Feeds and speeds. Some tips for a newbie please!

[Richard]

Tried a new 12mm carbide bit today.

Lovely finish but degraded after approx 5m of cutting distance.

I tried upping speed from 8k and feed from 800mm/min

Here's some pics of the bit afterwards, some heavy wear.

Maybe I should have lub'ed...

Am I still going too slow in rpm/feed or should I flood with coolant?

(the reason I did this dry was that I haven't got my cooland set up yet...)

[Dave_stoke]

To me (and the pics arent very clear) it looks like the tool lacked lubrication and/or ability to clear material fast enough. A 2 flute is more forgiving.

I didn't have my coolant running. I doubt it would have made any difference tbh.
I can't slow it down it doesn't get near the stock. It's started acting up again. Losing steps for fun. Certainly doesn't like helix.
I think it's time to give up tbh. The machine is what it is cheap but not cheerful. But £800 isn't cheap.

Thanks anyway buddy

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[Chaz]

I didn't have my coolant running. I doubt it would have made any difference tbh.
I can't slow it down it doesn't get near the stock. It's started acting up again. Losing steps for fun. Certainly doesn't like helix.
I think it's time to give up tbh. The machine is what it is cheap but not cheerful. But £800 isn't cheap.

Thanks anyway buddy

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The issue is, in this world, £800 is not a lot.

[Dave_stoke]

The issue is, in this world, £800 is not a lot.

It is when there's nothing left in the bank lol

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[Chaz]

It is when there's nothing left in the bank lol

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Agreed. Machining is an expensive hobby.

Can any of us help with machining this for you?

[Dave_stoke]

Agreed. Machining is an expensive hobby.

Can any of us help with machining this for you?

Thanks buddy, I have listed it for sale. But also reminded the seller I bought it from that they must provide me with a solution as to why it doesn't do what they promised.

As for parts I might drop it for a while, have a break and finish up all the drawings in fusion. I wanted to make a scale hawker hurricane in its entirety with a 1.5mtr wing span. And then maybe a Lancaster. But watch tools were my main project. Haven't managed one yet.

I'll stay on the boards keep watching, reading and learning. Then maybe if things get better buy a proper mill and convert it to cnc.

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[m_c]

That looks like the cutter has been rubbing more than it's been cutting.

Speeds and feeds nearly always involve some experimentation to find what works best for your machine.
The key thing is tooth loading. Too much and the cutter will snap/spindle stall, too little and the cutter rubs. The smaller the cutter, the more precise the tooth loading has to be.

For most machines, two flute cutters are better, as it allows slower feed rates for any given spindle RPM (double the number of flutes, and you have to double the feedrate to achieve the same tooth loading).

Speeds and feeds calcs (I personally use FSWizard) generally only give you an estimate. If what they're suggesting isn't working, it can be worthwhile to look up the cutter manufacturer's specifications, and work out the figures manually to give you the recommended ranges. First work out the possible spindle speeds (manufacturer's will give a recommended surface speed range), then once you have the min/max RPMs, calculate the required feedrates at those two speeds for the min/max tooth loading.

[Richard]

That looks like the cutter has been rubbing more than it's been cutting.

Speeds and feeds nearly always involve some experimentation to find what works best for your machine.
The key thing is tooth loading. Too much and the cutter will snap/spindle stall, too little and the cutter rubs. The smaller the cutter, the more precise the tooth loading has to be.

For most machines, two flute cutters are better, as it allows slower feed rates for any given spindle RPM (double the number of flutes, and you have to double the feedrate to achieve the same tooth loading).

Speeds and feeds calcs (I personally use FSWizard) generally only give you an estimate. If what they're suggesting isn't working, it can be worthwhile to look up the cutter manufacturer's specifications, and work out the figures manually to give you the recommended ranges. First work out the possible spindle speeds (manufacturer's will give a recommended surface speed range), then once you have the min/max RPMs, calculate the required feedrates at those two speeds for the min/max tooth loading.

Hi m_c, assuming you're looking at my photos, that cutter cut beautifully for the first 5m of the cut (it was a zigzag path 350mm long, moving across 10mm each pass, doing 30 passes in all).

It left a very clean smooth cut then suddenly it seemed to get noisy and the surface finish got worse. I'm assuming this is when the edges went off for some reason....

This was supposed to be carbide, but no idea if it really is, it was a very cheap set, 2mm to 12mm, 8 end mills, for £25! LOL. (Just checked, the carbide bit is almost exactly twice the weight of the HSS one and it much less magnetic, so probably is carbide)

If there was a build up of aluminium on the tips, would that errode the edges like this?

[spluppit]

It's is pretty hard for anyone to diagnose the problem fully unless they are there. A few very simple and basic pointers that are basics you need to know and cover, if you you dont cover these then you are fighting in the dark.

Machining is a process of logic and forethought. If those are not applied when you are trying to learn and its going wrong, stop and think to yourself, 'apply logic and forethought.'

