Jaws in the chuck

I went to fit a 2" bsp plug into the 3 jaw today & it was too big so I took out the jaws to reverse them. They would not fit. I had a look at them & realised the thread cut was the other way round so would not fit.

I then remembered when I bought the lathe , there were other sets with it. Of course the correct ones were in the box. So fitted them. Beginners mistake I guess.

Also looking at the pictures which way is the best . I plunged for the jaws in so there was no rotating jaws sticking out. Is this correct. Also yes I did give the jaws a dam good clean. This part is having a 9 1/16" hole down the centre & then a taper cut down it to self centre coins in the punch I am making. 316 Stainless & machines very well.

Steve.

Steve,

Second picture with the jaws in is the best for the reason you stated (safer) and also because more of the scroll is in contact so less likely to damage the chuck if you horse it up.

Paul.

Ah thanks for that. Feel silly asking these questions. But I guess I only have to ask once.

Steve.

While most 3-jaw chucks have two sets of jaws, small precision 3-jaw chucks for use on instrument lathes normally only have one set. which are reversible. The 'threads' on the rear of the jaws are like a very flat ellipse.

Andrew

If the 9/16" hole is through-drilled, there could be a risk of hitting the chuck jaws if they are as shown in photo no. 2. Best to check.

3 step jaws, he is on middle step so a step worth of clearance behind at 9/16" should be plenty of room. When it's spinning you should be able to see the drill breaking through.

Paul.

Isn't there a trade-off between depth of engagement with the scroll and the distance between the work and the face of the chuck? Neither setting is ideal in my opinion.

The chuck is apparently a Grip Tru and if it is in good condition it would be a shame to overtighten it.

Depending on the taper it may have made it easier to set the topslide over to cut the far side of the taper than the nearside. At some angles you can have issues with handles interfering with each other or even knuckles hitting things. The position may just have made it easier to turn the handle evenly for a better finish, straight wrist compared to bent wrist comes to mind. I have not seen the video so am just speculating.

One other thing is that the pressure on the topslide leadscrew, nut etc, will be in the same direction as a conventional external cut. There may be a reason he wanted this to be the case.

Martin C

I see what you mean. But I thought it was always best to have a downward pressure on the slides. The way he did it means the pressure is trying to pull the cross slide upward. Or am I missing something. Later today if I ever get up I plan to attack the taper. I will be doing it from the front of the work. I have not even worked out the angle I need yet.

Steve.

Could it be that the 'Geordie guy' was running the lathe in reverse? That way the pressure on the cross slide would still be downward.

Sometimes (screwcutting for example in a blind hole) this is better because the tool is moving out of the hole with no chance of running the tool into the job.

Brian

Steve,

One reason for the way he did the internal taper may be he was trying to get a matching taper - turned the male taper first and then wanted to do the female at the same setting? Saves a lot of faffing around resetting the compound to pick up the correct angle again!

ega,

As to what is ideal, that is a matter of opinion. If you feel so, perhaps you can share the benefit of your experience and tell us a better way? In my limited 40 odd years of experience the best way to do an awkward job is the one that works and gets it done. There are many compromises that have to be made when deciding on a method of work holding, not least the size of the machine and the available kit.

Paul.

Turning an inside taper

This is the taper turning from the rear side. ?????

Skip the 1st few minutes.

Steve.

Edited By Steviegtr on 13/02/2020 12:31:19

Paul got it correct, he cut the external taper first and left the cross slide at the angle used (he says so in the video).

Martin C

Ah I see said the blind man, to his deaf daughter. Thanks for that. I thought it was so the video could be seen. Umph.

Steve.