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View Full Version : Useless degree of freedom?



MotorradMike
09-16-2010, 08:56 AM
I have Busybee's CT054 mill.
In addition to X, Y, and Z, the head tilts either way to cut on an angle.

In addition to that, the head can swivel on the column like on a round column Mill.

I can't see any practical reason for that.
Am I missing something?

MuellerNick
09-16-2010, 09:21 AM
That gives more reach along the X-axis.


Nick

SGW
09-16-2010, 09:41 AM
I have a different mill, but it's the same setup. I've actually used the head swivel feature, once, to drill some holes. I'd agree though -- its practical use seems pretty limited.

mochinist
09-16-2010, 10:11 AM
Limited by your imagination maybe. I have used mine plenty of times for parts that were to tall to sit on top of the table, so you clamp them to the side of the table and swivel the head over where you can now reach your part.

A.K. Boomer
09-16-2010, 10:14 AM
A turret mill is the name for that and my mill has four large bolts with a degree wheel to calibrate,

Like stated it can give more reach on the X axis in one direction and then when put more to the other side and the part is picked back up it can then cover a total overall length that's much more than if just left in the middle.

The other thing it allows for is when the head is thrown down 90 degree's to one side and your using the mill as a lathe it's not only your tramming adjustment but you can utilize it to induce any degree of taper that you want,
So It's kinda like having a built in taper attachment on a lathe.

rkepler
09-16-2010, 11:01 AM
I've had some largish parts that wouldn't mount on the top of the table so I swiveled the head to where I could mount them on the side of the table.

oldtiffie
09-16-2010, 12:29 PM
Here is the machine we are discussing:

http://www.busybeetools.com/product_images/59/1959/CT054_std.jpg

at:
http://www.busybeetools.com/products/KNEE-MILL-WITH-STAND-2HP-220V-CRAFTEX.html

Many turret mills - BP and its clones included - have a similar feature - where the head can swivel left-right about a vertical axis.

whitis
09-16-2010, 01:09 PM
That is a very common feature on knee mills, popularized by bridgeport. It isn't very good for general 5 axis work but it is handy for working on large pieces, horizontal milling, milling the back surface of parts, etc.

Use it in combination with sliding the ram in and out like a radial drill press to drill holes on a large diameter bolt circle, for example on a large annular ring piece that has been divided into sections. Likewise, suppose you want to cut an arc, without CNC. You can do that by swinging the ram while cutting though usually the machine itself doesn't provide a worm gear to advance the cutter so you would require eternal control - using it a bit more like a router than a mill. And there may be just too much slop when the swivel isn't clamped down.

Imagine you have clamped a piece of rectangular bar stock parallel to the table. Now eyeball the left rear top corner and the direction it points. 45 degrees rotated around one axis and 45 degrees around the other. Now you want to drill a hole along that angle. Some combination of the two rotations of the head will let you do it. Not very easily as you have a lot of alignment to do and you can only work on the left side of the table. In a lot of cases it would be more convenient to clamp the work at an angle but that isn't always practical. For 5-axis work, it is very inconvenient having the pivot parts of the two rotational axes located so far apart.

Now, run your table as far forward as possible and as far left as possible and mount a big rotary table on the left end of the table. Pivot the head off to the right. Now you can cut holes and do some other work around the periphery of a very large disk, limited by what can clear the column.

Now, mount a big piece of work on your table as long as the table or even a little bigger - longer than the X axis. Swing the ram to the left and machine the left half, then swing to the right, align with a hole you drilled near the center of the part to reestablish your coordinate system, and machine the right half.

Swing your ram 90 degrees to the left and retract the ram. Now pivot the spindle 90 degees so it is facing you. Raise the knee. Mount the work up on blocks if necessary. Now you can do some machining of the back side and maybe some horizontal miling as well.

Suppose you want to mill some 30 degree angle slots in a piece of work, without CNC. Swing the ram left 45 degrees and move it in and out - this requires a lead screw on the ram or other ways to control the motion which usually isn't provided and must be externally supplied.

On some bridgeport models, you could swing the ram around 180 degrees and use the slotter attachment located on the back end of the ram.

It is a feature that is not necessarily as useful on imitation machines as it was on the "original" and even the original was lacking in features to let you make full use of that feature. Exactly what you can do with it depends on details of the machine geometry that may be someone lacking on a copy that copies the features without actually paying attention to the details that let you use it. Like how high you can raise the knee (all the way to the swivel) and how high the table sticks up from the knee, how far the spindle sticks out from the pivot point relative to the distance from the column to the table, etc Can you slide the ram and rotate the ram independently - i.e. unlock one motion without unlocking the other..

Your machine looks like a poor second cousin to the round ram m-head early bridgeports. They had more ram travel and another swivel on the end of the ram which meant you could swing the ram left 90 degrees and swivel the other swivels as well to put the spindle over the table with the axis of spindle rotation parallel to the Y axis. The nice thing about yours is the weight of the motor balances the weight of the spindle but you don't have as much flexibility. They weighed about 20-25% more than your machine. However those old machines weren't terribly rigid and were low power and weren't good for hogging. Bridgeports and similar knee mills in general trade rigidity for flexibility.
http://www.lathes.co.uk/bridgeport/page15.html

Paul Alciatore
09-16-2010, 02:09 PM
I've had some largish parts that wouldn't mount on the top of the table so I swiveled the head to where I could mount them on the side of the table.

Probably one of the most common uses for this feature. Imagine a 30" long shaft, 1 - 2 inch diameter. And you need to mill a slot or dovetail on the end and drill a couple of holes in it. Not possible ON the table unless you have a right angle attachment for the spindle. But strapped to the side of the table it becomes easy if you can swing the head to one side.

I have a milling table set up for my lathe to do similar work. I could work on the ends of almost any length that will fit in the shop as long as it is under about 5 or 6 inches in width and 3 or 4 in depth and I can find some way of supporting the weight. Like the feature on the mill, it is of somewhat limited use, but can get you past some problems.

Lew Hartswick
09-16-2010, 02:21 PM
I've had some largish parts that wouldn't mount on the top of the table so I swiveled the head to where I could mount them on the side of the table.
As a Matter of fact we just had to do that last week to machine part
of a cast arbor press. ( one of those KITS from Harbor Freight). :-)
...lew...

MotorradMike
09-16-2010, 06:00 PM
Thanks guys:

Unlikely I'll ever use the feature but it's nice to know what it might do.
I'm afraid it will affect tram which is pretty good at present.

Most of the Mill is excellent for my needs. Some things are pretty flaky but they are easy to fix. I've found that this Chinese stuff has the important things quite good enough but some of the less important things aren't quite right.

Examples are:
The knee lead screw skewers whatever is in the drawer if you lower the knee too much.
The top cover open brace is about to break off, I'm in the process of modding that now.