Pros and cons of climb milling in wood

[Richie]

Hi everyone,

All my previous experience in machining has been with metal cutting, but now I'm working with solid hardwood which is proving to be an altogether different creature.

I was wondering what peoples views are on the pros and cons of climb milling when profiling wood. For instance changes in the direction of grain, keeping the cutter cool, snatching the cutter, pushing the feedrate to the max, getting a tidy breakout etc, etc,... so much to learn, so little time.

Do you prefer climb milling or conventional, and why? Any thoughts appreciated.

Thanks

Richie.

[Tenson]

For hardwood, climb milling I think.

[Jonathan]

Google it?

http://www.cnczone.com/forums/woodworking/38190-climb_conventional_cutting.html

http://www.woodweb.com/knowledge_base/Climb_Cutting_and_Bit_Rotation.html

http://www.woodweb.com/knowledge_base/Climb_Cutting_Versus_Conventional_Cutting.html

[JAZZCNC]

Completely different ballgame to metal and choosing wrong can wreck wood in blink of an eye.!!
I nearly always 99% conventional cut in soft woods and man made boards MDF etc. Hard woods then I rough with Climb and then do a finish pass conventional, this cleans up nice any fuzzy bits.
You have to be carefull and mindfull of the grain and how the woods been cut in some woods and use a bit of common sense to whether the direction choosen will rip and split on breakout.?? It's not rocket science thou and taking a bit of time checking the grain and programing accordingly can save some heartache and fire wood.!!

[Richie]

Thanks for your views,

I have some inch thick oak to profile. Most of the full diameter cutting is going along the grain, and less than half the cutter diameter is cutting across the grain.
I'll do some experimenting and see what works best.

Thanks.

[Tenson]

What do you mean by profiling? You mean like 3D engraving?

[Richie]

It's just a 2D shape cut out of a flat rectangular piece of planed oak. It's got one straight edge which I've pushed up against a location block, then clamp on top and whizz round three remaining sides to produce the profile.

[Ger21]

Generally, conventional cutting will almost always give a better quality cut than climb cutting, but there are exceptions.

The most important factor when cutting wood is preventing tearout.

To avoid tearout with conventional cutting, you need to make sure there is always some wood on both sides of the bit. Say you use a 6mm bit to remove 3mm from the edge of the board. With conventional cutting, the tool is pulling the wood towards the edge, which will result in splintering. So any time I cut rebates, I always climb cut. It gets more complicated when going across the grain, though, as both climb and convention cuts can result in tearout at the end of the part. If possible, I use the method in the third pic for crossgrain rebates.

For best results when cutting a proile, conventional cut and always have more material than the tool diameter outside the profile to eliminate tearout. Attempting to trim 3 sides of a board will almost alway result in one chipped corner, whether climb or conventional cutting. Climb cutting will chip at the start of the cut, and conventional at the end of the cut.

[Richie]

Thanks for some useful tips.

I've just tried cutting a few shapes both conventional and climb cutting.

Climb cutting seems easier on the ear, less vibration, but it tries to pull the wood into the cutter when going across the the grain. I beefed up my clamping a bit to fix that.

There was a bit of fuzziness along the grain, but I can live with that, and it seems to have improved after the cutter had done a few hundred pieces, not sure why that should be (I'm using solid carbide, compression spiral, two flutes).

I'm leading into the start of the profile with a radius, and also breaking out with a radius, to blend with a straight edge. That eliminated the tearing problem at the start of the cut with climb cutting, but it didn't with conventional cutting when breaking out at the end of the cut.

So after some experimenting I've chosen climb cut.

It's down to trial and error I know, but your insights helped inform some of my guesswork.

Thanks again.

[Ger21]

Climb cutting seems easier on the ear, less vibration, but it tries to pull the wood into the cutter when going across the the grain.

Are you sure you were climb cutting? Climb cutting will push the board away from the tool, not pull it towards it.

[HiltonSteve]

Are you sure you were climb cutting? Climb cutting will push the board away from the tool, not pull it towards it.

Gerry,

In my experience climb milling always wants to drag the material, table etc towards the cutter.... get an old milling machine with a bit of backlash, put a decent size cutter in and put a good size cut on. Watch what happens when you try to climb mill... you end up tightening the bed locking screws to stop it from jerking towards the cutter. When toolmaking and using aluminium I always used to rough the sides of plates by conventional milling as you could rip the material off quick but left a rough finish, then leave 0.5mm or so on for climb mill finishing which left a nice smooth finish.

