# Troubleshooting a Comet II Lathe, bouncing motor.



## wormil (Nov 19, 2011)

So I'm working through this used Comet 2 I bought, mostly it involved catching up on overdue maintenance. But the motor is bouncing and I'm not sure what is causing it. It's worse when the belt is farthest from the motor, has the most leverage. I made a video that shows the problem better than I can ever explain it. You can see it best around 10 seconds in. Maximize the video to see it best. Set screws in the pulleys were checked/tightened. Bolt on backside of motor was tightened. Problem is worse when lathe is on slowest pulley configuration (belt farthest from motor).





View on YouTube


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## HapHazzard (Jan 9, 2016)

If I had to guess I'd say the upper pulley is moving. When you show it in low gear, the thumping sounds like it's about once per revolution of the headstock shaft. The motor is turning much faster, so it doesn't seem to have anything to do with the motor. Either the set-screw is loose or one of the bearings is seriously bad. Try taking the belt off and see if you can wiggle the pulley while holding the handwheel.


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## dhazelton (Feb 11, 2012)

It just looks like a flimsy mount to me.


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## Kentuk55 (Sep 21, 2010)

Bearings maybe?


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## kiefer (Feb 5, 2011)

How about the upper pulley out of round or the bore too large pushing the pulley of centre when the set screw is tightened or bad belt ?

Klaus


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## LeeMills (Nov 2, 2014)

Just guessing but may be…
the "motor mount screws" are loose (3 screws) item 12…
too much tension on the belt… should only be the pressure from a couple of fingers, then lock down.
http://www.teknatool.com/products/lathes/CometII/Downloads/Comet%20II%20Manual%20Final%20_19%20April%202013.pdf
Other items on page 24 of manual.


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## wormil (Nov 19, 2011)

> Just guessing but may be…
> the "motor mount screws" are loose (3 screws) item 12…
> too much tension on the belt… should only be the pressure from a couple of fingers, then lock down.
> - LeeMills


I checked both, the screws were tight but I removed, cleaned, and reinstalled them but I haven't remounted the motor yet. I also removed the bottom pulley and am realigning it.



> If I had to guess I d say the upper pulley is moving. When you show it in low gear, the thumping sounds like it s about once per revolution of the headstock shaft. The motor is turning much faster, so it doesn t seem to have anything to do with the motor. Either the set-screw is loose or one of the bearings is seriously bad. Try taking the belt off and see if you can wiggle the pulley while holding the handwheel.
> 
> - HapHazzard





> How about the upper pulley out of round or the bore too large pushing the pulley of centre when the set screw is tightened or bad belt ?
> 
> Klaus
> 
> - kiefer


I'll put a dial indicator to it later and check.

The belt looks okay.



> It just looks like a flimsy mount to me.
> 
> - dhazelton


Definitely but it still should not be doing that.



> Bearings maybe?
> 
> - Roger


The bearings are coming due. I don't think they are causing this but I could be wrong.


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## JoeinGa (Nov 26, 2012)

Just curious… Is the lathe bolted down to the bench?


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## wormil (Nov 19, 2011)

There are no problems and no runout with the motor, motor mounts, motor shaft, or bottom pulleys that I can find. The pulleys are aligned. The belt is properly tensioned. So the problem pretty much has to be in the top of the headstock or the belt (although the belt looks fine). Not bolted down Joe,

I checked each part with a dial indicator. There is some small runout, 5 thous, but nothing I wouldn't expect for a used lathe in this price range. I pulled on the spindle with the DI measuring and it barely moved but it was tricky getting the DI and my hand in there. I'll contact Teknatool tomorrow and see what they say.


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## MadMark (Jun 3, 2014)

You're hitting a resonance with the motor mount & motor. Since you're using variable speed DC motor, if there is a resonance at *any* speed, you'll find it. The solution was at your fingertips in your video. Put a firm rubber spacer under the free end of the motor & the problem should vanish.

M


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## MadMark (Jun 3, 2014)

Depends. Customers like drawers that slide and doors that open & shut properly. In kitchens I use stainless steel, for ornamentals usually wood. In any case if the cust asks, I do it their way. If your stuff is functional, who cares?

M


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## HapHazzard (Jan 9, 2016)

If there isn't any appreciable headstock runout and both pulleys are tight, you're definitely looking at bearings. Probably the cage has worn out in one of them and it's letting the balls make contact, which causes a regular, rhythmic jump in the turning resistance. You may or may not be able to feel it if you loosen the belt and turn the handweel.


