Endmilling direction

[WolfieParticipant @wolfie]

Following through Harold’s book I am now making some T-nuts and I read in that section that once one pass of an endmill has been made (to reduce something in height) you return it back to the start for your next cut.

 

Why? An endmill is symmetrical, it should perform the same whichever direction it goes in??

[WolfieParticipant @wolfie]

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Wolfie, you sould return before your next cut otherwise you will be climb milling in the other direction. This has been discused in one or two threads, but the one below may help you understand the difference

http://www.model-engineer.co.uk/forums/postings.asp?th=44840

 

Regards Nick.

[JasonBModerator @jasonb]

Provided the part is not wider than the cutter dia then you can run back & forth

 

If your work is say 3/4″ wide and you are using a 1/2″ cutter to reduce its height there is a risk of climb cutting if you go both ways. Due to one edge of the cutter cutting into fresh metal in one direction the cutter will be rotating away from the work, in the other direction it will be cutting towards the work and there is a risk of it being drawn into the work which may result in overcutting or at worse a jam up.

 

You are likely to be in this situation making one side of your tee nuts so do as Hrlod says.

 

J

[WolfieParticipant @wolfie]

Sorry yes I should have made it clear that I am talking about cutting something down in height where each pass takes off a complete layer.

 

I know about going against the cut when cutting a shoulder.

[TerrydParticipant @terryd72465]

Hi Wolfie,

 

An end mill should only be used to take off less than half of it’s diameter when using it to cut a ‘layer’ off a face. Otherwise part of it is climb milling and at a certain point in the cut may dig in and cause all sorts of problems, including broken cutters (don’t ask). You may get away with light cuts but it is bad practice. Climb milling can occur with any cuts not just ‘shoulders’ unless you plan your work properly. Think about it.

 

You really must learn the difference between ‘up’ milling and ‘climb’ milling. In the latter the cutter is trying to ‘climb’ onto the job and will pull it into the cutter. Made worse by the backlash in the lead screw which allows the work to be pulled even more and making the problem worse. And then !BanG! or worse.

 

Best regards

 

T

Edited By Terryd on 11/01/2012 21:35:59

[Anonymous]

Hmmmm, if I’m using a cutter to face a surface I always cut in both directions, on alternate passes. I also use a large stepover, usually about 75-80% of the diameter of the cutter. This is true for both manual and CNC milling. Like this: bearing blocks in gunmetal, 20mm slot drill, depth of cut about 2mm, stepover about 16-17mm, cutting both ways:

 

Ah well, summat else I’m doing all wrong.

 

When using a cutter predominately on its side faces then I’m much more cautious about climb milling; only for materials that take a better finish when climb milling, and then only small depths of cut, say less than 20 thou. That’s for manual mills, for CNC anything goes.

Regards,

Andrew

[Ramon WilsonParticipant @ramonwilson3]

Hi Guy’s I think Wolfie means as he has taken a pass across the top of the workpiece why does he have to return to make the next pass.

 

If that is the case Wolfie, as Jason confirms, you don’t . If you are face milling using the full width of the cutter or the cutter is overlapping the work it does not matter which way the cut is applied. Technically you can make the first pass at x deep and then come back making another pass at x deep again. It’s only if the cutter – end mill or slot drill is cutting on the side flutes significantly that the good advice given above regarding climb milling applies.

 

If the work piece is considerably wider than the cutter then you can still move back and forth taking a cut each way providing the depth of cut is not sufficient to pull in on the down cut side(Climb milling) Personally however I would always return and then move over to make the next pass on the finishing cut to acheive the best finish.

 

Hope I’m reading you correctly

 

Regards – Ramon

[David LittlewoodParticipant @davidlittlewood51847]

For facing a wide workpiece you can in appropriate cases save time by working round it – going anticlockwise you will never be climb milling. If surface finish is important it may be best to do the last cut in the rigorous fashion described above though, not least because most small mills do not have power feed on the Y-axis and finish is always better under power.

 

David

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