Hi,
the part number of the BEI encoder should tell you the 'number of cycles' the optical disk it has been fitted with. If that number is 250, which seems highly likely,
then it is a 250 line/rev encoder and therefore a 1000 count/rev encoder. That, with the reduction you mention on 5mm screws would result in 2um
resolution, or 0.05 thousandths of an inch.

Just as a matter of clarification, have you measured the screws? Being Bridgeport I would have guessed 0.2 inch pitch screws or 5.08mm. They are so close to 5mm
that its easy to mistake one for the other.

My Delta servos have a 160,000 count per rev encoder (40,000 lines), but that would result in ridiculously fine resolution and be totally impractical to signal
at the rate required to get max speed. Using 'electronic gearing', and almost universal feature of AC servos, I have an effective encoder of 5000 count/rev. The servos
are direct coupled to 5mm pitch screws for a resolution of 1um or 0.025 thousandths of an inch, if you prefer. The point is that this resolution is as fine as I could
conceivably use, and in most cases finer than I can measure.

Your set up, if indeed you have 250 line encoders, would still be very fine resolution indeed. I do not think there is any need to swap them, the resolution as is is probably finer than
you can use anyway. That is certainly my experience. Additionally.....do you think it likely that when the machine was built they would use encoders that had less resolution than
is required? I rather think not. Bridgeport do not make those sorts of mistakes, then or now.

Craig

The first batch of Bridegport Boss machines came with Inch screws. Shortly thereafter, they switched to metric screws. So they went from .2 inch pitch screws to 5mm pitch screws. That along with 2:1 belt drives between the motors and the screws. So the system sees 500 encoder lines for one rotation of the screw. 500 lines for 5mm. Y axis rotates the screw, X & Z rotate the nut, with the screw on Z being about 2" + in diameter at the top of the spindle.


Got the caps for the servo low voltage power supply and found a blown trace, the one cap really blew out hot, and will be trying it out over the next few days.

Hi,
kool, that all sounds promising.

Craig

Well, Replaced the caps in the low voltage DC section of the drive amps and the next set of caps decided to blow. Some smallish tantalum caps made a couple of very nice bags and stunk the shop up. Looks like i will be needing to order parts to get this working. So I will have to get my KX3 sold to generate the cash for the next phase.

At least the High Voltage DC supply for the output of the drives is working. It is a couple half wave rectifiers and a string of large capacitors with nice copper bus bars down the top.  And the necessary relays and contactors for the high voltage DC section all seem to be behaving.

So now to pull the computer section, 2 boards with Motorola 68000 processors and the related memories. Will have to put them away and see what I might be able to do someday getting a 68000 computer to play with... Doesn't seem t be much demand for those boards these days. Probably others are doing the same thing I am.

Now begins the hunt for some tool holders. Not a lot of CAT30 stuff out there. Might need to look at BT30 and ISO30 but they will require changing the drawbar from 1/2-13 thread to 12mm. Should not be overly difficult, or modifying NMTB30 holders by getting rid of the straight nub on the end. Have done that with a NMTB50 for the horizontal mill at work.