Are you a Man or a Mouse When Milling?

[SillyOldDufferModerator @sillyoldduffer]

I think Andrew's demonstration was of potential rather than a recommendation to owners of small milling machines. Andrew shows that a Carbide cutter can be run much harder than most of us would be comfortable with.

A big disadvantage of cutting fast and hot is that the shower of smoking swarf is unpleasant. Making hot swarf on my lathe is particularly uncomfortable because it lands on your hands and arms, ouch. Extra nasty if it gets in your eyes. Slowing down makes the job more civilised.

What limits the speed a machine tool can remove metal is:

• The maximum temperature the cutter and job can take.
• The power of the motor, and the time the motor can deliver power before overheating.
• The rigidity of the machine, ie it's ability to apply power to the work via the cutter without vibration or bending.
• The strength of the machine – gears, belts, spindles, bearings, frame etc. What will break first if you over do it!

Hobby machines are less heavily built than professional machines, and their motors may not be rated for continuous operation. DC motors have brushes that wear quickly if the motor is flogged.

In practice, I:

1. calculate an approximate rpm with 10000 / diameter (mm).
2. increase or decrease the approximate rpm depending on the cutter and material I going to use. (6 to 4x faster with carbide, 20% faster with HSS if flood cooling.) Brass 20% faster than steel.
3. Depth Of Cut – 10 to 20% of cutter diameter, but note the advantage of Andrew's point about using the full length of milling cutters where you can.
4. Adjust the feed-rate for – in steel – straw chips with HSS, blue chips for carbide.
5. MOST IMPORTANT – all of the above is to get into the zone, not a formula for guaranteed success. I listen for signs of stress – chattering, labouring, excessive noise, belts slipping, poor finish – and back-off until the job is cruising. This part has to be learned by trying. I suspect I'm too gentle.

As operator faults go, being over-cautious produces disappointing results especially if tools rub rather than cut. But being over-cautious is unlikely to damage the machine. At the opposite end, some people have gross over-expectations. If you wind the tool up to full power and smack the cutter into the job (causing severe shock loadings), and then force the cutter through the work ignoring signs of stress, then expect blown fuses, worn brushes, damaged electronics, broken sheer pins and stripped gears.

Attitudes to machines vary as well. If I owned a fine watchmakers lathe I would treat it with respect. I see my Chinese kit as consumable. If my lathe lasts 5 years, it only cost £1 per day. If I wear it out or expensively break it, I'll replace it. Going well so far, light to moderate use, kept clean and oiled, no sign of wear after 4 years.

Dave

Edited By SillyOldDuffer on 07/08/2018 11:39:49

[BazParticipant @baz89810]

During my working life I worked in many sub contract shops and if swarf was not coming off blue you were not making time on the job and not making bonus. Consequently machines and cutters were pushed to the limit, two or three cutters per day were blunted and were thrown in the regrind box and a cutter grinder was employed full time to sharpen them. The machines were mostly Bridgeport’s, the heads had to be re clocked almost daily because they moved no matter how tight the bolts were done up.

In my own workshop I have to buy my own machines and tooling and so they are treated with respect. Swarf is never blue and much smaller cuts are taken both on mill and lathe and I can actually enjoy the machining operations, where does that put me on man or mouse scale?

[JasonBModerator @jasonb]

I think one of the differences between the power of a modern hobby mill and the power of a Bridgeport is that one adjusts it's speed buy electronically and the other mechanically so unless the hobby machine is being run at the motors max speed you will get a reduced wattage or HP. So that 750w brushless soon becomes 375w when run at the mid speed of the machine. I suppose it depends on the design brief whether it is a flaw or not if the brief was to make a machine below a certain price and an electronic speed control works out cheaper than gears then it has met that brief.

Yes motor starts to get a bit loud as you get up to the mills max but still quieter than my X3(gears), motor is at 7000rpm when mill spindle at 2000rpm

The hot swarf can be reduced by thinking about the direction of cut on the mill and if a carbide insert is working well on the lathe will throw the swarf away from the cut face which is usually out of harms way

[Mick B1Participant @mickb1]

Hah!

