Boring in the lathe - imbecile question

My aluminium stock arrived today. I decided to go for 60mm OD tube with 10mm wall thickness, so no problems with tool clearance. Had to teach myself how to use the 4-jaw chuck as it is too large for my 3 jaw - not sure if I'll ever go back now!

The problem I have, though, is when I increase the inner diameter from

40mm to 50mm, for a 20mm section, it leaves a step (which is good - it's what I want) but when I feed the tool in automatically, when it gets to this step on each cut, a horrid squealing noise ensues as the tool is trying to cut on 2 faces. I generally disengage the dog clutch on the leadscrew and have offset the compound slide by 15=BA so I can wind it away from both faces at once - is this the right technique or is there something different I can try?

I hope that I have understood correctly. Basically in my mind you are traversing too far! It sounds as if you have little or no clearance on the front face of the tool and you are hitting the step that you are producing, each time full face. In my mind you should be power traversing to a carriage stop and changing to manual feed before hitting the stop. Alternatively depending on your tool profile you may be better facing out to the required radius then power traversing away from the chuck.

If you want to end up with a 50mm THROUGH bore then just traverse all the way through on each cut. The original statement suggesting 20mm at a time was based on a solid bar. Given hollow bar you have bags of room for chip clearance so cut all the way through.

But maybe I misunderstood.

Richard

The original post was about using a solid bar but the tool clearance problems and enormous amounts of swarf I'd be producing made me go for a thick tube instead with 40mm inner diameter. The workpiece is 80mm long and I need actually a 23mm section bored out to 50mm. Perhaps I'd better build a carriage stop or just disengage the power feed earlier and, as you suggest, manually feed the rest. I do love watching the lathe power feeding - find it very therapeutic.

Not sure how I'd face out to the required diameter and then power away from the chuck and don't think my tool profile is really designed for cutting in that direction but will have a play!

Easiest way is power feed out from the chuck. Set up a stop which can be as simple as a bit of bar resting on the lathe bed up against the headstock. Set the tool a bit shy of the depth you want to finally bore to - say 22mm in your case. Position the tool in the bore and wind out manually to the depth of cut you feel you can handle. Power feed out, rinse and repeat. When you get close to final diameter you can take things a bit slower and then just finish the base to depth.