Your Home Lathe Tooling

[Powder keg]

Bob, The tool I am making is tool steel not HSS. It is the same stuff they make drill rod out of. It comes fairly soft, then you heat treat it so you can cut with it.

Later, Wes

 

[Bogstandard]

i mainly use my tipped tooling if i am removing large lumps, for fine precision work i invariably use hss ground up tooling.

i do also relap the worn out carbide tips, using a water cooled lapping grinder, to the very sharp profiles of hss, but only use them on very fine surface work. if you try to remove too much material with them they just chip off almost instantly, but it will make a nice job on materials where hss struggles to keep a keen edge. i suppose you could use a diamomd lap to do the same thing.

as my motto is, use it until it has no further use.

john

 

[rake60]

as my motto is, use it until it has no further use.

john

I like your motto John.
During WW2 we had a similar motto here. It was:
"Use it up - Wear it out - Make it Do or Do Without"
How well does THAT fit a home hobby machine shop?

Anyway...
We have carbide insert salespeople come into our shop on a regular basis.
Much of the new products lines are made up of insets with extremely aggressive
rake geometry's. Being I operate a CNC machine, I can click on the Load Meter
screen and see exactly what kind of tool pressure is being generated.
It's amazing to see what's going on there.
Higher SFM speeds, lower tools pressures and very little heat being transferred to
the work piece.

Those manufactures are not interested in selling a couple little inserts to some home
hobbyist, but I can guarantee that someone how IS will soon be making the small scale
tooling.

The most recent new carbide that I am personally testing out at work is made by
SECO/Carbaloy. In looking through the documentation they provided with it, they list
the TCMT 21.51 inserts that I use in my home tools.
Their recommend depth of cut is .020" :

Rick

 

[S_J_H]

I no longer have the 9x20 and a rebuilt 1960's 9A South Bend is my main lathe now. Carbide is used 90% of the time on it. I use a 7rib serpentine belt flat side against the pulleys to replace the leather belt and it has a Leeson industrial 3/4hp DC motor and variable speed drive. Belt slip is almost impossible with this setup. It'll stall the motor first. Top speed is around 1400rpm. It will take a .125" DOC in 6061 without even breaking a sweat. CCGT inserts from Seco will easily take .001" finishing cuts and produce some beautiful finishes.
For boring I use only solid carbide bars. Under .001" doc is no problem when sneaking up on a bearing bore. I keep them razor sharp with a diamond file.
I only use HSS for form tools and parting/grooving. I personally love using carbide tooling.

Steve

 

[chuck foster]

i have a 9" south bend lathe and i use carbide tools about 90% of the time and i have no troubles with it.
i have a 1/3 hp ac motor on the lathe and i can take about .200" cuts in aluminum with the feed on the slowest setting.
the only time i use hss is if i'm grinding a form tool.

when i got the lathe i could not get a good smooth finish on my parts no matter what i did.
after a while and allot of bad words i discovered that the main bearings needed tightening. so i took about 3 or 4 tho. worth of shims out of the bearings and all has been good since.
for parting i use hss cutoff tool in a rear tool holder, with this set up i can part off square,hex and round very easily.

chuck

 

[S_J_H]

Chuck, you might get some interest out of how I line bored my 9A and made my own bronze bearing shells-
http://bbs.homeshopmachinist.net/showthread.php?t=26578

Yes I agree, .2" DOC are well within the limits of this machine. Not to take anything away from my old 9x20 and it even had a 1hp 3ph inverter motor and VFD, But my 9a SB is much more rigid lathe and the plain bearings produce a much nicer finish than the tapered rollers on the 9x20. In back gear which is a sorely missing feature of all the 9 and 10" import lathes, the SB is a massive step up in cutting power, At least with a modern belt on the flat pulleys. I run my bearing clearance at .0007". I loosen it to .0015" for 1400+ rpms and it will run well with well for extended periods getting only warm.
Carbides and the old machines work very well.I find the good inserts to be much much better than brazed tip carbides.

 

[BobWarfield]

Chuck and Steve, your two posts make me wonder whether anyone has ever modified a 9x20 or other import to run with bronze bearings instead of cheap tapered rollers. Sounds like it would be an improvement and not all that hard to do with a line boring setup. I would think line boring would even have the virtue of (possibly) making the lathe more accurate in spindle to ways alignment if done carefully.

