Helical engagement question

[amishmafia00]

Hello,
I have a boss5 and I am trying to use helical engagement. I am wondering if it matters if i use climb milling or conventional milling direction? looking at one failed attempt due to spindle coming out of gear it seems like conventional may be better.

Thank you!

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[Jim Dawson]

Climb milling actually puts less load on the system because there is less rubbing of the cutter edge. As long as the machine has zero to reasonably small backlash climb milling is prefered. I use helical or tangential engagement and avoid straight plunging where possible. Where a straight plunge is required, then I drill a pilot hole when possible.

[amishmafia00]

I know climb milling is best under "normal" circumstances but I wasn't sure if it would have the same advantages when cutting with full radial engagement. I found some recommendations to use a helix diameter at least 110-120% of cutter diameter. Doing this will leave a small cylinder of material in the center of the hole. I am concerned that using climb milling could cause this piece to be pulled into the cut as the cutter begins to cut through the back side of the material.

Thanks!

[Jim Dawson]

I normally use less than 100% to eliminate that possibility. Depending on material and conditions 1 to 10 degree helix.

[amishmafia00]

I'm going to post my experience and thoughts here so that hopefully it will help someone else.

The material I am working with turns out to be AR400. on the first and second holes I used a helix diameter less than the cutter diameter (3/4) 3 degree helix angle and climb milling. I found that the "skin" that formed as I got close to breaking through tends to peel up and get pulled into the cut. After the second hole I found that I had 2 chipped edges. On the third hole I tried a helix diameter of 120% of cutter diameter figuring that the weight of the island in the middle may help pull the skin down and away from the cut. The best I could tell is the island got knocked off before it had any real chance to do anything. I am going to try my helical engagement using conventional milling hoping that it will keep the skin from getting pulled into the cut. I am wondering if i should also go with more helix angle. My 3 degrees equals out to a .125 depth of cut. I am just starting to get into this and I'm not too sure where this is on the heavy/light cut scale for my machine.

Another thought. normal climb milling (counter clockwise tool path) during helical engagement where there is a 100% radial engagement and helix diameter less than cutter diameter seems to break the rules as I understand them. If I understand correctly climb milling is supposed have the cutter creating a chip that is thick to thin. In this case isn't it the opposite? Wouldn't the beginning of the cut have half the cut depth because it has already been partially milled down by the cutter ? If I am right the only way to correct that is either to have a helix diameter larger than the cutter or have a clockwise tool path (assuming right hand cutter)

[deadlykitten]

hy mafia, i would like to help you, but onestly i don't understand this : normal climb milling (counter clockwise tool path) during helical engagement where there is a 100% radial engagement and helix diameter less than cutter diameter

i imagine a o14 endmill, cutting a o20 diameter without drilling before; the center of the tool describes a helix with o6diameter and some pitch

also, when you say 100%radial engagement, i imagine ae=tool_dia=14; to keep the ae=14, it would mean that the helix diameter is also 14, and the final hole is o28=tool_dia*2

i am confused ...

also you mentioned some "rules/recomandation" for helix ... share them

[amishmafia00]

The "Helical machining guidebook" recommends a minimum helix diameter of 110-120% of cutter diameter. What I probably should have said was where helix diameter is <= cutter diameter. I think it is very hard to explain what I am trying to say. If you were to create a helical toolpath where the helix diameter is less than the cutter diameter and stop it at some point after it has made a full revolution. I believe the cut depth closest to the center of the helix would be less than at the outside of the hole

I was doing a different part last night (mild steel) with much smaller holes and using a helix to make holes larger than the cutter. The first 4 holes I used climb milling and even though the holes were too small for me to see completely I could hear them catch the last little bit of material as it curled up right before it milled the last little bit away. The last 2 holes I used conventional milling. I didn't hear any material getting caught at the end of the cut, There is less of a burr at the top of the hole, and surface finish seems to be a little better.

[deadlykitten]

ok ok ; you wish for some details about climb and conventional milling, especially when a helix is there; so far so cool

you also have notice some difference between those 2, when you cut same hole... let's start from here, from those 4 holes from "last night"

please share :
... tool : dia, teeth, straigth or helix flute ? rpm + feed/revo; put a photo if possible
... is this a through hole ?
... 1st helix operation : helix dia, output hole dia, pitch, conv or climb
... 2nd helix operation : same as above
...... and so on if possible, make a photo with the conv_hole and with the climb_hole, so us to see what you see

do you use a drill before milling ? or do you mill direclty ?

i can not imagine exaclty how you cut it, but if you share dimensions and the specs, maybe it will help to have a clue about those details that you are asking for

pls don't get me wrong, but do you wish for a nice photo with miss world 2018, or do you wish for me to describe it for you ? kindly