Just Thinking

[Rainman229]

I have an older Eldorado with the 5 post mill head. What i was thinking was or has anybody made the z axis work off the head screw rather then the guile? Only reason why i was thinking of this is cause my guile has way to much play in areas. And would require and custom made pieces to get all the play out. So my thought is keeping the guile fixed (when the guile is all the way up i have no play) and moving the whole head as the z drive for cnc. What do you guys think? Is it doable ?

[sharpshooter90]

The machine my unit had was equipped with a 4 axes servo system. We had the 4th axis motor on the mill lift and in some cases we used it for what you are describing. To maintain the best accurracy, its always good to keep as much of the quill inside the casting as possible. So we would lower the mill as close to the part as possible to minimize quill extension. If we needed room to change a tool we would raise the mill up. We built a brace on the 5th column so there would be no lateral flex when the mill head went up and down. We also added a magnetic type scale to the mill head so we could return to the original position after changing the tool. We also had the servo driven rotary table, and when we wanted to use it we would just unplug the mill lift motor and plug it into the rotary table. You could do the same with your machine- I would suggest, first get the quill centered to the lathe axis, then adjust and plumb the 5th column and add a brace to keep it positioned. I think you can find those magnetic scales at www.enco.com for about 50.00 - get one with about 10" travel.

[mixdenny]

The problem that I see doing it that way is that it requires the overarm to be unclamped from the fifth column in order for the millhead to move up and down. You will lose considerable stiffness machining without the fifth column clamped. On my machine I wouldn't even consider machining without it locked up. On the few times I have trying milling and forgot to lock it, it is instantly obvious that something is wrong.

Also, on mine, the millhead tends to wobble a bit while the screws are turning, check this by raising the millhead while indicating off a vertical plate. Obviously, there is a slight bend or whip in one of my leadscrews, perhaps yours is perfect. I have them marked, so when I stop at the correct height to machine, I jog the z axis motor to line the screws up the way that produces the best tramming for the millhead.

Dennis

[fastlanecafe]

I think that is a characteristic of the quadra lift units with the twin lead screws. If they are just slightly out of sync, then one side lifts sooner than the other giving you that slight wobble. Mine had that same thing and I improved it by replacing all the original thrusts with torrington bearings and then carefully " clocking" the 2 screws under load. The new machines with the single center lift screw probably don't have that problem. In fact I am watching for a cheap ball screw, and plan to change mine to a single center lift like the new machines. I think it will be fairly simple, just need to drill a hole through the mill head for the screw to pass through.

[Rainman229]

Hmmm If i can come up with away to stabilize the head more. This could work. Need to figure this out. I know there are a few expensive options I can think of. But not sure i would want to go that route.

[fastlanecafe]

Years ago there was a guy who posted on one of the Delphi forums about his home built quadra lift. He used a ball screw for lifting and 4 linear bearings for the columns. He claimed good accuracy using CNC to raise and lower the head while keeping the quill locked in place. He also had an air powered drawbar. Sounds like that would be the way to go if you could find the ball screw and linear bearings cheap on some auction site like e-bay or here.

[Rainman229]

Well looking at the design of the quadra lift setup up. I see it's flaws. and why the 5th arm is needed. But I also see how to eliminate the 5th arm. Just need to take few things off the machine to get a feel of what i have to work with and lay out how to set it up. Once I get it all layed out I'll let you guys know.

On another note what do you guys think of about going to a 220 volt motor with a frequency drive capable of 6900 rpms Max. Think it's worth $500 to do. Only reason why i was thinking this is cause if i get the z to work off the quadra lift setup. I can Shim the pully play to reduce the charter and vibration it gives off. Since quile will never move up and down again.

[fastlanecafe]

I would suggest you keep or build the 5th arm- it is really the key to good stable milling. The 4 column quadra lift is far better than one of those single post drill press style units, but any time you put a heavy down load on the quill, it will want to raise the mill head- the 5th post eliminates this completely. Using a high speed VFD is feasible, but the cast iron pulley on the mill head is too heavy for that speed. You would need to find an aluminum one or replace it with a single pulley and use the VFD for speed changes. The stock bearings would probably be OK, but an upgrade to P5 bearings would guarantee smooth running at high speeds.

[mixdenny]

I installed the Quadralift myself and built my own fifth column. I took lots of measurements using up to a 220 lb uplift force as I built everything up, so I have an idea of how things flex and where. The fifth column is absolutely essential to the stiffness of the milling head. The Quadralift without it has double the movement compared to the original round column, and most occurs at far lower forces. The movement at low forces comes from the slop in the 4 columns. Replacing the sliding fit collars with linear bearings would eliminate that movement, now you would need to stiffen the structure of the 4 columns themselves.

It could be done by triangulating the top of the columns, rather than the overarm on the milling head. Or they could go straight up and bolt to the ceiling, I saw this done a long time ago to an early Quadralift, although this introduces new problems if the rafters flex from moving loads. The triangulation could even go back to the left instead of getting in the way of the bed to the right.

It would be difficult to get it as stiff as the locked fifth column, but can probably become stiff enough to work.

Dennis

[Rainman229]

Well many mills use a single column setup. And still have no flex. The quadra has flex for a few reasons. The main reason being relaying on the 4 post for rigidity. Not going to happen the Rods even being 30mm will still flex. But if i get the top plate and bottom plate to be solid. This will stop that. I have about 80% of it planned out. I would just need funds to do it.

[sharpshooter90]

In order for a single post design to be stable, the post must be huge and greater in mass than the head itself, such as in a big floor mill. When talking about machines of this size, those bench mills on a column or a 3 in 1 machine with a swing around head have a tremendous amount of flex. Because they have no indexing, if you loosen the clamps and raise or lower the head it will not stay in the same location. The quadra lift and the newer bridgemill heads are a good solution to this issue.

[smallblock]

My Quadra lift unit was very rigid and my new Patriot is even more so. The 4 post design is inherently superior to a single post, because you have greater bearing area and more walls to support the weight. Years ago i visited a race shop where they built NASCAR cars and noticed that for the cross member they used 2 pieces of 1 X 2 box tubing welded together. I asked the guy why they went to all that trouble when they could just use a single piece of 2 X 2- his answer was that now they have 4 wall thicknesses on the vertical support rather than just 2.