Eat your hearts out, yer rufti-tufti metal-rippers!

My chips come off yellow…

https://www.youtube.com/watch?v=CO8gPLiHlfw

…only not from heat

Edited By Mick B1 on 07/08/2018 19:20:32

[Ian Skeldon 2Participant @ianskeldon2]

Anyone seen the cheese?

I have a myford mill which is heavy and well built but I am somewhere in the middle and leaning towards mouse.

Looking at Andrews photo maybe I should be a bit more adventurous.

[Anonymous]

Posted by JasonB on 07/08/2018 13:27:43:

The hot swarf can be reduced by thinking about the direction of cut on the mill and if a carbide insert is working well on the lathe will throw the swarf away from the cut face which is usually out of harms way

Yep, I did the cuts wearing a short sleeve T-shirt. Not too much problem with hot swarf. I also wore goggles all the time. Swarf on the arm only causes some blue language, one in the eye will ruin your whole day and every day after.

Andrew

[JasonBModerator @jasonb]

I have another video but a client with a leaky pipe means it will have to wait until tomorrow. Why will some builders bury bare copper pipes straight in the screed

[Anonymous]

Posted by pgk pgk on 07/08/2018 11:32:22:

I find that if I try 'manly' cuts on my chester delux then as the cutter breaks through the end there's a clunk and chipped teeth on carbide if I haven't remembered to slow feed down enough early enough — so cheap cutter or main spindle bowing under load?

Cheap cutter? I don't recall ever chipping a carbide cutter during normal cutting. I did get fed up chipping teeth when touching off to set tool heights using a fag paper on the CNC mill. Just a bit too far and the end of the tooth goes ping. That's why I bought an electronic tool setter.

The only time I've taken the teeth off a carbide cutter was milling the spokes for the traction engine rear wheels. After several spokes had gone through I could hear the mill struggling. Turns out the endmill had been converted to a ballnose mill by losing its teeth. After changing the cutter, and a new workpiece, I proceeded to machine the remaining 40 odd spokes without a problem. The last thing I did was go back to the spoke that had caused the problem. Exactly the same thing a bit further along. All I can think of is that there was some sort of hard spot or crap embedded in the material.

Cheap cutters are cheap for a reason. Carbide cutters, and inserts, are not homogenous materials. They consist of tiny tungsten carbide particles embedded in a metal (often cobalt) matrix. Tungsten carbide is expensive, so cheap cutters reduce the amount and add more cobalt. Outside of a production environment it is quite possible that the reduction in lifetime will not be noticed. But there may well be other deleterious effects, like chipped edges.

Andrew

[JasonBModerator @jasonb]

I thought I would try the same 2-flute carbide cutter at a more sedate 760rpm. the frequency of the vibration was lower so there was little or no squealing but the actual vibration was a lot easier to see. Chips were a more pleasing shape but just bright steel colour.

As I was running at the lower speed I then thought I may as well try a 3-flute HSS cutter, that actually vibrated even more so decided not to continue the cut incase something got damaged.

Finally a budget 4-flute cutter, far less vibration, reasonable chips but not as cleanly cut as the carbide and even started to get a bit of a straw colour on some.

Well at least with these two videos I will have some material for the beginners series as a guide for what cuts not to make with these machines.

One other point on the machines not being able to use the motor power being a design flaw is that due to the use of electronic speed control over mechanical the motor size is specified to give enough power at the slower speeds which results in a motor that may on paper have more power than can be used at full speed.

