Lathe Dogs

[Tozguy]

While waiting for the heavy weights to shed some light, in my humble opinion any work that needs extra support from a TS centre, should be held between centers. Short work can be held in the chuck only. Situations where anything else is required should be dealt with on an individual basis.

In Tom's video, maybe the wobble is severe to make a point but doing a job like that would be a last resort for me. I would not make a habit of it for sure.

 

[jpfabricator]

If you are supplied with the material for a part with no "extra length" you would have to turn between centers.

Sent from somwhere in east Texas by Jake!

 

[12bolts]

Toms video is a bit misleading, and I think he has exaggerated the run out in that part to make his point. What he has avoided saying however, that if he drilled the centre with the work piece out that far then the runout he demonstrates will need to be turned from the outside to get back to concentric. You cant have it both ways.

...... any work that needs extra support from a TS centre, should be held between centers. Short work can be held in the chuck only. Situations where anything else is required should be dealt with on an individual basis......

Not at all. Hold your work short, centre drill, extend out as required, WITHOUT engaging the TS use a dial indicator to get the work running concentric, THEN run the TS into the work for support.
The TS is not there to force the work to run central. It is a support. You wouldnt use a steady to "force" the work to run centrally. Why would you try to do that with your TS?

If you are supplied with the material for a part with no "extra length" you would have to turn between centers.

Or you could turn 1/2, flip it around in your chuck and turn the other 1/2

Cheers Phil

 

[stupoty]

i made an arbor today by center drilling with the piece extended from the chuck I did have to turn off about 1mm of diameter to cut all the way round down the whole part it was just some cold roll steel that isn't super straight. It started at 15mm diameter and I had it sticking out about 100mm so I had to use a center to support it whilst I cut it. It felt totally safe.

As was said about drooping stock, if it's drooping then that's hanging out too far ;-) , that would be a good time to use a fixed steady for center drilling.

If the stock is bent at all then it will need to be turned until its strait. The further out it is sticking the more obvious this should be (visually) even if you dial it in carefully with a four jaw chuck.

Stuart

 

[Tozguy]

Or you could turn 1/2, flip it around in your chuck and turn the other 1/2

Cheers Phil

Phil,

Could you explain how that would be the equivalent of turning between centers please, I don't follow?

 

[12bolts]

Toz, Its not intended to be the equivalent of turning between centres. I was merely pointing out that just because you don't have any excess stock to grip doesn't necessarily require setting up to turn between centres. Depending on what the job is, the steps required to complete, and the accuracy required, it could be just as simple to turn 1 end of the piece, then flip it around and complete the other end. Turning between centres has its applications also, but it is not the be all to end all.

Cheers Phil

 

[Tozguy]

you know, ive never understood the purpose of a lathe dog and turning between centers. why not just put it in the chucks? if youre worried about chuck damage, youre still putting a set screw from the dog and risking damage from that...
in my mind, i cannot think of a single reason to use a dog. (im sure this is very ignorant of me... i await the onslaught, but im being honest!)

Who was it that said '' If you want to know ask questions, if you don't don't.''

Setting up to turn between centers can be a chore but it has its advantages. It is the way that gives the best results from a lathe. It is definitely worthwhile to be equipped to do it. A live centre for the tailstock is a worthwhile investment. Or a dead centre, which you can easily make, will work with the right lube.

A dead centre for the chuck can be easily made also. It is good technique to skim cut the centre every time it is chucked up.

Standard bent or straight tailed dogs are limited in their application. Improvising ways to drive work between centers is common and there are many simple but ingenious ways to do it. There is no need for the dog to mark the work. For example, often a hose collar clamp can be used to grip the work.

Once you have turned between centers a few times I bet that you will appreciate turning at its best.

 

[Tozguy]

Toz, Its not intended to be the equivalent of turning between centres. I was merely pointing out that just because you don't have any excess stock to grip doesn't necessarily require setting up to turn between centres. Depending on what the job is, the steps required to complete, and the accuracy required, it could be just as simple to turn 1 end of the piece, then flip it around and complete the other end. Turning between centres has its applications also, but it is not the be all to end all.

Cheers Phil

How can there be no stock to grip the work when it is between centers but enough stock to grip with a chuck?

I agree that some jobs can not be done between centers. But some other jobs can and should be done between centers.
My only statement has been that the chuck and tailstock centre option is not equivalent to turning between centers and should be used with discretion. If real turning between centers can be done why avoid it?

Also, flipping the work in a chuck to do each side separately has its place. But that too is not a substitute for turning between centers.

It is important to understand the pros and cons of any and all ways of holding work so that they can be applied to our best advantage.

 

[Tozguy]

Maybe the following can shed some more light on what to use when.

This is what Tubal Cain wrote about this subject. Quotes are from his Workshop Practice Series book number 15 titled ‘Workholding in the lathe’

From p. 27

‘’To sum up, provided the centres are correctly shaped and truly aligned (and all else is in order) between centres turning produces the most accurate and repeatable of all methods, even when the work piece is so short that it could readily be chuck held. Further, it is possible to contrive to hold the most unlikely objects between centres.’’


From p.62

‘’Just as most ….expect their lathe to do work far in excess of that for which it was designed, so they seem to expect quite unreasonable degrees of accuracy from their chucks.’’. In normal manufacturing neither the Designer nor the Production Engineer would expect to reverse the work in the chuck - apart, perhaps, for a simple end-facing operation…’’


From p. 67

‘’There was a time when the use of the tailstock centre in conjunction with a self-catering chuck was disparaged; a relic, no doubt, of the days when normal chuck run-out was far higher than it is today. With work of reasonable length, however, no harm at all can result from supporting the tail end of the work in this way, and there are many circumstances where it can be a great help. Trouble is often experienced when turning slender workpieces between centres, with chatter especially. If one end is held in a self-centring chuck (or in a properly set-up independent chuck) the work is stiffened, the natural frequency of vibration is altered, and the chatter may well disappear.‘’

‘’I never have any hesitation in using this combination (chuck and TS centre), with one proviso: that it is possible to cut an accurate centre in the end of the workpiece. There are certain limitations. A piece machined entirely in the chuck will be true; a piece machined entirely between centres will be true also; but a piece machined using both may not be.’’

‘’ There is a risk that as the work heats up during cutting it will be thrust further into the chuck as it expands….. feed dial readings used for locating shoulders - i.e. for dimensions along the length of the work - may be thrown awry if the work is thrust further into the chuck jaws. ‘’

 

[stupoty]

The biggest advantage to turning on centers has already been mentioned I think are it's biggest draws.

1, very good repeat ability when removing and replacing the work piece for measurement / test fit.
2, sizing parts to length very accurately before working them especially if doing a small batch of parts like stand offs or bolts.
3, very secure holding, almost impossible to knock out of alignment, only swarf or dirt in the center holes will mess that up.

down sides
1, can only work the outside of a part.
2, have to remember to hold the part when loosening the tail stock ;D

Stuart