Replacement For Logan Headstock Double Row Bearing

Like others I decided to replace the 70+ year old v-belt drive on the spindle of my Logan 400 Lathe. This would give me the opportunity to clean the various parts and inspect the bearings. I will not go into detail of how to disassemble the head stock because it is covered in other forums. What I discovered is the spindle bearings are metric and this gave me a mild surprise! The bearings were stiff and rough because the grease had turned to a hard wax consistency. I decided to replace the bearings using the metric dimensions and found there are many to choose from. The main bearing (ref 0674) has a 40mm bore, outer diameter of 68mm, and a thickness of 15mm. The main bearing also has a snap ring which is an option from several manufactures. The back bearing (ref 0675) has a bore of 35mm, outer diameter of 62mm and a thickness of 14mm. I used a local bearing supplier "Motion Industries" to purchase new bearings manufactured by SKF. Main bearing SKF 6008 2ZNRJEM, rear bearing SKF 6007 2ZJEM. Decode the SKF part number, 600x = 6000 series bearing, x is bore times 5 ( ie, 6008, 8x5 = 40mm bore, 2Z = 2 shields, NR = snapring, JEM is type of lubricant). The lathe runs very smooth and quiet with no wobble in the spindle as best as I can measure.
 
E Ragnar said:
Like others I decided to replace the 70+ year old v-belt drive on the spindle of my Logan 400 Lathe. This would give me the opportunity to clean the various parts and inspect the bearings. I will not go into detail of how to disassemble the head stock because it is covered in other forums. What I discovered is the spindle bearings are metric and this gave me a mild surprise! The bearings were stiff and rough because the grease had turned to a hard wax consistency. I decided to replace the bearings using the metric dimensions and found there are many to choose from. The main bearing (ref 0674) has a 40mm bore, outer diameter of 68mm, and a thickness of 15mm. The main bearing also has a snap ring which is an option from several manufactures. The back bearing (ref 0675) has a bore of 35mm, outer diameter of 62mm and a thickness of 14mm. I used a local bearing supplier "Motion Industries" to purchase new bearings manufactured by SKF. Main bearing SKF 6008 2ZNRJEM, rear bearing SKF 6007 2ZJEM. Decode the SKF part number, 600x = 6000 series bearing, x is bore times 5 ( ie, 6008, 8x5 = 40mm bore, 2Z = 2 shields, NR = snapring, JEM is type of lubricant). The lathe runs very smooth and quiet with no wobble in the spindle as best as I can measure.
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Just wondering how your SKF 6008 2ZNRJEM bearing is holding up to use.
 
Oldvetteman said:
Just wondering how your SKF 6008 2ZNRJEM bearing is holding up to use.
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The bearing SKF 6008 2ZNRJEM is working fine with no issues. The country of manufacture is (if I remember correctly) Argentina. I might add, that the lathe is not used very often. The bearings out of the box had extremely smooth feel while turning the internal ring manually with no indications of roughness - smooth as silk. The lathe with the new bearings is noticeably quieter in operation.
 
E Ragnar said:
The bearing SKF 6008 2ZNRJEM is working fine with no issues. The country of manufacture is (if I remember correctly) Argentina. I might add, that the lathe is not used very often. The bearings out of the box had extremely smooth feel while turning the internal ring manually with no indications of roughness - smooth as silk. The lathe with the new bearings is noticeably quieter in operation.
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Thanks for your response. I should have asked in my previous post, but have you ever measured the radial play in the bearing?
 
