Which mill should I get?

[Pcmaker]

I currently have a PM-25MV. I've been looking to upgrade to a much more ridgid machine where I can work with mild and hardened steel without any ridgidity issues. Also, I don't have access to 3 phase in my garage. 1 phase, 240v is the highest I can get.

I need a variable speed motor with an RPM indicator just like my PM25MV, a spingle brake, Z axis motor, X axis power feed, maybe a Y axis.

Not sure whether to go with a bench top or knee mill. I'd rather have a bench top, but I think knee mills are much more ridgid when working with harder metals. But it's a pain you have to bend over to lock the Z axis.

A lot more input on pros and cons would be appreciated.

 

[Morgan RedHawk]

If you have the room and the money, I would go with a knee mill. I have a 932 and just upgraded to a 949. The 949 is much more rigid. I convert my single phase 240 to 3 phase with a VFD. Now that I have used both styles, I prefer the knee for the Z axis.

 

[mksj]

Per above, I would recommend a full size knee if the budget allows. VFD is a fairly basic install, but there is also the mechanical vari-speed if you do not want to do the conversion. I cannot say that I ever locked the knee on my mill, unlike a bench top were you can get head sag, I see no difference with the knee. In most cases anyway I uses the the spindle adjustment to set the cutter depth, and I do lock it. A vari-speed head gives you a mechanical readout of speed, long term they are more maintenance. Adapting a tach. to a knee mill there are several approaches. Probably the easiest is a hand held tach. if speed needs to be quantifiable. My knee has a built in VFD, which I have modified, but these come with a factory Tach. Downside is cost, you are looking at a large cost range going from say a PM-940 mill to a factory installed VFD mill. I find X and Z drives to be the most useful, Y less so. Figure about $400 a drive for a decent drive like Align. I do not see any cons for a full size knee vs. a bench top mill other than sizes, weight and cost. Function wise, once you use a full size mill, hard to go back to a bench top other than for smalls. Really depends on the type and size of work, the PM-833 would be a mid point between the two based on capacity, cost and quality.

 

[Pcmaker]

I always lock the head on my PM25MV when I'm milling. I've never used a knee mill before. So you don't have to lock the Z axis when you're using a knee mill? I guess the weight of the table is already being pushed down when you're milling, so it's not moving.

 

[markba633csi]

Yes pretty much. It's a different animal. I do a lot of smallish parts, I'm using a small old horizontal knee mill with an added motorized vertical head. Cost me a grand. Does most everything I need. If I was upgrading, a small table Bridgeport or Millrite would probably keep me happy for years
-Mark

 

[davidpbest]

You might want to READ THIS. I have a customized PM935 with VFD and custom controls Mark did for me including tachomenter, and I'm generally satisfied with it. I have not found it as rigid as the Rong Fu 45 benchtop mill it replaced. All that flexibility of the Ram, Tilt/Nod comes at a price. So if you do go the knee mill route, I would recommend a full size PM949 or equivalent rather than a baby/junior sized knee mill unless space constraints dictate.

 

[ttabbal]

I ended up finding a Bridgeport locally in good shape. Needed some work, but it works great. If you have space and budget for a mill this size, it's worth it.

Don't worry about 3 phase. Just get a motor that can be wired for 220V 3 phase and get a VFD. You get 3 phase and variable speed all in one.

 

[81husky]

So if you do go the knee mill route, I would recommend a full size PM949 or equivalent rather than a baby/junior sized knee mill unless space constraints dictate.

I was under the assumption that all of the PM knee mills had the same head. The knees look beefier on the larger sizes, but the lack of rigidity mainly comes from the head. I have a PM935, and it's not the most rigid mill around. Please correct me if the heads are different on the PM mills.

 

[erikmannie]

If I were to do it over again, I would get a 3 phase PM knee mill. It is not a problem to buy a VFD or RPC so you can run 3 phase at your house.

 

[erikmannie]

You might want to READ THIS. I have a customized PM935 with VFD and custom controls Mark did for me including tachomenter, and I'm generally satisfied with it. I have not found it as rigid as the Rong Fu 45 benchtop mill it replaced. All that flexibility of the Ram, Tilt/Nod comes at a price. So if you do go the knee mill route, I would recommend a full size PM949 or equivalent rather than a baby/junior sized knee mill unless space constraints dictate.

FYI I was unable to read the PDF on my iPhone 8S.