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PMD

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Joined
Apr 11, 2015
Messages
930
Location
Martensville SK
Wow, the depth of equipment and experience here, as usual, never fails to amaze me.

I would love to live near a large manufacturing region to get all of the used equipment options, but they are rare around here where it is mostly job shops that scoop up all of the deals.

My lathe for the last 35 years is a Taiwanese 13 x 40, 2 HP gap lathe about 600 lbs. with MT3 tailstock. Rigid enough for light work, but you have to be very patient to do heavy stuff. I will get a much larger and heavier tool once I have new shop up and running, but this old thing does most of the turning I need to do, and I plan most things around its limited capacity. While I would love some fancy German tooling, reality is I need to get what is available and live with it.

I did most of my milling with attachments on cross slide of the lathe for decades, but several years ago and old Danish tool guy retired and my wife bought at auction his Chaiwanese little dovetail mill (IIRC 1 HP) also #3 MT draw rod tooling as per my lathe and drill press. For a beginner mill, a pretty decent thing and if it met his standards, it far exceeds mine.

What I also did over the past several years was watch Princess Auto for their bargain basement Chinese mini mill and lathes. I caught one where someone lost a handle on a demo lathe and got it for couple hundred bux and another one that was last of a stock changeover for same negotiated price (the replacement was a different colour paint on same mill for closer to a grand). These are tiny little VFD tools without enough rigidity to cut much more than aluminum, but I find I use them a fair bit since some stuff is just too small for the bigger machines.

I guess the idea I want to convey is that if you don't have access and skill set to source out the ultimate bargain in industrial top line CNC machining centers, DO NOT let that deter you. Buy what you can find and afford and learn to use it, and THEN you will have a lot better idea what can and will work for you. Just be aware of trying to keep some kind of rationality of tooling to minimize that cost and allow some carry forward to stuff you will need when you get equipment you may go on to.

Another snarky remark I will make is that if you start with iffy equipment you WILL have to learn to measure, fit and finish with a level of skill. If you start on really good stuff the quality of the equipment could mask a great shortfall in skill development.

Now, before I get declared a complete flat earth luddite: I just picked up an ultra-high precision CNC milling center (used to generate eyeglass lenses) for literally nothing. I won't be the lead, but some of my ME buddies will probably salvage the drives to make other CNC tools while I make off with the cooling recovery system. It probably cost the owner over $200 grand 14 years ago, but the demand for accuracy in their business makes its 0.0001 obsolete. I am tempted to mount one of the single piece diamond tools on a ring or pendant for my wife.
 

Aviacs

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Joined
Oct 21, 2019
Messages
349
The most convenient way, as others have noted, and it gives you variable speed flexibility, is a VFD. Many J head BP mills are only 1.5HP. I think some were even 1HP. Certainly for home use and "sensible" cutters (EM's rather than say 4" shell mills) the typical user is seldom going to use a full 1 HP in a cut, regardless the mill's stated maxHP. Mills don't start under load. So a .7 or 1KW VFD would run it fine. Nice thing is, if you do ever over power it, the VFD simply shuts down, like a sophisticated programmable breaker. Of course if price is not inhibiting, go ahead and get a larger KW capacity. Absolutely no downside.

The cheapest way to get full HP is to find a surplus 3ph motor of the same capacity, or prerably a little larger, and use it as an idler to convert 230v single phase to 230v 3 ph. With a typical 9 lead motor, follow the diagram inside the box on the motor to set it for "low voltage" (low v = 208 - 240 v as opposed to hi v which is 440v +/- ) Connect all 3 legs of your equipment to the motor leads. Connect the 2 hot leads from a dryer or range cord to 2 of them. Ideally, there will be a disconnect between line and motor. Get the motor spinning up to about 1/3 its design rpm, and flip the disconnect to "on". The idler motor will start and run normally, and generate the 3rd leg going to your machine.

Ways to spin the motor up include a pull rope starter, like old lawn mowers. or a fractionla HP single phase pony motor rigged through a clutch or slip-belt. Or a capacitor bank tuned to start the idler, but is cut out of the circuit as soon as it starts so the caps don't blow. A commercial 3ph "generator" is this set up, with the idlermotor shaft cut off flush. And an automatic disconnect for the capacitors built into the starting switch. Some (not all) commercial 3 ph generators do have run caps added to balance the voltage across all 3 legs. You can do this with a home-brew, too. Run caps are cheap. You need a multi-meter to keep track of progress, adding run caps is somewhat iterative depending on loads.