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## wormil (Nov 19, 2011)

> If there isn t any appreciable headstock runout and both pulleys are tight, you re definitely looking at bearings. Probably the cage has worn out in one of them and it s letting the balls make contact, which causes a regular, rhythmic jump in the turning resistance. You may or may not be able to feel it if you loosen the belt and turn the handweel.
> 
> - HapHazzard


I think you've nailed it. I sent the video off to Teknatool but I'm ambivalent in my hope they will reply. Reviews say Teknatool's customer service is nonexistent but I'm happy for those people to be proven wrong. Some of those reviews also speak to premature bearing replacement. So now, both my lathes are down needing a bearing change. Hell, I bought this Comet in part so I could use it and not be out a lathe while working on my old Delta, that and it was a steal of a deal.


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## HapHazzard (Jan 9, 2016)

Can I recommend some good, cheap, precision bearings? These are the ones I just put two of in my Excelsior.

http://www.amazon.com/6005-2rs-Premium-Bearing-Bearings-ABEC3/dp/B00XRWGLGA

They're asking $16.99 plus $5.99 shipping for ten. If both lathes take the same bearing, you'll use 4 right off the bat.

You don't need to buy bearings from the manufacturer. From what I've seen, none of them actually use precision bearings anyway. As long as the numbers are the same, it's the same bearing, and you only need to worry about the "6005" part. Some lathes come with 6005Z or ZZ, which just means they have metal shields instead of rubber dustcovers, but I really don't see why you'd need a shielded bearing on a lathe.


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## MrUnix (May 18, 2012)

Lesson learned and why I always recommend replacing bearings on any new to you used machine. You have no idea what use/abuse it may have seen in it's lifetime and bearing are cheap insurance. As always, yank them to figure out what you got, measure them to be sure, and give Lynne a call over at Accurate to hook you up 

Cheers,
Brad


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## wormil (Nov 19, 2011)

If the bearings are easy to replace, nothing wrong with cheap. But nothing wrong with using a quality bearing either especially if they are not easy.

Years ago I read a great article on bearings, told me more than I would ever have wanted to know, but it said that ZZ, metal shielded, bearings are what you want for machinery because they provide more protection against particles/dust and less friction. I'm no bearing expert but all my machines have metal shielded bearings.


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## wormil (Nov 19, 2011)

So for future reference, if anyone needs to know, the Comet II bearings are the 6005 HapHazzard linked to above. Mine are RZ, which apparently is a low friction rubber seal.


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## HapHazzard (Jan 9, 2016)

I can see why you'd want a metal shield on a skateboard bearing that's exposed to gravel and road dirt, but I can't see it on a wood lathe.

The bearings I posted the link to are quality bearings. They can't say they're ABEC 3 unless they have eccentricity ≤ 0.000197" (that's 197 millionths of an inch). If a bearing doesn't have an ABEC grade, it isn't a precision bearing. Close tolerances aren't the only measure of quality, but they're arguably the most important.

I wasn't able to find a description for an RZ suffix except that they're usually sold as replacement bearings for roller skates.


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## MrUnix (May 18, 2012)

> http://www.amazon.com/6005-2rs-Premium-Bearing-Bearings-ABEC3/dp/B00XRWGLGA
> 
> The bearings I posted the link to are quality bearings. They can't say they're ABEC 3 unless they have eccentricity ≤ 0.000197" (that's 197 millionths of an inch). If a bearing doesn't have an ABEC grade, it isn't a precision bearing.
> - HapHazzard


I'm curious as to what bearings you wound up getting (what brand?). JSB is a known importer of Chinese bearings of the no-name variety, and those are labelled as EMQ (electric motor quality), despite the 'precision' moniker given. There might just be a reason they are so cheap (and there are quite a few counterfeit Chinese bearings being sold out there with all sorts of inflated ratings). Equivalent SKF or Nachi's run about $4-$8 a piece depending on where you source them.

Also, rubber seals are better at keeping contaminants out than metal shields, and is why most bearing manufacturers recommend them in contaminated environments over their metal shielded counterparts, particularly in locations where a lot of dust and other smaller type particulates will be found. Older 'sealed' bearings used a metal cover, but had a felt seal behind them. The one disadvantage sealed bearings have over shielded is they typically have a lower max. speed rating by a couple thousand rpm… but on most woodworking machinery, that is not a concern, as you will never see any speeds even close to those limits.

