LumberJocks

Troubleshooting a Comet II Lathe, bouncing motor.

  • Advertise with us

« back to Woodturning forum

Forum topic by Rick M posted 03-31-2016 03:03 AM 1094 views 0 times favorited 24 replies Add to Favorites Watch
View Rick M's profile

Rick M

7909 posts in 1841 days


03-31-2016 03:03 AM

Topic tags/keywords: comet ii

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

-- http://thewoodknack.blogspot.com/


24 replies so far

View HapHazzard's profile

HapHazzard

92 posts in 329 days


#1 posted 03-31-2016 12:01 PM

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.

-- Unix programmers never die; they just > /dev/null

View dhazelton's profile

dhazelton

2322 posts in 1757 days


#2 posted 03-31-2016 12:44 PM

It just looks like a flimsy mount to me.

View Roger's profile

Roger

19865 posts in 2265 days


#3 posted 03-31-2016 12:55 PM

Bearings maybe?

-- Roger from KY. Work/Play/Travel Safe. Keep your dust collector fed. Kentuk55@yahoo.com

View kiefer's profile

kiefer

4881 posts in 2128 days


#4 posted 03-31-2016 02:03 PM

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 https://www.youtube.com/user/woodkiefer1/videos

View LeeMills's profile

LeeMills

271 posts in 762 days


#5 posted 03-31-2016 03:22 PM

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.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

View Rick M's profile

Rick M

7909 posts in 1841 days


#6 posted 03-31-2016 05:44 PM



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.

-- http://thewoodknack.blogspot.com/

View JoeinGa's profile

JoeinGa

7479 posts in 1468 days


#7 posted 03-31-2016 08:35 PM

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

-- Perform A Random Act Of Kindness Today ... Pay It Forward

View Rick M's profile

Rick M

7909 posts in 1841 days


#8 posted 04-01-2016 04:02 AM

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.

-- http://thewoodknack.blogspot.com/

View MadMark's profile

MadMark

977 posts in 914 days


#9 posted 04-01-2016 05:19 AM

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

-- Madmark - Madmark2150@yahoo.com Wiretreefarm.com

View MadMark's profile

MadMark

977 posts in 914 days


#10 posted 04-01-2016 05:23 AM

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

-- Madmark - Madmark2150@yahoo.com Wiretreefarm.com

View HapHazzard's profile

HapHazzard

92 posts in 329 days


#11 posted 04-01-2016 01:21 PM

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.

-- Unix programmers never die; they just > /dev/null

View Rick M's profile

Rick M

7909 posts in 1841 days


#12 posted 04-01-2016 05:33 PM



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.

-- http://thewoodknack.blogspot.com/

View HapHazzard's profile

HapHazzard

92 posts in 329 days


#13 posted 04-01-2016 10:39 PM

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.

-- Unix programmers never die; they just > /dev/null

View MrUnix's profile

MrUnix

4208 posts in 1660 days


#14 posted 04-01-2016 11:29 PM

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

-- Brad in FL - To be old and wise, you must first be young and stupid

View Rick M's profile

Rick M

7909 posts in 1841 days


#15 posted 04-02-2016 01:48 AM

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.

-- http://thewoodknack.blogspot.com/

showing 1 through 15 of 24 replies

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com