Low speed 3 ph motors make much better generators/idlers than the high speed units. low speed motors have more poles, so are smoother and torquier. They are also easier to start, since the starting rpm is lower. I like 1200 rpm motors. Have used 1800. 3600 should probably not be used. Mostly because 1800 are so much better, and about the same ease/cost of acquiring.

Read up online, there are lots of posts about it.

smt
 

blane.c

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Joined
Jun 27, 2015
Messages
6,064
Location
capital district NY
Under three hp unless you already have a 3 phase motor laying around to use as the basis for a rotary drive and it is roughly twice the power of the motor you want to power, it doesn't make any sense really. Better off with a VFD by the time you sort out all the bits and pieces.
 

Aviacs

Well-Known Member
Joined
Oct 21, 2019
Messages
349
unless you already have a 3 phase motor laying around to use as the basis for a rotary drive and it is roughly twice the power of the motor you want to power
For motors that do not start under load: mills, lathes, surface grinders, you do not need "twice the HP" for the idler. The same amount is safe. Less can work fine. Better yet, if you have a shop with more than one 3ph machine, the effects are cumulative. A Not-in-use machine that can safely be run idling, (say without a cutter, or with a fully enclosed cutter) can add to the converter capacity to start a larger motor, & it smooths out the delivery.

E.g.: I run a commercial woodworking shop on a 7.5HP idler. Including starting and running a 15HP widebelt sander, with a 3ph 2HP dust collector running at the same time. Also a 9HP table saw. & sometimes a lumber jointer with 2 ea 550v 5 HP cutter head motors, and a 5HP drive motor. (The air supply 7.5HP compressor is single phase so does not add to the 3ph load) Early on, i blew the pole pig across the road, so NYSEG sent an engineer to inspect & instrument my shop; and kept track for a month. When the pole pig blew again, they admitted that they had never upgraded it (despite charging for it) when i converted our service entrance from 60A pull fuses to 200A service. They upgraded the transformer and lines, and did not find any fault with my system or converter.

The important factor at all times is safety. Comply with local codes, protect all wiring and equipment with the appropriate devices (breakers for the wire, starters with heaters for the motors, preferably mag starters) Use appropriate wire (&/or wire and conduit) for the loads. Include disconnects as appropriate even when not required. etc. Generally, especially with mag starters, the generated leg should not be one of the 2 in the control circuit. (low voltage on the generated leg can cause mag contacts to chatter, sometimes) But if the voltage is balanced, even that will not be a factor.

smt
 
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8davebarker

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Feb 1, 2013
Messages
56
Location
Santa Barbara,CA

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Jay Kempf

Curmudgeon in Training (CIT)
Joined
Apr 13, 2009
Messages
4,523
Location
Warren, VT USA
I have a couple of 2.2KW VFD's both were near $100 on Ebay. They are pretty simple and reliable. I drive them from my CNC software using PWM input which is butt simple to set up.

These and all the other components needed to automate a small machine tool are all readily available and the forums are full of people that have already made all the mistakes so you don't have to.

First time I ran into a rather more commercial VFD was years ago when we got our hands on a ski tuning machine but it was 480v 3 phase. Back then the world wasn't as small and these units weren't as simple to figure out. For biggish HP the VFDs get a little more expensive but still way better than a decade ago.

Will be adding more soon to my shops for various CNC setups.
 

8davebarker

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Joined
Feb 1, 2013
Messages
56
Location
Santa Barbara,CA
Ok, I’ll bite, hw exactly does one get 220V at home and how exactly do you get 3 phase?

I’ve heard that residential have 220V (Electric dryer hookup) but how does one get 3 phase?

I have a Bridgeport mill that I’d like to bring home but the power isssue is my shortfall in understanding
banggood.com single phase to 3 phase 220v inverter 2.2kw ~$75
 

Rik-

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Joined
Sep 13, 2019
Messages
520
Location
San Rafael, California
banggood.com single phase to 3 phase 220v inverter 2.2kw ~$75
banggood.com single phase to 3 phase 220v inverter 2.2kw ~$75
This looks really simple. One per machine and it’s off and running

Wonder how much power one of these things consume in the process?
 
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