Why not true the bar up externally first, at least in the area where the steady sits ?

What is the finished bored diameter going to be ?

Best to drill the major amount of material before boring, that will allow a larger diameter boring tool to be used and help reduce any tool deflection.

Using the steady is no guarantee the lathe will bore parallel unless it is running on a truly turned surface, even then I wonder does the lathe turn parallel on external turning over the full depth being bored ?

If the lathe does external turning parallel it will be tool deflection causing the taper, check tool exactly on centre height, cutting tip does not drag or rub and is sharp before trying to take light correction cuts.

You may have to adjust speed and feed to get optimum results.

Emgee

Hi YouraT, set the bar up like Vintage Engineer says and then true the area where your steady will be running on while the tailstock is still in position. With long slim boring bars, I've often found that the spring becomes accumulative the deeper you go, i.e. as soon as the bar enters the bore it will have a small amount of spring, but of course there will be resistance to the cut which will make it spring a tinny bit more and can build up like that the deeper you go. To over come this, I take a cut, back out and then take another cut or even two without advancing the tool and then carry on this way until you get to the size you want, Always works for me.

Regards Nick.

Thats and awful lot of taper, and assuming your lathe usually turns true,the fault lies with steady and spring in the boring bar, The steady pads should always run on a true machined surface,and be careful when tightenind the pad screws they must only just touch the work,too much pressure and the work can be pushed to one side and therefore out of true.plus they must be kept lubricated when the work is revolving ,use some oil and squirt with an oil can.One cause of a severe taper when boring is swarf building up in a " birdsnest "around the tool and the bar and deflecting the bar away from the work .I would be using a bar at least twice the diameter,made from silver steel with a hole in the bar to take the toolbit, If the bit only protrudes a small distance from the bar then swarf quickly builds up ,particularly with materials that produce long strings of swarf ie steel and ali ,also check that the boring tool bit has adequate clearance. A pecularity of the steady is that if the three steady pads are set up so that they are not in in line with the centre line of the lathe,the work will work or "walk "out of the chuck,even if you are convinced that the set up is true keep an eye on the chuck end of work to make sure it is still well in the jaws, I have seen 'Walking" as it used to be called but never seen or experienced work come out the jaws. Usually caused by one pad screwed in too much and deflecting the work off centre and the other pads then screwed in .When working with a steady,lubrication is essential to avoid the pads marking the workpiece,if a near finished work piece has to be set up in a steady then some times it possible to make a collar ,which can be secured with grub screws, the collar is then set up true by either adjusting the grubscrews or machining the collar,to avoid marking the work piece small brass slugs can be fitted under the grub screws.Well theres some info on steadies but I would bet that the bar is deflected by birds nesting build up of swarf,I have seen large buildups of swarf put sufficient pressure on the business end of the bar to actually move the toolholder.

All sound advice above but one question…..how are you returning the boring bar to start another cut?

If you're using the self-act (or winding out with the lead screw hand-wheel) at the same setting to back out the tool this could be a contributory factor. The safest way is to stop the lathe at the end of the cut, release the carriage and wind out by hand. Now put on your next cut and continue to bore with the self-act engaged. Carry on ad nauseam.

(if you use self-act to withdraw the boring tool and there is slackness between the carriage and the lathe bed shears, the carriage can tilt and take off some more material from the bore on the return. I appreciate I'm inviting abuse for offering this but years back, on an old & worn ML10, I discovered this issue. It was when boring out the rear axle for the Clayton wagon. Eventually after stopping the 'powered withdrawal' I got it parallel).

• I see no advantage of setting the steady next to the chuck. If the stock is round and cleaned up, moving it along the ways should make no odds whatsoever – if it does you are already in trouble (possible ‘walk out’ from the chuck).
• Far better to simply set the steady at the tailstock end, with the centre still in place, and every thing should run the same after removing the tailstock support. Checking for running parallel is ‘belts and braces’ but always better to check, anyway. I do.

Put a centre in the stock.

With a live or dead centre in the tailstock, take a minimum skim of the od to give the steady a usable surface.

Set up the fixed steady 25mm from the end. Cut a disc of plastic or card to fit on the end to keep the swarf away from the legs of the steady.

Drill the hole close as possible to the finished diameter. Careful depth control needed if the hole is blind.

Use a boring bar of the maximum size to fit the drilled hole. Use a bigger boring bar if and when the hole gets big enough.

Pay attention to swarf build up, you may have to clean out the hole at every pass.

Never expect the top slide to bore parallel holes, always use the saddle.

If the size is critical, make a plug gauge with a stepped end first, when the front end goes in, then you can creep up to the second diameter which should be -0.025mm. An exact size plug will not enter a bore until the bore is oversize.

Edited By old mart on 13/04/2020 19:55:18

That will work too. Just extra work though. If the chuck is holding its end true and you set the jaws on that end before sliding it along , the jaws are set true. Thats the common way of doing it and has been for over 100 years. Quick and easy and works with long jobs that would otherwise need the steady in place to drill the centre hole in the first place.

Edited By Hopper on 13/04/2020 21:25:49

Hopper read my post again more carefully. You use the dial indicators to true the part with the fingers not touching. That gets the end of the part turning on-axis with no runout. Then you zero the dials and bring the fingers in until they are all touching and the dials are both zero. That means you have it constrained by the fingers AND still on axis. It's about as accurate as you can get it, the only rotational axis error then is in whatever runout you have in the 3-jaw at the other end (and he has a grip-tru so that could be brought to zero).

Setting the finger at the chuck works most times, done it many times but you can still have the part walk out of the jaws especially on thin walled parts. If you set the fingers touching at the chuck then slide it back, your fingers will be centring the part the other end off-axis by whatever runout you have in your 3-jaw. Flat bed ways have the extra potential for error by the amount of clearance between the steady and the inside shears.

Both methods work but to different degrees of accuracy.