Lowcost capable CNC - Make vs Buy?

[Andrewg]

Indeed Jazzcnc,
So given I don't have a business case, but want to explore what the capability would bring to my workshop....the choice comes down for me at least to buy a Workbee or build my own for a budget of £1.5 to 2k. This forum shows that this second route is viable and is the route I am keen to take.

So what have I learnt a 'correct approach' looks like?

I should say I want a machine to cut hardwood in my furniture making workshop. 600x600 work area because I don't have the space and have plenty of processes for which this is big enough. Also helps with accuracy keeping small I believe. Want to cut joinery so 0.1mm repeatability. It will be a workshop machine that won't run all the time but when used needs to be reliable and quick (5m/min cutting?). A build I can complete in two weeks full time ideally..(planning, dreaming excluded)

Frame
Stiffness directly effects performance so important. Unlike manufacturers, DIYer does not worry about shipping, so a steel frame, welded ideally. Epoxy leveling process allows imprecision to be addressed. However I would like to go Ali extrusion and shimming if possible alternative to avoid epoxy and steel working plus flexibility to extend/change frame in future.

Mechanics
Linear rails, ballscrews and correct support bearings sourced from good chinese supplier as set. Leadscrews seem possible compromise that many designs accept, attractive as their lower profile nuts allow leadscrews to more easily fit between bearing rails and keep design simole. Guess wear and lower efficiency not a killer for home machine that operates fewer hours or am I wrong?

Dual drive Y axis seems to be preferred for simplicity now electronics can cope with squaring Gantry especially if drivers have stall detection.This especially of value to me as I want to be able to machines end of pieces held vertically through table.

Principle design challenge are the plates required to mount the components and join it all together. Aluminium can be machined with wood tools. Aluminium tooling plate is already flat, so either they can be cut and drilled myself or waterjet cut by contractor. Adjustability is principle to adopt rather than precision.

Gantry
Make it L shaped and use stiff large box section or extrusions. Extrusions make fitting everything much easier. Rails on front or top&front. One thing that eludes me is how best to join two extrusions to make L, what fitting works that way?

Electrics
Nema23 steppers are big enough for small/medium machine (exact force and inductance to be determined), matched with proper drivers (digital, stalll detection?) and serious power supply (toroidal). Homing limit switches, inductive for accuracy and reliability. Get shielding and earthing of wiring right. Think through positioning and routing of everything.

Electronics
Mach3 and printer ports are old hat. Ethernet and UNCNC or Acorn seem to get thumbs up, though there are also dedicated controllers and open source solutions based on grbl are getting better.

Build challenges
Machine accuracy is determined by build accuracy, so need a dial indicator and know how to use it!

A good design should make build process one of bolting together and aligning ideally, plus lots of wiring.

What have I overlooked?

[JAZZCNC]

Indeed Jazzcnc,
So given I don't have a business case, but want to explore what the capability would bring to my workshop....the choice comes down for me at least to buy a Workbee or build my own for a budget of £1.5 to 2k. This forum shows that this second route is viable and is the route I am keen to take.

Forget the WorkBee or any of those you will be disappointed I promise you that.!
The Budget needs to be 2K to do it right if building DIY.

I should say I want a machine to cut hardwood in my furniture making workshop. 600x600 work area because I don't have the space and have plenty of processes for which this is big enough. Also helps with accuracy keeping small I believe. Want to cut joinery so 0.1mm repeatability. It will be a workshop machine that won't run all the time but when used needs to be reliable and quick (5m/min cutting?). A build I can complete in two weeks full time ideally..(planning, dreaming excluded)

600 x 600 is the perfect size to start your first DIY build. 5Mtr/min cutting no problem, if done correctly you'll double that with a bit to spare.
0.1mm repeatability, again no problem and easily able to achieve better if done correctly.
Building within 2wks could be a stretch for your first build and would require everything to go perfectly and put in some long hours. And obviosuly you have to have everything needed to hand.
For reality's sake, I'd allow your self a full month for fully built and working machines and work shorter hours.
Don't underestimate how long some of this stuff takes, just the wiring alone could take a full week if you are not used to doing it.

Frame
Stiffness directly effects performance so important. Unlike manufacturers, DIYer does not worry about shipping, so a steel frame, welded ideally. Epoxy leveling process allows imprecision to be addressed. However I would like to go Ali extrusion and shimming if possible alternative to avoid epoxy and steel working plus flexibility to extend/change frame in future.

