12 x 36 lathe vibration

[canuck750]

I have a 12 x 36 Taiwanese gear head lathe, very similar to a Grizzly 12 x36, it’s about 40 years old and I have owned it for 8 years.
When I bought it the gearbox was not operating properly, I ended up replacing four gears and the shaft bearings in the gearbox.
I have not replaced any bearings in the gearhead assembly.
There is a vibration that varies at different speeds, most noticeable by the steel backsplash vibrating at times.
Removing the left side belt and gear shield the drive gears all look fine, are lubricated and set to not be too tight or too loose.
While running the electric motor has a bounce, the motor is bolted to a swinging mount attached to the backside of the lathe frame, gravity pulls the motor down and ‘tightens’ the rubber V belt.
I used a stethoscope to listen to the lathe spindles and bearings and there is no noticeable noise. I can watch the motor bounce slightly up and down on its pivoting frame.
When I disconnect the V belt and run the motor it is quiet.
I put a dial test indicator on the double row pulley on the lathe and it runs true on the side and in the deep V groove +/- 3-4 thou. The double row pulley is tight on the lathe input shaft.
The double row pulley on the electric motor is tight and clean and I do not feel play in the motor shaft.
The condition of the V belt looks good.

Trying to figure out why the motor has this bounce to it when connected to the V belt?

Am I missing something obvious?

The bearings in the lathe gear head are readily available, three are just standard deep groove ball bearings on the gearhead input shaft (the shaft the V belt runs to the motor) and there are two tapered roller bearings on the main spindle shaft, which I can get from my go-to online source out of Europe, 123 Bearings.

 

[MashingMetal]

I would go ahead and replace the belts, they often are not the best quality from the factory and very in width. Then I would start checking everything for run out starting with the motor pulley.

 

[David]

I'd try link belts as they don't seem to take a set the way a V-belt can.

 

[Susquatch]

Belts.

If yours is a double or triple belt, try removing all but one and rotate the other belts in to isolate the bad one.

But they might all be bad. In fact, the belts on a typical hobby lathe are not used that often and may take a set.

Edit @David posted before I did. Link belts are a good investment even if the belts are not the cause of your vibration.

 

[Arbutus]

If the machine is running smoothly without the belt, that implies that the belt or the pulleys are faulty. Vee belts can develop flat spots where the belt is stiffer is some places so it doesn't wrap around the pulley exactly. I have seen this when the machine is running slowly- the belt can be seen to misbehave at low speed and there is usually an audible sound that goes with that.
Replacing the belts is a first step. Personally I prefer timing belts over Vee belts for this application.

 

[PeterT]

On my Taiwan 14x40 I have a similar swing plate for the motor. I started to notice increasing vibration & assumed it was the belt stretch/wear. Replaced belt with new one but it still vibrated. I assumed the hinge plate was supposed to be loose in order that the motor weight would self tension belt & compensate for stretch like you sometimes on table saws. That the state my plate was in when I first looked at things. But turns out (at least in my case) motor/mount has to be fixed in position by tightening the pivot bolts but also with the correct belt tension. I'd play with this to see if it helps first. Doubtful you motor itself has loosened but another thing to check. Sometimes the lug holes & plate slots are have generous allowance or just made sloppy, so another check is that the sheaves are in alignment.

 

[Tom O]

Check the set screw for the pulley maybe?

 

[PeterT]

Coincidentally I was under the hood of my lathe changing gears for metric threading so I snapped a pic of my motor hinge plate. But I just realized, I recall some kind of retention bolt connecting the 2 plates together kind of mid plate which is hidden from view. I'm getting mixed up with another machine where the pivot bolts are tightened & supposedly that retains the motor position.

 

[PeterT]

While I'm here, probably unrelated to your vibration issue, but just an example of something that seems to go along with the Asian machinery territory. I don't do a lot of metric threading but the few times I have, I have been greeted with an unnatural chug-A-chug sound, coming from the gears. I chocked this up as introducing new gears to the train from my normal IMP setup in order to do metric threads and/or additional gears to the train, 4 surfaces vs 3. I had the same tooth spacing about right with the paper trick & they are always well lubricated.

Well this time, it sounded its typical chug-A-chug growl, then it improved a bit. Then after an hour of threading a new semi clackety noise started which I did not like. I looked at the gears & observed they had slipped out of position just a bit, yet all the bolts were tight.

Adjusting the gears on the swing arm has never been smooth. After some investigation I could now see what was going on. The curved slot is not machined, its just cast so lots of flashing & irregular width. At the position I was adjusting into, one side of the slot was hanging up on the bolt shaft. Not only making positioning difficult, I think it was actually putting some undesirable bend into the big gear plane. So I just ground & filed some clearance in the curved slot until the arm moved smoothly & unencumbered over the bolt. Instant happiness. The gears immediately quieted down. Knock on wood. So sometimes its these QC headaches that cause secondary problems.

 

[Ironman]

When you have a belt flutter like that, the other thing that happens if you run it long enough, is that the pulley itself wears oval because at the high side of the bounce the belt will slip under heavy load.
New link belts, new sheave, problem gone.

 

[Susquatch]

So sometimes its these QC headaches that cause secondary problems.

Ain't that the truth. My change gears have always been quiet and happy. Maybe that's one reason why I don't mind changing gears.

But your point about quality issues lurking in the background is a really good one. I think we can all relate to that with something.

 

[canuck750]

Thank you everyone for your prompt and thorough responses!
I will purchase a new belt on Monday. I don’t know of a local supplier in Edmonton for a linked belt.

My lathes motor and corresponding gear head input shaft pulleys are double row - stepped V pulleys but my lathe has always had just one belt. I have never even looked at the stepped pulleys to determine if I can (or should) run two belts.

