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  #11  
Old 02-23-2019, 03:17 AM
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camdigger camdigger is offline
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Quote:
Originally Posted by Ironman View Post
Cam, you can run a 3hp three phase motor all day on a single phase 15 amp breaker.
The killer current is in startup and the VFD takes care of that surge. My mill is very happy sucking off a 15 amp breaker.

My Lagun has the same thing going on, when you go into low range you have to reverse the motor to keep quill rotation correct.
Thanks IM. I have no idea how big a Bridgeport motor is. If it is 1 1/2 hp, then I can see how a +/-3300W circuit (just under 4 1/2hp) would run it very well, especially with an integral soft start from the vfd.

IIRC, 1hp = 746W & 220V x 15A = 3300W. As has been pointed out to me in the past, 3 phase power calculation is a bit different.

It has been nearly 30 years since I did anything with a vfd. I am a bit surprised that reversing direction isn't done in the vfd?
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  #12  
Old 02-23-2019, 04:47 AM
threepiece threepiece is offline
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Originally Posted by bunkclimber View Post
most of the "Bridgeports" I see have a cam switch that changes motor speed and direction.(Never seen one that does it with gears,usually a belt on step pullys)
I find this most unusual. I have played on seven different Bridgeports over the years that were made from 1953-2015. None had a cam switch that could change both motor direction and speed. Moreover they all had spindle reversing two speed gear trains.
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Last edited by threepiece; 02-23-2019 at 04:56 AM.
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  #13  
Old 02-23-2019, 11:43 AM
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I went to work yesterday and the mill was gone. Bastards!
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  #14  
Old 02-23-2019, 11:52 AM
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Quote:
Originally Posted by camdigger View Post
Thanks IM. I have no idea how big a Bridgeport motor is. If it is 1 1/2 hp, then I can see how a +/-3300W circuit (just under 4 1/2hp) would run it very well, especially with an integral soft start from the vfd.



IIRC, 1hp = 746W & 220V x 15A = 3300W. As has been pointed out to me in the past, 3 phase power calculation is a bit different.



It has been nearly 30 years since I did anything with a vfd. I am a bit surprised that reversing direction isn't done in the vfd?


It is. In my case a switch, three wires, and four parameters in the vfd now have me going forward-off-reverse.

When I drop into low range, it becomes reverse-off-forward, same as running a standard mill.

In my case the vfd will mostly be ‘forgotten’ unless for something specific. Use the switch as the motor control, and the mill speed control.


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  #15  
Old 02-23-2019, 12:47 PM
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terry lingle terry lingle is offline
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Remember that this discussion is about running three phase machines in a shop that only has single phase 230/240 VAC available.

Once you decide to install a VFD you give up the two speed forward reverse switch as well as one of the motor speeds because the VFD must be wired directly to the motor.
This is not a big sacrifice as the VFD more than compensates for the unused motor section.

Unfortunately The VFD is not always the best solution nor is it always the most cost effective.
Each situation should be carefully evaluated and the choice RPC or VFD made at that time .

I have an RPC for my shop. My lathe has an excellent set of internal speed ranges and at 7.5 HP is relatively expensive to power with a single phase VFD.

My mill has the magic 5 position switch and a two speed motor that covers my mills speed requirements when coupled with the mechanical two speed range selector.
My big table saw runs perfectly from the RPC and would not benefit from a VFD.
That one converter replaces 3 VFD's for about the cost of the least expensive VFD it eliminates. Should I add more machines would run them at no additional cost.
Without the RPC the next machine would come with the added cost of another VFD.

On the other hand my drill press is fitted with a VFD even though it would run from the RPC.
This was done because I explicitly wanted the soft start and variable speed plus some other features only available when using a drive.
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Last edited by terry lingle; 02-23-2019 at 12:52 PM.
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  #16  
Old 02-26-2019, 10:38 PM
Don_S Don_S is offline
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Most Bridgeport's and similar knee mills use a drum switch to change forward / reverse of the motor. Speed changes are generally via a Reeves drive or a belt change. All of the Bridgeport / clones / Lagun / etc have a low geared range that reverses the spindle compared to the "high" speed setting. This is kind of like a 2 speed rear end in a truck in that it is a separate function of the machine but it does change the direction of the spindle. So your forward / reverse switch is backwards when in low gear. I'm not familiar with the large frame Bridgeport's so they may deviate from the "normal".

So far I've done ok with a 10 hp RPC for my 3PH machines (Jointer, Vari-speed drill press w/ 2 speed motor, belt grinder, and Lagun mill). When I get my metal lathe, I'll most likely just wire it into the 3PH side of the RPC. But, if I pull the trigger on an older wood lathe, I'll do a VFD for that unless it already is a vfd driven setup or DC drive. I have a spare 3PH motor to retrofit if needed.
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