Longs 3 axis CNC kits - are they suitable for Bridgeport Series 1 conversion?

[heb-cnc]

I've got a Bridgeport Series 1 CNC with shot 3 phase electrics. I've come to the conclusion it's best to give up the original motors and go for new steppers and a complete rewire etc. I've trawled the forums for hours trying to educate myself but I'm still not exactly sure what I need. Something like this kit from Longs (https://www.ebay.co.uk/itm/EU-Free-Ship-3Axis-Nema-34-Stepper-Motor-1700oz-in-6A-Step-Driver-DM860A-CNC/283216499189?hash=item41f104d1f5:g:R24AAOSwMPxbkIM J) which includes motors, power supplies, BOB and drivers. Longs offer different versions of NEMA34 and NEMA42. Does anyone here have experience with how many oz-in are required to power the XYZ axes on a BP Series 1? I was thinking maybe the Nema34 1200 oz-in would work but I'm really not sure?

I'm on a budget so a servo motor conversion is out of my reach, hence the interest in these relatively inexpensive Chinese kits. Thanks in advance for any advice or links you can point me to.

[john swift]

I don't know what torque you need to move the Bridgeport but

looking at the kit you linked to

the motors 8mH inductance is too high when using the 60V power supply supplied

you either need to have a motor inductance about 3.5mH to use the 60V supply or
stepper drivers that will work with a 90V power supply if you use the 8mH motors

I would use another breakout board that does not have opto-isolators on the outputs connected to the stepper drivers

connecting the KITs BOB to stepper drivers with opto-isolated inputs will degrade the sharp edges of the step pulses

John

[heb-cnc]

Thanks for the info John. I need to do some homework so I can get my head around the relationship between mH and volts!

[john swift]

a rule of thumb from Geckodrive .com is the supply voltage to the driver is
32 times the square root of the motors inductance in milli henry

the higher the inductance the greater the voltage needed to ensure the current builds up to the desired current in limited time between step pulses

John

[heb-cnc]

you either need to have a motor inductance about 3.5mH to use the 60V supply or
stepper drivers that will work with a 90V power supply if you use the 8mH motors

John

Investigating further, their NEMA34 1100 oz-in motors have 3.5mH inductance.

https://www.ebay.co.uk/itm/Free-Ship-3Axis-Nema34-Stepper-Motor-1100oz-4-0A-Driver-DM860A-CNC-Mill/271978181168?hash=item3f5329b230:g:bhUAAOSwy6lbkJ1 q

But does that combo have sufficient torque for a Bridgeport...?

[routerdriver]

I don't know what torque you need to move the Bridgeport but

looking at the kit you linked to

the motors 8mH inductance is too high when using the 60V power supply supplied

you either need to have a motor inductance about 3.5mH to use the 60V supply or
stepper drivers that will work with a 90V power supply if you use the 8mH motors

I would use another breakout board that does not have opto-isolators on the outputs connected to the stepper drivers

connecting the KITs BOB to stepper drivers with opto-isolated inputs will degrade the sharp edges of the step pulses

John
I am obliged for this answer as I have a Longs 3 axis kit for my tiny hobby router.I was hugely pleased just to get it moving and anticipate a series of upgrades.I liked the idea of opto-isolators as it appeared to make it less likely that the magic smoke would escape;I had no idea there was a performance penalty.Can anybody suggest what might be an improvement?I am currently using on old Dell with a parallel port and wouldn't mind a more modern type of connection.I hope the OP won't mind me asking as I believe he might also benefit from an answer.

[john swift]

with stepper drivers like the dm860a that has its own input opto-isolators
24997


you don't need a breakout board with output opto-isolators like this supplied in the kit-
25001

these two BOB's only buffer the printer port outputs and only opto-isolate the 5 inputs -

a breakout board like this found in some of the ready made control boxes
24999

the closest available on ebay is something like this
24998

note it does not have the 5V DC/DC converter found on the TX14175 and requires another power supply

the least expensive change will be the breakout board but it may not make any noticeable
difference when using the original motors and drivers


As I don't have the longs kit to test, I don't have a definitive answer but
problems the original breakout board will only show up at high speeds
the original motor / driver combination may limit the maximum motor speed first

without going through all the stepper motors , stepper drivers and power supplies on sale

its not easy to say which is the most cost effective change

using a higher voltage supply & stepper drivers verses replacing the motors with lower inductance motors

John

[heb-cnc]

As I don't have the longs kit to test, I don't have a definitive answer but
problems the original breakout board will only show up at high speeds
the original motor / driver combination may limit the maximum motor speed first
without going through all the stepper motors , stepper drivers and power supplies on sale
its not easy to say which is the most cost effective change
using a higher voltage supply & stepper drivers verses replacing the motors with lower inductance motors

John

A very informative and educational reply! Allows me to analyse motor and driver specs with a little more knowledge than I had yesterday. Thanks for taking time to explain things in such detail.

[m_c]

It's worth highlighting the main reason opto-isolators are added to BOBs is for protection.
Using a parallel port, get something wired wrong, or have something short and connect power to pins they can't withstand, then more than likely your PCs parallel port (and likely entire motherboard) will be dead.

With newer motion controllers, the path of destruction from a wiring problem isn't likely to be as long, but it's still potentially a couple hundred pound controller that could be releasing it's magic smoke.

It's a calculated risk not using them, but at slow speeds, they shouldn't cause any problems. I certainly wouldn't be searching out a BOB without them, unless I was really going to be pushing pulse rates.


Regarding suitable motors.
A good starting point would be to try and find out the torque for the existing motors, or even a datasheet with torque curve (it's surprising what a google for the model number turns up).
You can then run a few figures and see how the various options compare. You'll likely find some suitably geared NEMA23/4s provide better performance than NEMA34s directly coupled, especially when running from lower voltage.

[Boyan Silyavski]

I would Not retrofit a precision metal cutting machine with an Open Loop system :suspicion:, given prices of new cheap servo motors and drives, used servo motors and drives and closed looped steppers which i dont like much pricewise

[john swift]

adding more detail to post 7 for any one wanting to use a BOB with opto-isolated outputs and stepper drivers with opto-isolated inputs


the problem with the BOB supplied as part of the kit is ue use of the slow PC817 opto-isolators used for the outputs


I would expect the DM860A stepper drivers would have a PC817 on the enable input and a high speed isolator like a HCPL2531 for the step and direction inputs
as used on this Tormach driver input

25010

the diagram is from
https://www.cnczone.com/forums/tormach-personal-cnc-mill/347610-microstep-driver-pinouts.html#post2107952


if I used a breakout with opto-isolated outputs then I would look for a BOB like this -

https://cnc4you.co.uk/resources/Breakout%20board%20HG08.pdf

or this

http://www.electronics-lab.com/project/optically-isolated-lpt-breakout-board-for-cnc-routers/

they are just two of example found


John