1) What is the brass you are trying to machine? I'm fairy sure i know the grade looking at your pics, without seeing it in person, but the point is do you know? It's so important SO important to know the material you have to machine. Different material have different properties and are for different purposes. I think what you have there is known as 'half hard' ... and the clue is in the name, half hard meaning it's ductile, Not gummy (No such material property has ever existed) This means it can be bent and is not generally used for machining. You should be using CZ 121 which is a fully hard and free machining brass and is the go to brass for general machining. It chips beautifully and there is no need for coolant, brass self lubricates and tools should last a very long time. The only real need for Coolant is for chip removal if making a lot of swarf or an air blast, It will add little to nothing to machining ability in this instance. Softer brasses are totally machinable but its not the right stuff to learn on, experience counts for everything in this game. Brass is one of the simplest materials in the world to machine, so if its not going right, then something is radically wrong.

The way your image shows the brass burring up indicated either: It's half hard or a soft brass or tool tool was blunt from the outset. You said the tool was new tool (assuming an acceptable quality) so go back to the material and look again

2) Your cutting tools. Only buy from reputable seller. If you have crap tools then expect crap results. Just because it's carbide doesn't means its good..and there is a lot of crap carbide out there. It's pretty simple fundamental basics. You don't have to spend fortunes, go to somewhere like shop apt (google it) The quality is fair for the price point and perfectly usable for home and small business. The odd problem can occur with cheaper produced cutters from places like apt but its pretty rare from my experience.


Generally when using a helical entry into the part the (pending software also) you should denote X and Y feed rate and a Z feed Rate. The Z federate is the helical plunge rate and pending machine, cutter size, cutting conditions will be about half of X, Y feed rate.(this doesn't apply to larger heaver machines where this can be wacked up) The info from speeds and feed calcs unless they ask for a machining strategy will not take things like helical entry into account.. Its a big learning curve I'm afraid

If you cover the basics and its still not right, then you need to start looking else where.

A small vid of brass being machined with small tools, a light air blast only is used and see how cleanly it cuts with the slotting using a ramp strategy. The slot is 2mm.

https://www.youtube.com/watch?v=pGAoW4KAGeA

[Dave_stoke]

It's is pretty hard for anyone to diagnose the problem fully unless they are there. A few very simple and basic pointers that are basics you need to know and cover, if you you dont cover these then you are fighting in the dark.

Machining is a process of logic and forethought. If those are not applied when you are trying to learn and its going wrong, stop and think to yourself, 'apply logic and forethought.'

1) What is the brass you are trying to machine? I'm fairy sure i know the grade looking at your pics, without seeing it in person, but the point is do you know? It's so important SO important to know the material you have to machine. Different material have different properties and are for different purposes. I think what you have there is known as 'half hard' ... and the clue is in the name, half hard meaning it's ductile, Not gummy (No such material property has ever existed) This means it can be bent and is not generally used for machining. You should be using CZ 121 which is a fully hard and free machining brass and is the go to brass for general machining. It chips beautifully and there is no need for coolant, brass self lubricates and tools should last a very long time. The only real needs for Coolant is for chip removal if making a lot of swarf or an air blast, It will add little to nothing to machining ability in this instance. Softer brasses are totally machinable but its not the right stiff to learn on, experience counts for e Everything in this game. Brass is one of the simplest materials in the world to machine, so if its not going right then something is radically wrong.

The way your image shows the brass burring up indicated either: It's half hard or a soft brass or tool tool was blunt from the outset. You said the tool was new tool (assuming an acceptable quality) so go back to the material and look again

2) Your cutting tools. Only buy from reputable seller. If you have crap tools then expect crap results. Just because it's carbide doesn't means its good..and there is a lot of crap carbide out there. It's pretty simple fundamental basics. You don't have to spend fortunes, go to somewhere like shop apt (google it) The quality is fair for the price point and perfectly usable for home and small business. The odd problem can occur with cheaper produced cutters from places like apt but its pretty rare from my experience.


Generally when using a helical entry into the part the (pending software also) you should denote X and Y feed rate and a Z feed Rate. The Z federate is the helical plunge rate and pending machine, cutter size, cutting conditions will be about half of X, Y feed rate.(this doesn't apply to larger heaver machines where this can be wacked up) The info from speeds and feed calcs unless they ask for a machining strategy will not take things like helical entry into account.. Its a big learning curve I'm afraid

If you cover the basics and its still not right, then you need to start looking else where.

A small vid of brass being machined with small tools, a light air blast only is used and see how cleanly it cuts with the slotting using a ramp strategy. The slot is 2mm.

https://www.youtube.com/watch?v=pGAoW4KAGeA

Wow thanks for that,

I hadn't even considered the brass hardness. It's just a strip off ebay. I know the bars I had cut an awful lot better. But there's never really a spec on those ads.

The tool was from ew in Stockport. It's where I get them all from.

The machine really doesn't function very well in helix you can hear the motor clunk back like it's hitting resistance just before it gets to a full step. Yet mach is counting down so it can register - 0.9310mm when it's still at +2.5000. Which might also be the case when it does actually plunge. It might be over plunging?
It's set for multiple depths of 0.5mm looking at the piece it seems deeper than that.

So it must be partly the machine or software and the rest the user.

I have a great deal to learn before I can work a machine even half decently. And if I don't do something with the steppers, the software and myself. I'll be forever buying bits.

I did think it can't be that hard. Usually very quick at picking things up. But if it was that easy, everyone would be doing it.

What I need is a source of income now. And stop fkn about. That way I will have a clearer frame of mind and I'll grasp it better.

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