New CNC user mistakes and info

[Pilsbury]

Hi all. Currently awaiting a build so in reality not even a new CNC user yet!.... But, doesn't stop me thinking and planning. So one thing I've been reading is about mistakes, some minor, some more costly. Snapped bits seem a common issue. I'm assuming this is down to incorrect feed rates or more likely errors in the programming and plunging too deep. Hopefully this is short lived and checking your toolpaths thoroughly is a must early on. Anyone experienced this when a novice? Or still experiencing this? How much is down to user error or can it sometimes be hardware error?

I have a few carving/inlay projects planned. Hopefully in some nice hardwood. I'm thinking of during early days running the project on some cheap pine or ply first as a test before buggering up an expensive piece of oak. Is this a reasonable idea or am I thinking over cautious?

I already have a decent dust extraction system in my new workshop. Dust shoes seem a good idea as carving produces a lot of chips/dust. But again as a novice user, I'm thinking I want to be watching the cut, firstly out of interest, but secondly out of safety. Are you all confident enough in your cutting to be blind to the cutting bit? Are you confident enough to leave your workshop while cutting is in progress or would you at least want to be in the workshop doing other things so you can hear an issue and stop it swiftly? Do you expect issues or is it now rare when experienced?

Maintenance. Apart from keeping clean and dust free, what general maintenance is required? greasing ball screws? I'd guess that attracts dust sticking? WD40? silicone spray?

What were your first projects? Why? Anything nice and simple that teaches a new user a thing or two or just blast straight into what you are after doing and make mistakes to learn?

Any other tips/tricks, need to know, nice to knows?

Cheers

Mark

[ngwagwa]

Hi, There is a free program called Camotics https://camotics.org/ which is a 3 axis simulator, this can be used as an initial toolpath check.
Instead of cheap pine you can use Kingspan insulation boards (though I haven't looked at the health and safety rules regarding machining this) it is firm enough to cut yet soft enough to give if you accidentally plunge in too fast/far.

[JAZZCNC]

So one thing I've been reading is about mistakes, some minor, some more costly. Snapped bits seem a common issue. I'm assuming this is down to incorrect feed rates or more likely errors in the programming and plunging too deep. Hopefully this is short lived and checking your toolpaths thoroughly is a must early on. Anyone experienced this when a novice? Or still experiencing this? How much is down to user error or can it sometimes be hardware error?

Broken bits are just part of the learning process and they can and probably will happen from a mixture of all of the above, however the one error I see most often from new users is forgetting to reset the Z axis offset (Zero) after changing tools.
Checking toolpaths carefully with a simulator is a good pratice to get into however then it won't always stop crashes.? Common things that can and will bite you at some point are Clamps and screws which hold the material.
Many jobs require the tool to move around between cuts and the code doesn't always move in ways you'd expect so it's very easy to hit a clamp when it moves locations or hit the head of a screw you are using to hold waste material etc which doesn't show in the simulation.

This can and does happen even for experienced users, but obviously I've never done this..:whistle: . . . It's 99.999% user error most of the time.



I have a few carving/inlay projects planned. Hopefully in some nice hardwood. I'm thinking of during the early days running the project on some cheap pine or ply first as a test before buggering up an expensive piece of oak. Is this a reasonable idea or am I thinking over cautious?

I'd advise at first to cut Air by setting the Z zero in Midair. This will prove your code is working as expected.
Then I'd practice on soft materials like Dense foam(kings span) or MDF. However, you will have to tweak the speeds n feeds, DOC, etc, to suit the material your using and MDF is a better practice material than foam because it's harder and closer to Real wood.


Dust shoes seem a good idea as carving produces a lot of chips/dust. But again as a novice user, I'm thinking I want to be watching the cut, firstly out of interest, but secondly out of safety. Are you all confident enough in your cutting to be blind to the cutting bit? Are you confident enough to leave your workshop while cutting is in progress or would you at least want to be in the workshop doing other things so you can hear an issue and stop it swiftly? Do you expect issues or is it now rare when experienced?

