Bridgeport Series 1 MDI Conversion

[Chaz]

I'd aim for servo's similar power wise to what was fitted, as too big has the potential to do a lot of damage if things go wrong. I got told from a very reliable source that those interacts will handle the original servos running the axis into the end stop without doing any damage, if something does go wrong.

Plus you want inertia to match somewhat, as too big an imbalance can cause tuning problems. I was advised 110 would be better for my Shizouka which is a couple hundred kilos heavier than a Bridgeport.

One thing to be aware of with the cheap Chinese servos, is they use mains voltage for control power, so if mains power gets cut i.e. due to an e-stop, you've lost position. It's not the end of the world, but one of the things I like about my lathe is the position never gets lost during an e-stop, as the encoders are permanently live.
If you want a copy of the BST servo manual, drop me a message, and I'll email it over.



Oh, and is this a potential replacement for Thor, or are you just wanting to burn a few more KW to help keep the workshop warm? :-)

Hi, thanks for the info. I'm in two minds about the sizing. One part of me wants to get the machine running quickly and without too much fuss, so near bolt on replacements is nice. In terms of limits, assuming they work, is there still a concern?

For E - Stop, depends how you wire it. If you use normal E Stop circuitry via the Acorn, you will likely just disable the drives (like what happens on Thor and CS Labs). You do not switch off anything else.

Not a replacement for Thor, I dont think. The table is not as big as I had hoped for but it will do. The idea was to have something that can deal with big flat steel / hard metal plates for things. With Thor, it was designed for high speed alu type machining. I might make new brakes for Thor (motor mounts) on the Bridgeport. It was too good a deal to pass on and I've always wanted one.

I could buy the replacement drives and run with the DC motors but Ive had DC motor issues before (Spindle on Triac) and not keen on that. I just want something that works reliably.

A lot of the drives being shown are all the same manufacturer, so perhaps just find the best priced ones?

[m_c]

Hi, thanks for the info. I'm in two minds about the sizing. One part of me wants to get the machine running quickly and without too much fuss, so near bolt on replacements is nice. In terms of limits, assuming they work, is there still a concern?

For E - Stop, depends how you wire it. If you use normal E Stop circuitry via the Acorn, you will likely just disable the drives (like what happens on Thor and CS Labs). You do not switch off anything else.

Not a replacement for Thor, I dont think. The table is not as big as I had hoped for but it will do. The idea was to have something that can deal with big flat steel / hard metal plates for things. With Thor, it was designed for high speed alu type machining. I might make new brakes for Thor (motor mounts) on the Bridgeport. It was too good a deal to pass on and I've always wanted one.

I could buy the replacement drives and run with the DC motors but Ive had DC motor issues before (Spindle on Triac) and not keen on that. I just want something that works reliably.

A lot of the drives being shown are all the same manufacturer, so perhaps just find the best priced ones?

When was the last time you checked all the limits were working on your machines?
With modern AC servos, limits aren't as high priority as they used to be, as if an encoder fails, the drive should realise it's outputting the AC to get the motor to move, but it's not seeing the encoder move, and fault out.
With DC servos, the drives have to rely on the controller realising there is an encoder problem, but often by that point they'll of run into a limit switch, as the drive will of been outputting an ever increasing voltage in the hope the encoder moves, not knowing the motor was still moving at an ever increasing speed.

My concern of using more powerful servos than what was originally fitted, would be potential damage should you do something stupid while using the machine. I know you could always lower peak current, but I'd personally put in the extra effort to mount smaller servos, than cripple bigger servos.

E-stop is always a bit contentious. Personally for CNC machines, I prefer that all drive power is ultimately cut in e-stop. It might not cut immediately (I'd guess the BST drives have a switch mode supply running from the mains, and not the main DC capacitor bank, so would need power to remain on to control a fast stop), but I'd want it to cut as soon as practical. The chances of a drive failing in use are pretty slim, but it's more for during setup, where a wrong setting could cause a runaway. Plus in future, you never know what/who may be changing things they shouldn't.


DC servos do work well, but you need to weigh up the benefits/costs of drives for them. They do need maintenance (clean out, and new brushes occasionally).
If you still had the original servo amps, then it would make economic sense to go with a suitable +/-10V controller, especially as they've already got quadrature encoders fitted, then swap them out for new AC servos as and when needed. However the cost of suitable drives, is likely to be not much less (possibly even more...) than new cheap AC servos and drives, so the economics don't really make much sense for spending money on drives for motors that might not be working correctly.

[Chaz]

Acorn control board and MPG ordered yesterday, so getting ready to start retrofitting.

I managed to get a quote from DMM. Great company, quick response.

They have a Nema 42 replacement motor (fairly new, released a few weeks ago). My motors (According to them) are Nema 42.

The ones they are proposing are same shaft size which is very helpful (5/8th inch) as I am struggling to find direct replacement pulleys with 12 and 13 teeth respectively (14 is minimum generally).

