[Emc-users] Question on image of default tool in backplot window

[Gene Heskett]

Greetings everybody;

This code, using g33 to cut a mildly tapered thread, I noted that my x
axis increment, and my Z axis increment, were describing an
approximately 45 degree path where the tool turns the corner. But it
ran, and made a tapered nut I needed on TLM.

I had increased the per-pass DOC from .055mm's to .070mm's and thought I
waste a nut to see how it looks. At about the time it was cutting a
full depth thread, it broke the chip.

Looking at the backplot pattern it occurred to me that my math foo was
being funkity again. It made common sense that if the included angle of
the thread was 60 degrees, Or a thread width of 0.866 of the tpi. But
tats both sides of the cut, where I wanted the usual 29.5 degree, in
this case applied so that the right, front side of the tooth is being
shaved. Then I got the idea that the tool image would be a good
comparison, the left side of the tool taking only a very thin shaving,
essentially the same setting that pitch offset per pass as used in a G76
when its told to advance at 29.5 degrees. The resultant backplot, when
comparing that turn the corner point with the side of the default tool
when that image is moved to coincide results in a several degree
missmatch, leaving a gap at the non-cutting side of the tool that
gradually gets wider. This says my Z advancement per pass is too much.
And the lack of braceing of the non-cutting side of the tool is
generating a low frequency buzz to the cut, possibly indicating I do not
yet have the spindle bearings snugged up to zero clearance, a buzz that
might go away if I can get the advancement per pass at 29.5 degrees

So, is that default tool image, un-rotated, supposed to be a 60 degree
included angle at its top tip, image? Or is it worthless for use as an
on-screen gage pattern?

Thanks.

Cheers, Gene Heskett

[andy pugh]

Post by Gene Heskett
So, is that default tool image, un-rotated, supposed to be a 60 degree
included angle at its top tip, image?

I don't think it is "supposed" to be anything. It's just a cone. It's quite
possibly a 60 degree cone, but why wouldn't you set up your tool table with
the actual real angles for your threading tool?

[Gene Heskett]

Post by andy pugh

Post by Gene Heskett
So, is that default tool image, un-rotated, supposed to be a 60
degree included angle at its top tip, image?

I don't think it is "supposed" to be anything. It's just a cone. It's
quite possibly a 60 degree cone, but why wouldn't you set up your tool
table with the actual real angles for your threading tool?

Its a very small insert that seems to a popular item for internal
threading, and that I don't recall running across the full description.
From the size of the single tooth, I don't think its intended for
threads below 22 tpi as it would be cutting, or smashing, the peak
height of the adjacent thread. Something with an 08 in the part number
IIRC. Pretty much at home for 27 tpi on up to 50 as I've used it at 50
quite a few times. Internal and external holders came as a set from a
supplier on your side of the pond and use chips that are mirrors of each
other IIRC. But I've no specs that give tooth height or tip radius
profile, so the best I could do at composing a tooltype would be a SWAG.

The holder sets the chip at about a 10 degree down angle, which I assume
is a way for obtaining clearance under the cutting edge in small holes
while maintaining a decent chip cross-section for strength, and I
generally try to put the tip as centered vertically in the hole as my
eyeballs say is centered. I could by choosing the right motions, start
it in a 7/16" hole, but getting a usable retrace backaway that also
clears the rear of the hole can be tedious indeed. Nice tooling if used
correctly, but fragile if you try to use brute strength to dig a good
sized piece of swarf out in one pass.

I'll have read up on the tooltable and its allowable contents. Maybe I
can make a pair of profiles that are usable.

Another feature the tooltable should grow is a stop action snapshot
triggered by the index pulse so that its backplot would only draw/show
the tool offset at its position once per revolution. That way the
backplot could actually show the thread pitch as opposed to the straight
line the tooltip draws now. An added advantage would be the
visualization of the tools incremental advance. You could see in the
backplot it your attack angle is correct long before its too late to fix
the code and salvage the part still in the chuck.

Thank you Andy.

Cheers, Gene Heskett

[andy pugh]

Post by Gene Heskett
But I've no specs that give tooth height or tip radius
profile, so the best I could do at composing a tooltype would be a SWAG.

The tool table doesn't do height anyway, but you should be able to set the
included angle exactly to the correct 55 or 47.5 degrees. (or that silly 60
degree angle that the foreigners use :-)

It might be useful to measure the tip radius and tooth height, just to know
what thread the insert can manage. (in theory you could use the radius
number to help touching-off, touch off to the notional perfectly-sharp
dimension)

[Gene Heskett]

Post by andy pugh

Post by Gene Heskett
But I've no specs that give tooth height or tip radius
profile, so the best I could do at composing a tooltype would be a SWAG.

