Chattering

[earlgo]

In a message on the topic about a searching for a new lathe Logan Fans, Conrad_R_Hoffman said

or a big chuck stuck way out, it will chatter like crazy

His thought was that the smaller lathes' spindles were not rigid enough to handle a large chuck. Is this a common problem for smallish lathes similar to the 12" Atlas/Clausing?
I have noticed far more chatter with the 6" Shar chuck that weighs about 3x more than the 6" 4 jaw Atlas chuck that came with the lathe. The CG of the bigger Shar is further from the spindle nose by about 1.5". I would have thought that a larger chuck would have more flywheel effect and help to reduce chatter, but I am often logically wrong.
Any thoughts?

--earlgo

[ctwo]

I'd think the same way, but I only have a 5" 3-jaw and a 6" 4-jaw. Even a 6" 3-jaw would have a bit more mass than the 4-jaw I have. I've not tried to compare chatter between my 3- and 4-jaw chucks. I think I want a 7" 3-jaw for my 10" Logan, but not if it will reward me with more chatter.

[earlgo]

I bought the 6" 3 jaw because it has removable top jaws and is/was the smallest I could find with that feature. I wanted to be able to use soft jaws because someone suggested it was the best way to go.
I am still having brain cramps believing the spindle is vibrating between the bearings enough (or at all) to cause the chattering.
Perhaps it is time to pry open the wallet and get the bed reground and the carriage mated properly.
Does anyone know if Conrad_R_Hoffman is still around to be queried?

--earlgo

[Harold_V]

Does anyone know if Conrad_R_Hoffman is still around to be queried?

His last appearance on the board was May 7.

If you'd like me to send him an email, let me know. If you don't have access to his email address, that's one way to find out if he's willing to talk with you.

Harold

[earlgo]

Harold, if you don't mind, CRH might have some useful insight into the lightweight lathe issues.

I have contacted a local machine rebuilding company about trueing the Atlas lathe bed, but have not heard from them yet.

--earlgo

[Mr Ron]

What type of cut are you trying to make and what is the material? Certain materials can chatter when the tool used is not mated with the material. Chatter can be caused if the material is not rigid enough; a large thin disk for example. My lathe has a 2-1/4" spindle swinging a heavy 8"-3 jaw chuck with no chatter problems. It's only if I try to do a facing cut on a large thin disc, do I experience any chatter; so your chuck may not be the problem.

[jpfalt]

You're going to find that the deflection of the workpiece at the cut is going to be determined by the spindle diameter and the workpiece overhang. With the same diameter spindle and a greater overhang due to length of chuck, you will get more deflection and more chatter.

A second issue is that the more massive the chuck, the lower frequency the chatter will be. Sometimes you can slow down the cut to get under the resonance frequency and sometimes you can speed up to get above the resonance frequency and reduce chatter, but usually the chatter gets worse rather than better. With a light, short chuck and a stiff spindle, you can usually slow the cut to get below the point where chatter starts.

[ctwo]

for example, I have a 2" long aluminum round 1". I'm using a 90 degree champhering 3/8" HSS bit to champher the end. When the champher gets 1/2 the width of the cutting edge, the chatter perks up. The whole dang machine is vibrating, it might even walk itself across the floor. I just figure it's the whole machine flapping and bending and nothing can be done about that, and just hoped increase chuck mass would absorb more of that vibration. Now I have to find another tool and use the compound to get a large enough champher.

[earlgo]

I get chatter up close to the chuck with nearly any sized material. Steel is the major problem, but brass will sometimes if the cut is too wide. If a 6-10" long piece is centered and supported by the tailstock then a cut can be taken at the tailstock end with no chattering.

Yesterday, I took the entire carriage apart and off the machine. The bottom of the carriage that rides on the rails was obviously worn on the leading and trailing ends. I cleaned it and then put everything back together, making sure that all the gibs were adjusted properly and all the shims in the right location. I set the magnetic stand for the DTI on the cross-feed dovetail and put the finger on the rail. I could pick up the carriage by hand by about .002. This has me convinced that I need to see a machine builder.

Today I picked up the front corner of the carriage and was able to run the carriage over a .003 brass shim between the carriage and the rail. With a .025 DOC the chatter was very nearly gone until I hit the shoulder of the cut. More proof that my wallet is going to take a hit.

Oh well.

--earlgo

[Harold_V]

Harold, if you don't mind, CRH might have some useful insight into the lightweight lathe issues.

I have contacted a local machine rebuilding company about trueing the Atlas lathe bed, but have not heard from them yet.

--earlgo

I'll send him a message, asking for him to check this thread.

Harold

EDIT:

Unfortunately, I was not successful.

Delivery to the following recipient failed permanently:

choffman@rpa.net

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain rpa.net by sitemail.everyone.net. [216.200.145.235].

The error that the other server returned was:
550 Recipient Rejected: No account by that name here

[earlgo]

Thanks Harold, I appreciate the effort.

--earlgo

[ken572]

I bought the 6" 3 jaw because it has removable top jaws and is/was the smallest I could find with that feature. I wanted to be able to use soft jaws because someone suggested it was the best way to go.
I am still having brain cramps believing the spindle is vibrating between the bearings enough (or at all) to cause the chattering.
Perhaps it is time to pry open the wallet and get the bed reground and the carriage mated properly.
Does anyone know if Conrad_R_Hoffman is still around to be queried?

--earlgo

Good Morning earlgo

In addition to finding Conrad,
(Step 1) why not do some noise and slop
forensics, so to speak with indicators and stethoscope,
with the spindle gear and the chuck removed from the
spindle while turning slowly by hand, and or a very
small motor, and light belt turning the spindle while
watching the indicators and listening to the bearings with
no load on them. (Document all you see and hear)

(Step2) Then repeat after reinstalling the chuck while it's
snugged up around a small piece of bar stock. (Document all you see and hear)

(Step 3) Now repeat again with the spindle gear reinstalled.
(Document all you see and hear)

Note: You will be paying close attention to rubbing and or
grinding sounds around the cast area's around the bearings.
(Document all you see and hear)

Also do a static push test on each end of the spindle at every 45 deg., or so.

(Document all you see)

It might tell you a story on how, and what you need to do to fix it.

Just a thought.

Ken.