Tapered ID Thread chatter

[Jay Fleming]

I'm cutting an ID thread of a custom thread form, on a slight taper. The thread is close to a stub acme on form and the inserts are topping. Total cutting edge engagement is about .150" when topping. The setup is listed below.

New Haas ST35
1.5" steel boring bar extended 4.25" from holder
DOC from .001-.005" radial
Total thread depth is about .030"
6 TPI
Threading 3.5" deep
Total part length is 5.000"
Gripped length is 1.40"
Protruding length is 3.60"
400-1200 RPM

Before the insert starts topping, it'll cut nice but starts chattering as soon as it tops. I've ran from 400 up to 1200 RPM. The chatter is noticeable at all speeds, just the frequency and interval between "bumps" changes. I've tried wrapping some amount of rubber around the part. I backed off 2 set screws on the tool block and cranked the other two. Another shop that is making a similar part for us is using a 2" bar and they have better luck and they're using the same lathe. That may be the ticket but I've got to get through these 2 parts with what I have. Every other feature is perfect but the thread is causing me to scrap parts. Any help is greatly appreciated.

 

[hanermo]

You wanna fix it, find the cause, or do the job (for now) ?

S(olution, optionally, ghetto):
Split a steel/tube pipe of around 1-2" D, clamp to the bar, pour molten lead/tin into it.
Takes 30 mins and no money.
It will kill chatter and vibrations.

Exposed lead is a hazardous material, technically, of zero importance short term.

I did a lead-pour funnel for very deep boring (ISO 30 taper), and had excellent results.
My funnel was a split can of beverage, and ladle was an old kettle.


In your job, something rattles somewhere.
Something might be loose on the lathe.
Highly unlikely to be the spindle.

PO - possible option:
Disassemble, reassemble, saddle components down to the linear guides.

Diagnosis option:
Vibrate the spindle, HS and TS, separately, with a suitable hand-held tool.
Or clamped-in motor with an offset weight.
Look at a DTI while pushing/pulling/twisting the saddle/ts/hs.

Something somewhere will show sudden dramatic errors on the dti, in some cases.
The vibration may be necessary to see the error.
Then call Your HFO, or Haas.
They will fix it, probably FOC (or mostly foc).

Optionally just call you HFO and ask for a special urgent fix due to machine-down-//unfit for purpose.
Note my verbiage.
Quote the other machine, that works fine, and ask for them to fix it to also work fine.
Be nice.
Never ever be nasty, abrasive, abusive to the HFO guys.

They really, really, really want to help You, so that they can get the next machine order.
Really.
When the problem is complex, or unusual, they can ask and get special help from Haas, and get free parts if needed.

 

[litlerob1]

I doubt it's a Machine problem (I say that grudgingly).

You didn't say what the Major Diameter or the Pitch are.

If it's a 10" Major then you are turning a little bit on the quick side.

How thick is the wall of the part?

Bars can be a real bitch sometimes. You have to learn when to yell at them and when to buy them flowers.

Hanermo's advice is good, though it's probably the last thing I would try. (molten metal makes me whimpy).

 

[Bobw]

When I get stupid chatter, this is what it usually boils down to, especially if I
shouldn't be getting chatter, and its something that you really need to pay close
attention to if you are doing something that requires a TON of tool pressure,
like an acme thread.

Are your jaws bored correctly???? Of course they are bored "correctly", you didn't
crash when you bored them, but do they have uniform contact from Z+ to Z-...

Have you checked with a feeler gage?? Just a few thou off can cause horrible things to
happen when there is a ton of tool pressure..

Try wrapping the part with some tape, or using some thin plastic shim stock.. If
I'm being lazy and I only have a few, I'll wrap the part of the part that is in the
chuck with some of the high temp masking tape.. McMaster Carr has it, its thin
plastic, pretty amazing stuff.

*****

I'll toss in another odd one that is easy to check. A while back, the nut in the
center of my turret backed off a bit, so I wasn't pulling down as hard as I should
on the curvic coupling. What a frustrating cluster fuck of a mess that was....
Until I found it.

 

[Ox]

I'm cutting an ID thread of a custom thread form, on a slight taper. The thread is close to a stub acme on form and the inserts are topping. Total cutting edge engagement is about .150" when topping. The setup is listed below.

New Haas ST35
1.5" steel boring bar extended 4.25" from holder
DOC from .001-.005" radial
Total thread depth is about .030"
6 TPI
Threading 3.5" deep
Total part length is 5.000"
Gripped length is 1.40"
Protruding length is 3.60"
400-1200 RPM

Before the insert starts topping, it'll cut nice but starts chattering as soon as it tops. I've ran from 400 up to 1200 RPM. The chatter is noticeable at all speeds, just the frequency and interval between "bumps" changes. I've tried wrapping some amount of rubber around the part. I backed off 2 set screws on the tool block and cranked the other two. Another shop that is making a similar part for us is using a 2" bar and they have better luck and they're using the same lathe. That may be the ticket but I've got to get through these 2 parts with what I have. Every other feature is perfect but the thread is causing me to scrap parts. Any help is greatly appreciated.

