Subject: Boring on Sherline Lathe

From: [email-masked] (Chuck Sherwood)
Date: 13 Dec 1996 19:06:14 GMT

Hi everyone.

I have some questions on boring holes and on sherline carbide insert tools.

I need to bore a hole in a bronze steam engine casting several inchs deep.
I ground a 3/8 round tool bit as a boring tool and made a toolholder
for my Sherline lathe. I was able to use this tool to bore the cylinder
(1 inch deep x 5/8 dia) However, I was unable to bore the body which is
a 3/4 hole by 3.5 inchs deep. The tool would just ride on top of the part
and polishs it.  It seems like the tool is flexing too much. I was holding
the part in a 4 jaw chuck and had a steady rest on the outside with
the tool running down the throat.

I started looking at the Sherline boring bars with the valenite inserts.
These boring bars are 3/8 dia by 6 inch long. What is the maximum depth
that I can expect with a 3/8 diameter boring bar. 2, 3, 3.5 inchs???

Also, sherline makes left and right hand holders for these inserts.
Are these inserts unique to sherline tools? They sort of imply that.
If they are, should I be concerned ?

Sherline does make a tool holder that does use standard 55 deg negative
rake inserts, but I need to solve my boring problem first and it would be
nice to standarize on inserts. (The boring bars use postive rake inserts)

One other idea that Im working on is building a boring bar from 1/2 in
diameter steel drill rod. I got some small broken end mills that I was
thinking about grinding into cutters. Is this a good approach or a lot
of work that is destined for failure?

I also am making a fixture so that I can clamp the part using a long
bolt through the spindle. This might tighten things up a bit.

All advice appreciated !

chuck sherwood
[email-masked]

-- 
--
Chuck Sherwood
[email-masked]

---

From: [email-masked] (Fitch R. Williams)
Date: Sun, 15 Dec 1996 01:00:45 GMT

>I have some questions on boring holes and on sherline carbide insert tools.

Chuck,

I have never used any of the Sherline tools but would offer
the following from my own experience.

In general, use the biggest boring bar you can get in the
hole in a practical usable sense.  Bigger is stiffer.  So is
shorter.  

I have had better luck with carbide insert types of tools in
my 12 X 36 lathe that weighs about 1,100 pounds than in my
South Bend 9" that weighs maybe half of that.  I believe the
difference is the increased stiffness of the bigger lathe.  

I've had relatively good luck boring things with ground HSS
bits in rather inexpensive commercial boring bars with
square holes in them.   

I did some line boring recently when I was having trouble
getting the conventional held on one end bar to work well -
it was a 5/8" through hole that had to be about 3" long.  I
don't own any reamers (yet), so I arranged the bar between
centers on the SB lathe with the work mounted on the "T"
slotted cross slide and bored it that way.  I set the bit by
removing the bar from the lathe so that I could get at it
easily on the bench.  

After the first pass, I carefully measured the hole, and
measured the bar setting with a micrometer (the bit did not
protrude through the back of the bar so I had a good
reference for the micrometer).  I then carefully set the bar
and used the micrometer to measure the incremental
increases.  I kept a log of my progress and was able to get
the finished bore within about .0005 in dia and .0002 end to
end.  

I used a home made 7/16 diameter boring bar with a cutter
ground from an old center drill.  I locked it in place by
grinding a flat on the shank and using a set screw.

A line boring approach like this might work in your
situation if you have enough room (and it isn't a blind
hole).  Holding the bar at both ends is much more rigid than
holding it at only one end.

It took a while.  I had to make the bar, grind the bit, etc.
but the result was quite satisfactory.

Fitch

---

From: [email-masked]
Date: 15 Dec 1996 02:42:58 GMT

In article <[email-masked]>, [email-masked]

>that I can expect with a 3/8 diameter boring bar. 2, 3, 3.5 inchs???

 A rule of thumb I heard one time was that you could stick out a bar up to
6 times its diameter. I have however violated that rule several times. One
thing is that with that much flex I don't think you will be able to take
any really fine cuts. Somthing like .0015" cut or .003 out of the diameter
would be the smallest cut I would try. And to get a cut like that you had
better make sure the cutter is really sharp. From you're description it
sounds like you might not have enough relief under the cutting edge. The
edge may not be getting to the work before the bottom of the cutter is
rubbing.

