TarheelTom
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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.
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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