Newbie: What am I doing wrong?

Newbie: What am I doing wrong?

Post by Haze » Sun, 24 Dec 2000 09:59:44



This is wordy, but I am trying to be complete.
I fired up my 'new' lathe for the first time today. I used a 7" x 5/8" bolt
which was removed from my tractor after it was stripped as test stock for
turning. I used a brand new carbide cutter bought today. A left cutting
tool, if that makes sense. I set the lathe feed to 480 threads per inch and
took only very small cuts. The dial on the feed said .020 for what that's
worth. I lubricated as I cut using 10W40 motor oil. Wrong oil I am sure, but
darned if I know where to find the recommended lard oil.
Now here is the problem. The cut is VERY rough. I was amazed at how rought
the cut is. What am I doing wrong? Surely a tuned lathe should turn a smooth
finish (I hope)! Any comments are welcomed.
 
 
 

Newbie: What am I doing wrong?

Post by Foxey » Sun, 24 Dec 2000 10:12:19


Is your cutting tool set at the centerline of the piece being turned?
What grade of carbide are you using? There are different grades for
different materials.......if your using a C2 or so grade on a steel
bolt its not going to work right....
It helps to grind a slight radius on the edge of the cutting tools,
and not a sharp point.
Try a sharpened piece of HSS in place of the Carbide..HSS is great for
many materials.
Bolts and other such rounds may be hard to get a decent finish on, as
its anyones guess what alloy it is..some bolts are impossible to get a
nice finish on..........
Any oil is better than no oil.
Although you should not need any oil for what you were doing it never
hurts.
For  some tips and ideas and setting up your lathe pay the below
website a visit.It has a wealth of information on it.

http://www.btinternet.com/~chrisheapy/homepage.htm

regards

Quote:

>x<>-This is wordy, but I am trying to be complete.
>x<>-I fired up my 'new' lathe for the first time today. I used a 7" x 5/8" bolt
>x<>-which was removed from my tractor after it was stripped as test stock for
>x<>-turning. I used a brand new carbide cutter bought today. A left cutting
>x<>-tool, if that makes sense. I set the lathe feed to 480 threads per inch and
>x<>-took only very small cuts. The dial on the feed said .020 for what that's
>x<>-worth. I lubricated as I cut using 10W40 motor oil. Wrong oil I am sure, but
>x<>-darned if I know where to find the recommended lard oil.
>x<>-Now here is the problem. The cut is VERY rough. I was amazed at how rought
>x<>-the cut is. What am I doing wrong? Surely a tuned lathe should turn a smooth
>x<>-finish (I hope)! Any comments are welcomed.
>x<>-


 
 
 

Newbie: What am I doing wrong?

Post by mulli.. » Sun, 24 Dec 2000 10:36:03




Quote:
> Now here is the problem. The cut is VERY rough.

I'm going to throw some stuff out here, pardon if I belabor some
obvious point.

1) Do you have the spindle turning in the correct direction?
2) Was the bolt "hard," ie, can you mark it with a file?
3) The engine oil is not right, but will not make the cut very rough
4) The tool has to be set 'on center' or with the height at the
   spindle centerline.  It will cut very rough if not.
5) The cutter must have the correct relief and rake angles for
   the material being cut.  A commercially purchased tool should be
   set up right.
6) Your feed rate sounds quite slow, that should be ok, what speed
   was the spindle running and what diameter the bolt - ie what was
   the surface feet per minute the tool was cutting at?

I'm sure others will add comments, but check the rotation direction
and tool height (should be on center) as these are likely problems.
If the tool is low, it will dig and chatter, if high it will scuff
on the front relief.

Jim

Sent via Deja.com
http://www.deja.com/

 
 
 

Newbie: What am I doing wrong?

