Best direction for lathe machining

[chola]

Hi,

I'm hoping some of the old shop hands will be able to chime in on this one (hopefully doesn't cause too much of a debate!), as well as young ones! All opinions valid.

Simple question, what is the best tool setup for machining on a lathe. Very open question but I have attached a (dodgy) pic of what I am asking. It's early and I coundl't be bother doing the whold CAD thing for this, gotta love Paintbrush

Basically to do with tool position. I have seen both positions used, but was wondering if there are any specific benefits / drawbacks from one to the other - A or B (other than the obvious clearance drawback when making longer cuts using option B below).

Would be interested what way is preferred, and why.

Thanks.

COlin

[mrainey]

It looks strong, but I'd think you'd need to evaluate the part geometry and the mix of other tools in your turret before deciding on what's "best", or even feasible.

[Geof]

I am not sure it makes much difference. When tool A is facing it is cutting on the tip in much the same way as tool B cuts on the tip when it is turning. The opposite is also true; when tool A turns it is cutting in a manner similar to tool B facing.

[mrainey]

Only the same with an 80 degree diamond or trigon. If you were doing undercuts, say with a triangle, 55 degree, or 35 degree diamond, the toolholder would only work one way. Lots of jobs lend themselves to using a triangle or dnmg for moderate roughing of straight diameters and undercuts with the same tool.

I still think it's somewhat application-dependent.

[Geof]

I should comment that I was looking at the pictures at the tools seemed to look like the brazed carbide bits that are readily available; my comments apply to them.

When insert tooling is being used it may be completely directional and then you match the tooling to the application as mrainey states.

[mrainey]

Geof,

You're probably right. I just assumed insert tooling because that's what I've used for turning 99% of the time.

Mike

[chola]

Hmmm, that was just a general pic I drew as an example, but interesting point (pun intended) about insert tooling.

I know there are a lot of variables (eg: type of part being turned etc), but for arguments sake; let's say it's to turn down a bar to a specific diameter along its esposed length.

It may be there is no right way or wrong way, but I'm still a little new to all this, and wanted to know what the more experienced thoughts were.

Colin

[One of Many]

Not only is it application dependant, but it is also dependant on the tool grind and method of cutting. If you don't need a tailstock for drilling or support, then the following will be the basics.

Application being the material length verses cut length, material type, depth of cut per pass and strength of cutter body or mounting.

The grind, as in rake angles, clearances and nose radius. Much of this directly related to tool cutting pressures and chip break or direction of peel.

Method being roughing, finishing, facing or turning based on the circumstances above.

If using mutliple tools to complete as much of the part as possible in one setup. Utilizing the different holding directions can reduce the amount of air cutting getting successive tools to the next point of operation.

DC

[judleroy]

I would say that feeding toward the spindle as the drawing indicates drawing b would be a bad idea.
I don't know what tools tou are using but if the drawing is any indication then you are leaving no releif for turning tool where as in drawing a you show good releif.
For facing it would be the same problem but backwards.
Drawing b has goog releif for facing but not for turning.
Without releif your tool will be in contact with your part
along the whole edge and will cause the tool to be forced away from the part throwing accuracy out the window. In my experiance the only part of the tool that should touch a part is the point where the actual cut is made.