Again Ali extrusion is perfect for first machine as it's easily worked with and accurate. However, you must use the correct type, size and not go with the light duty stuff often found on machines like the Workbee's etc.
It's also very very important how it's all fastened together and plates etc. Done correctly it's very strong and perfect for wood routers.

Mechanics
Linear rails, ballscrews and correct support bearings sourced from good chinese supplier as set. Leadscrews seem possible compromise that many designs accept, attractive as their lower profile nuts allow leadscrews to more easily fit between bearing rails and keep design simole. Guess wear and lower efficiency not a killer for home machine that operates fewer hours or am I wrong?

Don't compromise go with ball screws every time. A quality lead screw and nut that can get close to ball screw efficiency/accuracy will be just as expensive as Chinese ballscrew and won't be massively better in quality.

Dual drive Y axis seems to be preferred for simplicity now electronics can cope with squaring Gantry especially if drivers have stall detection.This especially of value to me as I want to be able to machines end of pieces held vertically through table.

Not strictly required on a machine this size if just cutting woods. However, it is better if you want to cut aggressively or want to cut very hard materials or aluminum, brass, etc.
Not all Drives have stall detection, in fact, very few do, even then they only work in a limited way. A much better solution is to use Closed-loop Steppers which have come down in price massively. Far better than the standard stepper system.

But again going back to usage and Budget, using a single screw setup is much cheaper and if you don't plan on cutting aggressively or harder materials then it could be wasted.
The other thing is that if you design the machine and plan the control box correctly it's not a very difficult upgrade at a later date to just stick another ball screw on and fit another drive in the cabinet.
I've built many machines for people like your self who were on tight Budgets and didn't exactly know what their needs were going to be so this approach was taken (all my small machines are electrically designed to do this). Very few actually found they needed to upgrade and those that did then it was a simple few hours to upgrade which they did them selfs.

Principle design challenge are the plates required to mount the components and join it all together. Aluminium can be machined with wood tools. Aluminium tooling plate is already flat, so either they can be cut and drilled myself or waterjet cut by contractor. Adjustability is principle to adopt rather than precision.

If you cannot make them your self by any of the methods you mention then I suggest you get someone to machine the parts rather than cut them on a waterjet or laser. unless they are thin parts. Both water and laser leave a taper on the edges of thick parts which can cause you more grief than it would to cut them your self with a hand router.

Gantry
Make it L shaped and use stiff large box section or extrusions. Extrusions make fitting everything much easier. Rails on front or top&front. One thing that eludes me is how best to join two extrusions to make L, what fitting works that way?

The best method for the "L" gantry is to bolt into gantry end plates with the ends. On a narrow gantry like what you want you'll get away with just one Bolt in the center which goes from the underside into a T-nut on the upper profile.(or can drill and tap the profile directly) However, it's important that you have a piece of material which is a nice tight fit that goes into the slots between upper and lower profile. This stops movement from sliding and the single-bolt clamps the profiles together. More bolts could be added but on short length like this it's not required.

Electrics
Nema23 steppers are big enough for small/medium machine (exact force and inductance to be determined), matched with proper drivers (digital, stalll detection?) and serious power supply (toroidal). Homing limit switches, inductive for accuracy and reliability. Get shielding and earthing of wiring right. Think through positioning and routing of everything.

Electrics are the KEY to a great machine. Take your time, don't cut corners and if the budget allows use closed-loop steppers, in fact, save up a little, wait a little longer if needs be, it's worth the wait.

Electronics
Mach3 and printer ports are old hat. Ethernet and UNCNC or Acorn seem to get thumbs up, though there are also dedicated controllers and open source solutions based on grbl are getting better.

Again KEY don't cut corners. Forget Grbl or open-source, yes it's getting better but it's still miles away.
If you want quick and good at a reasonable price then go with UCCNC and one of there controllers like the AXBB, there is nothing better for a wood router for the money.
Or if your like a challenge then take a look at Linux CNC and Mesa but get ready for a big learning curve.!

Build challenges
Machine accuracy is determined by build accuracy, so need a dial indicator and know how to use it!

A good design should make build process one of bolting together and aligning ideally, plus lots of wiring.

What have I overlooked?

Design is VERY VERY important and if done with a forward-thinking attitude then you can have a great machine for not a lot of money.

Lastly, let me just say don't get caught up in the "Steel is better than Profile" or " Must use Steel if want a strong machine" because it's often said by those who haven't built a machine using it.
I build machines using both or Mixture of both as is often the case and I can tell you now profile is more than good enough for any router which is to be used in a DIY environment or even a Small/Med business environment where speed and high material movement rates are not required. Accuracy and repeatability can still be achieved with a profile just like it can with Steel, that's down to how it's built the design and components used.

