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Apr 6, 2010
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This is going to end up being a long thread. Wish that weren't true.

Started in on a 1/8 scale steam locomotive (from a kit) perhaps 7 years ago. Soon bought a Sherline mill to augment my ancient Unimat lathe. The kit consists of several hundred lbs of cast iron. Other builders tell me that over half of the cast iron in the original parts ends up in the trash can.

Soon started realizing that although I was able to machine a lot of the parts on my Sherline mill, it was really a stretch, as many of the parts were just too big. Along the way I started watching some youtube videos and realized that a lot of the simple wheel turning I was doing for hours at a time

Started doing some research on adding cnc to the Sherline, and just couldn't find enough information so that I could understand the process, so bought the Sherline cnc upgrade kit. The kit went on fairly easily, and eventually I was writing g code and knocking out some simple parts.

Tried to find information about various CAD/CAM programs, but had lots of trouble finding information. You really have to have a CAD program and start trying to make parts with it to begin to figure out what questions you should be asking. Eventually bought BOBCAD. Which seems to work. Who knows what I'll end up with in the end.

Having a CAD program and cnc on the Sherline opened my eyes to making curved parts. Gave me lots of ideas of what to do for Christmas presents for my many cousins, etc. I always like to give personalized presents. Seven months later, the first Christmas present has not yet been made.

Somehow, got in the habit of looking at craigslist and looking for machine tools. Came to the realization that used Bridgeports sell for less than a Sherline mill. So, eventually, a Bridgeport Series 1 CNC mill followed me home one day in early April. Knew that it had a 3 phase motor, but thought that it would be a simple job to add a three phase rotary converter to the motor, and simply run rest of the mill on single phase. It was still hooked up and runable in the shop where I got it, though it hadn't been run in about 10 years. He started the shop with the Bridgeport, but replace it with (eventually) 3 Mazaks.

Trust me, guys. Nothing is simple on a cnc Bridgeport.

Learned some interesting lessons on the way to buying a full sized mill. One is that Textron sold the rights to build the latest model Bridgeport mill to Hardinge. Guys at Hardinge didn't think to ask about getting all the drawings and spare parts for the older Bridgeport models. So, where are all the old parts and drawings? Probably at a dump somwhere in New England, buried under tons and tons of old cabbage, spoiled lobster tail, Boston Baked beans, and whatever else New Englanders eat. Lesson #1. Don't buy an old mill unless it's in top notch condition, and you are confident you can build every part on it. You may well have to. Outfit in Ohio has some new parts for some Bridgeports, stuff they've been building themselves, or farming out for years.

Another lesson is that big Bridgeports are big, and heavy. The book says mine weighs over 3000 lbs. Don't try to stick it in the back seat of your sports car.

Okay. Let's get this thing running on single phase. There are several places on the internet which will explain how to build with a solid state "converter", or a rotary converter. Again, on craiglist, found a 5 HP 3 phase motor for a reasonable price (okay, really cheap) and bought it on the way to pick up the mill.

Got home, and found that the garage door was about 6" shorter than the top of the mill. My riggers simply picked up the mill on the tips of the forks on a forklift, tied it to the forklift, and tilted it oven onto its nose, and drove it under the door (slowly). It really helps if you can find riggers who know what they're doing. Unfortunately, I was too nervous during this process to take pictures.

Some helpful souls on the internet convinced me NOT to use the rotary converter, but to use a Variable Frequency Drive to run the spindle motor. A VFD takes 1 phase or 3 phase ac, converts it to DC, then chops it up with several switching transistors and gives you 3 phase to pass to the motor. Obvious benefit is that you don't need to spend a million dollars having 3 phase power run to your house. Another benefit is that you can set the program time for the VFD to take the motor from stopped to running speed. This helps prevent the lights all over the house from dimming each time you start the spindle motor. It also lets you run the spindle motor at different speeds, depending on what you're trying to cut. Mine has the magic variable speed pulley system, so don't expect to use the variable speed function. But it's there. A 2 hp VFD runs around $300 or so new. Found a surplus warehouse in NJ which has NOS VFD's. Spent about $130 or so for a 3 hp VFD. Be prepared. The book with the VFD is about 70 pages. Expect to spend a couple of days trying to comprehend the book. Warning. The VFD's have some big electrolytic capacitors in them. These caps lose their "shape" when they're not used for a while. The surplus VFD I bought was about 3 years old. I fired it up, not under load, and let it idle for about 24 hours. This gives the caps time to "reshape" themselves.

