designing a good CNC : need some orientation, am i over thinking stuff?

[sky99]

You have a lot of good comments here but I think you need to step back and evaluate what your needs are and what you expect out of the machine. As others have said a machine suitable for machining aluminum must be far more rigid than one suitable for wood working. Rigid means a massive frame, ideally built from steel.

Even with aluminum we get into degrees of rigidity required. If all you want to do is engraving you can get by with a far lighter machine. If on the other hand you want to run end mills and use all the horse power in your spindle, you will need a very rigid machine. Actually the same applies to wood working, a light machine suitable for engraving will not do well running a 3/4" cutter.

In a nut shell what you expect a machine to do for you will dictate how it is built and how much it will cost.

This statement: "I don't have very specific materials to cut, so i'd say plastics, wood, and aluminum." is all well and good but it makes it difficult for people to zero in on an ideal machine design. What most people would think about when you mention aluminum puts you into a different class of machine. In this case a far more expensive machine.

Considering you are on an island you may have constraints the rest of us don't have. For example access to steel or aluminum suppliers and machine shops to help with material prep. I'd seriously look into what resources you have on the island or near by. In case it isn't obvious I don't know much about your island. However machine shops can be a huge advantage for a DIY build so I'd put a high priority on getting an inventory of resources on the island and near by.

I'm getting wishy washy indications as to what you really want to do here. Is it build a machine from the ground up or to assemble a kit? This might be a case where I would be OK with your buying a kit of T-Slotted extrusions that is ready to assemble. Generally I suggest steel as it is so cheap these days. {well it was until the tariffs increased} Steel has additional benefits including adding mass to the machines frame, easy weld ability and good strength. The problem in your case, with steel, is getting it there in good condition at a reasonable price. However for these sorts of machines I do believe steel is the best choice if you can handle it properly.

As for T-Slotted aluminum, I really don't like it for machine tool major structures, especially the three axis supports. Most of the T-Slots on the market are very light weight and the stuff that isn't is very expensive. You could look into plain old aluminum structural sections, again not cheap but maybe lighter. You would have to balance shipping costs against the increased material costs to determine if it is worthwhile to use aluminum.

You are most certainly right. Perhaps i should drop the aluminium requirement, and try to build a first machine that works, to do woods and plastics, and perhaps those very thin sheets of metals (less than 0.5mm, can be cut with scisors)
For the machine, i really want to build it from the ground up, because i want to learn, i want to know how it works exactly, so that i understand it's strengths and weaknesses.
I can forsee myself tweaking it quite a bit, upgrading it, so i want to build it to be able to improve it.

The more this topic goes, the more i think that i should make a simpler machine, like this one posted on the very forum : mdf madness
However, i don't know how to source the aluminium plate. I'll have a look at what i find around here for that.

I'm thinking that maybe i should go with such a machine, to do most of what i want to do (woods and plastics), and later on build another machine, this time dedicated to precise metal machining, and have it beeing smaller (20x20cm or 30x30cm cut area), full metal, ultra rigid, etc...

As of now, i don't have a CNC. I have access to a laser cutter, that's all. So i don't know what i can do with a CNC router, and what is better done another way.
When i started 3D printing, it was the same. Now i know what materials to use, how to design for 3D printing, and when to make the think another way.

[awerby]

If you do drop the aluminum requirement, then everything gets much simpler and cheaper. Round supported rails or grooved wheels with V-rails will be fine, and you can look at other materials besides steel for your frame. I agree with Wizard about the aluminum T-slot extrusions; they make construction easier, but not cheaper or particularly better. Your hand router will work as a spindle (for a while) and less accuracy in the ball screws will probably be acceptable (although acme screws costing the same will be more precise).

While stepper gearmotors have more torque, they trade speed for that, and in steppers the torque falls off with speed, so I don't see the point of using them, especially since they add backlash. You need all the speed you can get when cutting wood, or it starts to burn. Servo gearmotors would make more sense, since servos go faster and don't lose torque as they approach maximum speed. For a relatively small machine like you're planning, direct-drive NEMA 23 steppers should work fine, although you might consider deploying 2 of them to power the X axis.

