I want a knee mill but

Charlie Mike

Charlie Mike

Sober since 1-7-14 (still a Paranoid Nutjob)
Knifemaker / Craftsman / Service Provider
Joined
Nov 1, 2000
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I'm limited to single phase. Should I try to find a Bridgeport (used) and buy a rotary phase converter? Does Bridgeport make a single phase mill?
 
I have a Bridgeport. I have a rotary phase converter. I don't use the rotary phase converter on the Bridgeport, it isn't worth the bother. A cheap ass static phase converter is just fine for that application. If you need 3 phase for your manual knee mill just get a static converter and don't look back.
 
What Nathan said is correct, although if you're going to be pushing a small knee mill to it's limits, you may want to just get the rotary, as the static derates the hp of the machine, and long term, might not be the best for the motor.

My bridgeport type mill came with a static attached to the column, but I disconnected it and hooked it up to my rotary.. You can get a 10hp, digital, cnc ready rotary phase converter from American Rotary (the best) from their ebay store on sale for like $800 shipped usually. That's big enough to run most 3ph machines you'll likely be able to fit into your shop, with the exception of hard start items like 3 phase compressors.

I built my first rotary, when it blew up, I bought the one I currently have, and consider it one of the single best investments I've made in equipment. I rarely buy new, but this is the exception. I've got about half a dozen 3 phase machines, so it's a no-brainer. Only mistake I made was not getting a 25hp or bigger unit. They consume very little power (much less than meeting the usual 3 phase service minimums, let alone the installation costs), are quiet, and reliable.

Once you start getting bigger machines, it's just a matter of time before you've got a handful, and you'll have no choice but a rotary. Just go ahead and invest in one. It'll open you up to numerous possibilities for industrial quality machinery that most people can't handle, usually for much less than their "hobby" sized counterparts.
 
Nope, 230V or 460V 3 phase I believe. Recall that Bridgeport was bought out by Hardinge. Can't help you with the rotary phase converter. Good luck.
 
I'd like to stick to single phase only.
 
Good for you , go for a fyull size bridgeport, those little mills aren't as capable.
Go for variable speed, power feed and digital readouts.



A Bridgeport is a brand name, but it's also come to mean a type of machine too.

You can get them all in 3 phase and single phase.

If you use a VFD, you can use 3 phase motors to change speeds, very convenient.






A real brand name Bridgeport can be bought
$17,000 ish
http://www.kneemills.com/index.asp?html=prods&catID=1






The others imports are 5 or $6,000 ish depending on size, power feed, variable speed, digital readouts.

See the grizzly website there are lots to look at
http://www.grizzly.com/products/category/480000|700002

Single phase
http://www.grizzly.com/products/9-x-42-Vertical-Mill-w-Power-Feed/G9901


variable speed on 3 phase
http://www.grizzly.com/products/9-x-49-Vertical-Mill-w-Power-Feed-3-Phase-VS/G9903




You can easily find used ones for 1,400 2,000 2,500
It just depends on condition and such.
 
I just ordered one of these http://www.machinetoolonline.com/PM-932M.html from Quality Machine Tool, it is single phase, has power feed and I am also getting the 2 axis DRO, it comes with a 3 year warranty.

Not a Bridgeport or a Knee Mill, but I believe it should handle anything I would ever do in my home shop.
 
I have a precision Matthews 949V with a power feed and 3 axis DRO. It is a fine machine for what I do and was about $6600 to my place. A used Bridgeport is another good option if you can find the right one.

Ymmv but my machine will hold tolerances much tighter than I need to make knives.
 
I also used a static inverter on my knee mill for years. When I got a VFD I wired it to the mill and my disc grinders using plugs. Just unplug one and plug in the one you need. Then I picked up a rotary. I am VERY happy with the rotary. I got a 10hp from American Rotary for a great price, not much more than a quality VFD delivered to my door. Now I run my mill, hammer and my 5hp motor on the grinder direct off the rotary. It makes life much easier for me. I wish I had done it years ago.
 
Gotta agree with the guys who invested in rotary converters.

The biggest reason is that three phase motors are practically free. You will find used equipment with three phase for next to nothing, just because it has a three phase motor.

You will definitely come out way ahead in the long run buying a good three phase converter. Half my equipment is three phase because instead of buying expensive single phase equipment, the three phase door was open when I bit the bullet and invested in a 15hp rotary converter. It's paid for itself many times over by now.
 
Good morning Matt.

I have this and it works great on my mill. I would probably replace it rather than move to a rotary converter.
208 1 phase in, 3 phase 208 output.

vfdj.jpg
 
I have an older stephead Bridgeport and Im really happy running a VFD. Using the variable speed saves me a lot of hassle moving the belt around and its real handy tapping holes running nice and slow. I have a remote box wired up with my variable speed pot and fwd/rev/stop

Look around for a stephead, they usually go for a lot better price than the variable speed models.

But like anything used you have to make sure you dont get one that totally worn out or in need of an expensive repair
 
Can I ask why you are limiting yourself to single phase?

Do you have a 220VAC feed in your shop?

While I've seen a few used knee mills that have been converted to single phase, it's literally just as easy (possibly easier), and around the same cost (if not cheaper) to set up a VFD in order to convert to 3 phase.

Having a VFD will also allow you to run other 3 phase machines as you might get them, as well as easily varying the speed as necessary.

I got a chinese 2 hp VFD off of ebay for about 120 bucks. Not much more than a typical static converter would run, and much more efficient and better for the motor.

One thing to note: A VFD MIGHT not work well with the drum style switches on a brideport (used to reverse motor rotation), but I was able to wire up a $5 DPST switch in order to reverse rotation via the VFD.
 
220 VAC in my shop is not a problem.
 
In that case, I'd recommend a VFD. That way you can bypass spending extra money on a single phase motor and bracket that you'll need to convert from 3 phase to 1 phase. A 3 phase motor will give you more torque anyhow.
 
When I had my Mill hooked up the the vfd I had to bypass the drum switch and run it directly off the switch on the VFD. Worked good but like the rotary better.
 
I would check Craigslist for a nice knee mill.

In my area alone, there is 3 bridgeports for sale. One of which is a nice bridgeport 3 phase power feed that comes with a rotary phase converter and a bunch of tooling and clamps all for 1500.
 
Matt

As you can see 3 phase is not really a problem, you can use a VFD to give you variable speed from it.


The gotcha you have to watch for is the voltage.


If you have 220v single phase, you can use a VFD to get 220v threee phase.


The problem is many industrial machnes will have 440v three phase.
You can't hit that at home without a transformer, or changing the motor (pita plus cash)
or


You can read the motor plate to make sure it can be set for 220v three phase.
 
12345678910 said:
Matt

As you can see 3 phase is not really a problem, you can use a VFD to give you variable speed from it.


The gotcha you have to watch for is the voltage.


If you have 220v single phase, you can use a VFD to get 220v threee phase.


The problem is many industrial machnes will have 440v three phase.
You can't hit that at home without a transformer, or changing the motor (pita plus cash)
or


You can read the motor plate to make sure it can be set for 220v three phase.
Click to expand...

I'd say that MOST 3 phase machines in the 1.5 to 2 HP range will have motors that can be wired for 220VAC OR 440VAC. It's rare that it'd only be the latter.

I just bought a 2HP Kondia knee mill myself that I found was wired to 440VAC from the last shop that used it. It's usually just a matter of swapping a couple jumpers or wire nuts around, and you're good to go. Most nameplates will have the appropriate diagram.
 
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