Okay, after about 2 or 3 weeks, the spindle motor is almost ready to run. Now time to dig into the power supply for the computer. Should be simple.

It's not simple. The DEC computer in the Bridgeport runs off of a monster 3 phase 240 volt to 3 phase 56 volt transformer. We're talking perhaps 150 to 200 lobs of transformers. Provides power to 5 monster transistors in parallel which drive the stepper motors. The 5 transistors fail often. The resulting short is sometimes (often ?) enough to demagnetize the permanent magnets inthe steppers. Absolutely no way to run the 3 phase transformers off single phase.

Turns out that a guy in Illinois made a living rehabbing these old machines for years, and wrote a column in "The Home Shop Machinist" for many years. He's done a couple of series articles on gutting the Bridgeport and starting over. His name is Roland Friestad. Turns out that Village Press has many back issues of the mag, and can make photocopies of the ones they don't have. Lots of good guidance in these back issues. He also has a couple of articles on building a "Universal CNC Controller". His idea here was to have a box you can set beside any cnc machine in your shop, hook it up, and go to town.

So following Roland's instructions, I've started gutting my machine, and doing research on learning which bits and pieces I need to get the machine up and running again.

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Spent some time this week pulling a bunch of old stuff out of the electrical compartment, and some more out of the computer compartment. Am saving the computer boards and a few other parts, as there are still a few of these BOSS machines still running, and someone may need these parts.

Bought a 12" x 12" x 4" electrical box, couple of 3 phase airconditioning contactors (30 amp), a 24 volt transformer, and some push buttons and a couple of neon indicator lights, and already have a Variable Frequency Drive on hand.

DealersElectric.com in New Jersey has some excellent prices on NOS drives, about half of retail. Needed a 2 hp drive, they sent a 3 hp drive for about half what a new 2 hp would cost elsewhere.

The airconditioning contactors are frequently available used for a dollar or two at local ac contractors. You may have to pull them out of old equipment yourself, but that's not too difficult. You will need to bring a selection of long handled nut drivers with you. You just can't do much on ac units without long handled 1/4" and 4/16" nut drivers.

The 3 phase contactors are also available from your local industrial electric supply house, but the air conditioning contactors are generally a bit smaller.

George Carlson has written an interesting article on phase converters which is published on several different websites, including http://homemetalshopclub.org/projects/phconv/phconv.html. One idea of his that I really like is shown at the bottom of the page, under "Deluxe Magnetic Starter". He used a bell transformer (I used a HVAC transformer, same difference) to power the coils on the relay(s). But he powers the transformer from the shop lighting circuit. When you walk out of the shop at night, turn off the lights, and whatever phase converter you're using automatically shuts down. Many people mount the rotary converter in a remote location to suppress the noise. No point in leaving any of these converters running all the time. My VFD has a fairly noisy fan, which I don't want to listen to.

I put two sets of contactors, two sets of push buttons, and two different plug and cord sets with my control panel. The left hand set of contactors powers the VFD, and hence the spindle motor. The right hand set powers all the 120 volt stuff, the computer, monitor, stepper power supply, geckos, lube pump, etc. I want to be able to use the computer without having the VFD and spindle motor powered up.

