I have excessive play in the spindle of my old Bridgeport J-head, I can't recall the exact serial number but it's j-89xxx, so it is old. The spindle bore looks OK and the top end runs smooth so I decided to replace the bearings and once the bearings have been replaced the bore could be reground.
I picked up a pair of ABEC-7, medium preload 7207 bearings and the upper bearings but now I'm looking for information on how to install them. The four bearings were about $475 CDN so I really would rather set them up properly and only have to replace them once and in that regard I'd like the advice of anyone that has experience doing this.
you'd get more exposure in the bridgeport specific forum. there have been many discussions about spindle bearings there. a quick search should give you some information.
If there is a spacer between the bearings, you'll need to verify that the inner and outers are the EXACT same length and the ends are perfectly parallel to each other.
THis way, your bearing preload won't be affected by the spacers - REASON: sometimes they used unloaded bearings and uneven spacers to create the preload.
Pretty sure the bearings are mounted DB. You'll just need to make sure you get them fully preloaded when you install them.
Properly grease pack them - usually 30% full. Kluber synthetic is superior lube for greased spindle bearings. Pricey but good. The factory spindles were lubed with generic Andok C. Take time to clean up any crud anywhere. Debris contamination has ruined many a spindle rebuild.
Freeze the spindle and warm up that bearings on a hot plate or with a heat lamp - they should drop onto the spindle. Neither a press nor hammer should be needed or used. IF you get them installed, a heat lamp on the housing and freezing the bearing/spindle assy should enable the spindle to slip into the quill.
Take your time and keep everthing clean enough to eat off of.
Anything more than Scotchbrite needed to clean up the spindle should not be needed to 'fix' the outside of the spindle. Grind the spindle ID upon reassembly while rotating in the new bearings.
Plan ahead to figure out what needs to be pressed together and how you can do it thermally if at all possible. Most problems with noisey bearings are due to ham fisted, knuckle dragging assembly practices.
Thanks, that's what I needed and to some extent it's a confirmation of what I thought I would have to do. I have the bearings with a no penalty exchange policy as long as the package is unopened. When I remove the spindle they suggested that I should call them to verify that the replacement bearings are equivilent to the ones removed.
I just got off the phone to the local bearing supply where I picked up the bearings and was checking to confirm that the bearings I got were the right ones. The bottom set are RHP 7207CTRDULP4, medium preload bearings, what are the equivilents to the M206 K 132J30 bearings.
The spindle is out and looks good, no vise marks or the like and the last spindle rebuild was long ago enough that the top bearing is made by New Departure. I'll put the spindle on vee blocks to check that it's not bent. Can I warm the spindle and then pour alchohol that has been cooled with dry ice in the spindle to get the bottom bearings off or is that not a good idea?
For quite a while, BPT took generic deep groove ball bearings (6207's in this case) and turned them into psuedo angular contacts (A/C's) by either grinding preload into them OR using uneven spacers. They did this so they could use inexpensive sealed/shielded bearings in machine tool spindles. By preloading and selective fitting, they could get ABEC7 performance at a fraction of the price.
What you could find is that the bearings in the spindle could be 6207 variants and you have 7207's. Physically they differ drastically internally but they'd be interchangeable and the 7207's would provide superior performance.
HOWEVER, a bearing supplier who did NOT know how BPT crafted up their bearings might get cold feet on the sale and tell you to return them - they also might try to offer you some 6207's to save you some money. DO NOT USE 6207's!!!! They won't work ala the 7207's due to the lack of custome preparation/matching/selective fitting that the OEM bearings had.
The whole story of this phase of bearing use in BPT spindles was discussed in a previous post on BPT spindle bearing replacement on this site somwhere's within the past couple of weeks.
BULLETIN: a 7207 is NOT, NOT, NOT equivalent to the M206 ( ) bearing.
