Are you a Man or a Mouse When Milling?

[Anonymous]

This is what you get when you push hard; cutter glowing dull red and the swarf is bright red:

Old, and blunt, Garr 10mm uncoated 3-flute carbide cutter at 2000rpm, DOC 5mm, WOC 8mm and hand feed about 300mm/min. Material is hot rolled steel. In daylight the swarf on the table is dark blue/purple and smoking.

The cut was in the climb milling direction, relatively easy to wind the handle. Whereas with the same parameters conventional milling I could barely move the handle. Hooray for climb milling!

Before anybody says, yes I know it's a Bridgeport, but it's old and only has a 1.5hp motor, so equivalent to many mid size hobby mills.

So which one are you?

Andrew

[Anonymous]

[Roderick JenkinsParticipant @roderickjenkins93242]

eek eek!

😀

Rod

[Thor 🇳🇴Participant @thor]

I don't take as deep cuts as you but swarf is often blue when I use carbide tipped tools. Too heavy cut causes too much vibration on my small milling machine. Your Bridgeport may only have 1.5HP but it is several times as heavy as my milling machine and probably far more rigid.

Thor

[larry phelan 1Participant @larryphelan1]

Like many others,I suspect,I am a coward.

The only blue chips I like are the ones we used to get from investments,years ago ! Anyone remember those days ?

That was before the bean counters moved in.

I dont think I would have the courage to try that,although I must say,it looks good.

[AJWParticipant @ajw]

Is there a benefit from having a cutter glowing?

Alan

[David Standing 1Participant @davidstanding1]

Posted by AJW on 06/08/2018 17:32:02:
Is there a benefit from having a cutter glowing?

Alan

Saves on the workshop lighting bill when milling after dark, lights off!

[John RuddParticipant @johnrudd16576]

Posted by David Standing 1 on 06/08/2018 17:33:40:

Posted by AJW on 06/08/2018 17:32:02:
Is there a benefit from having a cutter glowing?

Alan

Saves on the workshop lighting bill when milling after dark, lights off!

Moreso in the winter when the shop is cold and damp, saves on heating…..

I tend to push my 626 hard when milling, has a 1.5 hp motor on it….but doc is not as Andrew…..

[JasonBModerator @jasonb]

Andrew, is there any chance of a photo of the finished surface as you seem to be keeping us in the dark on that one. No need to get the surface comparitor out.

Would a sharp cutter have got so hot?

 

I feel a Video coming on

Edited By JasonB on 06/08/2018 17:57:03

[Raymond AndersonParticipant @raymondanderson34407]

Most certainly a man if using the K&T 12mmm deep and 20 wide does not seem to bother it one bit, but most certainly more of a mouse if using the Chester LUX. depends on the machine in the end.

[John ReeseParticipant @johnreese12848]

My impression is that most hobby machinists are overly conservative in setting speeds, feeds, and depth of cut. I suspect part of the reason is the limitation of their machines. Even so, the spindle speed should be high enough to give straw colored chips with HSS or blur chips with carbide tools.

[SillyOldDufferModerator @sillyoldduffer]

Posted by AJW on 06/08/2018 17:32:02:
Is there a benefit from having a cutter glowing?

Alan

Yes, when speed matters more than cutter life. The heat softens the metal, making it even easier to remove quickly, a dubious advantage in my genteel cowardly workshop.

There's an economic trade-off between cutter life and metal removal rate. Time is money. I'm a hobbyist who prefers to maximise the working life of my equipment. Production is a different game and they tend to drive machines and cutters close to maximum, optimising power consumption, finish, & removal rate rather than cutter life. They're much more prepared to wear out cutters in short order when it pays to do so.

Running red hot destroys HSS – it can't take the heat.

I'm not aware of any research into optimum amateur removal rates. I reckon I'm over-cautious. Couple of times I've been advised to up the ante, and it worked. 'Don't pussyfoot' and 'Increase the feed-rate'.

Dave

[Anonymous]

Posted by AJW on 06/08/2018 17:32:02:
Is there a benefit from having a cutter glowing?

Alan

Time saving.

Carbide cutters retain their hardness at high temperature, the cutter in question is worn anyway, and I get bored waiting for slow cuts to finish. I'm not really interesting in machining, unless it's a new technique, but in using the finished part.

Andrew

[Anonymous]

Posted by SillyOldDuffer on 06/08/2018 21:10:55:

There's an economic trade-off between cutter life and metal removal rate. Time is money. I'm a hobbyist who prefers to maximise the working life of my equipment. Production is a different game and they tend to drive machines and cutters close to maximum, optimising power consumption, finish, & removal rate rather than cutter life.

I think you're focusing on the wrong metric. What is of importance is the amount of metal removed before a cutter is deemed at end of life. Clearly a commercial machine shop will get to end of life quicker than a hobby workshop since they're maximising machine on time. But that doesn't mean that they get less metal removed per cutter. So both shops may get the same cutter life, but the time taken to get there will be different.

Running with slow speeds and low feedrates may actually decrease cutter life. And you're paying for the full length of the flutes so why not use them?

Andrew

[Ed DuffnerParticipant @edduffner79357]

Pass the cheese!

[Anonymous]

Posted by John Reese on 06/08/2018 19:12:56:

My impression is that most hobby machinists are overly conservative in setting speeds, feeds, and depth of cut. I suspect part of the reason is the limitation of their machines. Even so, the spindle speed should be high enough to give straw colored chips with HSS or blur chips with carbide tools.

I'd agree with that. I think one issue is that when people get chatter and vibration problems the instinct is to slow down. It took me a while to work out that is often the wrong thing to do. Problems often go away by increasing parameters, especially feedrate.

