Bad vibrations; is it in my head?

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curtis cutter
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Re: Bad vibrations; is it in my head?

Post by curtis cutter »

Did this happen all of a sudden or get progressively worse with time?
Gregg
Just let go of it, it will eventually unplug itself.
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liveaboard
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Re: Bad vibrations; is it in my head?

Post by liveaboard »

It was quite sudden; but I think I found the problem today.
As baddog Russ suggested, I checked the end play. It was zero.
With considerable force on a prybar the needle barely made a visible movement.
The bearing was too tight.
After loosening the collar slightly, it seems to be ok now.

Why and how it got tighter than before remains a mystery.
Glenn Brooks
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Re: Bad vibrations; is it in my head?

Post by Glenn Brooks »

Two things: did you regrind your tooling? Also consider something gone haywire with your cross feed screw on your saddle. Your irregular surface looks a bit like chatter, which could be the tool bit moving around on the compound - loose gibs, loose nut holding your tool post down, (rocking tool post??) or a excessive wear in the cross feed screw and nut.

I had similar problems, not as severe, couple of years ago and solved everything with a new cross feed screw and nut.( you need both as the nut wears out at the same rate as the acme threads).

You could first try immobilizing the compound - run it all the way to the most rearward position, and tighten down the gibs, take a cut, see what happens. also check the cross feed screw preload and see if that stabilizes the tool bit and finish.

When the cross feed screw wears, it creates lash in the area where the tool holder grabs. This can allow back and forth play in specific spots, as the nut runs out and back on the worn thread. Hence the waviness in the finish. I could actually see the tool bit wavering when making a cut. Anyway, new cross feed screw and nut,(the primary lateral feed, not the compound screw), problem went away.

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Glenn Brooks
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Re: Bad vibrations; is it in my head?

Post by Glenn Brooks »

Also consider something gone haywire with your cross feed screw on your compound. Your irregular surface looks a bit like chatter, which could be the tool bit moving around on the compound - loose gibs, loose nut,holding your tool post down, or a sudden excessive wear in the cross feed screw and nut.

I had similar problems, not as severe couple of years ago and solved everything with a new screw and nut.( you need both as the nut wears out at the same rate as the acme threads).

You could try immobilizing the compound and
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RMinMN
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Re: Bad vibrations; is it in my head?

Post by RMinMN »

This may not be the problem but have you ever experienced a tapered roller bearing that has flaked off a bit of metal from one of the tapered rollers? No movement or slack in the bearing but lots of rumble.
armscor 1
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Re: Bad vibrations; is it in my head?

Post by armscor 1 »

Working in a oil refinery years ago, debutaniser reflux pump motor without standby, could not stop it without shutting down cat cracker, bearing rumbling badly, pumped a hazardous lead based grease for months to keep it going and yes the rollers had flaked
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liveaboard
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Re: Bad vibrations; is it in my head?

Post by liveaboard »

All;
Yes, tools were sharp [several different new inserts], cross feed screw + nut almost new, gibs all tight.
I did try immobilizing different parts without success.

The problem was the head bearings were TOO tight. After letting the pressure off the bearings, the problem went away.

There could be damage in there, but at the moment it's working ok.
Today I made some finished stainless 318 parts that came out very pretty.
John Hasler
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Re: Bad vibrations; is it in my head?

Post by John Hasler »

I'm baffled by how overtightness could cause that symptom as well as how it could come on suddenly and be curable by simply loosening the collar (I don't mean that I don't believe you).
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liveaboard
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Re: Bad vibrations; is it in my head?

Post by liveaboard »

Looking over some older work, I realized this has been building for a while.
Those lines did appear faintly on some susceptible parts.

I'm not experienced with machine work, but an over-tightened taper roller bearing will give a rough feel when rotated by hand.
I assume that was the rumble that caused the resonance chatter lines, because I'd already eliminated all other possibilities suggested.
I haven't made anything difficult yet, like a long rod or unsupported bore.
John Hasler
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Re: Bad vibrations; is it in my head?

Post by John Hasler »

I would have thought that you would have felt such roughness when you were first exploring the problem.

In my experience with tapered roller bearings in vehicles and farm machinery well lubricated ones in good condition feel draggy but smooth when overtight (they will overheat, of course). Those were greased bearings, though.
10 Wheeler Rob
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Re: Bad vibrations; is it in my head?

Post by 10 Wheeler Rob »

I have had that happen to me on my 1928 9" South Bend. It happens when the cross slide was set at very shallow angle to the bed. That ment the tool holder was almost 90 degrees relative to the crosslide, in which case it is not very rigid. I had had it set to do a very shallow taper on a valve stem, and then forgot to reset the angle before turning a part simular to yours.

Rob
KellyJones
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Re: Bad vibrations; is it in my head?

Post by KellyJones »

I've seen that pattern before.
The good news is that, in my case, it wasn't any problem with the spindle.
The bad news, is I don't recall how I fixed it. I am a beginner myself, so although I can't be specific, I can tell you I managed to make it go away. My recollection was it had something to doe with stiffness, though it's been a while.

Possibilities (based on things I have discovered I've done wrong):

dull tool
wrong speed
wrong tool location (height)
wimpy set up (lack of stiffness)
tool rubbing where it shouldn't
loose gibs somewhere
Kelly Jones, PE
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