At first, it's ok to watch the cutter for the reasons you stated but I'd advise putting one on ASAP because while it does obviously lower dust it does a more important job in that it stops chips from getting recut giving a poor finish and excessive tool wear.



Maintenance. Apart from keeping clean and dust free, what general maintenance is required? greasing ball screws? I'd guess that attracts dust sticking? WD40? silicone spray?

Keeping it clean and greasing the screws and bearings is often enough, bit of light oil on the rails won't hurt either just don't go crazy.


What were your first projects? Why? Anything nice and simple that teaches a new user a thing or two or just blast straight into what you are after doing and make mistakes to learn?

My first CNC job was making new gantry sides to replace the MDF ones.!

KISS is the best advice and in MDF to start off with. Start with simple 2D shapes with a few pockets and holes. If your feeling confident maybe try a bit of V carving.

A good practice exercise that will have all of the above plus more and will be useful is a Collet holder.
If your feeling really confident instead of collet pockets with straight sides make the pockets tapered and use a 2.5D toolpath with a ball-nose cutter. Also, try putting chamfers on the edges.
This will give you all the major tool-path types in one Job and will teach you how to do tool changes in the same job. Just about every job you do from then one will have one or a combination the tool-paths used in this practice piece.

[Voicecoil]

Instead of cheap pine you can use Kingspan insulation boards (though I haven't looked at the health and safety rules regarding machining this) it is firm enough to cut yet soft enough to give if you accidentally plunge in too fast/far.
Whilst nowhere near as toxic as say spraying polyurethane varnish, if you're making fine dust it's still potentially a bit nasty so some form of extraction wouldn't be a bad idea.

[Pilsbury]

Cheers ngwagwa. I shall check out that program. Looks like a good check to see nothing ridiculous will happen. I shall also consider things like kingspan after looking into it.

[Pilsbury]

JazzCNC. I have no doubt I’ll be cursing broken bits. Already have a few cheapo Chinese ones to lessen the blow. Some of the recommended bit sites are still rather expensive for a novice to be using in my opinion. I’ll treat myself when I’ve got over the worst! And yes, clamps and screws are going to be a giggle. A vacuum bed is way above my station!
“Air cutting” is also a good idea, as is mdf. Can see that being much better than pine being very fibrous.
I have dust collection now hard plumbed into my workshop with a branch and blast gate ready for where my cnc will sit. Putting up with dust and crap is now almost a phobia to me since my recent workshop build. All clean and tidy but takes minutes to destroy!
Like your first project ideas. Already thought of drill bit holders, router bit stands etc. Will take the KISS advice. Have some rather intricate projects in mind I’ll try my best to postpone until I’ve covered the basics. Had in mind I’d be producing show stopping work in a short time. Might be in for a rude awakening I think!

One further question for you, perhaps the only man on the forum who can answer ..... when do you think I’ll be making a simple collet holder? 😉

[Pilsbury]

Voicecoil. It’s amazing how only until fairly recently dust extraction has become a big thing. I’m on that. Health is important especially when cutting stuff like MDF. Plus my workshop is all new and tidy. Even went to sand outside the other day. Won’t last!

[Zorbit]

Removed.

[JAZZCNC]

One further question for you, perhaps the only man on the forum who can answer ..... when do you think I’ll be making a simple collet holder? 😉

At this moment I can't say as I'm still waiting for the slow boat but when the boat lands you are the first on the list.!

[Pilsbury]

Zorbit. Interesting about clearance planes. Shall bear that in mind. Also good to hear about HSS being more forgiving. The few bits I have bought are carbide as I thought they were the holy grail.... at least that’s what they said they were on Banggood!