Ah but the small machines aren't very rigid, so what! Suppose the machine deflects a thou or two when you're feeding at a thou or two per cutting edge. So the cut starts and the machine deflects and the cut stops. And then it starts all over again with the next edge. Equals chatter. But supposing we're taking a cut of four thou per edge. So the machine deflects a thou or two; sure the cut changes but the cutter is still cutting, so less, or no, chatter.

Andrew

[Anonymous]

Posted by Ed Duffner on 06/08/2018 21:34:36:

Pass the cheese!

You've lost me there, but my inclination would be to say hold the cheese and pass the port.

Andrew

[Anonymous]

Posted by JasonB on 06/08/2018 17:55:38:

Andrew, is there any chance of a photo of the finished surface as you seem to be keeping us in the dark on that one. No need to get the surface comparitor out.

Would a sharp cutter have got so hot?

I suspect that a sharp cutter would have run slightly cooler, but the swarf would still be red hot. Here's the part, about 20" in length:

I did get the surface roughness meter out, but I can say that the finish on all surfaces is smooth to the touch with no tearing, which can be a problem with hot rolled steel. The final finish isn't necessarily indicative of the roughing cuts. To finish the rebates I took a climb milling pass at full depth, 15mm, and up to 1mm width.Here's the swarf, nice 'n' blue:

And here's the bar in situ on the lathe, in preparation for using the hydraulic copy unit for face profiling:

Andrew

[Mark RandParticipant @markrand96270]

In defence of heavy cuts, the biggest problem I have with milling is the shower of razor sharp needles that lie in wait until you've brushed/hoovered every last one of them up. Heavier swarf, of whatever colour is much safer, once you get past the immediate third degree burns.

[JasonBModerator @jasonb]

Thanks for the extra photos Andrew

I don't use carbide that much so my choice of cutter was a bit limited and not ideal for a similar cut. I had to go with a spanking new 2-flute, 12mm dia one so dropped the speed down to 1660rpm which would give the same speed at the edge as Andrew was using.

5mm deep was OK but as there was less cutter width being used for the 8mm WOC I decided not to climb mill as there would be more chance of the of problems. Also the 2-flute cutter would not have one tooth always cutting so possabley more chance of chatter.

From the cuts I posted the other day in the Milling for Beginners thread I did not hold out much hope for a painless cut but as it was Ketan's machine worth a try.

Warning not for the faint hearted unless you like the sound of a mouse squealing in a trap!

 

I started with a brisk feed of about 300mm/min again similar chip loading to Andrew but very soon the chatter started and I could not feed that fast as there was too much resistance. So no red not chips or tool but at least I was man enough to give it a try.

 

Cut surfaces are quite poor though once the leading edge of the cutter had cleared the work the last 6mm or so was a lot better. may try a couple more cut sat same depth but less width and see what can comfortably be taken off. May also try at a slower speed

 

But for now I won't be making such cuts on a regular basis

Edited By JasonB on 07/08/2018 07:06:25

[Anonymous]

Posted by JasonB on 07/08/2018 07:05:28:

Warning not for the faint hearted unless you like the sound of a mouse squealing in a trap!

Good grief that's noisy! The machine that is not the cutting. Clearly plenty of vibration but the mouse must have escaped? I had a little vibration, the knee handle swung free, but no chatter or squealing. The non-cutting axes were not locked.

The surface roughness measurements I got were as follows. On the vertical surface within the rebate 5µm Ra. Not surprising really as the cutter flutes are fudged:

On the bottom surface of the rebate I got 3µm Ra. On the top surface of the block,where I took ~1mm DOC and 8mm WOC surfacing cuts to get rid of the mill scale, I got 2µm Ra.

Andrew

[Ron LadenParticipant @ronladen17547]

Now I dont know the first thing about mills or milling but I will be buying a mini mill in the future. I am quite prepared to be shot down in flames but is it right that a cutting tool is glowing red hot, my feeling is thats it not but what do I know..?

I can appreciate the need to want to remove as much material as possible and speed up the job but at what point do you decide that the DOC and WOC and feed is just too much. Andrew you say "so what" to "the smaller machines aren,t that rigid" but surely pushing a machine that hard cant be doing it any good in the long term.

As I mentioned I,m quite prepared to be corrected.

[Anonymous]

It's a carbide cutter so can be run pretty hot. To be fair it doesn't look red in normal lighting. If you run HSS at that sort of temperature you'll fudge it pretty quickly. Some of the more esoteric coatings on carbide cutters need to be run hot for them to function properly. So running slow ''n' steady can actually decrease cutter life.

In terms of speeds, feeds, DOC and WOC it's a matter of experience. Clearly a benchtop mill isn't going to have the same capabilities as a 8000lb floor mounted mill. But as said earlier I suspect that many users of smaller machines don't run anywhere close to the limits. A rule of thumb is that 1hp will remove 1 cubic inch of material per minute in low carbon steel. So one could assume that the machine would be capable of achieving that. As an industrial machine the Bridgeport does achieve that. I don't know about minimills, although JasonB pushes his mill fairly hard. If the mill isn't capable of utilising the available spindle power then it's a bit of a fundamental design flaw.

Horses for courses really.

Andrew

[Ron LadenParticipant @ronladen17547]

Thanks Andrew for the explanation.

You will probably have gathered that when I start out with a mini mill I will be in the mouse camp..lol

Ron

[pgk pgkParticipant @pgkpgk17461]

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? With cheap HSS I just burn them out with blue chips so resigned to modest speeds and depths.

pgk

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