How should I make this?

I need to make several 'Top Hats' out of stainless steel, below is a sort of cross section in my first attempt at ascii art.
The part is about 45 diameter and 45 long and will have a wall thickness of 1.5mm thick. The flange (brim) is 3mm thick and 48 diameter.
As 50mm barstock will not pass through the headstock of a 5" Boxford I have though about buying cut blanks, gripping the OD in the 3 jaw and fully machining the bore. Then machining the OD by holding the part on some sort of mandrel. (The inner and outer concentricity need to be within 0.2mm or so)
My dilemma is trying to decide how to hold the part on the mandrel (which I don't want to take out of the chuck until I've made all of the parts.
I have thought of making an expanding mandrel which is somehow activated through the headstock spindle but it seems overcomplicated
Thanks in advance for any suggestions
Ian Phillips
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What lathe and what type of spindle nose ? -- Regards,
John Stevenson Nottingham, England.
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wrote:

1970's AUD 5" Boxford, standard screwed nose.
Ian
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On Sat, 29 Mar 2008 21:50:59 -0000, "Ian Phillips"

In that case as you can't use expanding 5C mandrels then your best bet is a set of soft jaws and turn down so you can hole on the inner diameter which you turn first.
If in stainless get sawn blanks, let them cut them and wear their saw out <g>. -- Regards,
John Stevenson Nottingham, England.
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Have you got a pipe center? I' thinking about boring the centre portions from bar stock then turning the outer with a 3-jaw and a pipe centre. I'm very much a starter at this sort of thing but it looks quite do-able to me.
Chris
--
Chris Eilbeck
MARS Flight Crew http://www.mars.org.uk /
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As you`re limited by the spindle bore it would be better to get cut blanks about 47mm long. Grip in the chuck and rough bore the hole. Do them all to that stage. Grip in the bore with your three jaw and turn and finish the OD all over. Bore a set of soft jaws and grip on the OD and finish bore and face off flange. Mark.
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On Sat, 29 Mar 2008 21:29:10 -0000, Ian wrote:

Can you make soft jaws?
Do the hole and that side of the flange.
Flip it over and grip from the inside with the soft jaws; do the outside.
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Several folks have suggested something like that. As the actual item is not as robust as the sketch would suggest, is there a danger that it will distort when held by the bore?
Henry
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I suppose that is why I wanted to grip it with something that expands equally all round. I have considered Loctite'ing it to a mandrel then heating it after machining to loosen the bond.
Ian
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Soft jaws sounds a good idea but I don't have any.
Ian
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On Sat, 29 Mar 2008 22:33:06 -0000, "Ian Phillips"

Do you have any old jaws for your chuck ? If so you can weld some lumps of mild steel on and machine those down.
Sounds horrible and it is <g> but it works. -- Regards,
John Stevenson Nottingham, England.
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On Sat, 29 Mar 2008 22:53:34 GMT, John Stevenson

Why not do _all_ the turning and boring with the over-length stock held in the chuck. Then part off 20 thou over length. clamp the parted off part to a faceplate using the top-hat rim and face the parted off end to length. You waste 1/2" of stock per part. Use it to make washers with :-)
This does not seem to be a complicated part.
I would cheat and do the last operation on the surface grinder or shaper, but turning will work just as well.
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Not too bothered about starting with a longer piece of bar (more like an inch for chucking and parting) but the actual parting off would not be too easy on an AUD with 50 diameter stainless.
Ian
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wrote:

If I can manage 95mm EN24T on an ML7, then you can manage 50mm 316 or 303 on an AUD!
Carbide insert parting tools make a big difference with awkward metals.
Of course, one could always relegate the parting to a bandsaw or power hacksaw. In desperation, if the parting off was too great a step, would be to turn the entire waste part into swarf with a facing tool!
Mark Rand RTFM
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Mark
I can part 50mm SS but none of my assortment of parting tools are quite right for it. A recent eBay item I won is a parting blade holder for my Dickson QTP but it needs a new blade and I have not been able to find the correct size.
The short piece of blade that came with it is 5/8" high and about 1/8" wide. None of the suppliers I have tried list one that size. I suspect that the holder would work with a slightly narrower blade (2 to 2.5mm) but the toolholder has no makers name on it looks genuine Dicksons) so cannot be sure.
I also have an Iscar double ended replaceable tip holder (blade only ) but it is 32mm high with nothing to clamp it to the toolpost.
If only I had a miller, or room for one!
Ian
I have recently not op
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They're only about 20 for common chucks and well worth having. If you can weld you can make them by grinding down an old set of jaws and tacking lumps of mild steel on. You can hold on as little as 1mm of depth with a freshly turned set of soft jaws. I use mine occasionally for making thin washers.
A pro would do your job in two ops by holding the blanks with a few mm sticking out of the chuck, boring the i/d and turning the o/d of the flange part then holding on the flange with soft jaws and turning the rest. Total machining time on a cnc lathe would be about 5 minutes in a nasty material like stainless. You'd use a big F/O carbide insert drill with through coolant to rough the hole out in a single pass, finish with a boring bar, fit the soft jaws, turn the part round and turn the o/d.
On a manual lathe with conventional tooling figure on several hours per part and lots of burnt out tooling. Stainless is a pig. You'll probably start trying to drill the bore with successively bigger HSS drills just to get something you can get a boring bar into, shag them all and wish you'd never started the job.
--
Dave Baker
Puma Race Engines
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Dave Baker wrote:

That's the most sense I have yet seen on this topic.
--
Charles Lamont

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316 Se/ EN58JM/ 326S36
free(er) cutting 316 stainless ;-)
Mark Rand RTFM
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wrote:

303, even easier !!!
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Starting from sawn blanks 48mm diameter and 45mm long with some machining allowance on both dimensions.
1) Hold in 3 jaw with a few mm sticking out and drill/bore the hole to 42mm dia and 43.5mm depth. Check depth of bore and face off the bottom flange.
2) Turn round in chuck and face off the top flange. Part is now at finished length and i/d.
3) Now make a "pushing button" for use with a running centre - 44mm diameter bit of aluminium or mild steel about 30mm long. Stick the biggest centre drill you have into one end to fit over the nose of the running centre.
4) Chuck some scrap with 45 to 50 mm sticking out and turn that to a 41.95mm diameter plain mandrel. Chamfer the end. You can counterbore the end lightly to a diameter of 35/36mm if you're concerned that the bottom of the bores in your top hat bushes aren't perfectly flat or have a pip in them. Then it will just register around the outside of the end of the mandrel on a rim about 3mm thick.
5) Fit the bored blanks over the mandrel and press back hard with the pushing button and running centre in the tailstock. From now on you'll just be using friction to hold the piece while you turn the o/d and flange.
I use friction to hold more jobs in my lathe than I do chucks. I'm always surprised that no one else ever thinks of using it or realises just how hard you can machine into something held this way before it slips. The same people presumably also won't give a thought to the fact that the only thing connecting the engine in their car to the gearbox and wheels is the same principle transmitting 100 plus bhp.
--
Dave Baker
Puma Race Engines
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