Seeking Milling Machine Set-up Advice

The pony motor is a single phase motor that takes the place of a (dangerous IMO) rope pull.

The larger three phase motor that is being started this way is called the 'coverter' motor or more commonly the 'idler' motor.

You can see my setup with a 5hp idler motor and a 1/8 hp pony motor to spin it up before I turn on the power to excite the idler:

The entire thing was built for free, and runs all my machines, none of which are more than 1 hp apeice. Because the motor is large in comparison to the load motors there is no fancy tuning required.

The pony motor spins the idler up to speed, I turn on a fused knife switch to excite two of the three wires in the idler motor, and then it locks in to the line frequency and runs on its own.

I lift up the hinged platform that the pony motor sits on and the belt flies off. The thing is so quiet when running I've been known to nearly forget and leave it running. It consumes about 200 watts when it is not powering the load motor.

Jim

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you can also just use a start capacitor and a momentary push button to start a 3 phase 'idler' motor. This to me is a cleaner setup.

But I would consider a VFD

I leveled a machine with wood blocks

A mill doesn't *have* to be level, but it is nice if the coolant drains off in the correct direction, and if parts don't roll off the table on their own. Either leveling pads or shims would be fine to compensate for the tilt of your floor. It doesn't have to be perfectly level, but getting it closer sure won't hurt.

I'd use a VFD or a rotary converter. A rotary converter is dead cheap to build, I wouldn't buy a commercial one. You can make it self-starting, start it with a pony (small 1 ph motor), or even rope start it. For the size converter you need, self-starting design is very practical.

My rotary is bigger (20 hp), so I start it with a 0.5 hp 1ph pony motor to reduce the starting surge currents down to something my electrical service can handle. I use it to run several machines, including a 7.5 hp lathe. I'd guess I have $50 total in it.

The other alternative is a VFD. A 2 hp rated TECO VFD from Dealer's Electric

I like this one

Another option is DC drive:

It is not electronic -- purely electrical components -- voltage-sensitive relay, heavier relay, and starting capacitor. It is

Spending $500.00 for a rotary converter which you can make for less than $100.00 does not make sense -- except for a company, which is likely to be able to get the three phase from the power company.

A bit of mix-up of terms there.

The rotary converter uses an "idler" motor -- a *used* (and therefore hopefully dirt-cheap) three-phase motor with perhaps 50% more horsepower than your milling machine's motor. This is started by one of several ways:

Any of these can be improved by adding tuning capacitors to improve the balance of the generated third leg, and this can reduce the current drawn from your circuit breakers. (You would not be charged for that extra current, as it is reactive, not resistive, but it still wastes power heating wires, and sometimes tripping circuit brakers.

There is a lot of information on this to be found in the archives of this newsgroup -- in particular, look for the articles by "Fitch" covering this subject. He took a good analytical approach to the design of one, which can save others from having to repeat the work.

However -- there is yet a third approach, which *does* involve electronics. This is commonly called a VFD (Variable Frequency Drive). I *think* that your 2HP Bridgeport will have the variable-speed pulleys, so you probably don't *need* a VFD -- but one is more efficient than a rotary converter, and can allow you to fine-tune the speed if you have a step-pulley head on your Bridgeport. (It can also allow you to get a wider total speed range than the vari-speed pulleys alone.

Shooting Star would be a nice one. I'm sure that others will have their own suggestions.

Good Luck, DoN.

I have a textile machine shop and use the cheap under $100.00 ststic converter from McMasterr Carr on my Bridge-port... No problem for 10 years so far.... Works great...

The 3-phase problem is best solved with a VFD rated for single-phase input. They are commonly available for about $200. The VFD provides soft start, variable speed, dynamic braking, reversible on the fly. Another advantage is you will not have to use the BP variable speed pulley system which is a known maintenance item.

If you can spend a little more for a DRO, I recommend the Newall 2-axis. It is very easy to install, with hermetically sealed scales and reader heads. Plus it comes with an assortment of mounting brackets that will fit damn near anywhere on the mill.

Randy

I used a "static converter" for many years on a 2HP Bridgeport clone. The static converter is not really a converter, it just gives the 3rd phase in the motor a temporary kick of juice when you hit the motor power switch. This allows the motor to start turning, but then the motor drops back to running on 2 power phases.

The only drawback on this is that you only get about 2/3 of full motor power. However, on a Bridgeport type mill, that's usually plenty of power uniless you are planning on pushing the machine to the max. For the prototyping and small run work we do, I never had a time where the machine didn't have enough power with the static converter.

However, I recently switched to a VFD to get the variable speed, instant reversing and automatic braking. I bought a 2HP Teco unit from Dealers Electric. It works great, and I really like it and I put one on my lathe also. If you go this route, buy the optional braking resistor, the allows you to set the spindle braking and reversing time to about 1 second. The documentation for this unit is a little cryptic, but they have an 800 number with pretty helpful tech guys that really know the units.

If you're tight on dollars, I'll sell you my retired static converter for

415-467-7886 x122

Good luck-

Paul T.

What I did in your exact situation: level the machine adequately with wedges, I used wood, but you can now make aluminium :), and use a static phase converter. Worked passably well for me, I have stalled the motor a few times under heavyish cuts but I have a 1.5hp motor, so I am realizing only 1 hp. Upgrade later, unless you luck into a VFD at a great deal.

I just wanted to thank each and all for your input! This excellent kind of info xchange makes all the frustrations with computors tolerable. Type to you all later. Thanks again to all.

Fred