When actually building the control panel on the machine, Bob Warfield suggests using slot machine push buttons, which can be had for less than $4 each. Haven't measured the current draw on the contactors yet, but suspect that the slot machine buttons (which are supplied with six volt or 14 volt bulbs) are really only intended to switch data level signals, and shouldn't be used to control the contactor relays. Many of these switches are only rated for 10mA at 5 volts. This is fine for a control panel telling the computer what to do, but probably inadequate for powering the contactors.
One caution on wiring up the contactor box, if you decide to use one.

In my box there is a 24 volt transformer powering the relay coils for the contactors. So, I have a mix of 24 volt, 120 volt, and 240 volt all running around in the same box. This box will be wired into my main electrical panel with a double gang 20 amp breaker, using romex cable. So the box is conceivably subject to inspection by the electrical inspector. Even if it's not, the guidelines in the National Electric Code are there to help prevent fires, and should not be disregarded lightly.

When running 24 volt control circuits in most locations, I'd run nice small #26 teflon insulated wire. However, since there is 120 volts and 240 volts present in the same cabinet, the NEC requires that all wiring in the cabinet be insulated to suit the highest voltage present. This means 600 volt insulation. So, I need to find some multi-conductor cable, in #18 size wire, but insulated to 600 volts. 8 conductors would be handy, but probably won't find any, so will use a couple of cables to connect the interior of the panel to the buttons and lites on the door. I'll take a couple of feet of this same cable and strip the outer sheath to get some small hookup wire to run between the transformer and the contactor coil connections.

Otherwise, all of the 120 volt and 240 volt wiring is plain old #12 house wiring.

Note the two plug and cable type disconnects on the bottom of the panel. These serve several purposes. One is that you can unplug one or both of the cables and be assured that there is no voltage running around inside the cabinets. The exception here will be the big caps in the VFD and possibly in a power supply. The VFD brochure warns you to allow 20 minutes or more for the voltage to bleed out of the main cap there.

Another benefit of using the plug and cord disconnect is that the electrical inspector's jurisdiction ends at the disconnect.

Except for some labeling, the electrical panel is complete and ready to be installed and wired. I'll post a photo later.

that was a good read, cant say I personally understand every part of it ( now I shall roam google :big:)
I can relate mildly to the start with cnc programming, I thought I could get it down fast and when the time came purchase a mill and bang out my ideas. I have most of the Mastercam X2 training manuals but it turned out to be more then I bargained for. so I need to eventually find the time to get back at it and defeat lesson 2 :big:

where does it stand now?
Speedy said:
that was a good read, cant say I personally understand every part of it ( now I shall roam google :big:)
I can relate mildly to the start with cnc programming, I thought I could get it down fast and when the time came purchase a mill and bang out my ideas. I have most of the Mastercam X2 training manuals but it turned out to be more then I bargained for. so I need to eventually find the time to get back at it and defeat lesson 2 :big:

where does it stand now?

Well, I actually got power to the contactor box, and put power to the VFD and turned the spindle for the first time today.

Actually, being a first time project, it was kind of daunting at first. However, I'm finding that the more original stuff I remove from the big boxes, the easier it is to identify the stuff that's left behind.

Think I found yet another transformer today that can be removed. My buddy is keeping himself busy stripping the transformers for scrap iron and copper. Nearly 300 lbs of transformers removed so far. Maybe there'll be a couple of cases of beer there.

I'm finding a lot of evidence of hot components at some point in history. Glad that most of the original wiring is disappearing.

Have almost all of the bits and pieces that I can identify so far to start putting it back together.

A 54v volt, 13 amp power supply from Keling.

Three Gecko 203V drivers.

PMDX-132 bob.

four pairs of Amphenol plugs for the steppers. Only have the three steppers at the moment, but hope to have a rotary table going before Christmas. The plugs will be in place for the fourth stepper. Need a piece of sheet metal to mount the sockets for the steppers. Stumbled across the last couple of years license plates in the garage. One of them will become a connector plate. Might as well recycle.

