Powermatic/Burke mill

[ksouers]

I have an opportunity to buy a Powermatic/Burke knee mill, looks to be from the 1970's.

The table is 8x32, plenty big enough for me. But it has a 3 phase motor.
I don't want to get a rotary converter (another $500 or so) so I'm thinking of either replacing the motor with a single phase or having the existing motor rewound for single.

Does anyone know anything about these machines?

I'm guessing I will lose some torque by going to single phase, but the HP should be similar. Any thoughts?

 

[kvom]

Rather than a RPC, why not get a VFD? You get 3 phase plus variable speed without changing belts.

 

[ksouers]

I thought of that, but if I recall it cuts the power to something like 66% doesn't it?

 

[wareagle]

Anytime you power a 3 phase motor with a single phase power source there will be a loss of efficiency and the output power of the motor will be reduced. Your options for converting power from single phase to three phase are as follows:

Static phase converter: These units are fairly inexpensive and are easily installed. With this unit you can expect to have only two-thirds the rated HP of the motor (i.e. a 3HP motor will now be effectively 2HP).

Rotary phase converter: These units are advertised to provide 100% of the motor's rating and torque. In reality, this isn't the case, but they do perform much better than the static converters. I don't have and exact loss, in other words this is a SWAG, but with a RPC you can expect between 90-95% of the motors rating. The drawback is these units are expensive. One can be built out of an old motor, but if you choose to do this, be sure to fully understand the implications of the project before deciding to do that. I just built one for a friend and the cost of it was about 30% less than buying a manufactured unit, and he already had the motor.

Inverter/VFD: This is my personal favorite. You get a lot of bang for the buck out of these units. I put one on my milling machine, and it has performed very well. You will get an infinite control of you motor's speed, and that can greatly enhance your abilities to get great finishes. It is also very nice for not having to change belts each time a speed change is required. The drawback is you do loose some off of the rating of the motor with these units. My SWAG here is you will get around 85-90% of the motor's rating. THere is also some time that will be needed to make the programming work in your application, and that can be tricky. It is doable, and there are plenty here that can help you with that.

Hopefully this will give you some food for thought. When I first was using my mill, I had a static converter on it. It worked, but since putting the VFD on, it has made it a totally different machine. The price of the VFD was a bit less that twice the price of the static converter, but it performs many times better than the SPC in my experience.

A word on building your own RTC if you choose to go that route... I would advise against it. The unit I just finished for my friend works very well, but for the amount of money it took to buy all of the required components along with time it took to put it together and basically tune it out really makes this option non-attractive. Had he needed to buy a motor for his project, he would have spent more than buying a premade unit!! I did not charge him for labor, but my time invested in the project was about 10 hours.

 

[ksouers]

Thanks W/E.
That was a lot of great information. Electricity is magic to me so it was excellent to see a comparison of the various converter solutions.
It looks like the VFD is the way to go, about the same price or a little cheaper than re-powering and I get to keep the 3 phase. The machine only has 1 HP, I think can live with the 15% loss.


Does anyone have any knowledge of the machine itself?
What are the weak points?
What should I look for?

 

[zeusrekning]

I would say strongly to stay away from the static converter. I tried one with my series 1 bridgeport 1hp. It was like single pahsing a motor. I could stop the spindle by grabbing the chuck. I lucked out and found a old but unused 10hp Rotory converter. Hooked it up and runs great. Wish I had the VFD but cost was my issue. I hate changing belt. :-[
Tim

 

[CrewCab]

I've just fitted an Inverter/VFD to run my 3 Phase Boxford Lathe, now the wiring is sorted to the correct configuration : it really has made the lathe come alive plus, the variable speed and (almost) instant reverse is a nice bonus.



CC

 

[ksouers]

Thanks for the replys guys.

You've convinced me that the VFD is the way to go.

CC,
That looks great! I like that reversable feature, though I don't see much use for it on a mill. But the quick stop would be a plus. What brand VFD did you use? American? Brit? Jap? Other?

 

[CrewCab]

True Kevin, reverse on the Mill is about as useful as a chocolate fire guard

Mine is the same make as WarEagle's a TECO they are Taiwanese and seem well regarded, I didn't specifically go looking for that make, the company I bought it off was recommended to me by another forum member and I followed their advice, it wasn't the cheapest but then again it wasn't a much dearer than the cheapeast option (about £30 / $60 more) including the Remote controller total cost was a little over £200 but over your side of the pond they seem to be available at far better prices .........

