Bridgeport Manual to CNC conversion...

[Davek0974]

I guess if i do fit the servo, adding the enc module is a no-brainer really, daft not to fit it.

The bearings are sealed and hidden completely in this motor, i could likely get some WD40 in there but no grease. My main issues with fitting it are that it will fail some time, probably when i need it, and will then need my cabinet pulled apart to change from VFD to serve drive etc.

It sort of becomes a "might as well fix it now" option i think, then i can benefit immediately from the improved speed control etc. If i sell my tapping heads they would likely fetch enough to pay for the servo drive anyway :)

[Davek0974]

Decided to exercise my minimal CAD/CAM knowledge and plunge into a slab of 15mm ally for the Y axis motor plate.



Took 44 minutes on the mini-mill, used a single 5mm tool for the whole job and pocketed all the waste out ;)

Fitted perfectly...



Seemed a better place than hanging down below I think.

[Davek0974]

Decision is now leaning towards throwing the old motor back on!
Why?
One reason was that i don't have any idea if a 1.8kw servo will be a good replacement and 1.8kw seems to be the only (affordable) size that runs to 3000rpm, also, fitting an encoder for the rigid tapping module would be a total ball-ache on a Bridgeport - there is no clear access to the spindle shaft and I wrongly thought it would use the motor encoder signals which it does not.

So, back to plan 1 until the bearings fail 100% is to use the standard motor with my VFD and use the variable mechanical speed to give me two electrically variable speed ranges that overlap.

[Boyan Silyavski]

But your motor now has half the rating of this servo RPM right? 1.8kw servo has much more usable power in all revolutions than a standard motor. And higher momentary power.

I think you are mistaken a bit. I don't understand sth. The servo has an encoder. why you need a separate encoder for the rigid tapping? The servo drive surely has output of signals so what additional encoder? Read servo drive manual and you will see. My servos for example have encoder outputs and much more. Check manual.




It will be difficult for the bearing to fail 100%. It will make noise and so but i doubt it would fail if it has some grease in it.

[Davek0974]

Its all to do with power and torque, from another forum on this setup.....

Quote..

Well the 1.5Hp induction motor with variable mechanical drive would have (basing torque on 1.2Kw)

2880RPM 0.8kW and 3.94 Nm

1440RPM 0.8Kw and 7.9 Nm

720 RPM 0.8Kw and 15.78Nm

The 1.8kW Servo would have,

3000RPM 1.8kW and 5.7Nm

1500RPM 0.9Kw and 5.7 Nm

750 RPM 0.45Kw and 5.7Nm


As you can see, I would be losing a lot of power in the lower ranges but retaining constant torque, what is needed is both torque AND power.

It can be done but i would need to fit a 3.8kW servo to match the existing motor without losing performance, this is too expensive and they only run to 2500rpm.

I have just been advised that the encoder module CAN use the motor encoder ok, as long as the motor and spindle are at 1:1 ratio.

Will refit the original motor.

[Davek0974]

Finally got the replacement Y axis screw Got it fitted and got the table back on at last...


Not quite plug-n-play though - the new end bracket does not fit properly and will need machining, will have to get this done elsewhere as my mill not usable ;)

Can't simply file the holes longer as the counterbores need moving too. I had to get the new bracket as the original machine had power-feeds.

[Davek0974]

Found a local company to move the bores and counter-bores on the Y axis bracket - so annoying having to get stuff done outside when it would have taken me about 15mins to do, I had to leave it most of the day, make two 30min trips and stump up £40 :(

Anyway, done now and fits nicely, also mounted the motor plate using some spacers to pick up on the bottom of the counter-bores at the top face is not flat. Had to make a shim for the bearings to give a bit of pre-load but not bind up. Next job is to turn up a spacer tube for the pulley-to-bearing gap and then fit the belt - one axis finished.

Will also be planning limit switches this weekend, metal has not arrived so can't make the X axis plate yet :(

[John S]

Still got this step speed head unit with a brand new 3Hp 1425 rev motor and conversion plate, you just need a VFD to run it.
£300 to get it out of my way ?

[Davek0974]

Hang on to it a little longer, lets see if this one will survive, if not i'll be in touch ;)

[Davek0974]

Got X-axis motor plate fully fitted...



Limit switches next, Y-Axis Limits and home switches...



From the left we have Y--, Y-Home, Y++.
The home switch remains tripped once it trips so that i can home even if the switch is triggered, a home-offset value will take care of the switch position.

Then the X-axis, a bit harder this one, first idea...



From the right we have X-home then a dual-direction X-- & X++ switch. The picture is not quite right - imagine the right-hand switch is another roller type like the left one, I have one somewhere, just got to find it ;)

The only down-side I can see is that it blocks the chances of using flood coolant again as the switches are in the way of the left drain hole.

Still thinking on this one.