The issue is the motors are not a perfect fit (mounting holes are a bit different - 75 PCD vs 82 PCD, probably minimal effort to sort this but they are fairly pricy and potential import tax from Canada. These are 1.3 KW servos, running off 220V (so high volt feed). Including 3 meter encoder and motor cables plus the Acorn DB 25 cable and programming lead, these work out at around £500 ish per axes.

I know the stuff from BST Automation and other sources listed are cheaper. Id like to have as little mechanical fuss / changes to make this all work (most seem to have 19mm pulleys), so modifications will be necessary but it looks like exact like for like change, so mods will have to be done anyways.

Thoughts?

[m_c]

DMM sales are always very quick to respond.
Their tech support, not so quick. There have a been a couple guys using KFlops that have had issues. One just couldn't get a drive to tune in analogue mode until he fitted their suggested mains filter, yet all the other drives were fine without the filter, and the issue moved with the drive, not the wiring.
Somebody else blew a drive up within seconds of turning it on, which was apparently due to being over-voltage, and due to them not fitting the recommended mains filter they wouldn't warranty it, yet the other drives never failed.
Plus they use capacitive encoders.

Their big advantage as you've discovered is they've specced the motors so they're far more likely to be a drop in replacement for old stepper motor systems.


Personally if cost was the main concern, I'd opt for cheap Chinese.
What tooth profile are the pulleys?

[Chaz]

DMM sales are always very quick to respond.
Their tech support, not so quick. There have a been a couple guys using KFlops that have had issues. One just couldn't get a drive to tune in analogue mode until he fitted their suggested mains filter, yet all the other drives were fine without the filter, and the issue moved with the drive, not the wiring.
Somebody else blew a drive up within seconds of turning it on, which was apparently due to being over-voltage, and due to them not fitting the recommended mains filter they wouldn't warranty it, yet the other drives never failed.
Plus they use capacitive encoders.

Their big advantage as you've discovered is they've specced the motors so they're far more likely to be a drop in replacement for old stepper motor systems.


Personally if cost was the main concern, I'd opt for cheap Chinese.
What tooth profile are the pulleys?

Hi,

The pulleys are 12 (X and Y) and 13 (Z) respectively. H pitch. Beltingonline are telling me they can have them made to order but warned that they will be pricy (I need to send them some pics) as I've suggested that maybe I just bore them out and install a grubscrew.

In terms of costs, sure, I dont want to spend more money than I need but I could get this machine running on steppers for a lot less money, that's not the point here.

If the DMM stuff isnt much better or doesnt offer more than perhaps an easier fitment, then I might as well save the money and use that for a better touchscreen / PC whatever. I'm not trying to cheap out on the build but dont see value in paying for something that doesnt offer better. Of course the law of diminishing returns persists too.

As an example I have Panasonic drives and motors on Thor and cheaper Chinese stuff on my old Triac. The Triac worked OK but no doubt the Panasonic stuff is better. The only reason I bought them was that I got some stuff at good prices from an Ebay seller. I wont pay RRP or similar for Panasonic.

I can get away with a 750W system, been avoiding it due to mounting concerns, bracketry might be OK, motor shaft diameter and length are the main concerns. One guy on Youtube has basically extended his motor shafts to suit.

[Gary]

I bought some bar stock and made them myself. not that hard.
Or modify the existing pulleys to fit on the new motors.

Hi,

The pulleys are 12 (X and Y) and 13 (Z) respectively. H pitch. Beltingonline are telling me they can have them made to order but warned that they will be pricy (I need to send them some pics) as I've suggested that maybe I just bore them out and install a grubscrew.

In terms of costs, sure, I dont want to spend more money than I need but I could get this machine running on steppers for a lot less money, that's not the point here.

If the DMM stuff isnt much better or doesnt offer more than perhaps an easier fitment, then I might as well save the money and use that for a better touchscreen / PC whatever. I'm not trying to cheap out on the build but dont see value in paying for something that doesnt offer better. Of course the law of diminishing returns persists too.

As an example I have Panasonic drives and motors on Thor and cheaper Chinese stuff on my old Triac. The Triac worked OK but no doubt the Panasonic stuff is better. The only reason I bought them was that I got some stuff at good prices from an Ebay seller. I wont pay RRP or similar for Panasonic.

I can get away with a 750W system, been avoiding it due to mounting concerns, bracketry might be OK, motor shaft diameter and length are the main concerns. One guy on Youtube has basically extended his motor shafts to suit.

[swarf-boy]

Just been checking out your acorn control.
Interesting unit. Quite a lot in the Kit.

Options seem to get strangely pricey though
( $45 for a dual circuit E-stop, being a stand out).

See those 4 series drives look to have built in S curve feature.
Didn't know that was a feature in drives. ( every day is a school day, as they say).

[Chaz]

I bought some bar stock and made them myself. not that hard.
Or modify the existing pulleys to fit on the new motors.

Thanks Gary.