I am going to look into all the other pointers you fellas mentioned, again very good advice!

One other question, what type of oil is recommend for the gear head sump?

 

[David]

Thank you everyone for your prompt and thorough responses!
I will purchase a new belt on Monday. I don’t know of a local supplier in Edmonton for a linked belt.

My lathes motor and corresponding gear head input shaft pulleys are double row - stepped V pulleys but my lathe has always had just one belt. I have never even looked at the stepped pulleys to determine if I can (or should) run two belts.

I am going to look into all the other pointers you fellas mentioned, again very good advice!

One other question, what type of oil is recommend for the gear head sump?

Lee Valley carries link belts. Only 1/2" width so not sure if that will work for you.

Link Belt for Power Tools - Lee Valley Tools

www.leevalley.com

 

[canuck750]

Thank you for the Lee Valley source. I just checked Busy Bee and they have them in 3/8” and 1/2” width.
The Link Belt does not have a V profile, should the belt sit down into the pulley V or is it intended to span the full width of the inside of the pulley?

 

[David]

Thank you for the Lee Valley source. I just checked Busy Bee and they have them in 3/8” and 1/2” width.
The Link Belt does not have a V profile, should the belt sit down into the pulley V or is it intended to span the full width of the inside of the pulley?

It has a sort of V-profile because the tab fits into the narrow part of the sheave.
I originally bought 1/2 belting for my lathe and it was too small and slipped so I had to spring for the B size which is 11/16" wide.

 

[canuck750]

It has a sort of V-profile because the tab fits into the narrow part of the sheave.
I originally bought 1/2 belting for my lathe and it was too small and slipped so I had to spring for the B size which is 11/16" wide.
View attachment 62410

Thanks for the explanation and picture! I did t realize the tabs faced inwards.

 

[Susquatch]

When I bought my Hartford Bridgeport Clone, it came with a link belt. It was my first exposure to one. My first thought was to replace that "piece of junk" with a standard belt. Then I did some research and learned about their advantages and disadvantages. Their anti vibration properties are at the top of the list.

You might wonder how they do that. It's a lot like cast iron and concrete where the boundaries between granules are more free to move and thereby absorb energy.

Link belts absorb vibration in a way standard belts cannot. The links move slightly within each other, dissipating the forces that create vibration. They are also more flexible in general than V belts, and they do not take a set over time. Vibration may not be a real ogre breathing over your shoulder, but it does reduce vibration in most machines even if they don't have an obvious vibration problem.

Link belt sections are made of urethane elastomer reinforced with woven polyester fabric for durability. Each link, depending on brand, adds 3/4" or 7/8" to overall belt length. Individual sections are about 2" long. The links can be assembled by hand, but using a needle nose pliers makes the job easier on the fingers. Threading a belt around pulleys, and then joining the ends, is often simpler than any other method of belt installation. If the belt is too long, slip off a link. If it's too short, add a link.

For most hobby machines, 1/2" (A/4L) is the right width.

One quick check that tells you (at least in part) whether or not link belts will be helpful in your case is to remove the drive belt, and start the motor. Very often, you'll find the motor by itself is whisper quiet (sound familiar?), meaning problems start at the belt, though it's still possible that the machine has bearing or other problems further down the list of problems. If the motor runs whisper quiet with no belt and no load, then any vibration problem has to originate somewhere else. The simplest check is belt replacement. If vibration remains low after the link belt is installed, you're in great shape.

The obvious next question is size. Sizing a Link Belt is just like sizing a V-belt. It begins by understanding that V-belt should never contact the bottom of the V - only the sides. It is the sides of the belt that drive the machine. Thankfully, the profile of both types of belts are governed by a standard. A B C D & E. Here's a breakdown:

"A" section V-belts have a top width of approximately 1/2 inch.

"B" section V-belts have a top width of approximately 21/32 of an inch.

For reference C is 7/8, D is 1-1/4, and E is 1-1/2.

Of course there are smaller V-belts than A. These are the Fractional HP (FHP) belts 2L, 3L, etc

For reference they correspond to top widths as follows:

2L is 1/4, 3L is 3/8, 4L is 1/2, 5L is 21/32.

But 4L is not the same as A and 5L is not the same as B. They have different cross sections. Unfortunately - that is the range we Hobbiests usually encounter.

Usually, you can find the size written on the outside diameter of the belt and you can just get the same size Link-Belt.

However, most of our machines have Chinese origin. All bets are off. I almost hate to say it, but sometimes it's gunna be a matter of trial and error. I hope you get lucky.

That about sums up what I know and what has worked for me. If you can do it, remove one of your pulleys and your existing belt and take it with you to help select the right one for you.

 

[Downwindtracker2]

V-belts work by wedging .I'll add another couple of V-belt series. The V series, like 3V, 5V, 8V . These are the modern ones. There shape isn't a true V. They are more efficient but require their own sheave profiles. Industrial machines run them. Then there are metric ones, which I haven't studied, I just replaced with the same #.

I got my link belt at the local bearing store. When I replaced the sheave on my 1948 Callender Foundry Beaver band saw , it's even older than me, I couldn't slide a standard belt against the housing with the new sheave, so I had to use a belt that "broke" apart.

 

[Susquatch]

I'll add another couple of V-belt series. The V series, like 3V, 5V, 8V . These are the modern ones. There shape isn't a true V.

Awesome! A new (to me) standard.

How do you identify them - other than any markings on the belt circumference? Do you have any technical info I can add to the reference info I maintain for such things?

 

[Downwindtracker2]

Their sides bulge a little. They grip better. Belts require serious alignment, which they rarely get.

We never likely to find them in out little machines. They tend to be used in multiplies,. They would joke that when they fired up the big gang saws the lights in the town would dim. We don't have the trees for those sawmills anymore.