Post by Mawdee » Sun, 24 Dec 2000 10:53:51


Take some ti,e to read the info at the following link:

 U.S. Army's "Fundamentals of Machine Tools":
 Good tutorial, excellent lathe section, also includes heat treatment

 http://155.217.58.58/cgi-bin/atdl.dll/tc/9-524/toc.htm

Good on-line resource for teaching the fundamentals of many machining
processes. You will want to read  Chapter 7 . If some of the garphics don't
come up use the reload button in your brouser or right click on the broken
icon and use the veiw image option.  Your tax dollars at work. Link
courtesy of Scott Logan.

Regards

JIm Vrzal



Quote:
> This is wordy, but I am trying to be complete.
> I fired up my 'new' lathe for the first time today. I used a 7" x 5/8"
bolt
> which was removed from my tractor after it was stripped as test stock for
> turning. I used a brand new carbide cutter bought today. A left cutting
> tool, if that makes sense. I set the lathe feed to 480 threads per inch
and
> took only very small cuts. The dial on the feed said .020 for what that's
> worth. I lubricated as I cut using 10W40 motor oil. Wrong oil I am sure,
but
> darned if I know where to find the recommended lard oil.
> Now here is the problem. The cut is VERY rough. I was amazed at how
rought
> the cut is. What am I doing wrong? Surely a tuned lathe should turn a
smooth
> finish (I hope)! Any comments are welcomed.

 
 
 

Newbie: What am I doing wrong?

Post by Eddy Wel » Sun, 24 Dec 2000 11:22:12


Quote:

>I fired up my 'new' lathe for the first time today.

Haze,  Take a look at Frank Hoose's page for some pointers on
running a lathe. It's one of the best I've seen for learning about
grinding the tools, ect.

http://www.mini-lathe.com/home.htm

Eddy Wells
Conroe, Texas

 
 
 

Newbie: What am I doing wrong?

Post by Joe Fangoh » Sun, 24 Dec 2000 11:33:06


Often the carbide tipped tool bits are not reground to any particular angle.
I have gotten many of them that had no relief whatsoever. In that case you
need to grind them to whatever cutting angle you need. You will need a
"green" carbide wheel to do this, an aluminum oxide wheel found on most
grinders won't work. Joe

Quote:
> This is wordy, but I am trying to be complete.
> I fired up my 'new' lathe for the first time today. I used a 7" x 5/8"
bolt
> which was removed from my tractor after it was stripped as test stock for
> turning. I used a brand new carbide cutter bought today. A left cutting
> tool, if that makes sense. I set the lathe feed to 480 threads per inch
and
> took only very small cuts. The dial on the feed said .020 for what that's
> worth. I lubricated as I cut using 10W40 motor oil. Wrong oil I am sure,
but
> darned if I know where to find the recommended lard oil.
> Now here is the problem. The cut is VERY rough. I was amazed at how rought
> the cut is. What am I doing wrong? Surely a tuned lathe should turn a
smooth
> finish (I hope)! Any comments are welcomed.

 
 
 

Newbie: What am I doing wrong?

Post by Trevor Jone » Sun, 24 Dec 2000 11:43:17


First things first.Get Some Good Stock!Try to find some free machining
steel (ask at the local metal vendor for 12L14,a leaded steel)Check at
the s***metal places for some aluminum round bar stock.It often has
the alloy marked on the side,look for 6061 T-6 as part of the
designation.This alum.alloy is very easy to get a nice finish upon,with
HSS tools as well as carbide.While at the s***dealer,see if he has any
brass round or hex stock in sizes you can use.Try to avoid cast items
when buying at the s***dealer,as some castings machine well and some
don't.
 Try to avoid the temptation to buy the cold rolled(usually 1018)steel
that is the standard stocked (and usually the cheapest)material at the
metal dealers.It has its place,but can be a source of frustration,as it
usually does not finish well.
 Get a good book or two(a bit of an inside joke,as most of the metal
guys I know have extensive libraries).My personal recommendations are
"How To Run a Lathe" by South Bend and "The Amateur's Lathe" by
L.H.Sparey.Both these books contain enough information to have you
learning new things every time you get into them.
 As for cutting fluids,I think grocery store shortening is a near
equivalent to lard oil,but you would do better to get some proper
cutting oil whether it be a neat oil or water soluble one.Most of the
major oil companies have some in there product line,and they are
available through the many fine suppliers such as MSC or KBC.
 I have found,for most of the turning I do,that I can turn without
fluids if I choose my stock wisely.The materials I have suggested above
will all give reasonable results dry for the most part.With the
exception of some very expensive aircraft bolts,all the bolts I have
turned were tough,stringy things that were near impossible to get a
decent finish level on.Save yourself that frustration,you will have
enough others as you learn what you can and can not do on your lathe.
 Make lots of chips!If bolts is what you have,use them,just don't expect
miracles for the finish,though you can get reasonable finishes with the
right combo of speeds,feeds,and cutting fluids.Experiment,try to
remember how you got the results you get.
 Cheers
  Trevor Jones
 
