Setting up a long bar for between centres turning

I'm looking to turn a spindle for a lathe. I've a nice piece of 40 mm steel which will fit in the 7x14 lathe I have. It's about 300mm long.

I get the basics of centre turning, but I'm trying to work out how to get both ends centre drilled accurately.

If I just stick the bad in the chuck I would expect it to sag a little, so it will wobble as it rotates and the centre drilled hole will likely not be on centre. Also, I'm concerned about facing off the ends. I don't currently have a steady.

I can punch a mark in the end, but I'm unlikely to achieve particularly fine accuracy.

I think I read somewhere that the rotation will tend to pull the bar into the centre so will auto-centre, but I can't find the reference again.

I appreciate that this is likely to be a bit demanding for a beginner, but I do have a spare bar for when this goes badly wrong.

Thanks for your advice in advance!

Iain

Hi Iain

I wouldn't attempt to turn / face off that length of bar without a steady; all you'll do is push the bar out of true from the lathe axis, this will then make the bar trace an elliptical pattern & you'll end up with the bar whipping round on to the top of your tool & causing no end of trouble, try and borrow a steady. I don't know which machine you've got so can't comment on type of steady that may be available, if you can afford it buy one from the manufacturer / retailer of your machine, they're not that expensive.

If you do get a steady... set it up so that the fingers are set on the bar near the chuck, then move the steady to the far end ( tailstock end ) close enough to give you enough working room, face off then centre drill, turn bar round & do the same for other end then you'll have the centres as accurately drilled as needed to run it between centres.

No doubt other members will offer their own methods...

George.

Iain Downs:

An alternative to using a steady would be to find someone with a larger lathe which will accept your bar for centre drilling purposes leaving you to do the bulk of the job yourself.

Anyone offering to do this would need to have some idea of your location (no public profile).

Presumably you'll need to machine the material down from its current diameter anyway, so careful marking out, punching and centre drilling could well get you close enough - say to half a mm of the true centre. So long as your stock is more than say 1 mm bigger than the largest finished diameter you need, that should be fine.

Facing the ends completely is another matter - and even more so if you want to drill out the spindle at all. Can't think of an easy alternative to using a fixed steady.

If you can't just buy one (and for smaller lathes, check its maximum capacity first) it might be worth making one. Google 'DIY fixed steady' for inspiration.

A cheap but temporary bodge (for centring, at least) is to fix a block of wood solidly to the cross slide (and lock the slide!), and bore it using a tool held in a four jaw chuck, to a sliding fit on your stock. Grease it before use and use low rpm to put in the centres.

A slightly trickier version which will allow facing as well is to mount the block of wood to the lathe bed, securely but so it can still slide along when pushed by the carriage. Do this to bore it, again using a tool in the four jaw. Now you can fix this firmly to the lathe bed, mount your stock (with the other end held in the 4 jaw), put in the centres and face the ends.

But if a 7x14 lathe is 14" between centres, and the part is 300mm long, you'll be close to the machine's capacity, so double check that there's going to be enough carriage travel available even with the steady in place... also that you have enough length available to get the centre drill mounted in the tailstock (in a drill chuck, probably) with the stock in place held by the chuck...

It would certainly be a much easier job on a bigger machine.

Edited By Bikepete on 12/12/2015 13:07:32

Edited By Bikepete on 12/12/2015 13:12:29

Thanks for the advice.

I think the fixed steady is the approach. The machine is a SPGTools 0618A (Real Bull CJ18A) and the bar fits quite comfortably.

SPGTools (and Amadeal and others) have a fixed steady which isn't expensive. What it is however, is of uncertain capacity.

I can't find a spec for it on either site (amadeal has a picture which makes me guess it will take 50mm, but I'm not entirely sure.

I could make one, of course - making the tools is more fun than making the project), but for 20 quid it doesn't seem worth it.

Anyone know what the capacity of this centre is?

Iain

Iain Downs:

Just a thought. Is your spindle intended to be drilled through the whole or part of its length and, if so, how will you do this?

Hello Iain,

I don't like to rain on your parade, but I think you are being rather ambitious in expecting your lathe to be able to cope with a job matching it's own capacity for supporting work between centres.

Looking at some of the practicaliities involved; how do you plan to make a through hole in the embryo spindle? Even with the best will in the world getting a drill with at least 6 inches of reach just to get half way adds to the overall length of the job which then exceeds your 7 X 14 lathe bed length by 4 inches and that is before you add a chuck or whatever to hold it. You also have to be able to withdraw it to clear swarf.

You don't say if this is a copy for your own lathe or for another, if it is for your own then the work planning needs careful thought for correct sizing to an existing pattern just at the time you need the lathe to do the work!

Better by far to put the job out to someone else with the machine capacity to do the whole job, including reaming the taper at the chuck end as one concentric job with properly sized bearing diameters. Alternatively, buy a new spindle from the sellers and save yourself the disappointment of not being able to start on it, let alone finish it.

Regards

Brian

This is my own design of lathe and will not have a through hole. I certainly don't have the gear to make that!

I see this as an opportunity for learning rather than a well planned project with a specific end goal.

The next two challenges are how to bore and align the bearing holes in the headstock and how to press the bearings into place with the kit I have on hand, but I'm trying to limit my pesteration to a reasonable level!

I must say that the helpful responses in this forum have hugely encouraged me.

Although a beginner I did do Metalwork at school to a good standard and some of it appears to have stuck in the intervening 40 years. Not much, but some.

Iain

Between centres work is one of the most skilful jobs you can tackle on a lathe

The hole down the middle isn't critical except at the morse taper nose end if you leave enough room between the workpiece and the inner shaft diameter

You'll need a good fixed steady too, everything, absolutely everything, has to be spot on at the nose end plus the outer shaft has to be spot on along it's entire length

A real challenge that will need careful planning and preparation

And lots of help! I'm trying to design it so that it is forgiving of my fingers.