[sky99]

If you do drop the aluminum requirement, then everything gets much simpler and cheaper. Round supported rails or grooved wheels with V-rails will be fine, and you can look at other materials besides steel for your frame. I agree with Wizard about the aluminum T-slot extrusions; they make construction easier, but not cheaper or particularly better. Your hand router will work as a spindle (for a while) and less accuracy in the ball screws will probably be acceptable (although acme screws costing the same will be more precise).

While stepper gearmotors have more torque, they trade speed for that, and in steppers the torque falls off with speed, so I don't see the point of using them, especially since they add backlash. You need all the speed you can get when cutting wood, or it starts to burn. Servo gearmotors would make more sense, since servos go faster and don't lose torque as they approach maximum speed. For a relatively small machine like you're planning, direct-drive NEMA 23 steppers should work fine, although you might consider deploying 2 of them to power the X axis.

Hi,
even if i drop the aluminium requirement, i'd still like to pursue with the square rails, because not only everyone agrees that they are the best solution,
but also that it comes at the same cost or lower for me than SBR, due to lower shipping costs.

Even if this machine won't cut metals, i see good rails as an investment for other machines, so i'll keep those.
I don't really mind using a steel frame either, i'm just concerned about cutting it accurately, and assembling it properly, something that i'm not sure i can do as of now.
Seeing the square steel tubes frame posted in a previous post gives me hope though. But i was considering komacel, that is an expansed PCV sheet, that
can be found here. It's a bit expansive for plastic, but it is really rigid, and should have stable dimensions (no reaction to moisture or heat as would wood do).

I think i could use this and have it machined with holes accurately placed for critical parts.
Of course, if i can have the same thing done in metal i'll opt for it.

So what do you think about this idea?

[wizard]

You are most certainly right. Perhaps i should drop the aluminium requirement, and try to build a first machine that works, to do woods and plastics, and perhaps those very thin sheets of metals (less than 0.5mm, can be cut with scisors)

I wouldn't drop the aluminum requirement if you really think it is needed. It does however require building a stiffer machine to get good results. Let's be realistic here you can build a machine out of wood products that will do aluminum but for a number of reasons it is a bad idea. The idea behind building a really stiff machine in steel is that you will get measurably better results in aluminum with such a machine. It will cost more no doubt there

For the machine, i really want to build it from the ground up, because i want to learn, i want to know how it works exactly, so that i understand it's strengths and weaknesses.
I can forsee myself tweaking it quite a bit, upgrading it, so i want to build it to be able to improve it.

Tweaking and improving gets to be expensive. The only good thing is that the expense is spread over time.

As for learning machine technology you are on the right track but I must highlight a DIY machine, to this extent, will require access to machining services.

The more this topic goes, the more i think that i should make a simpler machine, like this one posted on the very forum : mdf madness
However, i don't know how to source the aluminium plate. I'll have a look at what i find around here for that.

I really don't know what it is like on your island, from what I've seen elsewhere you will likely get taken to the cleaners for shipping charges.

I'm thinking that maybe i should go with such a machine, to do most of what i want to do (woods and plastics), and later on build another machine, this time dedicated to precise metal machining, and have it beeing smaller (20x20cm or 30x30cm cut area), full metal, ultra rigid, etc...

As long as you have the money no problem. There is one advantage to having two machines. The one handling wood can be kept dry. The one machining aluminum will likely be wet from lubricants / coolants.

As of now, i don't have a CNC. I have access to a laser cutter, that's all. So i don't know what i can do with a CNC router, and what is better done another way.
When i started 3D printing, it was the same. Now i know what materials to use, how to design for 3D printing, and when to make the think another way.

The one thing that people underestimate when coming from a 3D printing back ground is the need for rigidity. Cutting forces are relatively high in comparison.

[wizard]

If you do drop the aluminum requirement, then everything gets much simpler and cheaper. Round supported rails or grooved wheels with V-rails will be fine, and you can look at other materials besides steel for your frame.