J

[Martin ConnellyParticipant @martinconnelly55370]

I was milling some gauge plate/ground flat stock (take your pick on description) yesterday using a Ø16 insert milling tool. I have had this tool for some time and use it a lot and have yet to rotate or replace the inserts. The feeds and speeds calculator suggested that for a feed per tooth of 0.05mm I should have the rpm at 1300 and the feed rate at 130mm/min. Sure enough running using these figures gives blue chips. These chips are then thrown about with some force and when they hit paint they can stick and embed themselves in it. Landing on any material made from man made fibres has a similar result so keep to the cotton overalls. Having tried these recommended values I reduced the speed and rpm to 650 rpm and 65mm/min. The result is of course that it takes twice as long and the chips come off silver with a hint of straw. The other result is that the distance the chips are thrown is far shorter and they do not embed themselves in any paintwork they hit. In the approximately 3 hours I was working the actual time spent cutting metal by milling was only about 20 minutes. If I had gone at the recommended rates I would have saved maybe 10 minutes of machining time but lost more time clearing up the scattered chips.

One other observation is that the gauge plate chips that are blue are a lot harder than the silver ones. This is important if you don't have flood coolant and there is some recutting of chips taking place if they remain in the area of the cutting action. Recutting is going to reduce the wear and tear on any cutting tool as well as affecting the finish and is something that needs consideration if you can't clear them as they are produced.

Martin C

[Neil WyattModerator @neilwyatt]

For most of us machining metal is the end, as much as a means to an end.

That means for many folks, taking it easy and getting a quieter, less rushed and probably less stressful result is a preferred option, especially when working by hand and (as is often the case) less than pristine cutters.

Having much increased the rigidity of my old-style X2 it can take hefty cuts and climb mill, but my machining 'style' depends a lot on what I am doing and why..

Also power isn't just about metal removal, its about ensuring speed is kept up when a cut starts and avoiding stalling when using low speeds.

The original question forgets the all important fact that there are NO right answers as everyone's situation is different.

Neil

[Anonymous]

Just for the record the original picture was taken while feeding by hand and using a definitely less than pristine cutter. If people don't have the curiosity to want to explore the capabilities of their machines that's up to them. Hats off to JasonB for trying things out and getting some interesting results.

If it's true that there is no right answer because everyone's situation is different then there is no point in anyone on the forum offering advice because, by that definition, it will be wrong. Of course there are shades of grey, but there are definitely right and wrong answers irrespective of circumstance.

Andrew

Edit: Spell errors only show up after posting

Edited By Andrew Johnston on 09/08/2018 19:31:34

[Neil WyattModerator @neilwyatt]

Posted by Andrew Johnston on 09/08/2018 19:30:28:

If it's true that there is no right answer because everyone's situation is different then there is no point in anyone on the forum offering advice because, by that definition, it will be wrong. Of course there are shades of grey, but there are definitely right and wrong answers irrespective of circumstance.

It just means advice has to be tailored to suit someone's situation – as this forum regularly demonstrates. Someone asks a question and the first responses are usually asking for more information!

Neil

[HOWARDTParticipant @howardt]

Whilst we mention HSS and different coated carbides there is also a difference in the quality of carbide. I have some UK manufactured carbide cutters from my design days. There is a noticeable difference in the density of the carbide. When using these they outperform hobby carbide cutters by some degree. I wouldn’t go out and buy these cutters as the prices are beyond what I want to pay, but I have bought cutters from surplus tool outlets which are more affordable. So I would just say it is worth trying different sources for cutters.

[NigeParticipant @nige81730]

I don't own any carbide cutters, the few cutters I do own are mostly the non coated HSS (black) ones from Arceurotrade. Today I had cause to cut 6mm wide slots in some 12mm bright mild stee. I am quite conservative with how much depth I wind on, mostly because I don't have a large stock of spare cutters and don't want to be stopped by ruining a cutter half way through a job. Today howeve I decided to live dangerously. Instead of the usual 0.5mm DOC I have been using I wound on 1mm and then 2mm cuts. This was with a 3 flute cutter at about 1100 rpm and it didn't seem to mind a bit. I did try a cut the full depth, 12mm, of the slot but I was getting steel powder instead of chips and it seemed obvious by the noise, vibration and heat that it was too much for the SX2.7 and I stopped that particular experiment.

[Mark RandParticipant @markrand96270]

A common guideline for HSS cutters is half the diameter in width of cut and the full diameter in depth of cut or the full diameter in width of cut with half the diameter as depth of cut.

