Newbie has some dumb (for anyone who knows about boring) questions. I
am using an off-set boring head (APT) with "spoon type" cutters on a
vertical mill to drill a number of odd size holes (eg .342", .543",
etc), all between .3" and .75"; some shallow, some 1.3" deep, in
carbon steel FS 1141 (heat treatment: normalize @1200F air cooled,
hardened @ 1525F, oil quenched & drawn @ 700F) w/ Rockwell hardness @
A60-70.
1) Do these boring cutters plunge into the steel like a
center-cutter?..., or do they need a pilot hole to enlarge?...would it
be good practice to run a slightly smaller endmill down through the
center anyways?
2) Would you suggest boring these holes out in one pass?...or more
than one pass with increasing diameters? If so, what is a good
incremental increase per pass?
3) The surface where the hole will go is irregular, ie. not flat:
within the hole I want to bore the surface probably has up to three
different levels, and I have parallel holes partly within the target
hole. Does this present a problem for these standard boring cutters I
am using?
4) Does anyone have any suggestions rpm and quill feed rates
for what I'm describing? Without knowing any better, I would tend to
use 300-400 rpm and feed by feel.
5) My mill (Bridgeport Series 1) has an auto quill feed which I
have not used nor know much about. Should I be using that mechanism
either automatically or manually?...or is the standard quill feed
lever handle just as good?

As you can tell, I only know enough to be dangerous. Any advice would
help me lower the danger factor. Thanks for looking!

BTW if any of you have helped me out in the set-up phase two weeks
ago, I got this 25 year old machine up and running great! Shimming
with steel plates and a rubber anti-vibration pad under each corner
did the trick...and the VFD phase converter from that outfit in
Brooklyn, NY for my single phase source seems just perfect; and Harold
the tech was above and beyond: we got it running at 6:30 Friday nite
over the cell phone while Harold was stuck in NYC traffic.

I am missing one of the 6 copper electric contacts in the motor
reversing switch, just a ~3/8"x1+" piece of copper, no tools needed to
remove or install. What's a good source for parts?

Fred

FLowen wrote:

Newbie has some dumb (for anyone who knows about boring) questions. I
am using an off-set boring head (APT) with "spoon type" cutters on a
vertical mill to drill a number of odd size holes (eg .342", .543",
etc), all between .3" and .75"; some shallow, some 1.3" deep, in
carbon steel FS 1141 (heat treatment: normalize @1200F air cooled,
hardened @ 1525F, oil quenched & drawn @ 700F) w/ Rockwell hardness @
A60-70.
1) Do these boring cutters plunge into the steel like a
center-cutter?..., or do they need a pilot hole to enlarge?...would it
be good practice to run a slightly smaller endmill down through the
center anyways?

Start with a twist drill or center-cutting end mill, and take it fairly
close
to the final diameter, if possible. You might want to leave .020" on the
wall of the deep holes, in case the drill wanders.

2) Would you suggest boring these holes out in one pass?...or more
than one pass with increasing diameters? If so, what is a good
incremental increase per pass?

I usually can handle .010" per pass in a Bridgeport, a lighter machine
might need a shallower cut.

3) The surface where the hole will go is irregular, ie. not flat:
within the hole I want to bore the surface probably has up to three
different levels, and I have parallel holes partly within the target
hole. Does this present a problem for these standard boring cutters I
am using?

Probably not.

4) Does anyone have any suggestions rpm and quill feed rates
for what I'm describing? Without knowing any better, I would tend to
use 300-400 rpm and feed by feel.

Figure the surface speed in FPM for the diameter and materials. Then,
calculate
RPM from that. HSS on steel would be 60 - 100 SFPM, carbide could be
150 - 600 SFPM. For .3", 100 SFPM comes out to 1300 RPM, for .75" it
is 510 RPM.

5) My mill (Bridgeport Series 1) has an auto quill feed which I
have not used nor know much about. Should I be using that mechanism
either automatically or manually?...or is the standard quill feed
lever handle just as good?


The power feed gives a consistant feed per rev, and you should use it to
get the smoothest holes. You don't really have to use the auto cutoff if
you are going to be watching it.

