Convensional vs climb milling

Hi,

I am new to milling and want to cut a 60mm hole out of a 1.5mm plate using a small end mill and a rotary table, can someone tell me which way should I rotate the table.

I am guessing at anti-clockwise when viewed from above as the metal on the right side of the end mill is travelling ever so slightly faster than on the left side of the end mill which whilst effectively climbing is always lagging behind the right in speed.

Edited By C J on 10/10/2017 22:50:05

Edited By C J on 10/10/2017 22:51:04

I doubt it makes much difference. Ease of turning the table at a constant rate would likely be more imortant.

I hadn't thought of that but I splashed out on a 6" Yusa table with a very nice action.

Edited By C J on 10/10/2017 23:24:45

As Bogs says backlash is the enemy of climb milling. Ball screws do a good job of minimising backlash but you can also have anti backlash nuts or hydraulic eliminators. A balls screw conversion can be useful even if you do not intend to convert to CNC but is quite a bit to spend just to climb mill. Mechanical elimination by nuts tends to wear the screw and as wear tends not to be even along a leadscrew it will not have a constant performance, more complex nuts can compensate but wear will still be an issue. Hydraulic eliminators are not really going to be found on hobby machines. I suspect we all snug the locks down and hope a sneaky light cut will not overcome the drag but get it wrong and you will wonder what the bang was. I have seen apprentices learn the hard way and drag the job out of a vice on quite a powerful mill. Maintaining the buttock clench can be quite tiring aswell if hand feeding.

Mike

Hi CJ

The direction which you turn the rotary table depends on which side you are cutting your work.

Which ever side it is I would suggest that you use conventional milling so the work is pushing agains the cutter. The rotary table will have an amount of backlash in the worm and gear and will the cutter will try and turn the table and cause vibration when climb milling unless it is adjusted up tightly with brakes on. But hard to turn like this. Even with conventional milling, I would slightly clamp the table with the brake levers.

The teeth on the crown gear in some of the rotary tables are faily small and will not withstand hard knocks, which Is how I broke the teeth on my 6" Yuasa RT.

Paul

Hi,

One situation where it is definitely better to climb mill is when cutting gears in plastic such as acetal. If you cut the teeth using conventional milling you end up with a hairy finish on both the top of the teeth where the cutter exits, and the side of the gear the cutter exits on. If you climb mill, the hairiness is confined only to the side the cutter exits as the cutter enters the top of the teeth. It's easy to remove the hairiness on the side of the gear using a razor blade but very difficult to trim the top of each gear individually.

Regards,

Alan

Paul,

I am not going to cut from a side as such but cutting a continuously curved slot to make a large hole in the plate, or that’s the theory anyway.

My experience has often been that the middle diagram showing cutter deflection doesn't show what really appears to happen.

You can run a 'final' counterfeed cut across a surface with the flutes of an endmill or slotdrill, and then find when you return across the same surface with a climb feed that you're still taking a spring cut.

Sometimes you can take advantage of this to get a good finish, although probably more often you have to add a thou or two to the cut to get out the last little digs from the previous one.

C J, cut out about 59mm diameter first then clean up the edge to 60mm diameter. To finish to size turn the plate anticlockwise viewed from above to cut conventionally for the reasons given by Paul earlier. When the centre is close to coming free take care as it can be flicked into the tool or out towards your hand.

Martin C

Edited By Martin Connelly on 15/10/2017 10:21:35