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Rockford CNC Lathe Revival

Dabbler

ersatz engineer
Oh my. Here's where your surface plate comes in. Time to measure the crap out of everything. Timken bearings can exhibit this kind of binding behaviour when something gets out of alignment... it doesn't take much, a tenth or 2 will do it. The usual culpret is an angular misalignment. Axial misalignment would be the next to check.

regarding the goo. I suspect you are right. You'll have to get advice from someone else on this. I've had 0% luck with gasket goo.
I always fabricate my own seals and use low durometer eurothane foam, as it lasts longest and is most resistant to oil that i know.

question 3 - idunno.
 

Alexander

Ultra Member
Administrator
I don't know but it looks like you have two tapered bearings. The preload is probably set by that big nut. As long as you don't have any endplay or side movement I would imagine that big nut is tight enough. It is quite likely I am missing something but I don't see anything I would want to take apart. Have you tried running that motor with the belt off to see if it gets hot with no load?
 

RobinHood

Ultra Member
From the info you provided, sounds to me the bearings are too tight. As things warm up, the bearings expand hard into their cups and thus friction increases dramatically requiring more power to turn the spindle. Also, they don’t seem to be lubricated sufficiently, thus accelerating the heat build-up.

Oil seals:

Your lathe uses a labyrinth seal. You can see the two oil collector grooves (red arrow) and the return passage (green arrows).
DFEF4040-98F5-4D65-840E-DC4CC08BF3BC.jpeg

The oil seal ring just needs a thin layer of oil resistant RTV (the black goop you see ((blue arrow)) to seal the ring to the HS. This ring also retains the bearing cup (outer race).
Edit: on closer inspection, it looks like there is a paper seal stuck to the HS. The black goop is probably just seal retainer compound.

AE9B9FC0-61B0-4FCD-A20F-D8579ECC4A4E.jpeg

Did you remove the oil plug (yellow arrow)? It could be why the oil level will not go above the 3/9 position in the sight glass. The oil level in the HS will never be higher than the lowest point of the labyrinth seal as any excess will just run out between the seal and the spindle. So, in theory, you can not overfill the HS with oil.

Q 3

Yes, you can use the retaining nut to push the bearing cone (inner race) back onto the seat. A suitable tube could also be used to drive the cone back onto the spindle.

If you make a puller using ready rod, you could pull the spindle out the front.

You could try and use a heat gun on the rear bearing to help with removal. I doubt the cone is anything more than a very light press fit onto the spindle; it needs to be able to move relatively freely as it is used to set the pre-load of the system.

What kind of retaining / pre-load system is used on the spindle? Just the nut? In that case it would set the pre-load for the spindle bearings. The manufacturer would specify a preload. They would probably specify it in terms of torque required to turn the spindle in its bearings (without anything connected to it).
 

Janger

(John)
Vendor
Premium Member
From the info you provided, sounds to me the bearings are too tight. As things warm up, the bearings expand hard into their cups and thus friction increases dramatically requiring more power to turn the spindle. Also, they don’t seem to be lubricated sufficiently, thus accelerating the heat build-up.

Oil seals:

Your lathe uses a labyrinth seal. You can see the two oil collector grooves (red arrow) and the return passage (green arrows).
View attachment 19408

The oil seal ring just needs a thin layer of oil resistant RTV (the black goop you see ((blue arrow)) to seal the ring to the HS. This ring also retains the bearing cup (outer race).
Edit: on closer inspection, it looks like there is a paper seal stuck to the HS. The black goop is probably just seal retainer compound.

View attachment 19409

Did you remove the oil plug (yellow arrow)? It could be why the oil level will not go above the 3/9 position in the sight glass. The oil level in the HS will never be higher than the lowest point of the labyrinth seal as any excess will just run out between the seal and the spindle. So, in theory, you can not overfill the HS with oil.

Q 3

Yes, you can use the retaining nut to push the bearing cone (inner race) back onto the seat. A suitable tube could also be used to drive the cone back onto the spindle.

If you make a puller using ready rod, you could pull the spindle out the front.

You could try and use a heat gun on the rear bearing to help with removal. I doubt the cone is anything more than a very light press fit onto the spindle; it needs to be able to move relatively freely as it is used to set the pre-load of the system.

What kind of retaining / pre-load system is used on the spindle? Just the nut? In that case it would set the pre-load for the spindle bearings. The manufacturer would specify a preload. They would probably specify it in terms of torque required to turn the spindle in its bearings (without anything connected to it).
Thanks Rudy for the clear explanation.
 

Janger

(John)
Vendor
Premium Member
Is this the right approach to remove the spindle? I tightened it up a fair bit and nothing. Thought I’d pause for consultation and see.
 