[Pilsbury]

Dean.... only joking.... patience is a virtue I’m told. But I’m clearly not a very virtuous person. I’ve demonstrated that on many an occasion😏

[JAZZCNC]

Dean.... only joking.... patience is a virtue I’m told. But I’m clearly not a very virtuous person. I’ve demonstrated that on many an occasion😏

Yep, it is but it will be worth the wait I promise you that.

Regards the HSS then it depends on what your cutting but I'd always go with Carbide for a router as it suits high-speed spindles better as you can run them at higher speeds and higher loads without destroying the cutter. Only downside is they are more brittle and less forgiving if you crash them.

[Pilsbury]

So perhaps my carbide purchases weren’t all that bad. TBH I’ve bought some end mills, ball nosed v bits, flattening bits, v carve bits and still had change out of £20 including postage. Not the end of the world if some meet an untimely end. Think I’ll be more upset about nackering my project.

[Zorbit]

Removed.

[Pilsbury]

If you can use a decent diameter tool then do so, an 8mm cutter is a lot stronger than a 6mm.

You’ve just reminded me about another question! I’ve recently watched a YouTube vid about a bloke talking about the pros and cons of his small 60x90, medium 120x120 and large 120x240 machines. He surprised me when talking about their capabilities. All looked decent expensive machines but he said in the smaller and medium ones 1/4” bits in hardwood would struggle. Only in the big machine can you use them due to rigidity and spindle power. Suppose it depends on the machine, but they were branded gear which wouldn’t have been cheap.

[Clive S]

You’ve just reminded me about another question! I’ve recently watched a YouTube vid about a bloke talking about the pros and cons of his small 60x90, medium 120x120 and large 120x240 machines. He surprised me when talking about their capabilities. All looked decent expensive machines but he said in the smaller and medium ones 1/4” bits in hardwood would struggle. Only in the big machine can you use them due to rigidity and spindle power. Suppose it depends on the machine, but they were branded gear which wouldn’t have been cheap.

How about a link to the vid !!!

[Pilsbury]

How about a link to the vid !!!
Here you go!
https://youtu.be/_YQoOfAm7UU

[routerdriver]

I don't think you will go far wrong with the bargain level carbide cutters.I haven't even seen an HSS router cutter in twenty years or so although I suspect I have one at the back of a drawer.One thing to watch out for is that not all the TCT cutters have inserts all the way to the centre and consequently won't plunge cut.I bought a few of these myself and it doesn't actually cause many problems as I have the option of a ramp entry tot he cut.As for the holy grail,that has to be Poly Crystalline Diamond and really needs to be experienced once you are confident the cut won't go through a clamp or worse a high tensile bolt head-but if spotted in time and with a control that adjusts feed speed you may be able to machine a nice flat on the edge of the bolt head-not that I'm admitting anything.....

[Neale]

So much depends on what you need to achieve. That guy is a professional looking to maximize throughout from his investments. As a home user, the priorities are different. I try to keep cutter rpm up (I keep reminding myself that when I use a handheld router I'm running a 1/2" cutter at 26K rpm) and feed rate up - too slow burns wood. So I tend to use depth of cut to set the load on the machine. Maybe DoC = cutter dia might be a starting point, but a limiting factor will either be load on spindle (I probably wouldn't be using a 1/2" cutter at that depth...) or how well you can clamp the work, especially trying to hold down the piece you are cutting as you break through. Double-sided tape is great but a real pain to get off afterwards!

I use 6-8mm a lot in wood - and mostly 6mm - but have a 50mm cutter for surfacing. DoC is pretty small for that one. And I won't be trying to cut out 12mm ply in one pass - apart from anything else, my dust collection couldn't cope! On which subject, for the odd one-off, I often forget the dust shoe and just track the cutter with a handheld nozzle on the shop vac. Plastic nozzle, of course, which is looking a bit tatty now after a few years' use!

[Zorbit]

Removed.

[Clive S]

Plastic nozzle, of course, which is looking a bit tatty now after a few years' use!