 
 

Newbie: What am I doing wrong?

Post by Trevor Jone » Sun, 24 Dec 2000 11:43:28


First things first.Get Some Good Stock!Try to find some free machining
steel (ask at the local metal vendor for 12L14,a leaded steel)Check at
the s***metal places for some aluminum round bar stock.It often has
the alloy marked on the side,look for 6061 T-6 as part of the
designation.This alum.alloy is very easy to get a nice finish upon,with
HSS tools as well as carbide.While at the s***dealer,see if he has any
brass round or hex stock in sizes you can use.Try to avoid cast items
when buying at the s***dealer,as some castings machine well and some
don't.
 Try to avoid the temptation to buy the cold rolled(usually 1018)steel
that is the standard stocked (and usually the cheapest)material at the
metal dealers.It has its place,but can be a source of frustration,as it
usually does not finish well.
 Get a good book or two(a bit of an inside joke,as most of the metal
guys I know have extensive libraries).My personal recommendations are
"How To Run a Lathe" by South Bend and "The Amateur's Lathe" by
L.H.Sparey.Both these books contain enough information to have you
learning new things every time you get into them.
 As for cutting fluids,I think grocery store shortening is a near
equivalent to lard oil,but you would do better to get some proper
cutting oil whether it be a neat oil or water soluble one.Most of the
major oil companies have some in there product line,and they are
available through the many fine suppliers such as MSC or KBC.
 I have found,for most of the turning I do,that I can turn without
fluids if I choose my stock wisely.The materials I have suggested above
will all give reasonable results dry for the most part.With the
exception of some very expensive aircraft bolts,all the bolts I have
turned were tough,stringy things that were near impossible to get a
decent finish level on.Save yourself that frustration,you will have
enough others as you learn what you can and can not do on your lathe.
 Make lots of chips!If bolts is what you have,use them,just don't expect
miracles for the finish,though you can get reasonable finishes with the
right combo of speeds,feeds,and cutting fluids.Experiment,try to
remember how you got the results you get.
 Cheers
  Trevor Jones
 
 
 

Newbie: What am I doing wrong?

Post by Jeff Homol » Sun, 24 Dec 2000 11:47:03



writes:

Quote:



>> This is wordy, but I am trying to be complete.
>> I fired up my 'new' lathe for the first time today. I used a 7" x 5/8"
>bolt
>> which was removed from my tractor after it was stripped as test stock for
>> turning. I used a brand new carbide cutter bought today. A left cutting
>> tool, if that makes sense. I set the lathe feed to 480 threads per inch
>and
>> took only very small cuts. The dial on the feed said .020 for what that's
>> worth. I lubricated as I cut using 10W40 motor oil. Wrong oil I am sure,
>but
>> darned if I know where to find the recommended lard oil.
>> Now here is the problem. The cut is VERY rough. I was amazed at how
>rought
>> the cut is. What am I doing wrong? Surely a tuned lathe should turn a
>smooth
>> finish (I hope)! Any comments are welcomed.

If you were using a carbide cutting tool you may not have been
turning the work fast enough. Carbide needs high cutting speeds.
 
