Is there an error in the Bridgeport Mill manual or am I being stupid?

I am trying to get to grips with a Bridgeport mill with a J head. When altering spindle speeds there seems to me, to be 3 ways of doing it. a)The motor switch either position 1 or 2. b) High or low range on the mill. c) Altering the belt on the pulleys.

When looking at the manual it doesn't make a lot of sense to me. From the photo I can see that changing speeds from 67 to 115, or 115 to 180 or 180 to 275 could be done by moving the belt on the pulleys but it seems to say that speeds 67, 115, 180, 275,550, 920, 1500 and 2300 are all on Low Range and switch position 1, while all the other speeds shown underneath are on High Range and switch position 2.

Am I reading it completely wrong or are "Switch position 1 & SP 2" printed in the wrong place?

Edited By SillyOldDuffer on 24/08/2023 21:02:07

Only two methods, the switch only changes the motor direction. That is because the backgear is only two gears and therefore reverses the spindle direction for a given motor direction.

Andrew

Andrew, my switch definitely has 5 positions. Neutral, 2 speeds forward and 2 speeds reverse.

I've never touched a Bridgeport but can't resist having a shot at this. I think it is the "Low Range High Range" labels on the left side of the table that are misleading. At the top of the page it says that the motor runs at 1400 or 2800 rpm and the bottom two rows of speeds are double the top two rows so my guess is:

Top row is Switch position 1, Low Range

Second row is Switch position 1, High Range

Third Row is Switch position 2, Low Range

Fourth Row is Switch position 2, High Range

William.

Like you, I find it confusing and have to think each time I change speed, am I wanting to change gear or motor speed. I always end up looking to see if it is twice or half speed I am changing, if it is then change the motor speed. I keep thinking I should put a label on the machine to remind me what I want to change.

Baldric.

I think you may be correct William. I have ordered a tachometer/revcounter so when that comes I will put a piece of tape on the spindle and get some readings.

Not being damilar with the Bridgeport, I would ,understand it to be as Willaim says, with the belts giving the speeds shown in each row

Since the speeds shown in High Range are double those shown in Low Range, that would seem to result from the speed of the motor doubling.

The plate could have been printed to make this more obvious..

But once certain that this is the arrangement, it should not take long to become accustomed to mikt, and operation of the machine.

Howard

Sorted.

Thank you for your inputs. I'm sure Bridgeport had a good reason, but to me it would have been easier if the chart looked like this,

Good job Jim, looks right to me. One thing that struck me looking at your original scan is that the motor makes twice as much power at the high speed position, maybe another factor to consider when deciding on which permutation to choose.

William.