There is an endless variety of machine built successful to handle various chores in wood working. Some machines are designed to be dirt cheap to get the job done that the user had in mind. Like everything else he higher your quali expectations the higher the quality that you need out of the machine.

I like using the idea of boat building here. You can do frame components on a relatively loose machine if you want, that same machine might be useless cutting wood for cabinet work inside the boat.

I agree with Wizard about the aluminum T-slot extrusions; they make construction easier, but not cheaper or particularly better.

Actually if one isn't careful about the extrusions selected I would say you will end up with a significantly worst machine. That and paying attention to assembly details can make a hide difference in the success of a T slotted extrusion machine.

In some cases it would be a mistake to use aluminum T slots if they don't have the stiffness required. I'm not really completely opposed to T-Slots, there is a great deal used at work, often for secondary structures. The stuff will work but builders often cut corners forgetting about gusseting, lap plates and brackets. This can lead to really weak structures when assembled with just the bolts tapped into the ends of the extrusions.

Your hand router will work as a spindle (for a while) and less accuracy in the ball screws will probably be acceptable (although acme screws costing the same will be more precise).

While stepper gearmotors have more torque, they trade speed for that, and in steppers the torque falls off with speed, so I don't see the point of using them, especially since they add backlash. You need all the speed you can get when cutting wood, or it starts to burn. Servo gearmotors would make more sense, since servos go faster and don't lose torque as they approach maximum speed. For a relatively small machine like you're planning, direct-drive NEMA 23 steppers should work fine, although you might consider deploying 2 of them to power the X axis.

This is perhaps a good reason to have a machine dedicated to wood, the cutting and spindle velocities difference means that can adjust the performance capabilities of the spindle and the axis drives for a specific usage.

[sky99]

I wouldn't drop the aluminum requirement if you really think it is needed. It does however require building a stiffer machine to get good results. Let's be realistic here you can build a machine out of wood products that will do aluminum but for a number of reasons it is a bad idea. The idea behind building a really stiff machine in steel is that you will get measurably better results in aluminum with such a machine. It will cost more no doubt there

Tweaking and improving gets to be expensive. The only good thing is that the expense is spread over time.

As for learning machine technology you are on the right track but I must highlight a DIY machine, to this extent, will require access to machining services.

I really don't know what it is like on your island, from what I've seen elsewhere you will likely get taken to the cleaners for shipping charges.

As long as you have the money no problem. There is one advantage to having two machines. The one handling wood can be kept dry. The one machining aluminum will likely be wet from lubricants / coolants.

The one thing that people underestimate when coming from a 3D printing back ground is the need for rigidity. Cutting forces are relatively high in comparison.

Hi,
in fact, i have no requirement per say. I don't really need a CNC right now, i think that once i get used to it, i'll know why i need it
To be more serious, it's not just for fun that i want it. I understand that 3D printing will get certain jobs done, a CNC will get other jobs done.

I thought aluminium was an easy metal (they often say "CNC able to cut wood and light metals such as aluminium"), so i wanted it. But if i really think about it, the only aluminium i would mill would be parts to improve the CNC.

So i can easily let aluminium aside for now.
Perhaps it's for the better, and when i build a metal CNC, i'll make it super rigid and able to cut even stainless steel or hard metals.

I can access some machining service, at least from my fablab, but they don't have a setup able to cut metal. However, i should be able to find people doing it around.

So the only metal i'd cut on this CNC would be super thin sheets (0.5mm or less, can be cut with regular scisors), it should be easy i think?

[sky99]

There is an endless variety of machine built successful to handle various chores in wood working. Some machines are designed to be dirt cheap to get the job done that the user had in mind. Like everything else he higher your quali expectations the higher the quality that you need out of the machine.

I like using the idea of boat building here. You can do frame components on a relatively loose machine if you want, that same machine might be useless cutting wood for cabinet work inside the boat.

Actually if one isn't careful about the extrusions selected I would say you will end up with a significantly worst machine. That and paying attention to assembly details can make a hide difference in the success of a T slotted extrusion machine.