 

Generally speaking, the more depth you can use, the longer the life of the tool befire resharpening, since the corners tend to blow out first.

 

YMMV

Edited By Mark Rand on 10/08/2018 22:55:50

[MuzzerParticipant @muzzer]

Like indexable inserts, solid cutters have come a long way and some of the most recent ones are pretty darned impressive. I suspect many of the "hobby" ones mentioned are pretty traditional in geometry and material – and possibly fairly indifferent in terms of surface finish.

I recently tried out a new-ish cutter from YG-1 (Korean), the "V7" EMC85 series. There are various flavours available but mine was a necked long series that I used for both roughing and finishing steel. The removal rate was pretty special and the surface finish was pretty darned good. Many cutters leave a clear series of grooves where the cutting edge in not smooth but these boys were almost mirror flat.

No coloured chips here, as I was using flood coolant to clear the chips but as you can see, I was achieving a decent material removal rate. To get the most out of these you really need to use CNC, as you couldn't sensibly apply the correct feed rate consistently.

Here's the roughing operation.

And the finishing.

Murray

[JasonBModerator @jasonb]

Nige, those "black" cutters from ARC are coated with a TiAIN coating, the shanks are uncoated.

Thanks Murrey for showing what a specialist cutter can do in a manly machine but I do wonder if they would perform to their full potential in the lighter duty hobby machines and whether the extra cost would worth paying out for or would "Benchtop Man" be better off with four reasonable quality HSS cutters for the same price?

The YG-1 paper catalogue does make interesting reading when you look at the cutting data for all their various cutters tough little applies to what can be done on a benchtop mill.

Edited By JasonB on 11/08/2018 07:17:55

[MuzzerParticipant @muzzer]

Well actually my point was that the geometry of these cutters (tooth profile and asymmetric flute positioning) results in lower cutting forces and less likelihood of judder / chatter, which would actually benefit light machines. Hence my reference to the way insert geometry, materials and coatings have come on bounds. These cutters are as tough as hell but also razor sharp(!!) and make my Chinesium cutters look agricultural in comparison. True, you might not make full use of their potential but will most likely a better result. As ever, if you don't look, you don't find…

Think how the geometry ("chipbreaker" ), coating and composition of inserts has come a long way since we had basic, flat topped lumps brazed or clamped on the end of simple holders. That process of evolution continues today with solid cutters – they haven't been left behind.

If you buy them on offer, they don't work out too expensive.

Murray

Edited By Muzzer on 11/08/2018 11:37:45

[JonParticipant @jon]

Agree Muzzer, been using the smaller (2.5 to 8mm) YG carbide for about the last 4 years but not the V7, cheap as chips comparitvely, last a decent amount of time and cut well.
Get mine off ebay and work out cheaper than the average crap hss, more so if a decent brand. 2 for £7 delivered sub 6mm, gone up a bit now.

Its the carbide quality, hardening, coating and final grinding that makes these good. Have similar flute angles etc in hss and a different animal with wear and flex of the cutters.

Only time chipped a carbide cutter is dropping them.

Back to original post, the cutter would have indefinately lasted a lot longer if the cutter and job were not allowed to get red hot, coolants your friend.

[Neil LickfoldParticipant @neillickfold44316]

The uneven helix angle and spaced fluted milling cutters work really well on manual mills and the mini mills. They are way better than any HSS cutter as well. The face cutters with the positive geometry uneven spaced inserts also work really well on the mini mills. Got a good laugh from the man or mouse video. Using compressed air with a bit of oil works really well for milling , especially if you adopt the full flute depth of cut with a shallow radial cut techniques. All that you need is some way to stop the chip from being recut again, and the cutter life increases quite significantly. If you also have ball screws or some way to control the back lash, climb milling also increase the cutter tool life as well.

[John ReeseParticipant @johnreese12848]

Slightly off topic. I see quite a few videos with the work feeding right to left. That throws the hot chips toward the operator. I prefer cutting left to right so the chips are directed away from me, especially when the chips are coming off blue.

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