Bridgeport Disassembly

Last updated: March, 2018.
Original posting: March, 2006.

As part my scraping of a worn Bridgeport milling machine back to original precision, I had to disassemble the machine components. I had to repeat this disassembly later when I upgraded the leadscrews to ballscrews as part of my CNC upgrade project. Disassembling a Bridgeport mill is also sometimes necessary to move it into a small shop space or through a low doorway, or when using small vehicles.

You must be careful to not mar or force the precision dovetail way surfaces against each other when separating, lifting, and manipulating the heavy components. If you do accidentally mar the ways in a small spot, you must reduce this damage by marking against a precision flat and scraping. If you don't have the scraping tools and skill, you can approximate this technique by lightly rubbing a flat honing stone or precision file against the ridge that typically raises up around the impact point.

Here are the disassembly steps I performed:

• Table: The table is the most complicated. The table is constrained to the saddle by the rotary ball bearings on the ends of the leadscrew, and by the linear bearings of the saddle dovetail ways. You will first disassemble these contraints to free the table. Second, you will move the table free of the saddle in two separate, controlled, orthogonal moves: lifting the table vertically so it is suspended over the dovetail capture, and then translating the table horizontally off the dovetail geometry. These moves are best done with a controlled lifting device (an engine hoist, gantry lift, or forklift). If you are not so equipped, then I will suggest how the controlled lift can be performed with one or two persons lifting with simple rigging.

  Start by cranking the table so it is approximately centered on the saddle. The disassembly order then is: nut on right handle, handle, knurled stop, scaled dial, cap screws on bearing plate, bearing plate. Repeat these steps on the left end. Leave the leadscrew in place. Remove table gib screw and tap out the table gib using a thin rod against the opposite end from the gib screw. After the gib is removed, observe that the table will be only loosely engaged and captured on the saddle dovetail.

  The table itself weighs 215 lbs (42 inch long type, no screws, gibs, endplates, etc; more for the the 49 inch size). Attach a hoist (I used a shop engine hoist and lifting sling through two eye bolts on T-nuts on the table, placing the eye bolts about 1/3 and 2/3 along the length of the table for balance and hoisting stability). Pump the hoist to lift the table just enough to suspend the table, such that the table dangles freely in the un-gibbed dovetail space. Then work the table horizontally off the dovetails by wheeling the hoist gradually across the floor.

  If you have another person to help, but no hoist, you could bolt long handles (SuperStrut would serve well, or perhaps 2x4 lumber) onto the tee-slots in the table and lift as a team by hand, in the manner of carrying a body gently on a medic stretcher (or a king in a sedan chair!).

  You can also slide the table onto a sturdy workbench instead of hoisting; crank the knee up or down to match the bench height.

• Saddle: To get the saddle off, first remove the crossfeed ("Y" axis for the CNC-minded) leadscrew bearing plate capscrews and the plate itself. Remove the yoke capscrews, yoke, and both leadscrews. Remove the saddle gib screw and gib. Suspend and slide the saddle off the knee dovetail, using your lift device. The bare saddle weighs 92 lbs, so I was able to perform a controlled lift solo by hand, like picking up a sack of cement in a bear hug, by keeping the mass close to my torso. Steel-toed shoes and metatarsal guards are prudent for the feet you wish to keep after this stunt.

• Knee: Swing ram around to provide clearance. Crank knee up completely. Remove gib screw and gib. Hoist knee off dovetails. The knee weighs 257 lbs, and requires a long vertical distance to lift free, so a hoist and rigging are practically mandatory. I suppose two weightlifters with stretcher handles might succeed, but at some risk of damage or personal injury.

• Ram and Turret: I've not removed the ram and turret, but I am told there's just a spider under the 4 bolts on the turret after you remove the bolts. To hoist, I would use a 5/8 lifting eye in the threaded hole on top of the ram. Or a sling snugged fore and aft. If a forklift is available, you can lift with the forks under the bottom of the ram dovetail, and plywood shims to protect the contact area.

Don't mar any precision surfaces. On these components, almost all surfaces are precision!

The gibs and ways will be quite a mess with oil or grease. The knee will likely be filled with old chips. Standard cutting fluids in the past were animal fats, so the knee may be harboring a residue with the aroma of an ancient abbatoir. Kerosene, nitrile gloves, and a carton of paper towels are good for cleaning this situation. The big polyethylene mortar mixing tubs sold at the building supply store are a useful "wash basin" for containing the mess of solvent-cleaning big parts.

Be prepared for surprises and mysteries. I discovered the overworn saddle gib on the old machine I bought had been shimmed ... with a rough piece of metal pallet strapping.

The original Bridgeport design provided lubrication to the ways with grease forced in through zerk fittings. Having the components disassembled is the best opportunity to clean out the lubrication passages and upgrade them with central oiling tubes and a Bijur type lubrication pump system.

If you want to refinish or paint an old machine, it is best done while disassembled. With automotive bodywork materials and techniques (grinding, filling, masking, spray painting), a modest effort will yield a finer cosmetic restoration than the original. A simple scrubbing followed by a thorough shpritzing with canned industrial spray-paint is easy and worthwhile, if you're after a respectable look rather than museum quality.