In terms of "warm", I wonder what the limits are for the bronze bearings? I would hate to give up my 2K rpm upper end!

Best,

BW

 

[Powder keg]

For 10 years I ran a Giddings & Lewis Horizontal Boring Mill that was made in 1905 and I could usually hold + - .0005" with it. It had this neat tapered Bronze bushing in the head that you could take up the slack in. The whole machine had bronze bushings through out. It is a fun machine to run. But very slow to todays standards. I rarely ran it over 200 rpm.

Wes

 

[S_J_H]

Chuck and Steve, your two posts make me wonder whether anyone has ever modified a 9x20 or other import to run with bronze bearings instead of cheap tapered rollers. Sounds like it would be an improvement and not all that hard to do with a line boring setup.

Bob, I am sure it could be done. A few issues might be a serious problem though. The spindle surfaces were never intended to be run in a plain bearing. I know my 9x20 spindle was not even hardened. I figure you are really pushing it at 2000rpm in a plain bearing with no pressure fed lubrication so you might loose some speed if it's your only lathe. 1400rpm on my 9a runs well though. My little cnc lathe will turn 4000+ and not even get warm , so I am setup for the smaller diameter work. The finish blows compared to the south bend though.
I would run my old 9x20 to 4000rpm.,since it had a vfd 3ph setup. But it was far from smooth at that speed. I really enjoy the contrast of old vs new tech in my shop. I'm always on the lookout for another older lathe to restore.

Steve

 

[BobWarfield]

I assume the CNC runs in bearings? Tapered or angular contact?

Do you think that's the reason the finish isn't as good?

Interesting stuff here. Sorry to pester about these minutiae! ;D

Best,

BW

 

[snowman]

I think it's great that you guys are so fond of the carbide...and I don't disagree that it's very capable of doing the things you have posted. I've got probably close to 3x the value of my machinery in insert tooling. I just don't use it anymore, unless I really need it.

You take good pictures, they do not suprise me, I've done very similar things in the past....but I can do the same thing with a properly ground HSS bit of the correct size...and do it with less strain on the machine. Yes, you will occasionally have to touch up the edge, but you can buy a 1/2" HSS blank for what? $5 for quality stuff? It can be reformed into different cutters how many times in it's life? 5-20? Not to mention the amount of times it can be touched up. It may be lack of skill, but I rarely have a brazed carbide that "dulls"...it usually just chips, and doesn't leave much to grind back. I've watched inserts run for a loooong loooong time...and watched the spindle load, though they do use a little more power towards the end of their life, it is not something that I would likely ever notice on a manual machine.

Bob...on your list of 5, there's not a one I agree with, although I don't know how well carbide works on my 7x10 because I've never tried it All are very possible, with the right tooling, and a little play with the feeds and speeds....and all are done in industry quite often.

 

[rake60]

I know I've said this before here but I'm going to state it again.

HSS cuts metal.
It literally peels the material off the base stock, or separates the the
molecular bond material creating a stringer chip. It works best at
relatively low speeds and feeds.

Carbide pushes the material off the base stock.
In order for that to happen it has to have two things.
Pressure and Heat.
The tool pressure generates the heat that plasticizes the material
to make it plyable enough to be pushed away.

The new carbide insert geometries concentrate that heat and pressure
to a finer point in the base material. That allows then to cut with less
pressure.

It is an amazing study in it's self.

I've read many posts here and abroad from home machinists saying
they can't get a good finish using carbide.
That is caused by old school thinking.

HSS cuts very well at a 120 SFM
For a 1" piece of 1018 cold roll steel that would be 460 RPM.

Carbide needs SPEED! It cuts best at 300 - 400SFM
At the low end of that range it would be 1150 RPM for 1" stock.

Calculating SFM (Surface Feet Per Minute) is an easy formula.
It is: SPM divided by Diameter of Stock Multiplied by 3.82

If you want the spindle speed for 2" stock to be cut with carbide.
(300/2) X 3.82 = 573RPM

Cutting with HSS
(120/2) X 3.82 = 229RPM

Now for Aluminium or Brass those speeds change dramatically!
You can run 1000SFM with no extra pressure on the tool or the machine.
That's kind of like the difference between chewing gum and chewing
stones.

