• Make a cylinder with a flange, the cylinder a bit wider than the parts.
• Centre pop to mark the flange for jaw 1 and chuck in 3-jaw.
• Drill slightly larger than the spigot.
• Drill and finish with d-bit to make a flat-bottomed hole to suit the body of the parts.
• Remove, cut three slits and replace.
• Use as a collet to hold the finished example to set a tool and stop for cutting the shoulders.
• Now work through the unfinished parts and make the shoulders.

Not really worth the bother for 12 which are more easily done with a parting tool, and using the top slide to move it by the width across the flange + tool width.

Neil

I'd just bore some soft jaws.

Jim

My version of a spindle backstop as mentioned above is to put a rod or tube in a collet then fit a chuck over it.

Martin C

This is the sort of job the multi-position bed stop was invented for. Especially useful if you have a QC tool-post and longitudinal travel dial on the apron or, better, a DRO.

Here is mine :-

I use the apron dial to set the stop positions for workpiece extension from the chuck or collet for both turning operations and parting off as I don't have a DRO on the lathe. Big advantage is being able to do the whole job in sequence on the parent bar before parting off. I'd use a collet for that job as my spindle is native 5C and I have a full set of collets to fit.

I use the Morse Taper drill carrying block out of my Dickson QC to set-up initial workpiece extension. Side is flat to close limits so it makes a nice solid work-stop. As I have the device might as well use it for something! (Also use it for setting the tool-post square to the tailstock barrel. Yet to meet any Home Shop person who actually uses one for its intended purpose tho'.)

With this sort of step turned job I find it worthwhile to take the time to adjust tool projections so that the final cuts are made with the cross slide dial reading zero. Easier with a decent DRO as they all seem to be able to store multiple zero positions. Assuming you have the discipline to switch zero position number when changing tools.

Habitually setting up to finish on dial zero is an effective way of limiting the number of "Oh bother. Took off too much!" moments.

Frankly setting the stop up is about the tipping point as to whether a DRO is worth having (I have dual imperial / metric dials). I imagine that with a DRO set-up is so fast that using the stop would pretty much be the normal way of doing anything more than a couple of parts.

Clive

Edited By Clive Foster on 27/01/2019 12:02:48

Edited By Clive Foster on 27/01/2019 12:35:20