Cheers,
Brad


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## HapHazzard (Jan 9, 2016)

The bearings are made by HCH, a Chinese-based manufacturer with US Headquarters in Jacksonville, FL. They are ISO 9001 and ISO/TS 16949 certified. The OEM bearings were made by NBL, a smaller Chinese bearing company, also ISO 9001 certified.

EMQ is a largely meaningless designation. It just means that the manufacturer represents that the bearings are of suitable quality for electric motor applications. There are no industry standards for what it actually means. The only standards I care about are ABEC and ISO, and these bearings meet ABEC 3 and ISO 492 class 6 standards.

I really don't care about brand names anymore. They used to mean something once, but someone apparently noticed that brands had value and got the bright idea to leverage their value by using them to sell inferior goods. You can buy or license a brand and put it on just about anything the terms of sale or license agreements allow, and there are absolutely no standards for that-they are the result of business negotiations, not engineering initiatives. Whole companies are bought, sold and traded, and manufacturing operations are outsourced and offshored whenever somebody decides it will put a few more bucks in his pocket in the short term. If you can follow all that wheeling and dealing and come out of it with any solid understanding of what it means for the quality of a given product, more power to you, but it's way beyond my abilities. What I can get my pointed little head around are engineering standards agreed upon by engineers across entire industries and defined by measurable numbers that I can, if necessary, challenge. I don't test every bearing I buy, but if one fails before I think it should, you bet I will, and so will thousands of other manufacturing engineers, machinists, mechanics, technicians and hobbyists all over the world, and if we find things are not as they claimed, in violation of any standards represented, they are toast. They will be facing sanctions and lawsuits from standards bodies and class actions from consumers for years. To get a little idea of how serious this stuff is, look at what VW is going through for their creative workaround to get better emissions numbers. Now imagine how something like this would affect a bearing manufacturer whose only product is rolling-element bearings.

I agree about the rubber vs steel dust covers. That's why I was surprised to see some lathes using them. Manufacturers genearlly use whatever they can get the cheapest in quantity, but for every -ZZ bearing you can find, there's got to be an -RS one of equal quality for less. The only advantage I ever saw to steel covers was that they tend to pop off when the runout exceeds the compliance of the rubber gap seals, so when you find one lying on the floor, you can figure out where it came from and replace the bearing. In a noisy environment with lots of machinery, sometimes that's going to be your first indication, but that's really an edge case. I don't see any reason at all for them in lathes, and I couldn't find any 6005-ZZ bearings that were ABEC 3 for less than $10 a pop, so that's a lot to pay for a feature you really don't need.


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## MrUnix (May 18, 2012)

> The bearings are made by HCH, a Chinese-based manufacturer with US Headquarters in Jacksonville, FL.


That's what I thought… thanks 

Cheers,
Brad


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## wormil (Nov 19, 2011)

Since you gents know something about bearings, is it possible to replace a ball bearing with an angular contact bearing in a lathe. E.g. Replace a 6205 with a 7205? Specs say they are identical in size. I'm assuming the angular contact would be a superior bearing. Obviously this has nothing to do with the comet. I have a Delta 46-111 and 2 headstocks. One old one with taper Timken bearings that requires oil and a newer one (Rockwell) with ball bearings. My 3 options include a possible upgrade on the Rockwell bearings. Thoughts?


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## MrUnix (May 18, 2012)

I personally wouldn't deviate from what was in there originally… the major force on those bearings will be radial, not axial. The tapered roller bearings are actually good for both loads and swapping them out would be a downgrade. If you did go angular contact, you would really need to use double row to get the radial loading capabilities, but they will be much wider than the single row bearings you would be replacing. Here is a little chart that might help:










Cheers,
Brad


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## wormil (Nov 19, 2011)

That is a sweet chart, keeping that for reference, it helps a lot.


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## HapHazzard (Jan 9, 2016)

> The bearings are made by HCH, a Chinese-based manufacturer with US Headquarters in Jacksonville, FL.
> 
> That s what I thought… thanks
> 
> ...


Bear in mind that the lathe itself was made in China, so I wouldn't infer too much from what country the bearings are made in.


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