In some cases it would be a mistake to use aluminum T slots if they don't have the stiffness required. I'm not really completely opposed to T-Slots, there is a great deal used at work, often for secondary structures. The stuff will work but builders often cut corners forgetting about gusseting, lap plates and brackets. This can lead to really weak structures when assembled with just the bolts tapped into the ends of the extrusions.


This is perhaps a good reason to have a machine dedicated to wood, the cutting and spindle velocities difference means that can adjust the performance capabilities of the spindle and the axis drives for a specific usage.

What do you mean by boat building (sorry if it's a common expression, English is not my first language)?

[Jon.N.CNC]

Hello,
yes, i am able to use cad software. My software of choice is OpenScad.
I was considering such a frame, but i feared that the tolerences for such square tubes would not be good enough.
I bought a tube like that for a mast for my house. However, i dont' know if those square tubes are straight enough,
if the dimensions are coherent along the bar (i guess that they are, if they are extruded?, but are they
totally straight?)

I've read that h-rails require extremely precise positioning to work, and otherwise end up damaging themselves.
Then, assembling those bars, won't it be a problem? how do i ensure a precise positionning when whelding it?
Won't it deform under the heat?

Not really sure where you read that. You can hang half a ton off a hiwin carriage so it would have to be a very rigid un aligned frame to do it. There is a method to it, it's pretty straight forward. Search aligning hiwin rails in YouTube.

As they take more weight than sbr they are Infact less sensitive to alignment error. Serious error will screw up sbr carriages just with a push.

What you are reading is people that use square rail, make sure they do it properly. Don't read so much about sbr rail alignment because it's used by hobbyists.

[Jon.N.CNC]

If you do drop the aluminum requirement, then everything gets much simpler and cheaper. Round supported rails or grooved wheels with V-rails will be fine, and you can look at other materials besides steel for your frame. I agree with Wizard about the aluminum T-slot extrusions; they make construction easier, but not cheaper or particularly better. Your hand router will work as a spindle (for a while) and less accuracy in the ball screws will probably be acceptable (although acme screws costing the same will be more precise).

While stepper gearmotors have more torque, they trade speed for that, and in steppers the torque falls off with speed, so I don't see the point of using them, especially since they add backlash. You need all the speed you can get when cutting wood, or it starts to burn. Servo gearmotors would make more sense, since servos go faster and don't lose torque as they approach maximum speed. For a relatively small machine like you're planning, direct-drive NEMA 23 steppers should work fine, although you might consider deploying 2 of them to power the X axis.

Stepper gearmotors? Do you mean planatary gearboxes? I have some zero backlash planatary boxes. If you require more torque, than a nema 23 alone which for cutting aluminium you do. Then without either a sub standard belt arrangement. Boxes are the best way to go if you don't want to consider larger motors or steppers. speed lost (which isn't a lot, you still get descent Rapids) is going to be gained by speed cutting and if your running it right you are cutting 90% of the time. So Infact slower not to have more torqu as you can run a larger spindle, have more frame weight and subsequently you cut deeper.

[sky99]

Not really sure where you read that. You can hang half a ton off a hiwin carriage so it would have to be a very rigid un aligned frame to do it. There is a method to it, it's pretty straight forward. Search aligning hiwin rails in YouTube.
As they take more weight than sbr they are Infact less sensitive to alignment error. Serious error will screw up sbr carriages just with a push.
What you are reading is people that use square rail, make sure they do it properly. Don't read so much about sbr rail alignment because it's used by hobbyists.

Hello,
this is great news, so that means that if i go for a moving gantry, with such a load resistance, i could go for 2 rails for X axis instead of 4?

i'm also thinking about the way to mount those rails.

I'd preferably would have them lay flat on the table, but it seems easier to design a gantry if the rails are on two "boards", perpendicular to the bed (with the carriages facing outwards from the machine)
However, what worries me is that the full load would be exerted on the top row of the balls, wouldn't it cause premature wear?