Jon

In article ,
FLowen wrote:
Newbie has some dumb (for anyone who knows about boring) questions. I
am using an off-set boring head (APT) with "spoon type" cutters

Spoon type? Could you provide a pointer to an image? Do you
mean the ones with a reduced intermediate shank, and a wider cutting
edge (offset to one side), perhaps with a brazed carbide insert?

on a
vertical mill to drill a number of odd size holes (eg .342", .543",
etc), all between .3" and .75"; some shallow, some 1.3" deep, in
carbon steel FS 1141 (heat treatment: normalize @1200F air cooled,
hardened @ 1525F, oil quenched & drawn @ 700F) w/ Rockwell hardness @
A60-70.

You want to cut it *after* hardening? I don't know offhand,
what final hardness will result with that draw cycle, but it would
probably be a lot more difficult to cut than doing the same for the
same steel annealed, and hardening afterwards.

1) Do these boring cutters plunge into the steel like a
center-cutter?..., or do they need a pilot hole to enlarge?

If these are what I think, I would never have thought of running
them without a pilot hole. The stem is a bit to skinny to take the
forces involved.

...would it
be good practice to run a slightly smaller endmill down through the
center anyways?

Absolutely! Drills take the most material in one pass, a
center-cutting endmill is probably the next. Your boring head is
designed for removing relatively little at a pass.

2) Would you suggest boring these holes out in one pass?...or more
than one pass with increasing diameters? If so, what is a good
incremental increase per pass?

If you start with a small enough pilot hole (e.g. just a bit
skinnier than the width of the tool) you will want to take many passes.
As an example, I have a 1/2" diameter solid carbide boring bar (nice
when you need long extension on a lathe), and the carbide insert sticks
out perhaps 1/16" on one side. I tend to drill a 1/2" hole for
starting, and bore just large enough to clear the overall diameter of
the bar plus the insert's extension (say just a bit over 9/16", plus a
bit to clear the chips, so perhaps a 5/8" hole on the first pass.

3) The surface where the hole will go is irregular, ie. not flat:
within the hole I want to bore the surface probably has up to three
different levels, and I have parallel holes partly within the target
hole. Does this present a problem for these standard boring cutters I
am using?

Are those cutters HSS or brazed carbide? Carbide does *not*
like interrupted cuts. Nor do the rather skinny necks of the cutters
which I *think* you're describing.

4) Does anyone have any suggestions rpm and quill feed rates
for what I'm describing? Without knowing any better, I would tend to
use 300-400 rpm and feed by feel.

400 RPM with a 0.750" hole works out to 942 SFM, which sounds
high for HSS on a carbon steel, though it might be reasonable with
brazed carbide boring bars -- if the are not too hardened in the necks.
I've seen those break right at the skinny part with what I considered a
fairly light load.

5) My mill (Bridgeport Series 1) has an auto quill feed which I
have not used nor know much about. Should I be using that mechanism
either automatically or manually?...or is the standard quill feed
lever handle just as good?

Automatic feed will give a better surface finish. Be sure to
set the automatic trip so it stops before the tool hits something other
than the workpiece -- like the vise or the machine table.

[ ... ]

did the trick...and the VFD phase converter from that outfit in
Brooklyn, NY for my single phase source seems just perfect; and Harold

[ ... ]

I am missing one of the 6 copper electric contacts in the motor
reversing switch, just a ~3/8"x1+" piece of copper, no tools needed to
remove or install. What's a good source for parts?

First off -- when you are using a VFD, you really should *not*
be interrupting the current between the VFD and the motor. Far better
to use the contacts of the original switch to command the VFD to run
forward or reverse. That way, you won't need to replace the missing
contact, all you need is a SPDT contact and three wires to the VFD.

Good Luck,
DoN.

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--- Black Holes are where God is dividing by zero ---

In article ,
DoN. Nichols wrote:
In article ,
FLowen wrote:
Newbie has some dumb (for anyone who knows about boring) questions. I
am using an off-set boring head (APT) with "spoon type" cutters

[ ... ]

4) Does anyone have any suggestions rpm and quill feed rates
for what I'm describing? Without knowing any better, I would tend to
use 300-400 rpm and feed by feel.

400 RPM with a 0.750" hole works out to 942 SFM, which sounds
high for HSS on a carbon steel, though it might be reasonable with
brazed carbide boring bars -- if they are not too hardened in the necks.
I've seen those break right at the skinny part with what I considered a
fairly light load.

Oops -- I forgot the conversion from inches to feet in the
above. Make that 78.5 SFM. :-) Go with the HSS, unless your heat
treatment makes the workpiece too hard. :-)

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---