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Odd vibration in back gear ??...

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56type

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#1
Was using my Atlas 10100 the other day to face off some bar stock to make a bucking bar for riveting. Set everything up in the 4-jaw as square and centered as the old eyeball would allow (first time setting up square shaped material). Pulled the locking ring to disengage standard drive then flipped the lever for the back gear since I wanted to slow things down for the interrupted cuts on the edges.

Noticed a slight vibration that wasn't there when running in standard drive (laid hand on headstock, felt it shaking a bit). Took light cuts of 0.005 til I got the dimensions I wanted. Strange thing was when I returned the lathe to standard drive (pressed locking collar back in while rotating drive pulley by hand til it engaged the pulley), the vibration remained...??

Soooo....I disengaged the locking collar again, rotated the pulley 180 degrees, then engaged the locking collar again which seemed to bring it back to more of a "hum" as it ran in standard drive. Anyone else ever have this happen ?? Is it just the way the 10100 runs ??is it possible the locking collar acts as a balancer of sorts and can be positioned 180 degrees out ??

Spindle/4-jaw chuck have almost no play when a 1" X 8.75" round bar is setup in the 4-jaw and grabbed & pushed/pulled by hand. Set the dial indicator on the outer edge of the 4-jaw before flexing the bar. The DI needle stayed around 0,0005 in all directions the bar was flexed. So I don't think I have a bearing issue...How smooth is the Atlas 10100 expected to run ?? Thanks.
 

Eddyde

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#2
Is it possible you didn't fully disengage the back gears the first time? I've done that on my South Bend, the gears are out of mesh but the teeth are slightly rubbing.
 

markba633csi

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#3
Hi 56: how much runout do your step pulleys have? The big one on the spindle can have quite a bit of runout. Do you have the tensioner pulley over the belt or under? Should be over. How about your spindle bearings? Are they binding?
I have a 10100 and it's reasonably smooth- I run the belt a bit on the loose side
mark
ps also check the tensioner pulley bushing, if it's worn it will cause a chattering vibration- should be a good fit and well greased- I put a needle bearing in mine, and made a new shaft out of hardened steel
 
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56type

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Just measured the large spindle pulley at 0.023 runout according to the DI. The tensioner is running smooth with no discernible wobble on the shaft and is over the belt as pictured in figure 6 of the manual. Bearings rotate freely by hand and are always kept well lubricated, Also just turned the lathe on, then off, and allowed it to coast to a stop. While not under power there is ZERO vibration, absolutely none... Could it be I'm just feeling the motor running while the lathe is under power ??
 

Charles Spencer

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#5
This isn't relevant to your question but what I do to round off square stock is rough it out by grinding the corners down. This makes the job go faster and causes less shock to the lathe and bit.
 

Silverbullet

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#6
You will get some hum vibrations just from using the back gears , it's the gears meshing and the clearance they need to work properly.
 

markba633csi

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#7
I have found that the geometry of the tensioner pulley/runout of step pulleys can induce "tugs" on the headstock, especially when the belt is tight, that might be what you are feeling- a quirk of the MK2 square head Atlas
They really should have provided a spring-loaded tensioner, but it is what it is
m
 

56type

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#8
This isn't relevant to your question but what I do to round off square stock is rough it out by grinding the corners down. This makes the job go faster and causes less shock to the lathe and bit.
Thanks for the tip !!... I knew there would be some "thumping" as the edges were cut by the bit. Tried to minimize that by facing the sides off & taking light cuts to make it as easy as I could think of.
 

56type

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You will get some hum vibrations just from using the back gears , it's the gears meshing and the clearance they need to work properly.
So it's normal for the lathe to vibrate more while running in back gear than in standard drive ??... I've only used it in standard drive for turning round stock up to this point. What struck me as odd was that the increased vibration remained AFTER taking it completely out of back gear and only returned to "normal" vibration after I released the locking collar a second time, then rotated the spindle pulley 180 degrees and engaged the locking collar again...It would *seem* that the locking collar has one position where it's in balance with the spindle and unless returned to that engagement point will induce a vibration ?? Thinking I should mark the locking collar & spindle pulley to make sure to keep the alignment correct.
 

westerner

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#10
I was experiencing a similar issue with my 101.27440. Under certain loads/rpms, the backgear shaft would move sideways just enough to allow a backgear to rub on the belt countershaft pulley. Just had to loosen the collars on the backgear shaft, and split the clearances on all this stuff.
 

markba633csi

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#11
I wouldn't doubt there is less vibration in one position than the other- I don't think the factory took great pains to balance the parts on these little lathes
m
 

welderr

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#12
About 15 years ago my Dad brought home a used belt drive table saw from a garage sale. He cleaned it all up lubed what he could and powered it up, it shook so much it was scary. What was wrong was it must have sat unused for a long time and the belt took the shape of the radius of the pulleys just like old bias play tires used to flat spot. We put a link type belt on it and like magic it ran smooth.
 

wa5cab

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#13
It isn't surprising that the new link belt ran more smoothly than the old V-belt. Old V-belts that aren't used get stiff and take a set. Once in a while, after a few hours running, they will smooth back out. However, the best solution is to just replace it with a new good quality V-belt of the proper (same?) size. The trick is to inspect the belt at the joint before you buy it. If the belt gets thicker at the joint or if the two ends aren't aligned, the belt will thump every revolution.
 
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