For Instance .............. although that is a 1HP unit, fine for me as my lathe is only .75HP, you may want to go a little bigger, do a trawl and see what comes up.


Apparently they can be programmed to stop instantly, but I think that could just cause the chuck to unscrew ??? .......... so I've set it for about 3 seconds deceleration time at the present, plus a little longer to accelerate fire up ............ gives the Old Gal' time to warm up gently 8)


hth

CC

 

[ksouers]

Thanks CC.

I did the Google earlier with W/E's post, came up with the same vendor you did.
The prices are very reasonable, I think. About the same price as swapping out for a single phase motor, assuming I could find one to fit the machine. Maybe cheaper. A friend, a purchasing agent for a local shop, suggested getting the current motor re-wound for single phase, but that would still cost about the same as replacing the motor.

Now that I have the power squared away I guess I better go look at the machine and start clearing out some space in the shop.

 

[wareagle]

I will add that these VFDs can be tricky to get programmed. They are suited for a variety of different applications, and setting the parameters to suit the needs of a machine tool can seen daunting. If you decide to buy one, take your time to read and most importantly understand the instructions before you install your drive. This is the best piece of advise I can give to anyone who is considering installing one of these units on their machine.

One last thing, don't let the complexity of the devices turn you away. Though they can be tricky on the programming, once running they really are a dream!!

 

[kvom]

I bought the 2HP GS2 from AutomationDirect, whose warehouse is a couple of miles from my house. It's made in China, so possible available in OZ as well. My cost was about $235. It has one nice feature which allows the belt ratio of the mill to be entered and factored against the motor speed so that the displayed number is the spindle speed. It also has a detachable control panel that can be remoted to the base unit with a cable, so that the box can be mounted on the wall and the controls on the mill.

Some facts I've gleaned about VFDs:

1) Don't use the mill's on-off switch while the VFD is operating. It can cause the VFD to fail. In fact, removing the switch from between the VFD and the motor is recommended.

2) Don't use the mill's spindle brake; let the VFD stop the spindle.

3) If the VFD doesn't stop the rotation fast enough to suit, you can connect braking resistors to the VFD. These absorb the reflected energy from the motor.

As for reverse, it is useful when you are using the mill to tap. In reverse it withdraws the tap. Also, if the mill has a backgear engaged, then you need to run the motor in reverse.

 

[kennyd]

Another vote here for a VFD. I put one on my Clausing lathe and is a beautiful thing not to have to change the belts all the time!

Here are some pictures of my re-build:
http://picasaweb.google.com/kdeckster/Clausing4900#

 

[wareagle]

kennyd, that is a great restoration! :bow:

My lathe has a single phase motor currently, but in the event it decides to go to the motor heavens, then I will likely fit mine with a VFD set up!

 

[ksouers]

Kenny, that's some rebuild! Looks great!

kvom, thanks for the tips. I'll definitely put them to use.

Where do you guys keep your belts stationed with the VFD? Something close to the middle, 1:1?

 

[CrewCab]

kennyd, that is a great restoration! :bow:

Got to agree ............. cracking job 8)

CC

 

[kennyd]

kennyd, that is a great restoration! :bow:

My lathe has a single phase motor currently, but in the event it decides to go to the motor heavens, then I will likely fit mine with a VFD set up!

Thank you :-[

 

[kennyd]

Kenny, that's some rebuild! Looks great!

kvom, thanks for the tips. I'll definitely put them to use.

Where do you guys keep your belts stationed with the VFD? Something close to the middle, 1:1?

My belt is usually on the first pulley, which is 370rpm open and 52rpm in back gear. It has suited me for the small projects I've done so far-I am just a rank amateur!

 

[kennyd]

Got to agree ............. cracking job Cool

Thank you also :-[

 

[steamer]

Hi,

Noticed the thread about SPC and RPC.

I bought the Phase -0-matic static one for my Logan Lathe

Problem, the motor would still pull enough to pop the breaker on the lathe because the legs that were working were pulling too much.

What I did was to make the RPC using the Phase-o-matic. The SPC gets the idler motor running and then I run the lathe from the idler motor. You will need a momemtary on switch. A schematic was part of the installation instructions that cam with the PHM. I bought a used 3 hp ( 50% larger than load) motor/pump from a motor house for $50, and with some wiring...It worked fine.

Dave

PS if you look inside a Phase-o-matic you will want to puke.....there are about 3 parts and some cardboard....no magic there. Get the Heavy Duty as the standard duty if overloaded at all will pop and it's done. The HD unit has heavier components and is a bit more forgiving. But in all, they get a lot of money for what their selling.