Subject: Lathe Vibration at higher speeds

From: [email-masked] (Barry Wolinetz)
Date: 17 Jan 95 10:02:34 -0500

My Craftsman/Atlas 12x36 lathe has a nasty tendancy to start to vibrate as
I get into the upper speed ranges.  I have placed it on a sturdy bench with a
1.5" thick plywood top and bolted everything to the floor and wall, but it
seems that there is an imbalance in the spindle somewhere.

Has anyone out there had a similar problem?  What did you do to fix it?
Is it necessary to rebalance the pulleys and backgears every 40 or so years,
or is this just one of the drawbacks of the Atlas design?

Is the backgear lock pin heavy enough to unbalance the gear?  should there be
some kind of counterbalance to offset it? (It doesn't seem like it, but ya
never knows till ya asks!!)

I have the babbit bearings and there is negligable(?) (.001-.002) radial play.
There is virtually no axial play.

TIA for your help

Barry
--

Barry Wolinetz                       My opinions, Only!  I would not
The Northern Trust Co                claim to speak for my employer in 
Chicago, Il                          most matters discussed here!

Give some kid(s) a break, Be a Foster Parent!

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From: [email-masked] (Mike Rehmus)
Date: 17 Jan 1995 19:03:50 GMT

In <[email-masked]> [email-masked] (Barry Wolinetz) 

>There is virtually no axial play.

Couple of things come to mind, Barry

Comment
The upper speed ranges of the Atlas lathes are questionable because of 
the babbit bearings (I have a 6" Craftsman and a 14" Rockford, both with 
Babbit bearings)  The instructions with the 6" said to back off on the 
bearing clamp bolt if I wanted to run at high speeds.
BTW, I think you may have an excessive play in your spindle.  How did 
you measure it?  Is the measurement the peak, TIR or what.  On my 6", I 
have a screw that can be tightened to remove play.  I don't remember 
what my 12" Atlas had (ball bearings, I think).

Holding it down
Your bench is not sturdy enough, no wooden bench is.  You should have a 
Heavy steel bench and a thick steel top.  Look at the supports for high 
quality lathes from any era.  They had cast iron legs or heavy steel 
cabinets with significant bracing.  It makes a big difference.  I have a 
3" angle iron bench with a 2" thick aluminum top to which I mounted the 
6".  I then leveled the whole unit with the lathe bed as the reference 
point with a 0.0005/10" precision level.  The difference in the 
operation of the lathe between the wooden bench and this new one is 
substantial.  No more random tapers, very repeatable cutting and, a 
whole lot more rigidity.  The high-speed vibration was reduced.

Balance
A lot of these less expensive lathes were never in balance.  My next 
task is to statically balance the internals in both the lathes and my 
mill.  I would guess that the older the lathe, regardless of original 
cost, the less likely that it was balanced.

The first thing you could look for is the runout on your V-belt pulleys. 
I believe these things (at least those cast of white metal) do warp over 
the years.  A truing cut on even new ones can make a difference.

The other first thing to do is to look at the drive belts.  It appears 
that all V-belts are made from flat material that is then joined into 
the v-belt loop.  The joint can be a significant vibration source.  To 
see really bad belts, look at those coming in from China on the low cost 
drill presses.  The joints have as much as a 1/4" lump on the face and 
back of the belt.  Talk about your vibration generator!  Go down to a 
bearing supply house (for example) and purchase a belt that is made to 
drive machine tools (not the water pump on an automobile).  Goodyear or 
Gates seem to be reasonable choices.  I know I dropped the vibration on 
my 6" and my Chinese drill press (before I got rid of it in disgust) by 
about 80%.

Best
Mike

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From: [email-masked] (Ken Knaell)
Date: 19 Jan 1995 09:20:52 -0500

>>I get into the upper speed ranges.  I have placed it on a sturdy bench
Barry,
I have had two Atlas lathes, one babbited and the other with Timken
bearings.And built stands for one and a Clausing from wood.  I like
to build my wooden machinery stands out of 2x6 and 2x4's as opposed
to plywood since I think the machines run quieter than with plywood
which essentially makes a larger acoustic radiating surface.  The
design is sometimes quite arduous trying to get the maximum strength
at joints that carry heavy loads but I think the look of a machine
standing on a natural finished(varnished or polyurethane) is quite
nice looking.

I found with both my Atlas lathes that the motor cradle was the source
of all the vibration I had.  It seems this thing hangs the motor on
the V-belt and a hinge at the bottom.  The motor can bounce up and down
via the free rotational motion of the hinge and the v-belt running over
the pullies somewhat nonuniformly drives this oscillation.  I sometimes
just stick a screwdriver underneath the motor mount and a bracket fixed
solidly to the stand and the vibration is clamped to a stop. I have
not played much with the clamp screws that are on castings in close
to the hinge since they are hard to reach and make the belt change
between the motor and the countershaft inconvenient.

ken knaell
bethesda, md