Bridgeport 2J low speed troubles

Hey! I just traded some other equipment for a Bridgeport 2J mill. I've always wanted one.
This one works great in high speed but in low speed in makes kind of a light growling almost like a bad bearing and has low torque. It will actually pull quite a bit harder in high speed at 500 RPM than it will at 100 RPM in low speed. When it stalls in low speed it feels like a belt slipping. The motor keeps spinning but the spindle stops turning. Let up a little on down pressure and it will take off again.

Does anyone have any ideas on what might cause this? I've looked at the diagrams enough to see there are two belts in the head. What does the timing belt do? Does the timing belt run the low speed?

The timing belt is for low gear and is likely your problem.

Not very expensive to replace, just more of a pain.

The variable speed drive version is more difficult than the step pulley version. If you have the variable speed version, I would highly recommend rebuilding the variable speed sheaves. There are plastic bushings that the sheaves ride on that wear. If you let them get bad as in making a rattling noise, it will wear the motor shaft necessitating the need for motor rotor replacement.

JEFFAB said:

When it stalls in low speed it feels like a belt slipping. The motor keeps spinning but the spindle stops turning. Let up a little on down pressure and it will take off again.

Click to expand...

If this is a variable speed mill it sounds like a sheared key. Usually the motor key shears.

John

Thanks for the ideas and all the diagrams. I'm going to go ahead and order both belts and the bushings and open it up and check all the keys while I'm replacing the belts.

I'm thinking about buying this kit:
Top Half Rebuild Kit for a 2 HP Bridgeport

What do you think?

JEFFAB said:

Thanks for the ideas and all the diagrams. I'm going to go ahead and order both belts and the bushings and open it up and check all the keys while I'm replacing the belts.

I'm thinking about buying this kit:
Top Half Rebuild Kit for a 2 HP Bridgeport

What do you think?

Click to expand...

That kit does have everything you might need; bushings, keys, epoxy, bearings, etc.

JEFFAB,

Some things have not been identified:
Is this a variable speed mill? From the scant description I'll guess yes.
Is the motor 2 hp or 1 1/2 hp? There is a difference in parts for the two hp types.
ex; The 2 hp key will not fit the 1 1/2 hp motor shaft.
The spindle drive belt is not the same for the 1 1/2 hp and the 2 hp.
A new drive belt will range in price from $75 to $95 from a bearing supply.
Generally the belt does not go bad unless the spindle is stalled while making a cut. Then a narrow spot is
burned into the belt.
A rebuild that includes new bushing inserts lasts longer when a new belt is included.

There is a difference in spindle drive belts.
Goodyear and Gates.

Goodyear makes a belt compounded with a 'softer' rubber. This belt runs pretty quiet and would be my choice if the machine was located in a small space. This drive belt is easier to install than a stiff belt. The trade-off is a shorter lifespan. If the mill runs a steady eight hours a day expect to replace the belt in about two and a half years. In a home shop this may be the only spindle drive belt the machine will need.

Gates has a belt that has a harder rubber compound. This is my preferred belt to install in a production shop as it will outlast the Goodyear belt
It requires a little bit more effort to install. It is a bit louder than the Goodyear belt but will last much longer.

Low speed belt:

Rarely does this belt go bad.
It is a cogged belt that even in the older machines it continues to provide service.
When the belt starts to fail look for individual cogs that are ripped or separating from the backing.
Otherwise just re-install it. Belt failure is usually caused by overloading the machine with a task ment
for a larger hp mill.

You better match the part numbers to the diagrams. For instance, the two bearings marked 1491(2 required) are for the lower assembly.
Item # 35 in the drawing selling for $24.42 each.

This kit has other parts that do not address the immediate problem.
It does have a set of keys. Make sure they are for your mill.

John

Was talking to Barry about this, and it seems like maybe something isnt being described right.

He said if you would like, you can call the shop 800-285-5271 and he can ask some questions and get you to try some things.

Jon
H&W Machine Repair