OK, so which is it?


Doo you have room to hose cramp on some carbide endmills?

----------------------

Think Snow Eh!
Ox

 

[Jay Fleming]

I doubt it's a Machine problem (I say that grudgingly).

You didn't say what the Major Diameter or the Pitch are.

If it's a 10" Major then you are turning a little bit on the quick side.

How thick is the wall of the part?

Bars can be a real bitch sometimes. You have to learn when to yell at them and when to buy them flowers.

Hanermo's advice is good, though it's probably the last thing I would try. (molten metal makes me whimpy).

Major is roughly 2.80". Pitch is 6 TPI. Wall thickness is about .300".

Sent from my SM-G960U using Tapatalk

 

[Jay Fleming]

When I get stupid chatter, this is what it usually boils down to, especially if I
shouldn't be getting chatter, and its something that you really need to pay close
attention to if you are doing something that requires a TON of tool pressure,
like an acme thread.

Are your jaws bored correctly???? Of course they are bored "correctly", you didn't
crash when you bored them, but do they have uniform contact from Z+ to Z-...

Have you checked with a feeler gage?? Just a few thou off can cause horrible things to
happen when there is a ton of tool pressure..

Try wrapping the part with some tape, or using some thin plastic shim stock.. If
I'm being lazy and I only have a few, I'll wrap the part of the part that is in the
chuck with some of the high temp masking tape.. McMaster Carr has it, its thin
plastic, pretty amazing stuff.

*****

I'll toss in another odd one that is easy to check. A while back, the nut in the
center of my turret backed off a bit, so I wasn't pulling down as hard as I should
on the curvic coupling. What a frustrating cluster fuck of a mess that was....
Until I found it.

The jaws are bored correctly. I actually rebored them to make them through bored so I could move the threaded part back into the jaws. I dont think it's a machine issue.

Sent from my SM-G960U using Tapatalk

 

[Jay Fleming]

OK, so which is it?


Doo you have room to hose cramp on some carbide endmills?

----------------------

Think Snow Eh!
Ox

The bar was protruding about 4.25" and the part was sticking 3.60" out from the face of the chuck. I dont think I have the room inside the bore to attach a large enough piece of carbide to make a difference.

Sent from my SM-G960U using Tapatalk

 

[Ox]

Then it sounds like you can choke the bar up another 5/8" eh?
Even if you gotta lop some off the other end?

Of course - 200 RPM is an option too.
(I'd try that first)


----------------------

Think Snow Eh!
Ox

 

[Jay Fleming]

Then it sounds like you can choke the bar up another 5/8" eh?
Even if you gotta lop some off the other end?

Of course - 200 RPM is an option too.
(I'd try that first)


----------------------

Think Snow Eh!
Ox

I did choke it up as far as I could to clear the coolant nozzles. I also tried 250 RPM after posting this and it basically straight knurled the thread.

Sent from my SM-G960U using Tapatalk

 

[Ox]

Can you completely pull the coolant nozzles and let it blast?

Your hole is big enough, something should find it's way in there eh?


----------------

Think Snow Eh!
Ox

 

[litlerob1]

I did choke it up as far as I could to clear the coolant nozzles. I also tried 250 RPM after posting this and it basically straight knurled the thread.

Sent from my SM-G960U using Tapatalk

We're starting to narrow it down. Based on the above info. I'd say the part is Chattering, not the bar, so that's half the possibilities. Though tucking your bar in more will NOT hurt anything.

Im thinking thin wall harmonics. I have tied bike tubes and junk to the part.

R

 

[Jay Fleming]

Can you completely pull the coolant nozzles and let it blast?

Your hole is big enough, something should find it's way in there eh?


----------------

Think Snow Eh!
Ox

We've nearly given up and will be going to a 2" bar. I didnt realize we had time to do this. This suggestion came from 2 different shops that ran these parts for us in the past.

Sent from my SM-G960U using Tapatalk

 

[Ox]

Seems like you could cramp at least 3 pc of 3/8 endmills on that bar couldn't you?
You should have plenty of Clarence for 3/8 all around 'cept for the side with the insert.

???


AND - maybe you could clamp some carbide or ??? onto the part too?
If you don't have a big enough cramp, you can string 2 or 3 together to git where you need to go.


-----------------------

Think Snow Eh!
Ox

 

[Jay Fleming]

We're starting to narrow it down. Based on the above info. I'd say the part is Chattering, not the bar, so that's half the possibilities. Though tucking your bar in more will NOT hurt anything.

Im thinking thin wall harmonics. I have tied bike tubes and junk to the part.

R

I mentioned in a previous post that the threaded portion of the part is now within the jaws instead of standing proud. This didnt help. I just replied to Ox's post but we're going to a 2" bar. Maybe that will be the final solution.

Sent from my SM-G960U using Tapatalk

 

[Ox]

We've nearly given up and will be going to a 2" bar. I didnt realize we had time to do this. This suggestion came from 2 different shops that ran these parts for us in the past.

Sent from my SM-G960U using Tapatalk

Well, the results from this should shine the light.



--------------------

Think Snow Eh!
Ox