Mini Lathe – turning 6″ long, 1.5″ dia AL

[Finnian DawsonParticipant @finniandawson]

Hello All

Having a little trouble turning AL stock, piece needs to be 6" long, and I am starting with 1.5" diameter stock in the 4 jaw. I know that this exceeds the ideal length:diameter ratio, so I clearly need some support to counteract the cutting forces. My lathe is a Sieg SC2, so as far as i can tell, turning between centres isn't possible as I cannot get a centre in the headstock.

Is a fixed steady the best solution for my case?

 

Thanks

Edited By Finnian Dawson on 30/06/2019 20:17:29

[Finnian DawsonParticipant @finniandawson]

[JasonBModerator @jasonb]

One end in the chuck and tailstock ctr to support the other end.

 

I would have thought you could gt a CTR in the headstock as they usually have a morse taper socket but then you have to find a way to drive the work so chuck & tailstock will be easier

Edited By JasonB on 30/06/2019 20:31:58

[Mark RandParticipant @markrand96270]

Use a centre drill in the end followed by using a centre in the tail stock.

[Martin of WickParticipant @martinofwick]

lathe is a Sieg SC2, so as far as i can tell, turning between centres isn't possible as I cannot get a centre in the headstock.

Why exactly? you will need to remove the chuck to get the centre in I think, but not necessary to use centres unless super accuracy needed, in which case check your centres align in all planes before anything else.

In any case, if t'were me I would clock up the bar in the 4 jaw, then if you have a fixed steady clock up the bar at the tailstock end, then with fixed steady in place centre drill as required to fit your dead centre. Oil the centre drilling, wind in tailstock with centre and lathe away.

If you dont have a fixed steady, you can use a centre finder, punch and use bench drill or lathe.

You don't comment on your turned size – if much less than an inch, you may want to take lighter cuts as you approach size.

[Robert Atkinson 2Participant @robertatkinson2]

At 300mm between centres and a MT2 tailstock on the SC2 there should be no problem turning 6" between a chuck and centre. lots of choice in MT2 centres. why don't you think you can do it?

[Finnian DawsonParticipant @finniandawson]

Can't turn between centres in an SC2, just Chuck and centre.

Have a dead centre already, but no fixed steady, nor centre drill for that matter. Must get the bit and fixed steady and see how I get on.

 

Edited By Finnian Dawson on 30/06/2019 21:35:11

[Mick B1Participant @mickb1]

If you've got a carrier that can be driven by a chuck jaw, could you turn a centre from a piece of scrap in the chuck?

But I'd've thought a lubricated dead centre in the tailstock with t'other end in the chuck would be fine for most work. Centre drills are available at any engineer's merchant's or off the web for not much money.

[Martin of WickParticipant @martinofwick]

Riiight….

well, may be useful to invest in a 3MT centre in case you want to turn BC in future but also for checking your tailstock centre alignment for general work. When my minilathe came out of the box, the tailstock was way out of horizontal alignment and my first piece of parallel turning was a gentle taper!

Centre drills are not to expensive, best to get a few in a selection of sizes for future use.

Check the size of the fixed steady to be sure it will admit your 1.5 inches diameter – I opted not to purchase the factory device as it seemed too small to be useful, but it might just take your project.

As I suggested, you can avoid using a steady (because in this case it is only used as a convenient way to locate the centres for drilling).

Instead, you can use a centre finder to scribe 3 or 4 lines at as even spacing as you can eyeball across the face of the bar. Then centre punch as close to the centre of the resulting triangle as you can judge. You can either use a bench drill to centre drill the recess, or you can set up in the lathe chuck and manually guide the work bar on to the tailstock chuck and drill the centre recess as best you can.

If you don't have a centre finder, it is a bit more tricky but it is not impossible to scribe the bar face by careful measurement with a rule, plate and scribing block, or even just odd leg calipers (piece of glass will do as a surface plate).

[Nick WheelerParticipant @nickwheeler]

Posted by Finnian Dawson on 30/06/2019 21:33:34:

Can't turn between centres in an SC2, just Chuck and centre.

Have a dead centre already, but no fixed steady, nor centre drill for that matter. Must get the bit and fixed steady and see how I get on.

Unbolt the chuck and you'll find an MT3 taper in the spindle that will hold a centre. Or any other MT3 tooling.

[Nigel Graham 2Participant @nigelgraham2]

Reading between the lines here, there is a taper in the spindle but does the lathe have a carrier that can be used with the chuck removed? Is that the problem?

A tip I've seen (actually in the instructions for a Hemingway kit) for setting a steady is to set the bar central by dti at the chuck, and adjust the steady there, not down at the far end – though still verify the centering with the steady in its operating location.

[JasonBModerator @jasonb]

The other question is what part of the bar do you want to turn? if it is along the length than a fixed steady will get in the way, or if you want to turn the end then a ctr will get in the way so a bit more info on what you actually want to do will help.

[not done it yetParticipant @notdoneityet]

Other questions might be: What type of 4 jaw chuck and what are the starting length of your stock and finishing length of your workpiece?

Self centring and the job might need to be finished in the one operation, whereas with an independent 4 jaw the piece can be removed and replaced with zero runout.

Likely you mean a 4 jaw independent, but need to be sure…

Turning between centres offers the easy way to be able to dismount and remount the item if necessary without fear of misalignment.

Personally, if the work piece were too long to be safe (this is likely OK for careful facing and centre drilling) I would be using the steady to get it faced and centre drilled, then use a revolving centre. A solid centre in the tailstock would be OK as the centre drill leaves a cavity, beyond the centre cone, for lubrication.

[Neil WyattModerator @neilwyatt]

Posted by Finnian Dawson on 30/06/2019 21:33:34:

Can't turn between centres in an SC2, just Chuck and centre.

Have a dead centre already, but no fixed steady, nor centre drill for that matter. Must get the bit and fixed steady and see how I get on.

Hi, If you remove the chuck you will see an MT3 socket you can fit a centre in. If you haven't got an MT3 centre put a bit of scrap in the chuck and turn a 60-degree point on the end.

You can use an M6 bolt fitted in one of the chuck mounting holes to drive a dog.

If you don't need to turn the whole length of the bar, then as Jason suggests centering one end then supporting it from the tailstock while the other is held in the chuck should work fine.

You will need to extend and lock the tailstock barrel to make sure you can reach the end of the work with the tool.

Neil

[Author]

Posts