[Jon.N.CNC]

Hi,
in fact, i have no requirement per say. I don't really need a CNC right now, i think that once i get used to it, i'll know why i need it
To be more serious, it's not just for fun that i want it. I understand that 3D printing will get certain jobs done, a CNC will get other jobs done.

I thought aluminium was an easy metal (they often say "CNC able to cut wood and light metals such as aluminium"), so i wanted it. But if i really think about it, the only aluminium i would mill would be parts to improve the CNC.

So i can easily let aluminium aside for now.
Perhaps it's for the better, and when i build a metal CNC, i'll make it super rigid and able to cut even stainless steel or hard metals.

I can access some machining service, at least from my fablab, but they don't have a setup able to cut metal. However, i should be able to find people doing it around.

So the only metal i'd cut on this CNC would be super thin sheets (0.5mm or less, can be cut with regular scisors), it should be easy i think?

You either need to be prepared to do your homework, and take your time evaluating the advise and doing a self build or buying a semi professional machine or you rush into it and purchase a kit that higher chance than not won't be up to what you want to do with it. 2-4 years down the line still hooked on it you set about starting over with a new machine and that kit which hasn't done a lot of work Infact just been a bit of money pit is now obsolete and not worth a quarter of what you paid for it.

[Jon.N.CNC]

Hello,
this is great news, so that means that if i go for a moving gantry, with such a load resistance, i could go for 2 rails for X axis instead of 4?

i'm also thinking about the way to mount those rails.

I'd preferably would have them lay flat on the table, but it seems easier to design a gantry if the rails are on two "boards", perpendicular to the bed (with the carriages facing outwards from the machine)
However, what worries me is that the full load would be exerted on the top row of the balls, wouldn't it cause premature wear?

For sure, and like i say they will take a hell of a weight but no, if I'm understanding you correctly, what inbalace there is, when the machine changes direction the inbalace swaps to other rail so it's fairly even overall, but the less play in the frame the less inbalace there will be.

But can't be certain where your concern is, best bet is post a design here. People will point you in the right direction.

[cyclestart]

sbr blocks can be rotated a few degrees on the rails without stress, profile blocks can not.
The blocks are also more 'elastic' in nature, although 'elastic' may be better described as permanent deformation
I'm not advising the use of supported round but I do believe they will tolerate more misalignment before binding.

[Jon.N.CNC]

sbr blocks can be rotated a few degrees on the rails without stress, profile blocks can not.
The blocks are also more 'elastic' in nature, although 'elastic' may be better described as permanent deformation
I'm not advising the use of supported round but I do believe they will tolerate more misalignment before binding.

with square rail you set one rail, then parrallel second rail to first rail. Bolting a plate between carriages on each rail to set second rail is enough to avoid binding. The square rail are rigid enough in themselves that you would have to be pretty un careful to twist them to the point they bind. I at that stage then clamped bars to hold lose second rail in position and un attached plate from second rail carriage and fixed a dti instead and ran along the rail to check alignment. Shimming between clamped bars and rail to correct. Very simple. Use resin under rail if unflat.

if you have to use sbr because you can't align square rails, your cuts won't be straight anyway.

[sky99]

Hello everyone,
sorry for the late reply, i've been (and still am) ill.
This is really interesting, and i quite like the proposed method for aligning the rails.
I've also read from various places that SBR are more tolerent to mis-alignment than SBR, but considering
that the square rails may not be that hard to position, and that they're cheaper or same price to me anyway, i'll stick to using those.

So now comes another question : considering that i'm dropping aluminium as a requirement : i want to cut wood and plastics,
what do you think of a komacel bed? It is expansed PCV, and from what i've seen it's quite hard and won't move under
moist or temperature, plus beeing easy to machine.
The pieces i've had are extremely hard compared to wood.
So what do you think about this material as a bed for the build?

It's a bit expensive, but i can order it cut and is probably cheaper than metal (and i have to find someone to machine a thick aluminium plate for me!)