I have 4 150x150x20 steel plates which will form the headstock. I've got a larger front bearing (62 / 30) than rear bearing (60 / 25) so I don't have to be totally dead on in my set up (aligning the tailstock is a bit of a pain).

If I can assemble the headstock and bore out the bearing holes in one operation I have some hopes of accuragy. If I overbore a bit there is always superglue. If I can't bore in one operation then aligning the headstock afterwards is going to be interesting!

The drawing below (onshape - online and free and from the solidworks founders) is missing some bits but should provide an idea of what I'm trying to do.

Iain

And lots of help!

How are you going to assemble the headstock? if welding then you'll have stresses that will need to be relieved before boring out, Boring between centres would do it but have you got a boring bar to suit?, do you have the centre height to set up in line on your saddle, if bolted you could machine out bearing locations using a 4 jaw & adjust to line up with a dummy mandrel... or as mentioned... ask someone with a bigger machine .., lots of questions arising!

George.

Iain, give us a clue on location, some of us have large machinery if you run in to trouble. I hate to see projects stall for wont of asking for a bit of help; credit to you for trying and coming up with a design. Is it for a wood lathe ?

HiI, All.

I'm in Pannal near Harrogate.

I was planning to pin and bolt the headstock. Welding's not something I've mastered yet (I have a stick welder but at the making a spark stage).

Initially I'm planning a wood lathe. If I end up with something robust, who knows where it will go!

Off to finish cooking a curry!

Iian

Hello again Iain,

I was perhaps a bit harsh in my earlier posting, having erroneously assumed you were working on the spindle for a metal lathe. The absence of a through hole alters the job difficulties a great deal.

I live just ouside Thirsk and I could certainly put the centre holes in place for you, if in line boring of your new headstock would be possible on my Myford lathe I would be happy to help there too. Bolted construction with dowel pins as you have indicated for the headstock would take out alignment problems and avoid welding which would introduce them

A suggestion that has just come to mind is to make a dead centre nose to the spindle when you are machining the other detail, it might be invaluable at times

Regards

Brian

I think I would probably machine front and rear plates of the headstock in one operation (i.e. with them clamped or bolted together), to ensure they are the exact same size (machine all edges). Bore the bearing bores in one operation too (plates still bolted together), smallest first then open one out to the larger. Much easier to do a short compact bore like this (with the plates bolted together) than with them separated by the length of the headstock, especially on smaller machines.

Assuming the remaining plates are flat or can be made flat , when you assemble the headstock the bores should still be accurately in line.

Hi

Nobody has yet mentioned that the space availiable will not allow the cross slide far enough to the end of the bed for the tool to start at the end of the bar.Before starting check this out.

Frank

If I may add a comment from hard won experience. By all means rough out the bores for the bearings but leave the final sizing until after the headstock box is completed, things are bound to move and settle to final positions and doing the in line alignment at the end will correct any twist or misalignment coming from the assembly stage.

Bearings are fussy and unforgiving things and having to 'glue' them in at the end to allow for a very small error would be a shame.

Regards

Brian

Iain, I think you'll be pushing your luck with a 14" / 350 mm lathe on a 300 mm shaft, to put the centre holes in you'll need a drill chuck in the tail stock with the Slocombe / centre drill, and I don't think it will fit.

If your lathe is a modern (Chinese or other), it should have come with fixed and moving steadies, if not they should be available, and if your bit of steel was much thinner than the 40 mm you have, a travelling steady would be useful.

I have repaired / modified a number of wood lathes, and I bored the nose of the spindle to fit # 1 MT, because I have a # 1 & 3 MT reamers (3 too big). It's worth doing if you can, my first one was just bored with a boring bar.

Ian S C

Thanks, Brian. I'm still toying with how to register the chuck / faceplate or whatever on the spindle. at the moment I'm favouring using the outside diameter of the nose as the register and putting 3 or 4 threaded holes in the end. My main concern with that is how I can get 4 accurate holes in the top of a 12 inch bar with the kit I've got. The other thought was to thread the outside of the nose or have a central hole with an internal thread. Hmm, I've just had the thought that I could put the screws in from the side rather than the end. Has it's own issues, but different ones.

Bikepete - the outside diameter of the bearings is the same (62mm) - only the internal hole is different I doubted my skills at making two accurate holes of different sizes. And yes I had planned to machine the plates in one go. I hadn't thought of bolting them together, but that's an excellent idea.

bricky - I've checked that the cross slide will get to the end. It does with room to spare.

Brian - At the moment I don't have a boring head for my mill. My sister is delighting in telling her friends she's getting me a 'boring head' for Christmas. I can be geeky at times... I'm not sure that my mill (CMD10) and the head I'm getting will have ability to bore what is effectively a 7 inch deep hole (albeit with a 6 inch gap in the middle.

I've thought of boring the holes as Bikepete suggests, pressing in the spindle and then bolting the parts together with the spindle in place, but I don't really know if that would create stresses which would put it out of kilter. But at least this way I could have some what of adjusting (shims etc) afterwards.

Thanks again to all for advice. This has a better chance of success with your help! Oh - I'm expecting this to take quite some time, so if I go quiet it's not necessarily that it's so disastrous I can't show my face ...

Iain

HI, Ian.

I'll give the morse taper some thought, I don't think my cross slide is long enough for a 2mt which is what most of my tooling is and most of the other internal taper boring approaches are beyond me.

I'm also going to go out and fit my drill chuck in the tailstock and see if there is space for it. push comes to shove I can reduce the spindle length though I don't much fancy taking a lot off the plates with my poor little mill...

Iain