The tool table doesn't do height anyway, but you should be able to set
the included angle exactly to the correct 55 or 47.5 degrees. (or that
silly 60 degree angle that the foreigners use :-)

Uhh, Andy, as one of them foreigners, hadn't you noted that g76 for
instance, defaults to assuming a 59.5 to 60 degree included angle. At
least the instructions do. It's the folks with the Whitworth and such
bolts that are half a bubble off to the rest of us. ;-)

Post by andy pugh
It might be useful to measure the tip radius and tooth height, just to
know what thread the insert can manage. (in theory you could use the
radius number to help touching-off, touch off to the notional
perfectly-sharp dimension)

Andy, I don't have a thing that could measure those angles, or the tip
radii which is pretty sharp. So I attacked the tool.tbl editor,
assigned a tip radius of 0.0025, and tried front and rear angles with a
60 degree separation, then found the ORIENT figure does NOT turn the
tool image like it shows in the Documentation.pdf, but moves the
imaginary contact point around on the radius of the tip. IMNSHO, thats
a bug as it will force me to compose 8 tools just to match what I see in
the pdf's. And TBT, its fairly rare that the toolpost is tightened down
dead square. It may "look" square, but I wouldn't bet on it being
within 5 degrees to the axis's of the machine right now.

So I adjusted that for the center of the radii. So now I had a true 60
degree triangle. Next I played with a multiplier constant in the z
advance calculation until it would just touch one side of the tool, in
this case the advancing edge, and cut on the trailing edge as it went
deeper into the thread. So next (I'm inside feeding the missus ATM) I go
out and compose another tool image that is a mirror of this one and
check the exterior cutting as its all in the g33wrapper.ngc to do
either, with or without the taper. So back to the salt mine I guess.

Cheers, Gene Heskett

[Gene Heskett]

Post by Gene Heskett

Post by andy pugh

Post by Gene Heskett
But I've no specs that give tooth height or tip radius
profile, so the best I could do at composing a tooltype would be a SWAG.

The tool table doesn't do height anyway, but you should be able to
set the included angle exactly to the correct 55 or 47.5 degrees.
(or that silly 60 degree angle that the foreigners use :-)

Uhh, Andy, as one of them foreigners, hadn't you noted that g76 for
instance, defaults to assuming a 59.5 to 60 degree included angle. At
least the instructions do. It's the folks with the Whitworth and such
bolts that are half a bubble off to the rest of us. ;-)

Post by andy pugh
It might be useful to measure the tip radius and tooth height, just
to know what thread the insert can manage. (in theory you could use
the radius number to help touching-off, touch off to the notional
perfectly-sharp dimension)

Andy, I don't have a thing that could measure those angles, or the tip
radii which is pretty sharp. So I attacked the tool.tbl editor,
assigned a tip radius of 0.0025, and tried front and rear angles with
a 60 degree separation, then found the ORIENT figure does NOT turn the
tool image like it shows in the Documentation.pdf, but moves the
imaginary contact point around on the radius of the tip. IMNSHO,
thats a bug as it will force me to compose 8 tools just to match what
I see in the pdf's. And TBT, its fairly rare that the toolpost is
tightened down dead square. It may "look" square, but I wouldn't bet
on it being within 5 degrees to the axis's of the machine right now.
So I adjusted that for the center of the radii. So now I had a true
60 degree triangle. Next I played with a multiplier constant in the z
advance calculation until it would just touch one side of the tool, in
this case the advancing edge, and cut on the trailing edge as it went
deeper into the thread. So next (I'm inside feeding the missus ATM) I
go out and compose another tool image that is a mirror of this one and
check the exterior cutting as its all in the g33wrapper.ngc to do
either, with or without the taper. So back to the salt mine I guess.
Cheers, Gene Heskett

And when I set bore=0.00000 which should have made it do external, a
variable I had added so I had a proper exit diameter clearance as it
moves away from the work, was not being set, so now I am trying to
rearrange the code so all the vars are properly set regardless.

But now I need to so something I've not tried before because the final,
do the real work has a while[var lt var] format, so I need to be able to
use a string substition variable in place of the lt above. Probably a
gt. Is this possible? and if so, whats the format of the assignment
statement?

Thanks.

Cheers, Gene Heskett