Round column mill x-y registration loss on head movement

[martik777]

I am looking for a basic mill (RF25/30) but not sure I understand this issue.

Under what conditions would it be necessary to move the head? Is it the same issue with raising/lowering or swiveling the head? Wouldn't there be enough room to change tool bits with the quill/spindle movement without moving the head? Most of the work I will be doing is < 1" thick. I guess once you add a vice to the table it gets fairly tight. The RF25 has 3 5/8" and the RF30 5" spindle travel. If I am just working to scribed lines, is exact registration really required?

 

[8ntsane]

I dont know about the mills you have mentioned. I have worked on a few machines in the past that had round colomn. A few things I noted from using these type of machines were the small machines with round col, could not take very heavy cuts without the head creeping slowly out of ajustment. Keeping one set where you want it can be a problem. If the same machine has no knee on it, and many of the small machines dont. Your going to run into times when you can,t get the tooling into the spindle without swinging the head out of the way.

Round ram machines will work with in limits, but can be a royal pain in the butt. If you have a choice, I would look at something a bit larger, and has a knee ajustment at least. A mill is much more friendly to use when your not messing with the head at all.

Even with a knee to get you extra room, the round column mills can be frustrating to keep the head where you put it. Sometimes its better to get a bigger machine to avoid all the raising / lowering/ rotating of the head, after a while it gets really old wasting time setting up, and resetting up.

Even when you have a full size machine, a job will wander in your door, and you cant do it because of the limits of the machine its self.

 

[Rbeckett]

I have a round column HF mill/lathe combo. It is a little tricky sometimes to get just right, but it generally falls close enough to be able to take out the error by adjusting the handwheels and XY locations. As long as you have a good benchmark starting point and a reliable way of returning to that point you have 90% of the issue whipped. Tool changes and product alignment become the biggest issues and can easilly be surmounted with a little prior planning and caution. My biggest issue is column stiffness with the quill extended more than 1/2 way. If I can keep the quill retracted and close to the head all is well and it cuts chatter and vibration to a minimum and yeilds a great looking surface finish as well as an accurate piece. Those have been my only complaints and they are fixable and I would not buy a replacement just because I felt a square column would be easier. Just my .02
Bob

 

[Splat]

I don't have the time under my belt the others above have but when I was looking for my first mill I'd say 98% of what I read was against round column mills for all the reasons already listed above. If you can wait to get a knee mill, even a small knee like the Johansson B-12 or Atlas/Clausing 8520 for the home shop, you'll be ahead of the game.

 

[Hawkeye]

I have a ZX-25 mill/drill, which will be very similar. It has 4" quill travel, which is good for drilling. A few times, I ended up needing to raise the head in mid-operation. This, of course, necessitated setting the location very carefully to get back to centre on a hole I was working in a multi-step operation, such as centre drilling, tap drilling, then tapping. If milling is involved, I hesitate to extend the quill very far, as has been mentioned. All this lead me to consider a knee mill. I just wasn't expecting jumping up to a U2 sized mill. :yikes:

The real point of this post is this: If Shawn changes his mind about taking the ZX-25, I might not list it for sale. That size of mill/drill is quite useful, especially since the vertical attachment on the Victoria has no quill movement at all. I will, however, really enjoy the rigidity of the heavy mill. 1 1/2 tons vs. 450 pounds.

 

[Splat]

There are smaller knee mills and the average home shop doesn't need a full Bridgeport. I was seriously considering Grizzly's G0704 until I saw this small knee from Top Tech tools. Being that I'm only 30mins away from the retailer it would save on shipping and worrying about transport damage. Alas, I found a very good condition Johannson B-12 small knee..precursor to the Clausing 8520 at the last second and got lucky to have gotten it. Grizzly has a few smaller knee mills, some look exactly like that Top Tech, but of course the price jumps up big time because it's Grizzly.