I did use my indicator gauge on the spindle. My gauge has 0.001 inch divisions. The gauge shows some very small movement, much much less than 0.001 inch - that is the best I can measure and I would estimate several 1/10,000 of an inch. BTW, the SKF 6008 is an ABEC 3 bearing which then implies the balls in the bearing are ground within; ABEC 3: 0.0050 mm (0.000197 inches)
 
SKF JEM bearings are generally C3 clearance which is seldom used in a spindle bearing unless running at the bearing's maximum speed limit or in a hot environment like electric motors. Yours seem to be running with low runout but a CN or even C2 SKF Explorer ( ABEC 3 ) would be my choice. The higher the precision the lower the clearance that you can tolerate which is the key to tight runout. Dave
 
It all comes down to cost and availability. The SKF 6008 2ZNRJEM was a comparable replacement to the original bearing that was no longer available for the Logan 400.
 
James_Douglas said:
After weeks of research and a dozen conversations with bearing manufacturers I came up to a brick wall on finding a "correct" bearing for the Logan Lathes. There are several bearings that will in fact fit dimension wise, however the key design parameter is the fact that the original bearings had a preload in them.

The manufacturers all make a single row bearing with a preload, but no double row bearings.

I called Logan lathe and talked with Scott Logan before ordering his bearing. Since Logan Actuator sells the bearings, at a much higher costs than the other dimensionally same bearings, I wanted to know which of the 3 or 4 preloads that are generally available by the manufacturers he was using. I was interested in going up on step if possible. Since the bearing is a special order non-refundable item I wanted to know if there was any choice.

Scott would not discuss in detail the bearing. All he would say was that the bearing met the original specifications.

Below is an email I sent to Logan Actuator yesterday in the morning. I am waiting on an answer.

--------------------------------------Original Message---------------------------------------------------

From: James Douglas

Sent: Monday, April 13, 2015 10:35

To: 'Logan Actuator Co.'

Subject: Question on Logan 820 bearing

ATTN: Scott Logan,

Hello Scott,

I don't want to beat a dead horse. However, I was suspired when I opened the box with the bearings inside. They are SKF. Prior to talking with you on the telephone and prior to ordering the bearing from you, I had talked with SKF and a lot of other bearing manufacturers. They all told me the same thing. They did not make any double row bearings with a built in preload.

I assumed that you were having the bearings made by a specialty house with a preload just as the original 5000 series New Departure bearings that Logan used in the 820 lathe (see attached).

I emailed and talked with SKF engineering this morning. I read them off the part number on the box and the part number off the bearing. Their response was:

****************************************************

SKF 3208 A-2Z is by design a bearing that has internal clearance. This bearing has axial internal clearance equal to 0.0004/0.0011 in. which is considered in the "normal clearance" range. Other identifiers in the part number to specify internal clearance are:

C2: axial internal clearance smaller than normal

C3: axial internal clearance greater than normal

C4: axial internal clearance greater than C3

Again, this bearing cannot be preloaded as manufactured.

*****************************************************

There is no marking on the box or the bearing to indicate that it is anything other than a what SKF calls a "normal clearance range". Also, they stressed that clearance range and preload are not the same things and I was told not to confuse the two. They also made it clear that this bearing "cannot be preloaded as manufactured".

Since the preload is what makes the lathe shaft not walk forward or back and there is no provision to set any preload on the shaft (by design) then the bearing needs to have a preload.

Can you shed any light on this for me please? If the bearing was drop shipped, is it possible that I did not get the correct bearing?

Thank you for your time.

James.
------------------------------------------------------------------------------------------------------------------

If anyone can shed any light on the bearing issues I would be grateful.

It appears that what I got from Logan was a "tighter" bearing than the other generally available bearings of the same size, but still without a preload of any kind. If you see the attachment, which is a page from a New Departure catalog 19th edition 1948, all 5000 series bearings had a preload. The Logan 45508 bearing is a 5000 series ND bearing. The 4 in the number just denotes a snap ring.

I am starting to get somewhat upset with the fact that I did my homework, talked (or tried) with Scott Logan about the bearing and its issues, spent the money for his part numbers and then got a bearing that the manufacturer tells me has no preload which by definition does not equate the original specifications.

When I get a response I will let people know. And again, if anyone has any insights, I am all ears.

James

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