>of work that is destined for failure?
 At work we use boring bars that are shop made. For the most part they are
made from cold rolled though this is not an ideal material for a boring
bar they do work. Recently I've made several bars from some core that was
trepanned out of some pretty good stock. I don't know just what steel it
is but it machines harder than 4140. They work a lot better than the cold
rolled bars expecially for the smaller bars. Although when I'm talking
smaller bars the smallest boring bar holder we have is 5/8" as compared to
the biggest bar we have in the shop which is about 5" dia by about 40"
long. I've also recently made a bar that will hold a triangular carbide
insert. I built it similar to the way we make most of our bars. Which is
to mill a slot the same size as the tool bit we're going to use in the
bar. Then cut a slit back from the slot far enough to allow a socket head
cap screw to flex the now split ends of the bar togather and clamp the
tool.

>bolt through the spindle. This might tighten things up a bit.

   Wayne Cook

Quality is like buying oats,
        if you want nice, clean, fresh oats you must pay a fair price.

However, 
        if you can be satisfied with oats that have already been through
the horse...
                          
That comes a little cheaper...

---

From: [email-masked]
Date: 15 Dec 1996 02:59:18 GMT

>of work that is destined for failure?

Can't help on the Sherline inserts but with boring bars on deep holes, use
the largest diameter that you can get into the hole with a little
clearance for chips.

However if I were doing this I would start with a ceneter drill and drill
to about 1/2" then using the boring bar bore in about 1" or until it
starts to deflect away from the work. Bore this to 9/16 then continue
using a drill up to 1/64 short of the final size and then ream it. Machine
reamers are pretty cheap.

Once the hole has been trued up by the original boring to 9/16 the drills
*should* follow it as *should* the reamer.

With the boring bar you are using is it on center? Try about 0.003 to
0.005 above center to counteract deflection. For bronze, as with brass use
a zero top rake.

Peter

---

From: Elliot Burke <[email-masked]>
Date: Sat, 14 Dec 1996 23:55:14 -0800

> the following from my own experience.
My 2 cents worth:
I make boring bars from whatever steel rod is around and just a little
smaller than the hole.  I have a lot of old carbide (wood) saw blade,
uncement the teeth with a torch, they are brazed on.  Take a tooth, and
rotate it to an angle you want the edges to be at, and braze it into a
notch on the steel rod.  
This only takes a few minutes.  The carbide might have to be sharpened a
little, but generally takes torch heat well. 
You can make either boring bars or internal threading tools this way.
Some machinists I know make the boring bar out of carbide (SiC, not WC).
This has a much higher strength to weight ratio than steel, so the
resonant frequency is higher than a steel bar.
I find torch work lots of fun, and finding interesting ways to use
carbide amusing.

Elliot Burke
HighTide Instruments
[email-masked]

---

From: "w.j.ward" <[email-masked]>
Date: 16 Dec 1996 01:11:40 GMT

Elliot Burke <[email-masked]> wrote in article
<[email-masked]>...

...

I have a lot of old carbide (wood) saw blade,
> rotate it to an angle you want the edges to be at, and braze it into a

...

> [email-masked]

What kind of torch is used for brazing carbide tips?  Does this require an
acetylene torch with oxygen?
-- 
God ==> Man ==> State

W.J.Ward, Redford Twp., Michigan

---

From: [email-masked]
Date: 15 Dec 1996 17:52:08 GMT

>I find torch work lots of fun, and finding interesting ways to use

Great suggestion, Elliot. I love this NG.

Peter
Still, still learning.

---

From: [email-masked] (Fitch R. Williams)
Date: Sun, 15 Dec 1996 17:44:55 GMT

>> the following from my own experience.

<snip>

>rotate it to an angle you want the edges to be at, and braze it into a

<snip>

Elliot, 

Thanks for that tip.  Never thought of using old carbide
blade tips that way.  Probably wouldn't work to well on an
align boring bar, but where thw whole bar is used to set the
cut it sounds worth experimenting with..

I'll have to rig up something to sharpen carbide, but that
is on the list anyway.

Fitch

---

From: Paul Pierce <[email-masked]>
Date: Mon, 16 Dec 1996 08:22:10 -0700

Fitch R. Williams wrote:
> ......

Heck-I just put a green wheel on the elcheeeeepo 6" grinder.  Worked!

-- 
Paul in AJ AZ  NRA Endowment Member

Checkout the Metal Web News at:
new address (11/23/96)

http://www.ten.k12.tn.us/~wgray

Checkout the FAQ at:
http://PLAINS.UWYO.EDU/%7Emetal/index.html

---

From: [email-masked] (Fitch R. Williams)
Date: Tue, 17 Dec 1996 03:32:50 GMT

>Heck-I just put a green wheel on the elcheeeeepo 6" grinder.  Worked!

Thanks for the input on the green wheel.  I've seen them,
never used one.  And I definately have an El cheapo 6"
grinder.  At least I got that part right anyway!

Been thinking about buying a second one.  That would give me
a place for a green wheel and a buffing wheel both.  Do
green wheels come in grades, like corse and fine?

Fitch