How many shocks do you get off it. :whistle: If I touch my pendant the static kills it.

[Neale]

Clive - never had a static shock off it. Vac hose is plastic, usual kind of thing. My pendant/MPG is wireless and hasn't given me a problem in the few years I've been using it. I am fairly sensitive to static-type charges and would chase it down if it happened - with a history of heart problems, I'm not keen on that kind of thing!

[Clive S]

Clive - never had a static shock off it. Vac hose is plastic, usual kind of thing. My pendant/MPG is wireless and hasn't given me a problem in the few years I've been using it. I am fairly sensitive to static-type charges and would chase it down if it happened - with a history of heart problems, I'm not keen on that kind of thing!

Its probably because I use a dust commander so the hose is not connected to ground I will try it with a wire from the hose to ground. :stupid:

[JAZZCNC]

A good practice exercise that will have all of the above plus more and will be useful is a Collet holder.
If your feeling really confident instead of collet pockets with straight sides make the pockets tapered and use a 2.5D toolpath with a ball-nose cutter. Also, try putting chamfers on the edges.

Why am I getting a DaJaVu feeling here.? . . . If you are going to post at least use your own words.!!



You’ve just reminded me about another question! I’ve recently watched a YouTube vid about a bloke talking about the pros and cons of his small 60x90, medium 120x120 and large 120x240 machines. He surprised me when talking about their capabilities. All looked decent expensive machines but he said in the smaller and medium ones 1/4” bits in hardwood would struggle. Only in the big machine can you use them due to rigidity and spindle power. Suppose it depends on the machine, but they were branded gear which wouldn’t have been cheap.

He's comparing apples with oranges when he's talking about industrial machines and to honest his idea of industrial and sturdy machine honestly isn't. That Sabre machine as so many weak areas in it's design it only just classes as industrial.

You won't have any trouble pushing a 12mm cutter thru most wood or manmade materials on a smaller properly built machine with a decent spindle. How deep and how fast is all that will change between industrial and hobby sized machines.

He's correct when he says most small machines can not cut at the correct feed rates which the manufacturers recommend but that doesn't mean they can't cut perfectly fine within the limits of the power of the spindle.
Yes you won't be churning out the product by the 1000's per day but you can certainly produce enough to start a very healthy business, I've got dozens of customers using my small to medium machines that do just that.

To be honest, to cut correctly at optimum goes beyond just machine size, strength, or spindle power, Dust extraction also becomes massively important because cutting deeper and faster creates more waste material which if not evacuated fast enough becomes a problem quickly so huge dust extractors are required, then you have the explosive side of sawdust to deal with and so on.

Work holding goes to another level, Cutting deeper and faster creates more cutting pressure so holding force becomes massively important. Vacuum holding gets expensive very quickly, for instance, I've just a fit a 10Hp Vac pump that cost £5,500 and that's without the Bed and all the pipework ETC that goes with it. You don't get much change out of £8k for what is a relatively Average Vac setup, it's not uncommon to have 2 x 10Hp pumps working if cutting lots of smaller parts.
Small or large work holding as to be done and you'll often find industrial machines that have undersized Vac systems using just the same work holding techniques that are used at hobby level, ie: Screws and double-sided tape or whatever gets the job done.
I've got a friend who operates a 200K machine in a high volume furniture production environment and it's not uncommon for them to use Vac and double-sided tape because the 2 x 15Hp Vac pumps can't hold everything all of the time and the carnage that is caused if parts lets go and the 20HP spindle slings it across the building is a nightmare health and safety issue.

It's all about levels of Degree.!!.... These things also apply at the Hobby level just to a lower degree, it's still important to get the best from your cutter and machine but no so critical and much less forgiving.
Don't stress over the machine it will do everything you want for a long time before you'll outgrow it and even then it won't be because it's underpowered, it's nearly always the size which people outgrow.

[Zorbit]

Removed.

[Pilsbury]

Brilliant info all. Thanks for replying.