How to Prevent Chatter.

[MicroE]

Unnerv---That is a scrupulously clean set-up. If only I had more time to clean the shop.........

 

[jtice]

Thats just rediculous.

I dont think he uses it guys,, just likes it sitting there. /ubbthreads/images/graemlins/wink.gif

Mine is a MESS !!!!
All I do is brush the piles of chips off onto the floor. lol

Yours seems bone dry also. Mines covered in oil and grease, and all the chips are stuck all over it. /ubbthreads/images/graemlins/icon15.gif

 

[unnerv]

I use mobile 1 synthetic for the ways and it says pretty clean. Plus aluminum makes some big chips so they are easier to clean up, unlike when I work with brass. I really do use my lathe, I just like it clean after a project. /ubbthreads/images/graemlins/smile.gif

Now back to the regularly scheduled thread on chatter...

 

[chalo]

Use as short an overhang on your parting tool as you can get away with.

Grind a curved chipbreaker into the tip of the tool.

Use the recommended edge rake and relief clearance for the material you are cutting.

Autofeed at the minimum recommended IPR for the metal you are cutting.

Flow coolant directly into the slot while cutting.

If all else fails, turn the speed down reeeeal low. (Maintain a normal IPR).

Chalo Colina

P.S. Insert type parting tools have made my professional life as a machinist more comfortable. (The insert is wider than the toolbar.)

 

[tvodrd]

Chalo,

You could write the textbook! I am not a machinist but posess reasonable competency with the mill and lathe. Most of the folks here are dealing with the small "bench top" lathes and may not even have a bench grinder with a "green" wheel /ubbthreads/images/graemlins/grin.gif . Trying to enlighten them with grinding/sharpening bits (radii for surface finish, etc) will be a neverending class. I think the MMM forum should acquire some stickys for the basic "basics." What do you think? Are there textbook pics that can be "stolen" to post?

Larry

 

[chalo]

[ QUOTE ]
tvodrd said:
I think the MMM forum should acquire some stickys for the basic "basics." What do you think?

[/ QUOTE ]

Sounds good. Mike/Chief Wiggum seems to be a rich source of basic good practices. Perhaps he could be talked into archiving a fundamentals/FAQ thread.


[ QUOTE ]
Are there textbook pics that can be "stolen" to post?

[/ QUOTE ]

I'm sure. However, I went years as a self-taught and mentor-taught machinist before discovering that there were actually books on the subject. (Duh!) Therefore my references are limited to Machinery's Handbook and other similarly dense text-based manuals. Not any worthwhile pictures in there.

When I'm unpacked from my recent move, I'll recover my digital camera and take in-shop pix as appropriate.

Until then, here is a picture of me in my workplace shop, riding a bike I built there. /ubbthreads/images/graemlins/grin.gif

Chalo Colina

 

[tvodrd]

Clalo,

I'm mostly self-taught also. Years ago, I had a machining textbook that had excellent illustrations for cutter geometries and the like. (Long gone. /ubbthreads/images/graemlins/frown.gif ) That's quite a shop you have! I've been downsized twice to a Bridgeport, 15" lathe, 18" vert bandsaw, drill press, and a couple pedestal grinders. It's just an R&D support shop now.

Larry

 

[gadget_lover]

In another thread (which I can't find now, of course) I said that I didn't have any problems with parting aluminium or mild steel. Feed slow, make sure the parting tool is at 90 degrees to the work, lube, etc....

For the last month or so, parting has been a hit and miss proposition. Sometimes
it goes well, other times it digs in and stalls the lathe. Fortunately, nothing has broken yet, but it does mess up the work and sometimes pulls it out of true.

I found the problem. It was the stinking gibs on the compound slide. When I added the DRO I also replaced the lower part of the compound that had the lower part of the dovetail. I thought the gib was adjusted securely. It turns out that it was pretty loose. Even though it was loose, normal cutting seemed OK.

The give-away symptom was that as I was parting, the bit would dig in and it almost seemed like the tool post would lean away from me. I'd checked everything except the gibs. No swarf under the tools. The cross-slide had no play. The tools were secure in the tool post. It never occured to me that the whole compound slide was lifting just a fraction of an inch.

I liberally lubed the gib and dovetails with while lithium grease and tightened the adjusting screws so there's just the slightest drag. The compound is now solid as a rock.

I posted this in the chatter thread since the gibs can also increase the chatter, leading to poor finishes.

Daniel

 

[McGizmo]

On a recent Ti light I made, the boreing bar would "sing" if I tried a shallow cut. The carbide insert looked fine and I assumed that it was mostly deflection of the boreing bar as it was extended further than ideal. New carbide insert and the Ti cut like butter. Rigid and sharp; never have too much of either, I guess. /ubbthreads/images/graemlins/icon3.gif I missed this thread but glad it surfaced. /ubbthreads/images/graemlins/blush.gif

I am self taught too and likely have taught myself some pretty stupid things! /ubbthreads/images/graemlins/rolleyes.gif

 

[tvodrd]

They're really pricey, but you can get solid carbide boring bars that use inserts. I don't have any, but they gotta help with chatter. Rigidity (largest shank that will fit, minimum tool overhang, close to the chuck/collet as you can get, and minimum "slack" in the machine) really helps for accuracy and nice finishes!

