Climb Milling

The only factor against climb milling is the existence of backlash in the table drive, the use of ballscrews usually solves this at a stroke but other solutions are available, anti backlash nuts can be spring loaded or hydraulically loaded to eliminate any lost motion, I even worked on an NC mill that used hydraulic rams to move the axes. Unfortunately serious backlash solutions are not often fitted on home type equipment, my humble VMC has a crude pinch screw to tighten the nut but any wear in the screw will soon result in tight or loose spots. I often do light climb milling for a finish cut and adopt Davids suggestion of using the locks to provide more resistance to the axis being dragged by the cutter but this relys on having some feel for the cutting forces versus the table drag. Backlash elimination tends to wear the screw but converting to ballscrews could be done even if CNC is not the final goal but costs a bit just to eliminate backlash. If backlash did not exist I think climb milling would be the mode of choice as all the theory is in favour of it.

Mike

Exackertaly!

Neil

I was hoping you would all rush out and buy a paper copy!

Right click and view image if it's a bit small.

Someone has shared a Sandvik document with me that details why cutters last much longer when climb milling -

Conventional cutting gives chips that start thin and end thick, climb milling makes chips that start thick and end thin. The thickness on entry doesn't matter as the cutter is in compression but the shock of reaching the end of a thick chip causes rapid erosion of the cutting edge. Sandvik have the photos to prove it and the effect although worst for carbide also applies to hard metal cutters as well.

I had never realised that climb milling was better for cutters and always assumed it was a bit worse!

Neil

It certainly may start thick when the cutter engages Neil, much thicker than intended.

Sounds to me like Sandvik diidn't have any feed on as that will always tend to make the end thick.

John

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Either the spindle is running in reverse or the photo has been flipped horizontally. You can best see the orientation of the teeth at top left.

Phil

The photo hasn't been flipped, in the original you can see the headstock of the lathe in the background (it's on an old lathe with a milling attachment).

The end will always have approaching 'zero' thickness if climb milling (not sure where the arrow heads went - clockwise cutter moving right to left) ...

Neil

Can't say I've ever heard the reason for climb milling to be at the chip exit, but I'm not going to gainsay the Sandvik paper. Another reason given for not using conventional milling is that at the start of the cut, where the depth of cut is very thin, the cutter doesn't actually cut. What happens is that the cutter deflects slightly and rubs the cutting edge on the work until the forces build up and the cutting edge eventually penetrates the work. The rubbing does the cutting edge no good at all, and for those materials that work harden creates a very hard thin layer, which makes it more difficult on the next pass and so on. That information also came from a Sandvik paper.

On the CNC mill I normally used mixed milling for roughing and make the final profile pass climb milling. On the vertical manual mill I use both methods interchangeably. As Murray says once your over about 60% radial cut depth it makes no difference. For small radial depths of cut I normally use a bit less depth for climb milling. Here's an example:

The cutter is 10mm three flute carbide cutting full depth (20mm) per pass. Conventional milling was with a 1mm doc and climb milling was with a 0.5mm doc. No way I'm winding that lot back just to avoid climb milling. The Bridgeport has oodles of backlash, about 15 thou, so if needed I do add a little drag with the table lock. However, I have also found when the cutter does grab It has never broken, at least not so far. Which just goes to show that we're probably pussyfooting around with small feedrates.

I do not climb mill on the horizontal mill, despite the fact that it has a proper backlash adjuster, although it doesn't seem to work. Given that the table probably weighs 400+lbs I'm disinclined to take it off to see why.

One material where climb milling most definitely doesn't result in a better finish is plastic.

I always use keys when horizontal milling, irrespective of the type of cutter. I cut under power feed so in the event of a jam I'm not going to able to knock the power off quickly anyway.

Nobody seems to have mentioned a rather more fundamental problem with set up shown. The slitting saw is fine tooth, but is cutting a thick piece of material. That is just asking for the gullets to fill, jam the cutter and bang, a shattered cutter. Much better to use a coarse tooth slitting saw that is designed to take deep depths of cut.

For the record I am not offering to write an article; much too controversial.

Andrew

The rational I read advocating it was largely down to efficiency - less HP for bigger cuts / more rapid metal removal. I may be able to find it. Not sure, some books had to go some years ago.

One interesting aspect that I have mentioned before is that it's possible to make a lathe tool self feed. Normally it would be ground to stop short of that for obvious reasons.

I've had loads of papers thrown at me so always start of on the basis that they may be misleading and may contain no useful information at all. They often are like that - both aspects.

John

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With the new rodless pneumatic cylinders that are available today,they should be good enough to have on the axis to eliminate backlash , by preloading an axis with X amount of constant force. It is something that I intend to add to a machine when I get myself motivated to look into it further. Then there will not be any backlash apart from forces above the preloaded pressure. A friend has already done this to the X axis on his lathe. Works real well.

Neil

Andrew,

Not a short piece of Al bar either, I suppose you could always open the garage door!

0.015" backlash, you must have very knackered leadscrew nuts, with all the adjustment taken out!!!!!!

Gentlemen,

I've enjoyed reading this thread as it contradicts what I was taught as an apprentice, we were taught that we should "never" climb mill as it was considered an unsafe way to mill and we could be in trouble if we were caught doing it, so forty years on I dont do it.

Martin P

I'm not sure if Neil can put the Sandvik document up for people to download, however if you PM me Ill email it to you, like I said to Neil its really aimed at CNC users but is very relevant to manual mills, once you have read it you will understand much better how a cutter is influenced by step over etc, its sometimes counter-intuitive, although retired I occasionally make prototype injection mould tools at home, I also do some machining on site for a large plastics company, this entails machining a lot of P20, this article was given to me by a tool rep and it helped no end at increasing tool life, and by a surprising amount, the main point of tool damage is as the cutter exits the job, with conventional milling as the tool exits the job the chip is at its thickest and is unsupported, this allows the chip to bend causing a compressive load and so breaks the edge, with climb milling the opposite happens.

