7x12 lathe with bad transmission shaft bearings

[va2fsq]

Hi
I'm a new mini-lathe user having bought the 7x12 King lathe. I've used it for a while building the usual machinists hammer and it works fine. However, since the day I bought it it makes a loud noise when running. It did not seem right, but having never heard one running I wasn't sure.
The noise is loud to the point that at some RPM's you almost need to wear hearing protection.
So, I started to investigate. I though perhaps the motor had bad bearings, so I took off the belt and turned it on. Purrs as soft as a kitten. Of course there is no radial load on the motor but it really was dead silent.
Next I found that the Hi-Lo transmission lever can be put into an intermediate setting where the spindle is disengaged from the transmission shaft. Lo and behold, the noise is still there. This implies that one or two bearings on this shaft are defective. Or, could it be that the motor is making this noise when the belt is attached due to the radial load?
So, the bearings are cheap enough. However, to replace them means removing the head stock and then removing the transmission shaft.
I have a few questions here":
1) If you remove the head stock and then replace it, does this screw up the bed alignment? I've seen many videos on taper bearing upgrades and no one ever mentions this.
2) I can remove the c-clips from each end of the transmission shaft but do the bearings just pop out or do I need to use a press? If I do, then I guess it means that I have to remove the spindle to gain access.
Any hints would be appreciated.
Thanks, Tom

 

[Tom Kitta]

There are videos on mini lathe bearing upgrades. Bearings should be pressed onto the shaft and you need to press them off and press new set on. You probably don't need much pressure - you can use bearing puller from PA. You can simply place the bearings back on by using a home made pipe and a hammer - just make sure you hit on the inner reces of the bearing.

I think This Old Tony on youtube has a complete video.

Get precision bearings and you have an upgraded machine.

You can probably test the bearing "whine" by lubbing them manually and seeing whatever it get quiet for a bit. Also check their temp.

Not sure how bearings in mini lathe are lubricated - but I would check that it is as per specs - you may be killing your bearings with no lube.

 

[va2fsq]

Hi,
Thanks. This is not the main bearings though. It's the little shaft with the pulley and the plastic gear.
I'm pretty sure the bearings can be popped off, but the one near the check side, has little clearance to press it in.
Tom

 

[Tom Kitta]

Oh then just remove and replace with new ones. You may need a gear puller to remove and then put new back on. Write down the number you need and get it at PA or online first. Bearings have to fit a bit tight on a shaft - any bearing any shaft as if they did not then the bearing would itself just spin on said shaft. So there should never be a bearing that just easily slides on and off - unless it is a plain bearing.

 

[va2fsq]

I've ordered the bearings. Instead of the cheap Chinese bearings I ordered SKF. Still inexpensive.
I still have concerns about pushing the bearings out of the head stock with the chuck mounting plate still attached. Actually, not pushing it out but rather re-inserting it..
Before I do this though, is there any chance that the noise comes from the motor? With the belt removed, it is super quiet. When the belt is on, that's when I notice the noise. But it's not the belt itself. Here is a video with the noise:
https://va2fsq.com/wp-content/uploads/20200303_162301_428637733673858.mp4
Thanks, Tom

 

[Tom Kitta]

Well if you are concerned it could be from a motor - which I doubt it is - then run the shaft powered by sell a drill press - and eliminate it as the problem.

In the worst case you may have to remove the spindle as well.

 

[va2fsq]

Hi
Thanks for the suggestion. I removed the belt, and then drove the transmission shaft with a hand drill that had a rubber wheel attached to it. No noise. So it is coming from the motor.
I guess I am going to have to live with it. Wow, how they let that leave the factory is beyond my comprehension!
Thanks

 

[Tom Kitta]

Well, looks I was wrong and its a bearing in the motor then - even simpler to replace if it is a standard motor - replace in a pair - front and back.

One thing I am wondering is why the noise changes with RPM - motor should be constant noise.

Is there something else? Can you put some other motor in for a quick test?

 

[va2fsq]

I think I found the culprit....the lathe itself is acting like an amplifier...
I took the back splash plate of the lathe off and the motor housing and the noise was much less. A lot less. It sounds normal. Taking a look at the motor,

https://va2fsq.com/wp-content/uploads/20200303_184328-scaled.jpg

you can see how it presses against the head stock alignment bolts, thus amplifying any noise generated by the motor, pulleys and so on.
No, if I could find a belt one cm longer, I could lower the motor and that problem would be gone!
Thanks for all the suggestions!
Tom

 

[Brent H]

Take off the motor and grind down the tops of those bolts to give yourself some clearance - even a 1/16" would probably be enough and not interfere with the adjustment when required

 

[va2fsq]

Hi
Except I would worry about upsetting the head stock alignment right?
Perhaps I'm worrying for nothing?
Tom

 

[Brent H]

Looks like there are jam nuts holding the bolts from backing out or coming loose. Couple minutes with a die grinder might save your ears - provided you wear hearing protection during the grinding - LOL

Make sure things are tight before taking a few skim grinds

 

[PeterT]

Seems odd to me the motor would end up cramped in there like that. Is there any belt tension adjustment or hinge plate type mechanism where it can be displaced slightly? I tried searching but don't have a clear picture of how the motor is mounted or residing.

 

[YYCHM]

Jam some rubber between the bolt heads and the chassis?

 

[va2fsq]

Seems odd to me the motor would end up cramped in there like that. Is there any belt tension adjustment or hinge plate type mechanism where it can be displaced slightly? I tried searching but don't have a clear picture of how the motor is mounted or residing.

The motor has two bolts in the side and they ride through two slots in the cast iron bed. So the motor goes up and down...the belt is already quite tight. If the belt was a little longer I would be all set.
Tom

 

[Brent H]

Any Belt type/number that you could go up an inch?

 

[va2fsq]

The belt is a 1.5x70.
Where could you buy such a belt?

 

[Brent H]

any features on it? Flat belt or ?

 

[YYCHM]

It's a toothed belt. Apparently 1.5 X 70 is pretty common for 7 X 12's.

Send it to @Chicken lights . He'll stretch her for ya LOL.

 

[va2fsq]

Ok, From what I can see, the mini-lathes use a 1.5 x 70 belt. That's what is written on the belt. So that is 70 teeth with 5 teeth per inch. You can buy these at little machine shop. However, if I go one with 75 teeth, this would make the belt 1" longer and probably provide the necessary clearance from the bolts to make it much quieter. So, I presume this is an XL type toothed pulley. I can buy a 150XL037 which is 9.5mm wide. I measure the belt at 9.8mm so this might work.
That assumes that the belt is 5 teeth per inch and not 5mm pitch...
I'm going to give this a shot.