Larry

 

[Rothrandir]

the other day at work i was setting up some pretty big parts (15inches diameter, 7inches long, shaped kind of like the letter "T"), and the bore was 2.8305, 5.5inches back.
i was using a 1.5" boring bar (the largest diamter this particular machine will hold), sticking out just far enough to bore all the way in, and was getting lots of chatter, like we do every time we've run this part for the past xxxyears.

anyway, the boring bar is held in place by 6 tiny setscrews, maybe .250 diamter.
i drilled out the holes and tapped them for a larger setscrew size (about .400), popped the boring bar back in and secured it.
you wouldn't believe the difference that made. just a little bit more clamping area and pressure on that boring bar, but it made the difference between ear popping racket and a smooth cut.
same boring bar, sicking out the same amount.

rigidity is sooo important. there are so many things to consider when machining something. bar sicking out too long? sharp insert? spinning too fast? feeding to fast? spinning to slow? feeding to slow? cutting too shallow? cutting to deep? part held securly? tool rigid? tool held securly? machine secured down? machine rigid? cutting fluid? correct angles? correct insert? dirty tooling pockets? crappy tooling? currect height? enough material to be rigid?

sometimes it can be as simple as adjusting the order you do things in. for example, if you're od threading a part with a bore, simply threading before boring can provide enough rigidity to prevent chatter in the threads. the same can be said with grooves.

another thing to keep in mind when grooving, is that the sharper the tool, the better it will cut. this doesn't only mean a fresh insert, but it can also mean that using a narrower groove tool will provide less tool pressure than a wider groove tool.

 

[McGizmo]

Larry,
I picked one of those up in a micro size. Would be nice to have in the larger sizes but I don't cut the tough stuff much anymore. /ubbthreads/images/graemlins/grin.gif

A while ago, I ran across a page Hardinge Hard Turning that makes our issues with rigidity and other considerations just pale! /ubbthreads/images/graemlins/icon15.gif

Good job Roth! /ubbthreads/images/graemlins/thumbsup.gif /ubbthreads/images/graemlins/grin.gif

 

[tvodrd]

Hi Don,

My fireFox browser doesn't display the "items on the left" to click and "learn more." /ubbthreads/images/graemlins/frown.gif I have a good friend who machines! and grinds carbide every day for header dies. You're thinking "green" carbide, but appearantly not. /ubbthreads/images/graemlins/faint.gif He says he uses carbide, not diamond tooling to do it! There are a lot of things I wouldn't care to do for a living!

Hey Roth, when you gonna move into sales for your employer, and start offering services? /ubbthreads/images/graemlins/grin.gif

Larry

 

[McGizmo]

Larry,
Here's a quote at the beginning:

[ QUOTE ]
Hard turning is defined as the process of single point cutting of part pieces that have hardness values over 45 Rc. Typically, however, hard turned part pieces will be found to lie within the range of 58-68 Rc. The hard turning process is similar enough to conventional “soft” turning that the introduction of this process into the normal factory environment can happen with relatively small operational changes when the proper elements have been addressed.

[/ QUOTE ]

One proper element is operator with brass ones! /ubbthreads/images/graemlins/icon15.gif

It goes on to discuss how hard turning can replace grinding.

 

[gadget_lover]

Ummm, did anyone else notice that the picture to the right on that Hardinge web page showed chips that were glowing yellow? Yikes!

Larry, the "items on the left" was a drop down menu; Home, about us, products, etc.

Daniel

 

[tvodrd]

Don, "carbide" is about 90Rc and you can cut case-hardened and full-hardened 60+Rc stuff ok. (Your cutter will take a beating!) Guys like you and me resharpen with a "green wheel" (SiC) but it results in some edge property deterioration(sp?) on carbide cutters. (Diamond wheels with coolant feed are really for production shops, though diamond stones for "touch-up" are cheap and a "must!)

Indeed, "brass ones" do help sometimes! /ubbthreads/images/graemlins/icon15.gif

Larry

 

[pbarrette]

Hi all,

I have never had a problem with chatter while parting. Then again, I think I'm the only one here with a Sherline lathe. The Sherline parting tool is essentially a .04" thick, steel blade ground to shape and held in a special toolpost. The toolpost provides a positive rake to the blade in relation to the part.

As I understand it, the increased attack angle (as opposed to a level attack) means that there is less pressure required to cut, but the tool will lose its edge more quickly. For me, it works well. I always end up with nice long curls that are right around .04" thick. I just have to remember to back out a bit so my curls don't get too long and start wrapping around my work piece.

Here's the link to the tool to give you an idea of what I'm talking about:
http://www.sherline.com/3002inst.htm

I'd take a picture of the setup, but I just got my CNC motor mounts installed, with motors and controller in the mail. Basically, the machine is non-functional (no handwheels) until I get the motors in.

pb

 

[nekomane]

You'll all laugh, but with the tiny lathe I have, I do a lot of parting by furiously cranking away manualy on an improvised handle. Never thought that sitting in front of a lathe would be so much exercise /ubbthreads/images/graemlins/thinking.gif

 

[Silviron]

Gee- I was going to recommend DUCT TAPE

That was before I read the thread and realized that you were talking about lathes, not your wife or girlfriend. /ubbthreads/images/graemlins/wink.gif

I often use one of those little "mini-hacksaws" for "quick and dirty" parting: They seem to be a little easier on the machinery and the stock than a full-size hacksaw, and a little easier to manipulate .

 

[1331]

For a reference book I have "The Model Engineer's Workshop Manual" by George Thomas. It has a good section on parting and tightening of the slides. He can apparently part at 300rpm. It has a lot pictures of techniques and tools to make for the lathe, boring, threading, tool height guage ,etc.