Boring problem

[Sam StonesParticipant @samstones42903]

Goodonya Katan.

Although down here we are nine hours ahead of most of you people, the following notes are beginning to lag behind.

However, having overlooked a third issue mentioned in the NGP link and mentioned more than once in this forum, is that the saddle etc. is driven by an offset force from the apron, whether it be the leadscrew or the rack and pinion. The tool will ‘lift’ after a (forward) surfacing cut (or dig in after boring), thus illustrating that the saddle indeed rotates, albeit slightly.

After more than 60 years of regular use (not all mine), by the time I sold the ML7 it wasn’t even necessary to test with a dial indicator. There was also obvious bed wear closer to the chuck than the mid-section and tailstock end that no amount of gib adjustment could alleviate.

Irrespective of the dimensions of the workpiece and tooling (e.g. boring bar), the old saddle of my ML7 was clearly worn.

Aside from the stress/strain pathway (tool-tip to workpiece), where deflections accumulate, I commend a ‘glance’ at the principle formulae (particularly cantilevers) of beam theory where the dimensions are raised to some power, i.e. cubed and indeed to the fourth power.

Keeping these in mind for both tooling and workpiece, may bring a clearer understanding of how stuff bends, twists, and tries to get out of the way.

I might add – ‘Know your machine’.

Enjoy your hobby, I did

Sam

Edited By Sam Stones on 10/07/2020 20:46:25

[not done it yetParticipant @notdoneityet]

One way of checking the carriage is, or is not, the culprit might be to bore using the top slide – with the carriage and cross slides locked down. OK, it would be hand-fed – most use the carriage feed, when boring, because it will be move parallel to the work-piece without the careful setting up for the top slide (which would normally be jammed tight at the end of its travel).

The gibs can be set tight-ish for a test. Only a good check if the top slide is in good condition, of course.

[Anonymous]

Posted by Andrew Williams 1 on 10/07/2020 20:36:32:

……whenever possible use an hss tool newly sharpened rather than an insert tool.

That's not my experience. I've just finished boring the cylinder castings for my traction engines. The bores are parallel and round to within 4 tenths of a thou over 5.25", but I've had all sorts of trouble with chatter causing a carp finish, around 6 to 7µm Ra at best. I tried several tools, two boring bars and different speeds and feeds. In terms of chatter I'd rank the toolbits as follows, starting with the worst:

Sharp insert CCGT

Home ground HSS

CCMT insert

Once the HSS toolbit started to chatter that was it, each successive pass (even a spring pass) just replicated the chatter marks. With the CCMT insert shallow, or spring, passes reduced the chatter marks rather than simply following them.

The cylinder boring was done on the horizontal mill, but when boring on the lathe I use CCMT inserts as standard, and CCGT on aluminium. Oddly I rarely have a problem with chatter on the lathe and get a much better finish that I did on the horizontal mill. The key to reducing chatter when boring on the lathe is to increase the feedrate. On the horizontal mill it appeared to be the opposite, ie, reduce the feedrate.

Dunno if the above makes me an expert, an ex-spurt or just plain awkward? Ketan?

Andrew

[Ketan SwaliParticipant @ketanswali79440]

Posted by Andrew Johnston on 10/07/2020 23:07:14:

Dunno if the above makes me an expert, an ex-spurt or just plain awkward? Ketan?

Andrew

I dont know what that makes you either Andrew.

Ketan at ARC

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