PM-833 PM-935 Alternatives

[Xyzzz]

Heads on bench mills often will incorporate a gas strut or counterweight system in a CNC application. In non-CNC, the gibs need to be locked otherwise there is head nod/movement. On a knee mill the knee movement is not typically used for fine adjustments in height, movement is way too course with the hand crank. A fly cutter uses minimal power, and you would not be running it a very low RPM, face mills you would run at much higher RPM so cutting power should not be an issue. A servo/close loop to the quill handle will not work because their is too much backlash, you would need to operate it directly on the Z-axis leadscrew, a complex setup which you may only rarely need. I have used my PDF once on my knee mill after having it for many years. There is the 940V if you need a wider operating speed with more low speed torque and it is available in a PDF version, albeit is a rougher build quality.

It all comes down to your space and budget, the PM-935 after adding a VFD is almost twice the cost of the 833TV, when you get into that price range there are quite a few full size knee mills and used ones in the 3-4K range that should be in good condition. If you have the space and the ability to move a 1+ ton mill, I would go with a full size knee at the end of the day.

It is space. For years, I thought about my next house/shop where I had the space for a Haas, knee mill, grinder, lathe, etc. when I took some time to think about a garage bench where I had a sander, a grinder, and some bench space that I rarely use, and a drill press that could be replaced by a mill in a pinch, I realized I could have a lathe and a mill, -maybe- if I were careful about squeezing them in. No way I could fit a full size mill. And a decent lathe. I could probably get rid of my CNC Router, but that is a beast, is fairly space efficient, and is here to stay. I’m using it as a mill but it has no low speed torque-at all. Drilling a 1/4” hole is ok in aluminum as long as I use carbide and spin it at 10k. Steel? At best it is a stretch. Maple, or Alder, or Mahogany? It is a beast.

Also, no milling machine is ever big enough. If you have x” of travel there will be a time when you want x+y” of travel. So there will never be enough travel on whatever mill you have and 95% of the time, enough. What torques me is when I have to cajole the machine into achieving accuracy and precision. That takes a lot of the fun out of it. so I’d rather have a mill that will give me better results more easily, than a mill that will plow a 1“ 4 flute. If I have to back off my Feeds and speeds, and take a few more passes? I can live with that.

ypu are probably right about the quill leadscrew, but I will have lots of fun seeing if I can add a servo and get consistent quill downfeed sufficient for boring. Or not. Maybe I am looking for performance that just won’t fit in the limited space I have. Could be fun finding out.

anyway, very much appreciate the perspective, and if u are near San Diego, a Steak dinner is yours!

 

[Xyzzz]

“IMO, best practice on a benchtop mill is to use the quill in conjunction with the quill DRO to set tool heights. Moving the head should be reserved for gross positioning moves to increase/decrease Z-height for differing tool heights (like switching from an end mill to a drill chuck with long jobbers twist drill). And the head-to-column locks should be engaged after repositioning the head to improve rigidity and tolerances.”

So the 833 I’m leaning toward (today, tomorrow it will be a Haas!) has no quill DRO. I will certainly add one if that’s what I buy. I bet there is someone here that has added one and has a good solution? Sounds like a fun project, if not.