questions about 4 axis machines

[DWAS]

Hi all. My work would like to purchase a CNC and I am being looked at as the one to chose what we need. I am thinking of a 4 axis machine for the type of work we do would be good, although A 3 would cut it..., and I don't think a 5 is cost affective. What i'm wondering is really what to look for. Can all 4 axis machines do simultaneous movements on all 4 axises at the same time? I have used the Haas controllers a little, but primarily the centroid and a fanuc. Can any controller go on any machine. This end of the machining world is very new to me( purchasing a setting up I mean) I am used to just walking up to a machine and using it. With a good understanding of 3 axis programming, how much more of a leap is it to utilize a 4th axis? If you have any good links could you please post them.

Thanks for any answers in advance

[HuFlungDung]

If your Haas has been prewired for the 4th axis, then yes, it can do simultaneous moves on all 4 axis. The indexer does not require a controller if your mill is wired.

If you have to use an indexer with an external control box, then I think it gets quite a bit more complicated to run simultaneous movements involving the 4th axis, but not having done it, I don't know for sure.

Having said that, there are probably not many times when you would actually be contouring with 4 axis going all at once. I cannot say I have had a need to do so. This is because typically, the tool needs to stay above the centerline of the indexer axis, while said axis is under rotation. This means that the Y axis would not be moving.

Perhaps a 4 axis rapid motion would be the most common simultaneous movement.

You need to watch the type of servomotor used in the indexer. There are brushed and brushless models, and they are not interchangeable on the same mill hardware.

Quite often, using an indexer is a simple matter of index, lock, do some machining, release, index, lock, do some more machining. This is the most elementary programming and is not that difficult to do manually.

Actual rotation of the 4th during machining can get quite a bit more involved, and a CAM program is a big help, as it can do things like interpolate arcs that involve XA from G02/G03 into line segments that the mill can actually execute.

Some complex looking things like helical milling can also be done relatively simply with one command line repeated many times over. It all depends what you intend to do with it.

I use OneCNC and I think their 4th axis implementation is easy to learn and use, plus it simulates the part appearance after running the program. This gives a lot of confidence in using the 4th axis to full potential.

[DWAS]

thanks for the reply. from the pictures that i have seen of 4 axis machines, can you still use a kurt vise on the "table" of the 4th axis? it looks small compaired to the table of a 3 axis machine. Are there machines that the entire table rotates? Is the top of the work piece typicaly at the centerline of the axis of rotation? Also, should i move this thread and if so how? Thanks

[HuFlungDung]

Mounting a vise on the platter of a 4th axis is possible, if you buy one that is large enough. But it might be unusual to do so, because normally, the 4th axis would be set on the machine table with its axis parallel to the X travel, and not face up, parallel to the Z travel. So usually a chuck is mounted on the 4th axis to hold stuff.

I'm not sure what you mean by "compared to a 3 axis machine" because we are not referring to the same sort of thing at all. The table of a 3 axis machine is on a linear axis, not rotary. Are you confusing 4th axis mounted on a 5 axis trunnion?

[DWAS]

from the pictures i have seen the 4th axis is bolted/a part of the table and the 4th axis would run along the x. I thought a 4th axis was simply the entire table rotating around the x axis. If i had a block that was 4" tall and 6" x 6" and wanted to do machining on multiple sides, I was envisioning clamping it in a vise and having 3 sides open to machining (the 4th side being face down on the vise) so how would i do this on a 4 axis machine? Is it a matter of using a tailstock and making a "table" for the vise to bolt to?
Would the 4th axis of a machine be comparable to using a rotary table on the bed? Would there be a downside to using a rotary table instead of a 4 axis machine? Can the controller comunicate with a rotary table?

[Matt@RFR]

We are fighting nomenclature here. I think what you are calling a 4 axis machine is in reality a horizontal mill (HMC). Do yourself a favor and go to youtube and look for videos of 4 axis machining and horizontal machining centers. I think that will clear things up. If you still have questions after understanding the nomenclature, feel free to come back. Until then, we are just spinning our wheels.

[Geof]

Here are some pictures of typical 4 axis setups when the fourth axis is just used for indexing the part into position.

Attaching a vise to the face of the fourth axis is possible but probably it would not be possible to rotate the axis a full 360 degrees because a vise is normally too long; the centerline of the fourth axis shown is only 6" above the machine table.