An old computer in a mini case. Have a used regular tower case to put the computer in, as the old power supply failed, and couldn't find a small enough power supply to fit in the mini case.

Probably need to buy another keyboard and mouse.

I'll be installing Linux and EMC2 in the old computer, which now has windows xp on it. The Sherline runs EMC2 also. Something to be said for keeping a standard interface between both mills and the lathe. (Although I've never yet run the lathe on cnc.)

As I strip out old wiring, seems as if I need to pick up a bag or two of smaller wire wraps, or ty-wraps, whatever you prefer to call them.

Also need to identify the place where the lube pump gets its power. Looks to be a fairly standard, older, Bijur pump. Need to find the relay which powers this pump, so that I can have the computer tell the bob to power this relay and start the pump running. I've run the spindle about 10 minutes today, but would feel much better knowing that the lube pump is sending out oil to the spindle.

Feel sure that there is a 24 volt transformer in the bowels of the mill somewhere. If not, I'll get another one from the heating and air supply.


You don't give up easily do you ;D

Going to be an interesting thread

doubletop said:

You don't give up easily do you ;D

Going to be an interesting thread


Well, when you've got a 3000 lb tool blocking access to the garage and motorcycle, it makes an incentive to get it done.

Hi Tom, ive found this a fascinating read, not from a machining standpoint, but an exercise in 'learing a new skill', have you kept a log of the cost of the project? Im just wondering if it would have been cost effective to simply buy a newer more (electrically) suitable machine?

Good luck
Artie said:
Hi Tom, I've found this a fascinating read, not from a machining standpoint, but an exercise in 'learing a new skill', have you kept a log of the cost of the project? I'm just wondering if it would have been cost effective to simply buy a newer more (electrically) suitable machine?

Good luck

Well, as they say, hind sight is 20/20.

Made the original decision to buy based on only having to find a way to supply 3 phase power to the spindle motor. The machine was running when I looked at it in the shop. Providing 3 phase to the machine can be done easily for less than $300.

What I didn't know was that the internal power supply for the steppers also requires 3 phase power.Surprise !

That said, I'll still probably be between $3000 and $4000 US when I finish.

The other part of my answer to your question is simple. What is there out there in the under $4000 range with the rigidity of a Bridgeport, and this amount of table range? I'm not saying it's not out there, but I'm not familiar with it.

Also, in the middle of looking, I watched a very nice smaller Bridgeport (not cnc), in excellent condition, sell for $500. This machine had never been in a production shop, a hobbyist machine its whole life.

Also, in disassembling the older electrical components, I'm find a lot of evidence of hot components. Anytime you buy a used machine, you're generally buying a pig in a poke. All I can do is hope that this pig doesn't have long sharp fangs and teeth.

Not much has happened lately, other projects keep getting in the way.

Finally got the power cabinet finished, mounted, and wired to the panel. Had a couple of wires reversed, so got to take it apart a couple of time.

But now, it's up and running, and needs some sort of a label.

The outlet on the left (yellow cord) provides 240 volts to the VFD for the spindle motor. The outlet on the right provides (black cord) 240 volts with a center tap neutral to everything else in the cabinet, and is run through the original heavy duty disconnect switch on the back of the cabinet and the original 20 amp fuses. One blade on the disconnect doesn't seem to make good contact every time, so it'll not be used under normal circumstances.

Inside the cabinet is a 24 volt transformer and two air conditioning 3 phase contactors. The green buttons (NO, momentary contact) energize the contactors, and the third phase points energize the coil to hold it closed. The black buttons (NC, momentary contact, which will soon be painted red) interrupt the 24 volts to the holding coil, allowing it to drop out.

The 24 volt transformer is powered by a plug to an outlet for now, but will be eventually connected to switched power to the overhead light in the garage.

The two neon indicator lights show that the side is energized.

One problem is that one of the two contactors is extremely noisy, chattering much of the time. Need to open the cover once again and find out why it's chattering, and perhaps replace it, or rubber mount it.