The inside of a Bridgeport Mill Head is not the most environmentally friendly place to put a bearing and then turn it at 4,200 RPM.  When we rebuild a head, we remove all the old grease as best we can then we put all the components into a high temperature parts washer.  It operates a lot like your dishwasher at home.  No, no, no, don't even think of using mama's dishwasher.  You will wind up with well deserved lumps, bumps and burses over a large portion of your body, starting at your head and working their way down to high priority areas.

Shielded Bearing

When we start the rebuild, we have a choice of bearings available to us; open, shielded and sealed bearings.  With the exception of the spindle bearings, which are open, we use the double shielded bearings.

The question is, why do we use double shielded bearing instead of double sealed bearings?  I wish I had a nickel for every time I've been asked that.  No, I wouldn't be rich, but I would have a whole pocket full of nickels.

Sealed Bearing

The answer is simple, it's all about heat.  If you take an OPEN bearing, say a 6208, lock the outside ring and bring it up to top speed of 10,000 RPM (oil lubricant), the bearing temperature will increase from room temperature (72� F) to approximately 120� F.  If you do the same thing with a DOUBLE SHIELDED bearing, the result will be about same within a degree or two.  But, if you did that with a DOUBLE SEALED BEARING, the temperature will increase to over 220�

F.   Please don't try this because in fact, the double sealed bearing will most likely fail around 6,000 RPM.

Open Bearing

 

If you replace all seven bearings in the upper head with Double Sealed bearings, you start to accumulate some BTU's that you just don't need.   Double Shielded bearing gives us the best of both worlds, low temperature rise and they protect the rolling elements from external contamination.

 

Can we supply you with Double Sealed bearing?  Sure.  Like everything else, they just cost a little more.

 

 Of course the spindle bearings are a different animal altogether.  While the upper bearings is a double shielded bearing to keep contamination out the bottom set of bearings are ABEC7 Precision bearings that are open and when purchased from us in the Spindle Rebuild Kit (SRK-00) we provide special high speed grease for the spindle bearings as well as step by step instructions to complete the job. 

If you decide to complete a top half rework on your Bridgeport mill we have three kits for you to choose from.  The 1hp Step Pulley Head is kit RBK-J1, the 1-1/2hp Variable Speed Head is kit RBK-15 and the 2hp Variable Speed Head is kit RBK-20.  Just click on the part number and it will take you to that page on our web site.  If you have another machine or need individual bearings just visit our web site at www.HandWMachineRepair.com or call us at 800-285-5271 and our friendly staff will be able to help you with your bearing or parts needs.   

Grease Access in Housing

If you could remove the upper sections and look inside you would see that this passageway is internally modified, resulting in two exit ports.  As you can see in the picture to the left, those ports discharge the grease into two grooves that wrap internally for about 270 degrees.  CAUTION, the instructions clearly state, one half tea-spoon every six months.  From an average grease gun, that is about 1/2 of one pump.  Don't over do it, there is no place for the extra grease to go and as the instructions say,work the hi-lo lever while greasing.  This action coates the internal wall of the casting and the external wall of the Bearing Sleeve.

From the Lubriplate website:  "LUBRIPLATE No. 107 is an outstanding concrete form release agent because it does not stain concrete.  Also, LUBRIPLATE No. 107 is an excellent anti-seize compound for the threads on bolts which hold metal forms."  You will find it is available in 1 gallon, 5 gallon and 55 gallon drums which may be a little more than you need for this particular job.

We use Mobil products throughout the shop so we went to them for a recommendation.  Much to our delight they recimmended Mobile EP-1 which happens to be the same lube we include in our rebuild kits.  It is available for $4.88 a tube.  Our part number is EP-1 and it is available by calling us or placing your order online.