DRO or VCD?

wawoodman

wawoodman

himself, himself
H-M Supporter Gold Member
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Mar 19, 2011
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I have a SB 10K, 3Ø, running through a static convertor. I have a Rockwell knee mill, also 3Ø, on the way. The static is too small for the mill.
I know I'm going to need another phase convertor to run the mill. Unless I go for a VCD.
Or should I go for a rotary, big enough to run the mill, and the lathe, and try to get a few bucks back on the static? (They won't be running at the same time.) Which machine benefits more from the variable speed of a VCD?

But if I do that, I'll have to wait even longer for a DRO, which is what I REALLY want.

Opinions? Commiseration? A little sympathy?

I have spent (way) too much money this month...
 
Well, all I can say based on my limited experience....

I currently have a rotary phase converter and DRO on my mill.
My lathe is now set up with a VFD but no DRO.
If I could do it over, I would put a VFD on the mill as well. Having the speed control on my step pulley mill would be great, but I would never give up my DRO now. That has me REALLY spoiled! ;D

I personally feel that the DRO is more important on the mill, and the VFD is more important on the lathe. Of course I would love to have it all, but as you know you have to pick your battles with your funding. :-\

My opinion -- go for a VFD for both machines. Which machine did you want the DRO for?
I do feel your pain though.
 
Mike

My lathe is 3 Phase, VFD controlled and is run on a Rotary Phase Converter. It came with an Accurite 2 Axis DRO, I use the DRO all the time, but must say it is weird looking up at the screen, not down at the work.

My mill is a single phase, variable belt drive mill with an Accurite 3 axis DRO. The DRO is very useful on the mill.

Now it is a mute point having a mill with a DRO that you can not even get to run as you do not have the power for it, so before you even consider the DRO, you need to sort out the power aspect.

Static Phase converters are very ineffecient. They will derate what the motor the control can produce and are generally not a good option.

Rotary phase converters are great, they produce a bit more back ground noise, but they allow you to run a number of items at once, give full power output to the motor and generally a good way to go.

Another route that is becoming more popular than RPC's is the VFD. a poperly sized VFD can convert single phase into three phase at full power and adds the variable spped and braking. I really like the VFD on the lathe. Now as commented earlier, it is VFD controled, but fed from a RPC, as the VFD was factory installed and was not sized to run on single phase, they need to be rated larger to handle the differnece between 1 and 3 ph. ie 3 hp motor would requuire a 5 HP VFD, or one that is rated by the manufacturer, in which case they have already derated it for you.

There are drawings and pictures of my set up in the electrical folder under 1 to 3 phase conversion

http://hobby-machinist.com/index.php?topic=1159.0

Walter
 
Actually, you can remove the keypad on that unit and mount it remotely if you wanted to.
I have a SJ200 mounted on the rear of my lathe and mounted the keypad up front by the head stock.

Hitachi makes a darn fine VFD with a good reputation. I'm extremely pleased with mine. Their technical staff is great with any questions you might have as well.
I got mine from Drives Warehouse as well. No problems what so ever. :)

th_Lathe_3phase.jpg th_VFDandtachulatorpanels.jpg
 
Ed,
Thanks for your input. What does "sensorless vector" mean, and what difference would it make in the operation? (Non-electrical-engineer terms, please!)
 
Hi Mike
I used to run my Mill and Lathe on a rotary phase converter, I no longer do that, and have both machines equipped with VFDs
I see some have a phase converter and a VFD. I cant figure why? You should need one or the other, not both.
Most all the VFDs will run on single phase input, so the need for a converter as well is not needed.

You will need a VFD for each machine. The VFDs are cheap enough now, why mess with rotary phase converters?
As said I used to run a rotary phase converter to power my machines, and I can say this, its cheaper to run VFDs, easyer on the electric bill. Plus you dont have to listen to the converter running in the back ground all the time. If your running a static converter now, your really feeding the machine single phase power anyway.
DROs are another matter and topic really. I have DROs on both lathe and Mill, and make jobs on both machines much faster. You dont need to be stopping to measure all the time.
Paul
 
Paul

Yes a VFD is generally a better option to power a 3 phase motor off of 1 phase, but there are limitations.

If you have more than one motor on a machine, then you need a VFD for each motor, plus line chokes. Also if you have a lot of motors, even though VFDs are relatively cheap, they add up.

My system has a combination of both. The main converter is a 7-1/2HP / 22 HP RPC.

My lathe has two three phase motors on it, and the main drive motor had a factory installed VFD, but it was sized at factory to be run on 3 phase, so to be able to plug and play from 1 phase meant replacing that VFD, plus adding another one.

Next was my T&C grinder which has three 550 and 575V motors. Only about 1-1/4 total HP, but to get 3 phase 600V from a VFD was going to be very difficult. Installing a 220 - 600V three phase transformer did the job quite nicely.

Then after I had the system set up, along came a 5 HP 3 Ph compressor that the owner was having a hard time selling due to the 3 ph issue. Onto the RPC it went, with no extra cost. The other option was another large VFD.

Also looking at my power bills for the last few years before and after I put the RPC in I can not see much difference in power consumption.

Yup the drone of the generator motor, would be nice to have that gone, but overall I went the most practical for my shop. Other clients shops I have supplied only VFD's and did not bother with the RPC, depends on the users needs.

Walter
 
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Turbo
Ive been running my lathe with a 5hp main motor and the 1/4 hp coolant pump off the same VFD. I just have a disconnect on the 1/4 hp motor. If I need the coolant pump, I just start both motors at the same time. The coolant pump isnt used very often though.

Paul
 
Couls someone please explain the function and purpose of chokes or reactors between VFDs and motors?
I have two VFDs (one VERY old and huge 1.5kW running my mill) and one tiny chines one (also 1.5kW) for the lathe.
I don't have reactors or chokes on either - they are simply connected directly to the motors.
Cheers,
Joe
 
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