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View Full Version : How/when/why would you....



QSIMDO
07-27-2006, 07:41 PM
..use a end mill with a left hand twist?

I tried one with the machine in reverse and it cuts just fine but I'd hate to insult the manufacturer of my milling machine by ignoring the switch position they marked "FORWARD".

Significant cheek on my part.

BobWarfield
07-27-2006, 08:02 PM
Well first, it's going to affect whether you are conventional or climb cutting depending on your direction. It may be more convenient, therefore, to be able to reverse which style cutting you are doing while still allowing the travel in the same direction, simply by switching the end mill and the spindle rotation.

Second, let's suppose you have an application to cut mirrored parts. This is common in aerospace and a lot of other cases. It again might be convenient to be able to have the end mill's behavior "mirror" as well.

Some people also feel they lift the parts less for some applications. The trouble here is going to be where the chips go and what impact recutting has on the final finish.

Best,

BW

Tin Falcon
07-27-2006, 08:08 PM
If memory serves me RH twist tends to pull up on the work LH pushes down also RH can dig into the work. LH refers to the twist not the cutting direction sounds like you have a LH twist with a RH cutting direction.
regards Tin

SGW
07-27-2006, 08:24 PM
Left-hand twist, but rigiht-hand cut? Used for profiling thin work, because it tends to push the work down, not lift it up. However, you need chip clearance space at the bottom of the end mill because the chips are forced downward, and if there's no place for the chips to go they'll clog up and you'll run a good chance of breaking the end mill.

QSIMDO
07-27-2006, 08:31 PM
Nope, these are left hand twist, left hand cut.

Pulls the chips up and pulls up on the work just as if the machine was in forward but, naturally these only cut with the switch in reverse.

I know some screw machine operations use left hand drills but this has got me stumped.

Many tool suppliers list them but you think with an explanation?

Naah!

Mcgyver
07-27-2006, 08:37 PM
they're made for use in Australia

GRH
07-27-2006, 08:55 PM
I did a job in Aluminum using a 1/2" ball end mill to cut a slot 1/2" wide with a 1/4"radius in the bottom, one side of the slot(from the center in the bottom was really nice finish the other side rough as hell, my only explanation was one side conventional milling and the other side climb milling????????????

Graeme

JCHannum
07-27-2006, 09:08 PM
I did a job in Aluminum using a 1/2" ball end mill to cut a slot 1/2" wide with a 1/4"radius in the bottom, one side of the slot(from the center in the bottom was really nice finish the other side rough as hell, my only explanation was one side conventional milling and the other side climb milling????????????

Graeme

The short answer is yes. Ball mills pose a special problem as the center is not cutting at all due to the relative speed of the cutter. This can cause some funny problems.

The other problem is that some aluminum alloys tend to produce sticky swarf that welds to one side of the slot leaving a gummy mess. A good cutting lubricant like WD40 will help some as will a chip brush or air blast to remove the chips from the cut.

When using a ball mill, the best finish will be obtained by making one pass, and moving the part over a tad and making a second pass feeding in the opposite direction on the ragged side of the cut.

sch
07-27-2006, 09:21 PM
A local outlet that sells 'stuff' that is derived mostly from the Lockheed plant in Atlanta has really nice endmills, some of which are LH. Unfortunately most of their cutting tools are 1" and up, sometimes way up, in size, but the 1" endmill works nicely for doing edges with the mill running in reverse. The cutting edge is about 3.5" long. One thing I noticed, all of the hundreds of endmills had radiused ends. Lockheed wants filleted cuts.
Steve

alcova
07-27-2006, 09:44 PM
One reason for the fillet is, sharp corners can cause stress fractures, not something you would want in a aircraft part.

Walt

japcas
07-27-2006, 09:49 PM
One of the thing the left hand rotation end mills can be used for is when hexing nuts on a cnc mill. Screw them down through a plate that is tapped for the bolt you are making and then mill around the head. A pipe wrench can be used to tighten the nut before the flats are cut. It keeps the bolt from trying to unscrew while being machined. That is if it is a right hand thread anyway. ;)

miker
07-28-2006, 12:03 AM
http://img.photobucket.com/albums/v448/mikerr/Scan10100.jpg

IOWOLF
07-28-2006, 06:06 AM
OK,As for reverse on a the mill, forward and reverse is academic,Think about direct drive and back gear,on my mill they are different directions.

machinist1964
07-28-2006, 07:34 AM
Some companies like GM, Ford, GE etc use specially built machines with several spindles all running at the same time. I have seen applications at GM that are used to clean up a casting on an engine block. The block actually travels between the two cutters. One cutter is running clockwise and the other runs counterclockwise, so one is RH spiral, RH cut, the other is LH spiral, LH cut.

Mcgyver
07-28-2006, 08:11 AM
http://img.photobucket.com/albums/v448/mikerr/Scan10100.jpg

Miker no offence mate, figured everything must spiral in the opposite direction as here

Wirecutter
07-28-2006, 10:28 AM
Ha ha. Some of my first (and most handy) endmills came from an assortment I purchased used off of FleaBay. It was a good deal - some were sharp, some not, but it was a good assortment and a great thing for a beginner. The first time I chucked up a LH mill and tried to use it, I couldn't figure out why it wasn't cutting and kept gumming up. Hell, it's only aluminum - what's going on here? Doh! Well at least I figured out what was going on before I broke something. :D

-Mark

Scishopguy
07-28-2006, 12:08 PM
One of the places I worked did a lot of vacuforming of pvc sheets, making aircraft seat backs and arm rests. They had several "pin routers for cutting the parts from the sheets, once they were clamped into cutting jigs. They used a two flute, half inch, LH spiral end mill because it pushed the chip down and out of the way of the jig. The only trouble with them was that they were a tapered shank and could not be used in a regular mill without a special holder or a trip to the spin jig on the surface grinder.

Jim (KB4IVH)