Re: [CAD_CAM_EDM_DRO] Cutter geometry (Was backlash)

> Hi Chris:
> Can you tell us a little more about the problems that you are having
> with your current setup?

First I should appolgize for posting to the wrong group... this
was brought up by a thread on the south bend lathe list and I hit
the wrong address when I changed the subject line.

> I'm a little unclear about what you're trying to cut, and I can't quite
> visualize your setup.
> Are you trying to cut a tapered part in one pass?

Yes, 2 to 4 feet long in half inch stock with a guide bushing right in
front of the tool.

> Is your problem related to finish, or dimensions, or both?

No specific problem in early tests other than heat, but finish and
dimensions are both important.

> What speed are you running the machine at?

The highest ;-) I think around 1200 rpm but don't remember clearly.

> Is your tool positive, negative or neutral rake?

positive

> Is it honed?

sorta

> What diameter is the stock?

.453 in drill rod, .500 in 12L14

> How well is it supported by the travelling steady?

Fairly well, probably better when I replace the slit & bored pipe plug
(taper threads!) with a slit bronze bushing fixed inside a 5C collet.

> What do you need to achieve?

Dimensions within say +/- .001", smooth finish at least after going
over it with emery paper

> Why did you choose drill rod? ( tends to be poor for turned finishes unless
> hardened.)

It's a tool... so I use tool steel, right? Seriously, somewhat for
durability and mostly because it is readily available in precision
ground. But I'm now thinking I'll switch to 12L14, hope I don't have
to get that ground before I can run it.

> How many do you have to make?

Probably 10 to 20 over the next year, all different.

> PS: To answer your question as best I can with what I know so far, HSS is
> often a good choice for applications where finishes are hard to achieve
> because of spindle speed limitations.
> I wouldn't bother with 1/2" square HSS though; it's way too hard to grind,
> and on a small lathe the limiting factor will be the rigidity of the spindle
> and carriage.
> A 1/4" square tool will be ample.

1/2" may be overkill. But way it's set up, the only contribution to
rigidity the lathe makes is the cross slide dovetail and
screw... everything else is in the guide bushing, it's mount, and the
tool holder. As such, it's a small machine only in that it is a 1/2
hp belt drive with a low speed spindle.

> Get a 5% cobalt tool, grind a bit more top rake than you normally would and
> grind the point dead sharp.
> Then get a medium to fine India stone and dress a 0.005 rad on the tip.
> Hone the tool really well.
> Run with heavy oil as a lubricant for the tool and the steady at as high a
> speed as you think the tool can stand.

Sort of what I was planning, only I was going to try mist coolant.
But flood would be easier to rig, just harder to contain. I'm more
worried about siezing the guide bushing than overheating good HSS
given the limited hp and speed.

Chris