Fastening a three, four or six jaw chuck to the face of the fourth axis can be very useful for gripping all manner of shapes.

http://www.cnczone.com/forums/attach...4&d=1144814522

http://www.cnczone.com/forums/attach...2&d=1151711731

http://www.cnczone.com/forums/attach...0&d=1180581778

http://www.cnczone.com/forums/attach...8&d=1180581778

[DWAS]

in the attached picture is what i was horribly trying to describe. Could you take a plate and mount it to the 4th axis unit and have a dead center on the other side and mount a vise in the center of this plate?

In the pic, everything associated with the 4th axis, the "headstock" if you will, and "tailstock" (what are the technical names for these?) can these be removed/moved out of the way to mount pieces to the work table? Can the distance between them be changed?

When i was referring to a rotary table instead i mean the unit on the right side of the picture as a rotary table and was wondering the difference between using what is seen in the picture and a rotary table. Pros and cons if even possible. can controllers make simultaneous movements with a machine axis and a rotary table?

What is the max rpm of the 4th axis units? just out of curiosity.


Sorry for confusion and re asking questions I just don't want them to be overlooked.

Thanks

[Geof]

So many questions.

Headstock and tailstock is good enough nomeclature although your 'headstock' is the rotary table, also referred to as the 4th axis or A axis when it is oriented as shown parallel to the X axis..

Yes you could attach a plate between the two and mount a vise crossways or longitudinally, either approach has its problems. Crossways means the vise is probably going to limit the rotation as I mentioned previously, longitudinally means you have difficulty clamping the vise. Also you have the problem of losing Z travel because everything finished up well above the machine table.

As you can see from my pictures the platform between the rotary head and the tail bearing is dropped down; this is to maximize Z space.

Yes the distance between the two can be changed. My pictures show the setup I have on a Haas Super MiniMill and the rotary head is mounted on a baseplate cantilivered off the machine table on the right so that the rotary platform occupies the entire X travel. This also allows me to mount a pair of Kurt vises between them so I can change from vise to rotary quickly just by removing the tailstock and rotary platform. However, with the vises in place I cannot rotate the platform through 360 degrees when large parts are attached because the vises interfere.

You can mount the rotary table flat on its back so its axis is parallel to the Z axis of the machine but there is not much utility in this as it does not really give any extra capabilities.

Yes the controller can run all four, X, T, Z, A axes simultaneously but as mentioned normally Y is left stationary.

With rotary tables it is not a case of rpm but more like mpr, they rotate slowly although haas does have versions that can rotate a few revolutions per minute. Bear in mind that when the A axis is rotating the feed rate at the cutter depends on the radial distance from the centerline of the rotary table out to the point of contact. If this distance is 4" then one revolution per minute is a feed of 24" per minute.

[DWAS]

so a 4 axis machine is literally just a 3 axis machine with a rotary table on it? HWat is the difference between buying a machine, say, from Haas as a 4 axis vs. a Haas 3 axis and then buying a rotary table?

[Matt@RFR]

Originally Posted by DWAS so a 4 axis machine is literally just a 3 axis machine with a rotary table on it?

Concerning VMC's, that's exactly correct. To put a 4th axis rotary table on a 3 axis VMC, you buy the rotary table, have the machine wired for the 4th axis (or buy a new/used one allready wired) and you're off and running.

[Donkey Hotey]

I saw your other threads. You don't need a 4th axis. You probably don't need the side-mount tool changer either. It's up to you. If you're just making occasional molds, you're trying to keep the cost down and you're going to be the guy learning the machine, I'd make a strong argument for one of the following:

• Go for the extended Y-travel option. It'll buy you another 4" of Y (20 instead of 16"). That will translate into a larger work envelope for unknown future work. The downside to this option is that the longer overhang might bounce a bit more and leave machining marks (per other threads posted on here).
• Try to move up to a VF-3 or VF-4 but, with the Umbrella tool changer. The additional Z height will somewhat offset the penalty of the tools hanging in the workspace. You also gain the benefit of the next larger family of casting (more rigid).

As Geof pointed out to me a long time ago, the side-mount tool-changer isn't exactly space-neutral. The umbrella always has the tools hanging down but, that's as low as they go. The side-mount has to pull the tool down out of the spindle, then swing it across the workspace as it swaps.

Oh yeah:
DO NOT CONSIDER ANY MACHINE WITHOUT THE RENISHAW PROBING OPTION!