 
 

Newbie: What am I doing wrong?

Post by Hugh Stron » Sun, 24 Dec 2000 14:41:16


Haze,

Your problem probably comes from use of too low a feed (480 TPI corresponds
to .0007" feed
on some older designs, notably South Bend - this is the slowest speed on the
lathe ) combined with too low a speed (go for at least 300 SFM) or a very
shallow cut (try .010 or more) .  Since you are machining steel,. your chips
will be coming off the work blue when the other paramters are right.

Honing the edge of the insert with a diamond hone will increase edge
sharpness, improving surface finish and lowering the speed requirements,
which many lathes would have trouble meeting on 5/8" work.


Quote:
> This is wordy, but I am trying to be complete.
> I fired up my 'new' lathe for the first time today. I used a 7" x 5/8"
bolt
> which was removed from my tractor after it was stripped as test stock for
> turning. I used a brand new carbide cutter bought today. A left cutting
> tool, if that makes sense. I set the lathe feed to 480 threads per inch
and
> took only very small cuts. The dial on the feed said .020 for what that's
> worth. I lubricated as I cut using 10W40 motor oil. Wrong oil I am sure,
but
> darned if I know where to find the recommended lard oil.
> Now here is the problem. The cut is VERY rough. I was amazed at how rought
> the cut is. What am I doing wrong? Surely a tuned lathe should turn a
smooth
> finish (I hope)! Any comments are welcomed.

 
 
 

Newbie: What am I doing wrong?

Post by Errol Gro » Sun, 24 Dec 2000 11:56:06


Quote:

>This is wordy, but I am trying to be complete.
>I fired up my 'new' lathe for the first time today. I used a 7" x 5/8" bolt
>which was removed from my tractor after it was stripped as test stock for
>turning. I used a brand new carbide cutter bought today. A left cutting
>tool, if that makes sense. I set the lathe feed to 480 threads per inch and
>took only very small cuts. The dial on the feed said .020 for what that's
>worth.

Of course this is difficult to diagnose long distance but my first
thoughts would be..

At a setting of 480 TPI that would work out to about 002 per
revolution of the spindle.  Slow but OK  IF  the half nuts are being
used to engage the lead screw.  If the friction clutch is being used
who knows what the feed is?   Next,

The dial on the feed said .020 for what that's

Quote:
>worth.

This would seem to indicate that the feed is set ot .020 per
revolution of the spindle.  Way too fast I should think.  That will
leave a threaded effect approx equal to 50 TPI.  Not good if the goal
is a neat finish.

As previously suggested the character of the bolt material is suspect.
I would second the suggestion to get some leaded steel and see how
that works, if possible.

Errol Groff
Instructor, Machine Tool

H.H. Ellis Regional VoTech
Danielson, CT 06239

860 774 8511 x146

 
 
 

Newbie: What am I doing wrong?

Post by Errol Gro » Sun, 24 Dec 2000 12:24:32




Quote:
>Haze,

>Your problem probably comes from use of too low a feed (480 TPI corresponds
>to .0007" feed

Hugh:

How did you get a feed of .0007?  Pitch is found by the formula
P = 1/ N so 1/480 = .0021 by my calculator.

For Haxe   We are converting threads per inch (TPI) to feed per
revolution  to see how fast your tool is advancing into the work as
the spindle turns.  This is what we call feed in the trade.

On a single start thread pitch (the distance from a point on one
thread to the corresponding point on the next thread) and
lead (the distance the thread advances axially in one revolution) are
equal.

Several fellows mentioned surface feet.  As a beginner you probably
don't know what that is or how it affects the cut.  All materials have
a rate at which they cut best and that is refered to as "cutting
speed" or "surface feet per minute".  It is defined as "the abount of
work surface, measured in feet, passing the tool in one minute"

As the diameter of the work changes the RPM has to change to maintain
the correct cutting speed.  The bigger the work diameter the slower
the RPM and the smaller the work diameter the higher the RPM in order
to maintina the proper cutting speed past the tool.