[Jon.N.CNC]

Hello everyone,
sorry for the late reply, i've been (and still am) ill.
This is really interesting, and i quite like the proposed method for aligning the rails.
I've also read from various places that SBR are more tolerent to mis-alignment than SBR, but considering
that the square rails may not be that hard to position, and that they're cheaper or same price to me anyway, i'll stick to using those.

So now comes another question : considering that i'm dropping aluminium as a requirement : i want to cut wood and plastics,
what do you think of a komacel bed? It is expansed PCV, and from what i've seen it's quite hard and won't move under
moist or temperature, plus beeing easy to machine.
The pieces i've had are extremely hard compared to wood.
So what do you think about this material as a bed for the build?

It's a bit expensive, but i can order it cut and is probably cheaper than metal (and i have to find someone to machine a thick aluminium plate for me!)

Foam pvc sheet. Not very good for a bed As it Will compress. Mdf works if it's cheap your looking for. Or for a quality bed, Tufnol is excellent, is rather expensive tho but better than aluminium and there are some cheaper brands of tufnol around. And you can get it made to over an inch in thickness if you wanted.

[louieatienza]

Hello everyone,
sorry for the late reply, i've been (and still am) ill.
This is really interesting, and i quite like the proposed method for aligning the rails.
I've also read from various places that SBR are more tolerent to mis-alignment than SBR, but considering
that the square rails may not be that hard to position, and that they're cheaper or same price to me anyway, i'll stick to using those.

So now comes another question : considering that i'm dropping aluminium as a requirement : i want to cut wood and plastics,
what do you think of a komacel bed? It is expansed PCV, and from what i've seen it's quite hard and won't move under
moist or temperature, plus beeing easy to machine.
The pieces i've had are extremely hard compared to wood.
So what do you think about this material as a bed for the build?

It's a bit expensive, but i can order it cut and is probably cheaper than metal (and i have to find someone to machine a thick aluminium plate for me!)

Phenolic sheet....

[wizard]

What do you mean by boat building (sorry if it's a common expression, English is not my first language)?

Boat building as in building ship that floats soon the water. I use the term to describe uses of a machine where accuracy might not be the most important aspect of the machines design and usage. Imagine someone fabricating a mold upon which steam bent timber or foam for a fiberglass lay up will be mounted. Often a lot of the fairing of the form is done by hand. This is sort of like the work a carpenter does building a house as opposed to what a carpenter does inside the house. One is rough work the other is fairly process work.

The idea here is that how accurate a machine is, depends upon what you will be doing with it. A work site table saw for example is a different beast than a table saw in cabinet makers shop. The thought here is that you really can't spec a proper machine until you know what you intend to do with it or put another way what are your expectations?

In a case like this, where you are very nonspecific about what you intend to do with the machine, the tendency is to drive you to more robust hardware. The more robust machine is likely to be able to handle whatever you throw at it.

[louieatienza]

Foam pvc sheet. Not very good for a bed As it Will compress. Mdf works if it's cheap your looking for. Or for a quality bed, Tufnol is excellent, is rather expensive tho but better than aluminium and there are some cheaper brands of tufnol around. And you can get it made to over an inch in thickness if you wanted.

TUFNOL is fine as long as you get the lower grade paper-laminate type. Anything cloth based will be a bear to surface (but does machine nice). Forget about fiberglass-laminate... Cheaper however, are remnants of phenolic countertop material, like Richlite (also used by Gibson for fretboards), PaperStone, Trespa... And they come in cool colors to boot! Another source would be bathroom stall partitions, though they have a melamine outer layer, which you'll lose when you surface the sheet.

[sky99]

Foam pvc sheet. Not very good for a bed As it Will compress. Mdf works if it's cheap your looking for. Or for a quality bed, Tufnol is excellent, is rather expensive tho but better than aluminium and there are some cheaper brands of tufnol around. And you can get it made to over an inch in thickness if you wanted.

So; you say that PVC foam would compress more than MDF? untill now, the MDF i've used for various stuff seemed much softer than the PVC foam i've seen here!

i'll look into Tufnol, or whatever the french name may be around here
When you say better than aluminium, do you mean in terms of price, or in mechanical properties?