Taper trouble

[paul]

Noob question #917

I'm trying to but a small amount of taper on a (proportionately long) bar - the bar is about 6mm dia and 50mm long and I need to taper it to 5mm dia at one end (the tailstock end)

I've calculated the angle required and set it up as in the image but the top-slide handle is fouling the tail-stock casting. I can't get the tail-stock any further back and I'd guess that support at that end is required for this thickness (thinness) of bar.

I suppose I could extend the tool further out but that doesn't seem a good idea.

Is there an obvious solution that I'm missing?

[lancelot]

Yes Paul,
If I am correct, the top slide should be capable of turning through 1/4 of a circle so that the adjustment handle will be at your ''STOMACH'' loosen of the toolpost clamping lever and reposition the cutting tool, if the tool post clamping lever fouls the tailstock so as not to let you bring the tailstock closer to the job, unscrew the toolpost clamping lever handle.
All the best for now,
John.

[paul]

John, I can turn it through 90 degrees (clockwise as you say) but how then can I cut at the correct angle?

[Deleted]

Can you rotate the toolpost about 30 degrees clockwise, thus moving the tool nearer the work. This is my normal resolution to the problem, the tool should still cut fine.

[chameleonrob]

just allow more overhang in the tool, it looks like the tool is big compared to the workpiece so it won't cause a problem. If you want to keep the setup as rigid as possible tighten the adjustment gib on the saddle till it can't be moved and tighten the the gib on the cross slide till you can barely move it, oh and remember to unadjust them before doing any other jobs.

rob

[jgb7573]

Hi Paul,

I think your only option here is to have the tool sticking further out of the toolpost. For light cuts this should not cause you a problem, especially with tailstock support fior the workpiece.

If this is your first bit of taper turning, remember that it is important that the tool bit is at centre height. It's more important with taper turning than with ordinary parallel turning.

Good luck,

John

[paul]

usra: I can only rotate it in 90 degree increments.
rob: that sounds good to me

I thought setting it up like so means I'd only need to wind the top-slide 'forward' until it stops cutting then wind it 'in' a little more and so on until I get the required diameter at the right-hand end.

[paul]

Silly me - should have checked my bible first ('Model Engineering: A Foundation Course')! It discusses this very problem and suggests cutting the taper the other way round i.e. cutting a slot of the required final diameter at the chuck end. In my case it would mean rotating the topslide 10 degrees clockwise. Trouble is I haven't enough length to do it this way round now. Maybe I'll try rob's 'yank the tool out a bit' method after all!

EDIT: Oops John, missed your post - yes, it looks like that's the only option here. Thanks for the tool height tip

EDIT2: Oh yes John, this is part of the connecting rod for Vulcan (my special half size variant!).

[havoc]

What if you would cut it towards the head? So the large end of the taper is at the tailsock and the small end at the head.

[paul]

havoc said:

What if you would cut it towards the head? So the large end of the taper is at the tailsock and the small end at the head.

Yes Havoc, that's what my 'bible' suggests but I don't have enough length to do that now. It wouldn't be such a big deal if I had some 6mm rod lying around - the only piece of steel I could find was 19mm in diameter so I had a bit of turning to do to get to this point!!! LOL

[Tel]

Well you could drill and tap the end to take a small extension that would act as a chucking piece

[abby]

Why not simply set the tailstock over ?
Abby.

[Tel]

I've always avoided doing that. On the other hand, there are a few designs about for setting-over centres that fit the tailstock.

[Tel]

paul said:

EDIT2: Oh yes John, this is part of the connecting rod for Vulcan (my special half size variant!).

This being the case, it would probably be quicker and easier to just form the taper with a file - it's just got to be visually pleasing, not a precision fit to anything.

This rod was done thattaway

[SteveW]

Paul,

I'm with Abby, set the tail stock over and and cut the thing as you would parallel. For large offsets you really need concave centres and use ball bearings.

Chances are the tail stock won't be in exactly the right place for parallel turning anyway. Getting it back there isn't a big deal either if you've got a DTI you can mount off a face plate/chuck and finger the centre in the tail stock. You just need to twiddle until the reading from front and rear match. A final check by attempting a parallel cut on a long bar will confirm it.

An alternate is to invest in a taper slide that bolts on the back of the bed. This has a long dove tailed bar which you set over to match the required taper. A follower bolted to a free cross slide tracks the taper not the bed. You could actually make yourself one with a bit of long bar mounted off the back of the bed with a ball-race follower. It'll only work in one direction unless you make the bar/cross slide fully captive.

[PH]

Can't you put a washer under the tailstock handle so that it tightens in a different position or remove it and use a nut, since it's pretty certainly a standard thread?

[havoc]

Oh, I hadn't seen that the handle is the problem. I tought the whole topslide got in the way. Just unscrew it and put on a nut. Probably M8, M10 or M12.

[lancelot]

abby said:

Why not simply set the tailstock over ?
Abby.

Hi Paul,
this is what I assumed you had done in the first place, then follow the suggested idea? will it not work out for you?
All the best for now,
John.

[paul]

I can't set the tailstock over on this type on mini-lathe (if I understand it right that means having the tailstock offset relative to the lathe's centre line?).

Lot's of helpful tips here anyway, thanks all

For this first attempt it's extendo-tool time!

This being the case, it would probably be quicker and easier to just form the taper with a file - it's just got to be visually pleasing, not a precision fit to anything.

I hear ya Tel but I'm trying so hard to stick to the plan this time ;D - it's good practice for me!

[GeorgeRay]

One of the things you could have tried is to mount the tool on the other side of the 4way turret. However you then need to have a long enough length of bar so that the turret misses the chuck when you get to the full diameter end. Thats a way I have used in the past.