Thread: Turning betw. Centres

One way is to turn it end for end and come from both sides. I'd do this and get it close to size or even finish it off. If you really want to take the finishing cut in one go, make up a makeshift driver and stick it on the face with araldite or such. Make sure it's such that it can't fly off and hit you in the face if the glue lets got.

Driving from the face is often done in large scale production. If you look at the end of a car axel you will see two little tags forged into the inside of the shafts face, next to the centre drilled hole. These are for driving between centres when the axle is originally turned. Sometimes in production a driving centre, similar to a wood lathe, is used. This can require huge pressure from the tailstock. Both these way are probably of no use for you.

The only way I can see that it can be done is to tap a thread in one end of the work piece and then turn up a short section that is less than 45mm in diameter with an extended section threaded to accept the shaft . Dont shift it in the chuck after turnig and threading it so its nice and centered The other end of the work piece is held by a live or dead center in the tail stock.
You will have to center drill the work piece first then turn and thread the support shaft .
A righthand thread will not undo against turning force.

Good luck if you can achieve what you want with the three jaw.
Can the ends be touched at all or do you need a flat end.
I assume that you can use the ends to do your driving seeing you mentioned between centres.
You could make up a drive dog that will drive off the end of the shaft.
This dog would have to attach to the drive centre.
You can fabricate something that will fit over your drive dog with 2 taped holes in it.
drill clearance holes in the end of your shaft to suit the screws in your drive dog,you will also need 2 nuts to suit the thread you use to act as lock nuts.
You would be better to turn a drive dog in your 3 jaw ,make sure that there is enough material between your chuck and the end of the drive centre for you tp attach your fabricated dog to.
In essence the 2 screws in your fabricated dog will be doing the driving through the 2 holes you have drilled in your shaft.

I'll probably try all 3 methods in the end. The idea that I currently have after reading up on half and self driving centres is to glue the 3 jaw chuck centre to the centre drilled shaft and take multiple light cuts.

If that fails (which is most likely), I'll fab up a dog and do whatever it takes.

Very good suggestions gents and thank you for taking the time to help an idiot like me.

Regards.

I made a cylindrical square to use a master square. If you can tap a screw , say 1/4 - UNF or UNC into the end about 10mm in from the outer diameter then the rest is easy. Chuck up a short length of 12mm or 16mm diameter and turn a 60 degree center point on the end. Screw a cap screw into the job and have the screw long enough to be driven by the chuck jaw. This is the standard method of machining and grinding a Master Square. Both ends of the square were recessed first to forn an anulus about 8mm wide. The squares I made were 60mm in dia and The parts I made using the square were accurate in 90 degrees angles to less than 6 millionths of a degree, but I digress. Put a screw in the end and turn a center for the job.
Kody

Originally Posted by Kody

I made a cylindrical square to use a master square. If you can tap a screw , say 1/4 - UNF or UNC into the end about 10mm in from the outer diameter then the rest is easy. Chuck up a short length of 12mm or 16mm diameter and turn a 60 degree center point on the end. Screw a cap screw into the job and have the screw long enough to be driven by the chuck jaw. This is the standard method of machining and grinding a Master Square. Both ends of the square were recessed first to forn an anulus about 8mm wide. The squares I made were 60mm in dia and The parts I made using the square were accurate in 90 degrees angles to less than 6 millionths of a degree, but I digress. Put a screw in the end and turn a center for the job.
Kody

Great idea Kody, I like a lot.

Ta.

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Not to bad as long as if it does slip, he catches it quick enough so that it dosent burn out the spindle centre.

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As your not really machining much of the diameter. With your three jaw chuck, why don't you grip the steel by a mil or so on one end, put your live centre in the other end and turn the diameter right up to the jaws. Champher the tailstock end, then spin it around, put a nice little champher on the other end and Bobs your uncle. Job done.

Squirrel.

Originally Posted by radish

None too sure where anything can burn out, the dead centre is fixed in the chuck and it revolves with the chuck. If the workpiece is held tight/pushed up with enough pressure towards the dead centre, by the LIVE revolving centre, then how in the hell can anything burn ?

In the last 30 years of doing this, I am yet to even burn out a set of bearings in ANY live centre, spun the workpiece quite often, because of not enough pressure from the tailstock, or, too greedy with the cut.

None too sure what brand of live centre your using, but when your using it and it gets hot when it's revolving, then I suggest you better chuck yours in the bin and go get a new one.

Then again, if you aint tried this lot out, then 'how in the he!!' are you going to able to give an accurate assessment, of what actually happens ?

regards radish

Not wanting to get in a slanging mathch with anyone who may not of understood what I was Reffering to with Spindle Centre but thats the part that is in your Chuck attached to your HeadStock Spindle.
I have had at times when turning between centres had the drive dog come loose and the drive ceases causeing the centre to burn,as the Spindle is still rotating.
The problem can be compounded by the size of the centre being used.
I also would disregard any live centre that produced excessive heat whilst being used.

Guys, thank you for all the brilliant ideas. I have'nt got a live centre but sure have a good excuse to get one.

I'll report back when I'm done. I have quite a lot of projects going at the same time and nothing seem to get done due to lack of time or money or one project is put on hold waiting for parts/tools to be produced by another. Oh well, it keeps me off the streets I guess.

Regards.

Originally Posted by fluxcored

Hi All,

I've got a 46mm thick bright mild steel round bar of 62mm length. The length is spot on but I still need to take 1mm off the diameter to reduce it to 45mm.

I've only got a 100 mm 3 jaw chuck and a dead centre and think that I'll have to machine it between centres in order to make a single uniform cut across it's length. I'm thinking of using this fella's approach http://www.cartertools.com/turncent.html but fixing a lathe dog onto the workpiece itself will interfere with the cut.

I'm trying to come up with a solution to attach a lathe dog to the side of the work piece so that I can do an uninterrupted cut.

Has anybody got an idea how I could approach this.

Regards.

havent read all this but you need one of these

That's a nice page Patrick

Within some of the stuff that's now missing, Radish had a good suggestion which I don't think anyone was disagreeing with.

If you are careful to watch what is going on, so that you promptly stop proceedings in the case of slip, you can take a light finishing cut with the drive just coming from the friction of the ordinary head stock centre.