Shaun  

Edited By Involute Curve on 08/10/2015 10:56:49

Actually 4 stacked lengths of nominally 3/16" thick hot rolled steel. Careful examination will show a 'step' near the lefthand table clamp, as the table travel isn't sufficient to machine the total length in one pass. The carbide cutter was retired after use, but speeds and feeds were such that it was running dull red.

Having just been using the Bridgeport to make some copper busbars I 'measured' the backlash, rather than try and remember. Backlash was estimated by turning the handle one way until there was movement, zero the DRO and then move the handle the other way until the DRO changed. Results were X axis 0.7mm and Y axis 0.9mm. They'd probably come down a bit with some TLC, but basically the mill is pretty worn. Can't say it worries me, and I'm happy with the work that it produces.

Andrew

Edited By Andrew Johnston on 08/10/2015 11:19:14

Yes - and drill bits too. If you try machining brass with a tool / drill that is ground for aluminium or steel (lots of top rake when ideally it would have none) you need to don your rubber pants. Once it grabs hold, it pulls itself in and you have one of those moments we all know and love. It's even more exciting if you have lots of backlash so it's almost uncontrolled.

I use my slitting saws in an arbour with a half inch parallel shank that I mount in an ER collet on the mill. Consequently I tend to put the saw in the arbour first, usually holding it up side down in the vice. It's pot luck whether I get the saw in the correct orientation but since I put a VFD drive on the mill I can easily reverse the direction

By chance, I think I got it right in this photo. As an aside, it clearly demonstrates the result of releasing the locked in forces in BMS.

Cheers,

Rod

I was taught to avoid rather than never. Never makes some sense really especially on horizontal millers that can remove considerable amounts of metal in one go. Try climb milling with a setting like that. The miller should cope but the finish on the work may suffer and if not clamped down firmly things will move. Similar when vertical cutters are taking their max cut and feed rate. The need usually only crops up with end mill type cutters are used anyway.

John

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There can be advantages using climb milling on a conventional horizontal mill . One is to obtain a higher finish on a light finishing cut and another is to saw or side face thin sheet material, laid flat on the table, that otherwise would "bounce" with the cutting action unless extensively clamped down. The table lock does need to be applied enough to prevent "grab". Colin

long ago I was taught not climb mill unless the machine was designed to do it,no cnc in those days,and lightly applying the table lock was frowned by management, The books on milling by Cincinnati and Brown & sharp barely mentioned climb milling, the pages of pictures of horizontal millers with gangs of big cutters are using conventional milling. My Adcock and Shipley has a lever mounted just below the table,to engage climb milling but It does not work the levers loose,somethings broken before I had it and at 74 I don't feel like taking the table off,I don't need it but it would be interesting as I have never tried climb milling on a horizontal machine. The change over to higher speed cnc machines which tend to go very fast with smaller cutters and driven by ball screws to eliminate backlash.I do not know how long a ball screw would last if it was fitted to a Big horizontal with a gang of side and face cutters plus a roller mill,. It is surprising how a relatively small end mill say 3/4 dia can grab a 50 inch table ,so I avoid climb milling on either of my machines, though the finish on aluminium can be improved by climb milling,using the side of an end mill and taking off a few thou. I was also taught to mount thin slitting saws without a key,management considered it better to loose grip rather than shatter a saw particularly if it was a large 6 in dia one, the victoria horizontal mill at our works had a 1/16 th slot across the long horizontal arbour keyway where some one forgot to remove the key, the saw jammed and cut the neat slot,it was a good reminder to remove the key.

Nigel,

"the victoria horizontal mill at our works had a 1/16 th slot across the long horizontal arbour keyway"

That was the mode of failure I would have anticipated (as per my comments earlier). The relative strength of the two materials and the lever arms involved would tend towards this mode of failure rather than a "shattered" cutter which would require a buckling failure of the cutter which might happen on a very thin blade but is less likely on anything else (I suppose if the blade had a keyway cut in it there may be a stress point at the key corners that could promote cracking but you would need to be unlucky and need a cutter with a sharp cornered slot - in itself bad practice).

Mark

The B&S Treatise on Milling says

"Direction to Move Work Under Cutter. Whenever possible, it is advantageous to feed the work in the opposite direction from that in which the cutter runs. Then the cutter cannot draw the work in as it is liable to do when the table moves in the direction indicated at B. Moreover, when the piece moves as shown at A, the cutter teeth are first brought into contact with the softer metal, and as the scale on the surface is reached, it is pried or broken off.

On the other hand, in milling deep slots, or in cutting off stock with a thin cutter, or saw, it is sometimes better to move the work with the cutter, as the cutter is then less likely to crowd sidewise and make a crooked slot.

When the work is moving with the cutter, the table gib screws must be set up rather hard, for the teeth of the cutter tend to draw the work in, and if there is any lost motion in the table, the teeth may catch and injure the cutter or work. A counter- weight to hold back the table is excellent in such milling."

You need to be able to use both approaches, understand the benefits of each and know when they are appropriate. Many of the posts here start with the words "I was taught that...", without showing any obvious understanding of why. As an engineer that doesn't work for me.

Much of my milling has been done in climb mode, even on my old manual (vertical) Bridgeport clone. It's fine if you make sure the slides are just nipped up enough (you soon get the knack) and if you get the depth of radial cut about right, there's very little force required to feed the work into the table. Most modern machinery seems to default to climb milling - there must be compelling reasons!