Rick

 

[snowman]

Correct..you'd also be correct in stating that a lot of the time, the surface finish that carbide leaves is from it actually burnishing the material as opposed to leaving a clean cut.

 

[Mcgyver]

Oh gawd, are we back on cutting tools :big:

HSS cuts metal.
It literally peels the material off the base stock, or separates the the
molecular bond material creating a stringer chip. It works best at
relatively low speeds and feeds.

Carbide pushes the material off the base stock.

Rick, I don't know that is correct - both cut via pressure creating a shear plane, the angle of the shear to the surface of the work being governed by the rake angle. With carbine requiring a larger included angle to withstand a given force, it presents a smaller rake angle and hence a more shallow shear plane. This affects us two ways, the longer shear plane means more force is required and secondly, the longer shear plane doesn't work well with a small doc - the shear plane is too long for its width and the tool burnishes. The speed limitation on either tool material is primarily a function of temperature (not heat!) at the tool tip, hss not be capable of maintaining hardness at the temps carbide can. I agree completely with your point about the effect of high temps/pressures, that there are different angles, temperatures etc, however the process of the metal being removed by shearing is the same - the main differences with carbide is it maintains its hardness at a high temp that hss and is more brittle than hss....pretty much everything else comes from that and understanding how a cutting tool applied to material at a certain angle causes a corresponding shear plane to form.

just a general comment on this carbide/hss ongoing discussion to rationalize it for the new guy wondering whats going on..... An analogy to them might be to a professional photographer. He picks a lens for a job through balancing a bunch of different factors. That someone can say, well wait a sec, this lens can also take a pic, or, see I took a pic with a different lens doesn't really accomplish much and hardly negates the original choice. More constructive would be to try and lean F stops, depth of field and exposures and then try understand elements of composition and what he was trying to accomplish. Who knows, you may quickly surpass the pro and become new Ansel Adams....but you have to learn the basics as an important part of getting thereto be proficient

 

[rake60]

It is hard to comprehend Mcgyer, and dropping it on a beginner all at once would
be confusing.

The company I work for is very dynamic when it come to new tooling that can
increase our productivity. That means several seminars every year with the
manufactures sales people and engineers to teach us how to use their products
to their limits. Most of those seminars begin with the story of HSS tools and
progress to their newest inserts.

It does become very involved, but what is new and experimental in the large
job shop today will be available to the small scale hobby machines in the future.
The saying goes: "You Lead - Follow - Or Get Out Of The Way"
When it comes to tooling my company is definitely a Leader.
I'll suck up whatever information I can from being a part of that!

Rick

 

[snowman]

And the beauty of working for a company that is the leader, is the packets of test inserts and the cabinets of obsolete tooling.

 

[rake60]

And the beauty of working for a company that is the leader, is the packets of test inserts and the cabinets of obsolete tooling.

Good Point! :big:

If anyone is shopping 60 degree triangle carbide tool holders, just visit
your local machine shop. 5 years ago that was cutting edge technology.
Today those shops would probably sell those tools priced per pound.

Rick

 

[snowman]

I've got enough VNMG holders and inserts (and seats and screws) to last me a few lifetimes. Even have inserts in wiper, diamond and ceramic.

 

[rake60]

This isn't home tooling by any means, but I thought some might be
interested in seeing it.

When I ran a big vertical boring mill we would get a few heavy jobs in
that were of Chilled Cast Iron. If you've never worked Chilled Cast
imagine granite with spots of flint mixed into it.
It's tough stuff!

The parts we made were over 7 feet on the OD and called for a bore of
about 4 feet, 3 feet deep.

These are the carbide inserts we used to cut them.

The one on the left is new, the other had served it's purpose.
Surface speeds were very slow, usually around 150 SFM
Feeds were high, .032 to .044" per revolution.
The depth of cut was .375 to .500"
The holders set the inserts at a 10 degree angle but with "0" rake.
On a good day, one edge on that carbide would last 30 minutes of
continuous cutting.
That old machine didn't have a load meter on it.
It did have an Amp meter that read the current consumption.
Sometimes we'd see 200 Amp reading while running those tools.
That couldn't have been good being the machine was wired to a
100 Amp service. Many times it would blow the 100 Amp line
fuses before you had a chance to react.

Rick

 

[zeusrekning]

I have never worked with parts that large. What kind of tolerance was the hole to be held to?
Tim