reamer question

[Paulsv]

As to reaming after boring, it seems to me there are several reasons. First, boring can give you a tapered hole, because of the spring of the boring tool, and possible slight misalignment of the lathe. Reaming after boring takes out any taper. Second, in my experience, a good reamer gives me better finish than a boring bar. Finally, because of the difficulty of accurately measuring a bore, and the expense of accurate bore measuring tools, if I want an closely sized hole, I tend to drill to remove most of the material, bore to make sure I have a straight hole, concentric with the OD, and then ream to final size. My reamers give me accurate sizing, to the best of my ability to measure.

 

[gus]

A Between Centres Boring Bar will create a bore which is parallel and concentric-- regardless of the alignment of the tailstock.

What seems to be appearing is the wrong use of a hand reamer which is better suited to a task away from the refinements and inherent accuracy of the lathe.

Others are welcome to disagree.

Hi Goldstar,

I agree. It is very difficult to ream holes to perfection on a lathe.

Now about to start on a new project but I have two to pick on.
Spenging to much time on the Notebook.Must break this addiction.:wall::wall::wall:

Fishing been good.

Regards,

Gus Teng.

 

[MuellerNick]

First, boring can give you a tapered hole, because of the spring of the boring tool,

This is a common misunderstanding. The spring of the tool is the same, wether it is at the start of the bore or the end. It makes no difference. So you don't get a taper from that. You only see a short taper at the beginning, when the tool starts the cut and deflects. Then it is in equilibrium with the cutting forces and no more bends out of the cut.
You can make perfect bores with a boring bar. Only problem is with small diameters and/or deep holes.

With a reamer, the tailstock has to be dead aligned with the spindle. And -what most forget- also when you feed out with the quill.

By the standard, a tailstock has to be at center or a tad above. So it will always be a bit above. And it has to point upwards or be horizontal. So it will always point upwards. And it has to point towards the tool side (operator for a conventional lathe) or be parallel to the spindle. So it will always point to the tool.
And all the same is true for the spindle.
Now you realize, that even with a perfect toolroom lathe, that won't work.

That's why floating reamer holders do exist (they cost almost a fortune).


Nick

 

[Paulsv]

Nick- That is a very good point about the spring of the tool being the same throughout the cut. I guess i'll have to blame any taper on lathe alignment, tho it always seems to be worse when boring, for some reason. As to the requirement of perfect alignment of the reamer, of course I align it the best I can, but I understood that the cutting geometry of the chucking reamer, with it's 45 degree cutting edge, tended to make it self centering, so that it would follow the bored hole, and the long length of the reamer, in relation to its diameter, gave it enough flexibility to overcome some slight mis-alignment. I'd be interested to hear what you and others think about that.

 

[MuellerNick]

and the long length of the reamer, in relation to its diameter, gave it enough flexibility to overcome some slight mis-alignment.

Yes! I even crank out the tailstock's quill quite a distance to make that wobblier. So you get more wanted flex.
It is also good practice to turn a short starting hole. This is dead concentric and will lead the reamer into the right direction. I never use hand reamer.


Nick

 

[goldstar31]

I still think that some are missing the concept that an inline boring tool actually doesn't need a reamer to follow its cutting action. True, there may be a need to conduct a final hone.

Moreover, this alignment or mis-alignment is a misconception as a hole will be both parallel and concentric. It's not new- its old Archimedes. He is still around. The only time that the hole may be out is if the ways of the lathe are not straight and true.

Again, the bell mouthing is pie in the sky, it simply doesn't happen. Once a roughly drilled start hole is being truly the bored- the hole starts to form this perfectly parallel condition.
The final cuts have an equal 'spring' at the whole operation. As for sizing, the cutting edge is advanced under control and if the angle of cutting action is correct a controlled advance is possible.

Is this 'sic blether'? Well, look at the construction of the Quorn tool and cutter grinder. It's well documented but whether it is well read is quite another matter. The base castings are linked by two castings exactly 3.5" apart and separated by two precision ground bars of exactly 1" diameter and the work head in between the two castings has to traverse in between the two bars. It gets a wee bit complicated because the rear casting has to have one hole split but opened- 3 thous more- to adjust.

Now , gentlemen, before you rush off and cry 'Foul' or whatever- I've done it.- Twice.
On the last Quorn, I altered the construction to avoid the possible seizing caused by the splitting of the rear casting.

The possible shock comes when one realises that making an in line boring bar( or two in the case of a Quorn) is dead cheap. It only requires round mild steel bar and one round cutting tool bit. It helps if a 40 TPI tap is available to make the adjuster.

Point here- the proof is to actually prove these old engineers wrong. I simply followed the advice.

 

[jack620]

This is a common misunderstanding. The spring of the tool is the same, wether it is at the start of the bore or the end. It makes no difference. So you don't get a taper from that. You only see a short taper at the beginning, when the tool starts the cut and deflects. Then it is in equilibrium with the cutting forces and no more bends out of the cut.

Thank goodness somebody finally confirmed that for me. I've been reading about the spring in the tool causing a taper for years, but I could never understand why that would be the case. You've confirmed what I always thought Nick.