Bushes suggest ID, OD and facing off ends for a simple operation. You should drill and bore the ID first then you have a choice, you can turn the OD and face one end, chamfer the inside and outside corners and part it off then put it back in the chuck to face off the other end and chamfer the edges again.

Much depends on the dimensions of the part but that would be my sequence of operation. If you can, drill and bore to double-depth plus parting allowance so that you can cut both in one setup.

Generally, it’s best to plan cutting sequences to minimise moving the job.   Particularly important when using an ordinary 3-jaw chuck because these don’t reset accurately.   Thus, when a rod has to be drilled and turned so the hole and outside are concentric, do both operations without dismounting the work.  This guarantees the hole and the turning share exactly the same axis.  If job is moved between the two cutting operations, the common axis is lost.

Of course, most complex jobs can’t be done without moving them between machines, or into new positions on the same machine.  On a lathe, 4-jaw chucks are often used for this.   As the jaws can all be adjusted independently, the operator can accurately reposition the job  with a Dial Indicator.   With practice this can be done quite quickly so some machinists use a 4-jaw for everything.   Otherwise, three jaw chucks are fast, but not accurate when work is moved.   Four jaws take time to set up, but can reset work accurately.

If money is no object, accurately made and adjustable 3-jaw chucks are available.  They don’t perform better than a 4-jaw, but save time,

For speed and accuracy, collets are the best answer.  They’re repeatable without requiring the operator to measure anything.  Unfortunately collets are expensive and only grip over a narrow range, so not general purpose.  Brilliant for work like clock-making though, and occasionally useful in my workshop.  I mostly use ER32 collets to hold milling tools, but they’re also good for work-holding.  So I own an ER lathe collet chuck, and some Stevenson Collet Blocks.   Blocks can be held by a 3 or 4 jaw chuck, or a bench vice, or clamped to a milling table.  Again not general purpose, but they allow work to be reset accurately:

I’m sure other members know other ways of repositioning work accurately after it’s been moved.

Dave

As already said, the chances of finding a 3 jaw chuck that holds work concentric, at almost any diameter, are very small.

If you are making plain bushes, with just one internal and one external diameter, I would suggest that your procedure to ensure concentricity betweem Od and bore, is

1 Face end of material.

2 Centre drill

3 Drill almost to size, in stages. (slightly longer than you want the bush to be – allow for parting off, and final facing op.)

4 Bore to finished size  You might want to chamfer the bore before the boring operation begins.

5 Turn OD to size, (slightly over length).

By machining the bore and the OD without disturbing the work in the chuck, they should be concentric.

6 Part off slightly over length.

7 Reverse part finished job in chuck and face to length.

8 Chamfer finished bore.

Since you are making more than one bush, I would suggest leaving Ops 7 and 8 until Ops 1 – 6 have been carried oiut on all the bushes.

HTH

Howard

I would, and do, use Howard’s approach.

Some soft plastics are awkward to machine thanks to that softness. For the last operation, facing the flange end of something like a thin-walled bush, it can be better to hold it with the bore plugged with a short piece of metal or rigid plastic for support.

They can be awkward to machine in another way. I don’t know about ‘Delrin’ (it is a brand), but when drilling some thermoplastics the drill can bind, either by expanding from the heat more than the plastic does, or by the soft swarf jamming. So needs careful feeding and frequent swarf clearing.

Your options are:-

GripTru chuck 3 jaw

Soft Jaws

Between centres turning

Collets

4 Jaw independent chuck

Mandrels and Faceplate fixtures

this is a general list for you to explore and not all methods will apply to your bush job.

regards Martin

On 25 December 2023 at 09:32 Ramon Wilson Said:

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BTW Dave – surely that collet set up means the collet is only as good as that three jaw chuck 😉

Tug

Good point.  The set-up Tug questions is this one, which I copied off the web:

Obviously considerably inferior to a Collet Chuck mounted directly on the spindle, but I think it addresses the 3-jaw reset problem.  The Collet isn’t moved in the chuck, so the collet remains aligned on the same axis.   Therefore work can be moved in and out of the collet, and other collets fitted.    Accuracy must suffer though:  even if it’s perfect, the collet block overhang amplifies the 3 jaw’s run out.  But I think the arrangement is better than just using a plain 3-jaw.

I say “I think” because I haven’t tested it with a DTI, and I’ve no chance of trying today!  I’m already late for an appointment…

Dave

The basic 3 jaw is what it is, its for completing 95% of intended work just leaving parting facing and deburring.