Square column vs. small knee mill

AndySomogyi

Registered
Registered
Joined
Nov 9, 2018
Messages
377
I’m looking at buying a milling machine for my small shop, and I’m down to two choices. A new PM-932 or a used Enco 100-5200.

Which one is a better choice? Which one is more rigid?

These are both about the right size for me.

I’m sure many here are familiar with the PM-932. My concerns with it are the lack of a precision dial in the Z, and the backlash in the quill adjustment. I’m used to a Bridgeport where you have very precise control of the knee to adjust the depth, and only use the quill depth for rough adjustment. But it’s a new mill from a reputable company. The geared head is nice. I suppose for depth, I could just use an dial indicator between the head and table for fine adjustments.

My concerns with the Enco is that it’s 30 years old, and who knows what kind of shape. It’s a belt drive which is very annoying for speed changes. Is it worth the headache? It’s an 8x30 small knee mill, basically the same as the Grizzly G0731. I’ve found this used one on eBay for 1700.

I just used to have small grizzly round column mill which was effectively worthless for steel because the lack rigidity, and don’t get me started with the round column.

So, take a chance on a used one, or buy an new PM?
And a pic of the Enco

474AB215-B1DE-4312-B868-D070B81F1B67.jpeg

The PM932

8FA30167-5F20-4A9F-BCE0-68B8831CED52.jpeg
 
I would choose the knee mill over the movable head type. On the Enco, you may find it may be something other than 0.10 inches per revolution on the leadscrews- can be a bit awkward if you don't have a DRO
mark
 
i suppose it depends on how big of work you do.
for me i'd buy the Enco machine, only because i owned similar machines.
i like the charm of older (heavier) and more expensive to produce equipment.

the PM machine must be ok they keep making them
 
I have owned several square column mills (LMS, PM, Charter Oak) and managed to use the Z-axis OK. :)

However, I did have a DRO scale on the head to help with accuracy/repeatability and always made final translations in the upwards direction to keep the head/leadscrew interface in tension. Like you, I only used the quill for rough adjustments and drilling.

My personal preference has been to buy new instead of used, because you really never know what you're getting with a used machine. A used machine has wear, period. How much is the question. A little wear can be fine, but too much and you end up with a really large paper weight as a neighbor friend of mine up in CO found out.

Of course a lot of this comes down to what you want to do with the machine, and how accurate you want/need to be. Rigidity is less on smaller machines. That's a given. Doesn't mean you can't make anything with them. I built a competition pistol (1911) on my first machines which were Sherlines. After being told by a professional machinist that it couldn't be done. :)

Bottom line I guess is you have to decide between taking a chance on the little knee mill, or buying a new PM and adjusting to a different way of handling Z-axis translations. That and if you have issues with the PM you will get great customer service. Not sure what you'll get with that used machine.
 
I would prefer the Enco, but I think the price is too high at $1700 and with no tooling included. Don't buy it without test driving it.
 
Rigidity is less on smaller machines. That's a given. Doesn't mean you can't make anything with them. I built a competition pistol (1911) on my first machines which were Sherlines. After being told by a professional machinist that it couldn't be done. :)

That pretty much supports my theory that the accuracy is built into the machinist not the machine ;)
 
I have a Taiwanese made Rong Fu 45, I think they were the first with the square column mill/drill. I like the 8x32 envelope. They are not as handy as a baby Bridgeport style but are probably more ridged. The design would suggest that. They use less floor space as well. Just as a gearhead drill press they are worth their price. Rong Fu now has a power down feed for boring BTW. However I have noticed the clones of the RF 45 to be slightly or more than slightly, smaller and lighter. Check the weights.

I paid $1750 CDN (75% USD) ,but I got a DF 1224g lathe with it. I valued the mill at $1500. New RF 45s are over $5000 US.
 
I have the PM-932 converted to CNC. It's a very solid mill. The only complaint I have is the lack of Y axis travel. At 8" it's a bit on the skimpy side. You may want to look at the PM-940 with 12" of Y travel.
 
Hi Andy,

My preference would be the knee mill every time ! My mill is virtually the same as the PM932. I do some good work with it but it has a lot of limitations, but you learn to work around them.
 
Thanks for your answers guys. There are some differing opinions here, but at least I haven’t heard a single report that either machine is total garbage, so looks like I’ve come up wth a pair of decent choices.

Got some thinking and considering to do.

On one hand, I’m half way tempted to shell out the $4300 for a PM 835S, which literally is a baby Bridgeport with a real J head clone. But that’s it for me money wise.

34FFD821-1167-4CDA-BEC5-570C2B291226.jpeg
 
Back
Top