Nice screenset by the way....



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[Ger21]

If there is play in the machine, then climb cutting can cause a sudden jerk, and climb cutting will self feed. However, the cutter is still pushing the work away. Looking at your picture, the cutter enters the work almost perpendicular. The forces are pushing the tool away, but since it has nowhere to go, it appears to grab. If the cutter was actually pulling the work toward it, it would dig in. Instead, it rides along the edge.

Try this. Program two identically sized squares, and cut one with a conventional cut, and one with a climb cut. The climb cut will always be slightly larger, because the bit is pushing away from the material. With the conventional cut, the bit is pulling into the material, resulting in a smaller part. A lot of shopbot users use this to their advantage when cutting cabinet parts. They do a "rough" climb cut sluightly oversize, then finish with a conventional cut. By removing a very small amount with the conventional cut, it minimizes the effect of the bit being pulled into the parts.

[JAZZCNC]

A lot of shopbot users use this to their advantage when cutting cabinet parts. They do a "rough" climb cut sluightly oversize, then finish with a conventional cut. By removing a very small amount with the conventional cut, it minimizes the effect of the bit being pulled into the parts.

Thats exactly what and why I do it this way, the shop bot forum is where I learnt it also. . . It also removes the burr on end grain nicely.

[HiltonSteve]

Think that we are on a different wavelength slightly, i am not talking about the cutter pushing off as you describe I am trying to say that the effect of climb milling pulls the work towards (or across) the cutter.

In the 2 sketch's below I have shown worse case scenario....


The sketch shows the two operators standing next to the machine, Monkey B has bigger balls than Monkey A and decides to stand at the end of the table in the 'danger zone'. Monkey A puts a 4mm cut on a 50mm x 20mm piece of aluminium bar and starts a climb milling cut.

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Monkey A notices the clamps are not very tight but does not stand back or stop the feed, Monkey B can not see this from where he is standing and moves closer to see what the noise is. Job comes loose and gets pushed towards him with enough force to embed the job in his chest. Monkey A has no injuries and calls for an ambulance.

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Monkey C says, "can't believe that we are having a discussion about this"..... Lights up a fag...


Best get on with some work.....

[Ger21]

e I am trying to say that the effect of climb milling pulls the work towards (or across) the cutter.


The word "towards" is the key here. As you clarified, it does not pull the work towards the bit, but rather along it. I was just trying to say that it doesn't pull into the cutter. If the parts were not clamped down, climb cutting would simply push the work away from the bit, and not throw it out the end of the machine. In order to be thrown, it's position must be constrained in the perpendicular direction, so that the cutter can actually grab the workpiece. If not constrained, it won't be thrown, and monkey B's larger balls would remain intact. :joyous:

At my day job, we have a large router with two 25HP vacuum pumps to hold sheet goods down. When a part moves a little while climb cutting, it's simply pushed out of the way. If it moves while conventional cutting, the part is pulled into the cutter and typically gets cut in half.

[HiltonSteve]

The word "towards" is the key here. As you clarified, it does not pull the work towards the bit, but rather along it. I was just trying to say that it doesn't pull into the cutter. If the parts were not clamped down, climb cutting would simply push the work away from the bit, and not throw it out the end of the machine. In order to be thrown, it's position must be constrained in the perpendicular direction, so that the cutter can actually grab the workpiece. If not constrained, it won't be thrown, and monkey B's larger balls would remain intact. :joyous:
.

Totally agree....

Thing is, I was Monkey B! the job did not embed itself in my chest just hit me and made me jump. Still bloody hurt but I suppose thats what happens when trying to run 3 machines and answer the phone at the same time..... My mate found it funny though!


At my day job, we have a large router with two 25HP vacuum pumps to hold sheet goods down. When a part moves a little while climb cutting, it's simply pushed out of the way. If it moves while conventional cutting, the part is pulled into the cutter and typically gets cut in half.

Not enough experience with cutting wood but what your saying does make sense, with steel you tend to clamp things down the best that you can so they dont move at all, if they do move then it starts costing you money!