The formula for calculating RPM is  RPM = (CS x 4) / D  where CS is
based on the material and the cutting tool being used, 4 is a constant
when working in inches and K is the diameter of the work (assuming
that you are turning a part) in inches or fraction thereof.

So, for example, using a carbide tool and a CS of 170 SFPM for a depth
of cut of about .020 as suggested in Technology of Machine Tools (Krar
and OSwald) we would say

RPM  = (170 x 4) / .875 = (680)/4 = 170 RPM

This is a starting guideline only and may be increased or secreased as
you work demands.

Errol Groff
Instructor, Machine Tool

H.H. Ellis Regional VoTech
Danielson, CT 06239

860 774 8511 x146

 
 
 

Newbie: What am I doing wrong?

Post by Gary Sweat » Sun, 24 Dec 2000 14:45:30


Quote:

> Any oil is better than no oil.
> Although you should not need any oil for what you were doing it never
> hurts.

    Where'd this come from?  Using carbide tools, the intermittent
application of oils (coolants) is not necessarily a good idea -- the
result of intermittent cooling on the cutting edge can and does cause
thermal stress fracture.  It's been my experience than unless you can
maintain continuous cooling (flood, mist) then it is often better to run
a carbide dry.

Gary

 
 
 

Newbie: What am I doing wrong?

Post by John Hofstad-Parkhil » Sun, 24 Dec 2000 14:06:57


Haze:

Since I can't see this in a quick scan of the replies I've seen so far, you
are not mentioning how far out you've extended the stock - what the overhang
is. There is a formula, damned if I know it or care. If it looks like it's
sticking out too far then I change the setup.

While the tips you've seen all have merit, having the tool on center,
radius, and the like. They might lead you to believe it's an exact
science... it isn't. Not for the home shop at least.

What I've found helpful to remember when fighting chatter (what may be the
symptom you describe)
1). Rigidity. There is no substitute. The overhang not only of the work, but
the tooling.
2). Increase feed rate and/or decrease speed.

The forces involved are pretty amazing. Cutting steel in particular. I don't
know what you've attempted, but if you've got 5" of the bolt sticking out
and are trying to take .020", you're asking for trouble. The first thing to
do if you're experimenting is to cut it back to somewhere around 1.5" to 2"
(a swag but do-able). If you want to turn more in one pass then face,
center-drill and use a center (live or dead) on the tailstock to support the
work. Even then you might get some noticable deflection in the center of 5"
of 5/8" steel.

The note on 12L14 is a good one. Getting a really nice finish on CRS I've
found to be pretty elusive. Unless I employ some abrasive.

Since you're a self-proclaimed newbie:

"face" - A cutting operation taken across the end or "face" of the work. It
would be like cutting off the bolt head with a hack saw, then cleaning up
the hack saw marks on the end (face) of the bolt.

"center-drill" A term loosely described as starting a hole in the center of
the work (relative to the axis of the lathe). Often performed with a
combined drill/countersink that can be purchased where you got your carbide
tooling. It's a short, stiff drill that resists wander for starting a bore.

A dead center can be used to support the work by placing the point of the
dead center into the small hole you just made with the center drill. Needs
lubrication (I like STP). A live center is a dead center riding on bearings.

 
 
 

Newbie: What am I doing wrong?

Post by Gary Sweat » Sun, 24 Dec 2000 15:14:13


Quote:

> The formula for calculating RPM is  RPM = (CS x 4) / D  where CS is
> based on the material and the cutting tool being used, 4 is a constant
> when working in inches and K is the diameter of the work (assuming
> that you are turning a part) in inches or fraction thereof.

  K ==> what's 'K'  methinks you mean 'D'  as diameter in inches.  To
perhaps further clarify the constant '4', that's an easy way to 'rule of
thumb' it realizing that this will only give a starting point anyhow --
the '4' is actually an approximation of 12/PI should you actually figure
out the conversion absolutely.  

Gary