Re: [CAD_CAM_EDM_DRO] Thk slides

Bill,

Sounds like the bearings were shipped in Cosmolene, a preservative
coating (in)famous in the military world for the difficulty involved in
removing it. It should come off with any hydrocarbon solvent, like
kerosene or mineral spirits plus a generous application of elbow
grease. Work outdoors with good rubber gloves away from sources of
ignition. If you have removed the coating, have you repacked the
bearings with new grease? A liberal coat of new lithium grease should
smooth things out dramatically if the bearings are in good shape.

I would think that the coating might make the bearings stiff, but I
wouldn't expect them to run rough unless the ways were corroded or
contaminated with dirt. Shouldn't be the case if the bearings are new.
I guess the question would be how old they are, and whether they were
corroded. In any case, inspect the bearings from the bottom and see if
the line of balls is visible from the underside. There should be no
gaps larger than one ball diameter in the line of balls. However, on
the units that I have reassembled, even 3 or 4 missing balls didn't make
the travel detectably rough.

I don't know anything about the specific model THK bearing you refer to,
though I disassembled a great many different models in the machines I
salvaged. Most turned out to not be captive ball systems. Google is
your friend -- perhaps the pertinent spec page indicates it the balls
are captive on your model or not, but I'd assume the latter. If you
take the travelers off the rails, do it over a big clean container, or
else be prepared to crawl around on the shop floor with a flashlight for
a long time. It's really amazing how far ball bearings bounce when
dropped on a concrete floor, and they have an uncanny ability to find
expansion joints and floor drains from 15 feet away =:^o

Dave


Bill Davis wrote:

> Well Dave, you're scaring me. These Slides were represented as never used. When I got them, they looked to be in original package. It took me a while to clean what looks to be amber colored sticky substance. The package has been open (maybe to photograph for selling. I'm thinking either the bearing came off the rail and maybe some ball bearing escape or what ever the substance that I had to clean may ended up in side the bearings. Maybe I should do what you suggested in the first paragraph first. Do you know if the THK SR15 bearing have a way holding the ball bearing in place whenever I remove them from the rail?
> thanks
> bill
> ----- Original Message -----
> From: David Speck
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Sent: Thursday, August 24, 2006 4:47 PM
> Subject: Re: [CAD_CAM_EDM_DRO] Thk slides
>
>
> Bill,
>
> Rough running may indicate corrosion or debris in the bearings. If you
> look at the travelers from the bottom up, you should be able to see if
> there are gaps between the balls. If there are no major gaps, then the
> roughness is probably not due to missing balls. You may have to remove
> the travelers and clean them in kerosene before repacking them with
> clean grease.
>
> You will have to measure one of the bearing balls that you already have
> with a micrometer to get the size. Bearings are easily available from
> eBay or McMaster-Carr, and many other suppliers. They come out a whole
> lot easier than they go in!
>
> Reloading the bearings it lotsa fun. I scrapped some assembly machinery
> over the past 2 years and found to my chagrin that many of the linear
> bearings were not captive, so I've had more practice than I care to
> admit. Turns out that it was only the caked on grease and grime that
> held the bearing balls in the travelers. I have seen some new bearings
> that come with a blue plastic loading fixture, but have never had one to
> work with.
>
> Before you start, put a tie-wrap or piece of wire through one of the
> mounting holes at the far end of the rail so your "other" bearing
> doesn't slide off while you work on your end. (You can probably figure
> out why I suggest this!)
>
> I use a magnetized Allen key a bit smaller than the diameter of the
> bearings to pick up and manipulate the balls. I slide the partially
> loaded traveler to the open end of the rail, with the rail on top, and
> the traveler on the bottom, and pick up a bearing at a time with the
> Allen key, and push it into the ball channel between the end of the
> traveler and the rail. I use a wood dowel to push the bearing balls off
> the Allen key. When the race gets nearly full, bearings will start to
> push out of the recirculating channel as you push new ones in. Then you
> should run the traveler back and forth to take up slack space between
> the balls, until there is no more room to insert more balls, and your
> done. Checking from underneath the traveler will indicate whether there
> are still gaps in the stack of balls. It can be surprisingly difficult
> to get the empty spaces out from between the balls in the circuit.
>
> HTH,
> Dave
>
> wdavis364 wrote:
> > I bought a pair of THK SR15 slides off a Ebay and one of the blocks is
> > slides is moving rough as though it is missing some of the ball
> > bearings.
> > Can I reload the bearings here? I've seen ball bearing on sale for
> > reloading. Is there info on how to do this? If this is doable, where
> > can I look for this information and where to buy these ball bearing?
> > thanks
> > bill