If your bearing guy says so, he's an idiot. The M206 ( ) is a 6206 based bearing - hell, the damn things aren't even the same frigging size!!!! The suffixes in the ( ) is the special rework procedures they went thru to turn 6206's in to "spindle bearings".
I'd strongly urge you to find the prior bearing spindle post on this site for a more complete explanation of what BPT did to selectively fit bearings to spindles. It is too long to go into again here.
Don't force cool anything once you install it, let it cool naturally. Once the bearings cool to the point they tighten up, you can force cool/warm them by blowing clean dry air on them but don't, DON'T use liquids.
The bottom bearings that were in the spindle were RHP 7207 TU EP3 and the top bearing was a New Departure Q 30206 DTL and it appears that it was specially reworked as the 'Q' and the 'DTL' are etched by hand.
After speaking to the bearing supplier he said that the RHP 7207 TU EP3 is different than the original ones he supplied, but they were stock bearings and we hoped they would be the right ones so there would be little down time (I have a job on the go). New bearings to match the existing RHPs are $428 plus taxes (ouch!)
They haven't been able to come up with a match for the M206 K 132J30.
Tell your bearing guy to get off his a$$ and start reading the RHP catalog:
7207 = physical size
TUEP = denotes super precision bearing with "special' features
3 = accuracy level.
The current version of my outdated C826 catalog should be contacted for RHP's meaning of the "3" accuracy level. If they are ABEC3's which would be my guess, they are a bit sub standard for a spindle. I doubt they are anything but ABEC3's as there is NOT a 3 grade in ISO standards.
There should be more numbers to denote preload someplace on/in the part number.
Re the Q30206 DTL on the ND bearing:
Q30206 = shielded or sealed 6206
DT = dual tandem match/fit/preload
L = "light" preload value
Dunno what the accuracy level is as they were not consistant at marking accuracy levels on bearings.
But, even if/when the bearing guy does GOHA and read the catalog, he won't find the meaning of K132J30 in either the NSK or RHP catalogs (btw NSK owns RHP).
Why? Because that spec was an internal, unpublished, custom BPT spec that Fafnir or whomever made your bearings produced the bearings to.
The closest off the shelf 'drop in' bearing for the ND bearing would be a 7206CTYDULP4 and 7207CTYDULP4 for the RHP's. Both these numbers are NSK.
You WILL have to grind the spindle ID after installing these or any other spindle bearings you may ultimately use on the machine.
How do I know this?
Used to be a machine tool bearing engineer for a noted bearing company and did LOT's of work on the BPT bearing program. Oh, and I do happen to have copies of lots of the BPT bearing drawings.
Great, that's more info than I got all morning talking to half a dozen bearing suppliers. I did figure out that I should not have one half of an angular contact pair at the top end of the spindle so I'll order the bearings you suggested. BTW, I kind of suspected you knew more than the average poster here on the zone and I think that just might apply to more than bearings
Thanks again, looks like I'll be back at work soon!!
I ended up going to a machine tool dealer that sells thier own rebranded Tiawanese clone mills. They went through thier Bridgeport catalogue (a newer version than the ones I've seen on the net) and gave me the ones they use instead of ordering from Bridgeport. I went this route rather than through the Bpt dealer as the delivery time was going to be prohibitive and the price would be higher. The bearings I bought were; 1 piece - NTN 6206 ZZCM/2AS and 1 pair - NTN 7207CG/GNP4
One the 7207s there is a burnished mark, is this supposed to be lined up with the mark on the second bearing?
They said to wash out the bearings and pack the bearings about 30% full of Kluber grease. Is this best? I've heard somewhere that you shouldn't wash the bearings and I read, I think on this forum, but maybe the Bpt forum that the manufacturers don't always do a great job of cleaning the bearings either. If you do clean them, what is the best way? Is there a less expensive alternative to the Kluber grease, it's $202 for a 400 ml tube and I'd likely have $190 worth of grease sitting around for the next 20 years.
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