Straightening a pulley?

[cdhknives]

My grandfather's old Atlas is up and running well in my shop, except for the continual low frequency wobble/shake.

I have checked and double checked the legs and adjustable feet.
It still shakes with no chuck mounted.
Changing the speed with the 4 step pulley does not affect shake.
Changing the speed with the 2 step massively speeds/slows the shake.
There is a visible bounce to the motor that corresponds with the shake. I can slip a wedge under the motor and the shake stops. Recall that on this lathe the motor is mounted on a hinged plate and its weight provided the belt tension.
There is a visible side to side wobble in the 2 step idler pulley, likely from storage damage.

I have tried with moderate success to straighten (by the grab and twist method) the idler 2 step pulley. I held some chalk near the side so it would just touch to mark the axis and just gave it progressively harder pulls and pushes. It is quite flexible IMO. I would say I got half the side to side movement out...but no more. I'm wondering about possible up/down offsets and/or balance issues, but that is hard to see.

Is there a better way the poorly equipped home hobby shop could get this pulley closer to true?

Should I just put an adjustment screw/bumper under the motor to stop the bouncing since the non-rigid motor mounting seems to cause most of induced shake? Would this hurt anything?

I know I can (or could last year) get a replacement pulley...but that is not particularly cheap.

 

[12bolts]

You definately want to eliminate the vibration. Otherwise it will show up in your finished work.
Is it possible the motor shaft or layshaft is bent? Do you have access to another lathe? Is it possible to machine the 2 pulleys in question to get them concentric, and then rebush the pulley centres to suit your shafts?

Cheers Phil

 

[Dave Smith]

you maybe could try a new belt--if the one that is on set a long time with the weight of the motor in one spot it could have irregular sections on the sides ---you can also make sure that their hinge method is not loose or worn--some motor shafts also have too much movement in and out which may be affected more with a crooked pulley--you can put your pulley true in another lathe or mill and carefully retouch both inner sides of the pulley to true it up.---hard to totally help you from a distance but try a few things that don't cost much first--you will get the wobble problem fixed---Dave

*note--you can also make sure that the two step pulley shaft doesn't have a worn spot on it causing the pulley to wobble

 

[cdhknives]

The facts that there is visible wobble (maybe 1/8") in the pulley plus the fact that the wobble basically ends when I put a thin wedge under the motor lead me to the conclusion that the pulley is the primary culprit...though a new belt is also part of the plan.

But is wouldn't surprise me to fix this and find additional vibration from bearing issues. This lathe sat in my uncle's garage for 15+ years without being powered up once. I don't care if it isn't perfect...I understand the limitations of this light lathe, but if I can fix the big things I can get it good enough to learn on without feeling like it is the limiting factor in my output quality. Basically I want the lathe to be better than me so I can get better.

No, I don't have easy access to a lathe big enough to machine a new pulley...and buying one is likely cheaper than a custom turned unit.

 

[Dranreb]

Hi, My first Atlas had the same problem, maybe worse than yours, and I'm sure it was caused by the belts having been left under tension for years, both of the pulleys had become bent for the same reason. The belt was certainly hard and set oval which was the main cause of a rhythmic wobble to the motor.

Like you I tried to straighten the pulleys but never got them perfect, new belts had much more effect, but one I sourced from a motor factors (auto parts store) was slightly oval from storage and not as good as a link type for smoothness.

Be careful trying to bend he pulley straight they can just snap very easily with sideways pressure, check the bore, sometimes it wears oval due to the grub screw having been loose at some time, most of the ones I have seen have some runout.

I managed to buy a much better second Atlas which has good pulleys, still not absolutely perfectly straight though, but the finish on my work is very good, so my problem is solved, no help to you I know!

Good luck with it and enjoy using it, I find that sometimes using a live center on even larger diameters over a couple of inches stickout can have a marked effect on the finish, and is worth a try if you have problems.

Meanwhile just put new link belt on it and get turning while you look for replacement pulleys..have fun.

Bernard

 

[wa5cab]

Relatively minor (<= say a quarter of an inch) pulley wobble in the larger 2-step won't cause the motor to bounce noticably. That comes from the distance between the motor axis and the countershaft axis changing. Of the possible causes, belt set is far and away the most likely culprit. Just talking about the motor pulley, 2-step countershaft pulley, and motor belt, bounce due to the belt will be by far the lowest frequency, and should be visible even while turning the countershaft by hand.

Robert D.

 

[DAN_IN_MN]

Does the opening of your pulleys change width?

 

[Mondo]

I believe you are talking about the large countershaft pulley, part # 9-427, about 10" diameter.

That countershaft pulley on my lathe wobbled a lot and I thought the pulley was warped, until I laid it down on a surface plate. Hrmmm.. flat flat flat.

Measure the bore through the center and measure the diameter of the end of the shaft on which it is installed, that should be a close sliding fit, no wobble allowed there.

I cured mine by replacing the countershaft. Not with another suspect used part, but with a length of 3/4" drill rod purchased from speedymetals.com. It comes in 3' lengths and I have found it handy to have around. I sawed off the necessary length, a little long, and faced off and chamfered both ends then used my milling attachment to hold it perpendicular to the spindle axis and cut the necessary woodruff key slot with a key cutter chucked up on the screw-on spindle chuck. Once installed and the pulley mounted and positioned properly I used a cordless drill to pass a slightly undersized drill bit through the set screw hole to make a divot in the new shaft for the set screw to grab. Cleaned out the chips, put in and tightened the set screw.... No more wobble!

So.. before you go about yanking and pulling and upsetting things any worse check everything. Positively identify the root of the problem and fix that. A shot-gun approach of try this then try that is a waste of time.

 

[Ray C]

Oh boy did this bring back nightmares... Here's how to fix it. You have two different choices:

1) If your motor is connected to the door-hinge bracket and it's bouncing/pivoting up & down, take a stick and prop-up the motor (between the floor and underside of the motor) every so slightly. This will loosen (very slightly) the tension on the drive belt and this way, that inherent vibration (which I'll explain later) will not travel through the entire system. This works very effectively but, there are two disadvantages. First, you will not have full tension on the belt and under heavy load, it could slip a little. Second, if you switch the pulley diameter, you'll need a different length stick to prop the motor (PITA). The amount you prop-up the motor is about equal to 1/2 the amount that the plate bounces up & down. (Trust me on this, I nearly lost my mind figuring this out).

2) Let the motor dangle and vibrate all it wants. Build a box around your bench and fill it with concrete. That will stop the vibration. If you don't want to use that much concrete, use some other drastic measure to make the bench massive. It's the only other way to kill the vibration inherent in that setup. On my bench, I had about 550lb of barbell and gym weights on the shelves. That came close to solving the issue.

Over time, I found that solution #1 was the best.

The reason for the inherent vibration is two-fold:

A) Primary reason is that as the motor pulley spins, the motor is actually trying to climb up the rubber pulley and to some extent, it succeeds -then, gravity wins and it falls back down. A big heavy motor in a constant state of rising and falling will cause a lot of vibration.

B) The slightest bit of being off-center or out of round on any pulley, or a belt with a flat spot etc will show-up like sore thumb on any belt system that is not under forced tension. Do not attempt to put that system under forced tension. The setup is not strong enough for that and it will cause other problems in the top idler shaft.

Hope that helps...


Ray

 

[cdhknives]

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