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RobinHood

Ultra Member
Since you got my curiosity going when you mentioned bearing lubrication, heat, etc., I found this on the Timken website:


One can select different parameters to see what happens to bearing life. One big influence is operating temperature.

Looking for a bearing pre-load value which would be suitable for your installation…
 

Janger

(John)
Vendor
Premium Member
I had to make the puller beefier. Nothing like some 4140 scrap. It’s working now.
 

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Janger

(John)
Vendor
Premium Member
Since you got my curiosity going when you mentioned bearing lubrication, heat, etc., I found this on the Timken website:


One can select different parameters to see what happens to bearing life. One big influence is operating temperature.

Looking for a bearing pre-load value which would be suitable for your installation…
I was looking around on there for preload too and didn’t see much. Found an article on various ways to set the preload - but what is the value?
 

RobinHood

Ultra Member
I would go with what @Alexander said: eliminate all endplay (after seating them) and go from there. Monitor bearing temps. If they stay cold, make them a bit tighter. I run the bearings around 45C. Takes about 45min to an hour to get there and they stay there all day long afterwards.

SM recommends 0.56 ft-lbs of pre-load on their 1340 with Timken bearings. They are a different design from your Rockford and I found that the bearings run too warm for my liking. So I back them off until I get to the 40C to 50C range. Never measured the resulting torque - bet it is very close to their value though.
Colchester would not give me their pre-load spec. They told me to bring in the machine for service. I thanked them and just set the bearings for 45C.
I’ll be doing the same on the CMT (i just have not got the electrics running so I can’t start testing). Both the Colchester & CMT have auto temp compensating bearing pre-load systems.

Here is the procedure from SM 1120 manual (1340 is identical):

EEEF80F5-A325-4F0D-BF97-4D5EA890304A.jpeg
 

Janger

(John)
Vendor
Premium Member
Apparently I just hit 3000 posted messages. My I'm chatty. ;)

Anyway Thanks Rudy for posting that info on the preload procedures.

So I got the bearing off. Picture 1. That's good. I was hoping to then be able to slide the entire spindle out so I can easily get at the bearing covers and head stock seal area to clean them up. Well there is another problem. On the spindle inside the head stock there is a geared pulley so the spindle won't come out. That pulley turns a belt connected to the rotary encoder which is the digital equivalent of a thread dial. The encoder is the top left picture two and goes in the lower hole in picture 1. It has a concentric mount to allow the belt to be tightened. This lathe has a lot of fancy details I wish I knew what it cost in the early nineties when it was made.

Side note picture two shows the bearing cover. I cleaned the area circled with acetone and cotton swap. cleaned right up with the acetone. Bottom left is the big nut holding the spindle to the inner bearing race. it has a set screw with a brass pusher to prevent thread damage. Top right is the bearing. More to come next post.

IMG_1623.jpg 1641253029769.png
 
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Janger

(John)
Vendor
Premium Member
Now how does this pulley come off? Picture 1 is the inside of the head stock looking up at the pulley. You can see the belt hanging there. There is a small hole on the pulley. I've tried putting various hex wrenches it does not seem to be a set screw. Difficult to get a picture. I'm shoving my arm in there and snapping away. Can't see the screen it's too tight. Picture 2 in the blue circle shows what might be a keyway?

I might just leave it as I now have enough clearance to clean the headstock chuck side seal surfaces.

IMG_1603.jpg


1641253424323.png
 

Janger

(John)
Vendor
Premium Member
Looks like a pin in th picture. But if you don't have to remove it, I'd leave it alone...
A pin! That seems strange to me as how would you get it out? If you needed to change the chuck side bearing it would have to come off. How would you remove it? Pull and shear the pin off?
 

Janger

(John)
Vendor
Premium Member
Ah so after a call John explained that it's likely a roll pin and you could pound it through and out with the right drift. Looking inside the spindle it does appear to be a through hole. That does not explain the mysterious rectangular keyway like slot though. The pin is at about a right angle to that slot.
 

RobinHood

Ultra Member
If it is a roll pin through the timing gear and into one side of the spindle wall, there could be another one on the opposite side. They would be relatively short. All they would do is prevent the gear from moving axially. There for sure is a key way and a key. You can see the key in picture 1. Roll pins are hollow. If you put a light inside the spindle bore, you should see the light in the hole on the gear (assuming the hole is not gummed up). If you see light, it confirms a hollow pin.
 

Janger

(John)
Vendor
Premium Member
So what should I do to replace the oil seals.? I have this parchment paper I could cut out one and use that along with this ultra gray Pirma Tex gasket maker. Would it be better to use the parchment paper plus the gasket or only the gasket glue? Or something else entirely.? Thanks everybody for your help on my project
 

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