Good luck if you take this route and if I can help just ask.

[Andrewg]

Ah Kitwin, the siren call of ‘just make it a bit bigger’! But I take your point, extra Y length does not change the design or performance significantly.

And thanks for the appreciation Brian, I had hoped this would be of value to others. However others have already steered you away from gantry routers for steel

So where has Jazz left me:

Budget and spec is realistic (Hurrah) but time under significantly! I can live with the greater time commitment, though I expect I will be tempted into stretching the budget when it comes to the motors.and electronics. Definitely worth press on then:

Frame
Wood and plastic cutting router, so aluminum extrusion frame keeps things simpler for me.(avoids welding and steel work) Plates I will definitely be looking to cut/drill my own so will want to keep design simple.

It's also very very important how it's all fastened together and plates etc. Done correctly it's very strong and perfect for wood routers.
.

Sure I will need to come back to what joining methods for extrusions are best once I have a first stab at the design.

Mechanics
Ballscrews all round, but only 3
Single Y ballscrew will save a bit of budget, however I do need to cut ends of boards set vertically. With an under-table ballscrew and cross brace, I will needs to have the spindle sitting forward of the bearings enough to do this. I only need 65mm of cut distance beyond table. Is that a sensible design option?

Gantry

However, it's important that you have a piece of material which is a nice tight fit that goes into the slots between upper and lower profile.

I get the material in the slots to lock the two extrusions together, but see that 10mm aluminium bar is not a standard size so what to use? Options seem to be either machine a ½” aluminum bar down to 10mm slot size on a router table or forget the slot filler and have multiple bolts. By creating a gantry length ‘washer’ with regular clearance holes along it, I could use it as a guide to drill the access holes in the lower extrusion, then install bolts in it to mate with slot nuts in the upper extrusion, so they are bolted every 50mm or so. Avoids having to machine material to tolerance?

Electrics
Tempted by closed loop steppers - looks like for 2nm nema23 steppers it is about £40 stepper plus £20 driver vs £80 for closed loop motor and driver, so maybe extra £20 per axis well spent. Where will I see the benefit besides getting error rather than inaccuracy due to missed steps?


Electronics
There are enough challenged already, UNCNC it is.

Design is VERY VERY important and if done with a forward-thinking attitude then you can have a great machine for not a lot of money.

But still all down to the design, so guess I need to fire up Fusion360 and start designing. Plan to start from the Z axis and work out axis by axis. The Z seems a simple matter of sandwiching 15mm linear rails and 1605 ballscrew between two plates and getting the heights and clearances right...we shall see.

[JAZZCNC]

Mechanics
Ballscrews all round, but only 3
Single Y ballscrew will save a bit of budget, however I do need to cut ends of boards set vertically. With an under-table ballscrew and cross brace, I will needs to have the spindle sitting forward of the bearings enough to do this. I only need 65mm of cut distance beyond table. Is that a sensible design option?

Single or double ball screws it doesn't make any difference to if you can overhang or not. This is down to gantry design.
Many will sweep the gantry beam back from the centre of the bearing plates to recover lost tablespace. However, in your case this can't be done because you need the spindle to project past the end of the bed so your better with the gantry beam inline with the bearing plates.

There are other design methods, like having the long axis frame rails extend past the end of the bed. In this way you can have both methods and have any overhang amount you like(within reason). The cost is it takes up more physical room and slightly longer rails which cost more money.
I've used this design on several machines so that a 4th axis can be used on the end for turning and fluting etc. The same can be done with extending the gantry at one side and using the length of machine for longer work. (See pics)

Gantry

I get the material in the slots to lock the two extrusions together, but see that 10mm aluminium bar is not a standard size so what to use? Options seem to be either machine a ½” aluminum bar down to 10mm slot size on a router table or forget the slot filler and have multiple bolts. By creating a gantry length ‘washer’ with regular clearance holes along it, I could use it as a guide to drill the access holes in the lower extrusion, then install bolts in it to mate with slot nuts in the upper extrusion, so they are bolted every 50mm or so. Avoids having to machine material to tolerance?

Your way way over thinking this.!! . . . For machine this size it's not required. To be honest at this size you would get away with NO bolts. If not using the spacer method then 2 x M10 bolts spaced evenly along length and tapped into the upper profile will be more than enough.

Electrics
Tempted by closed loop steppers - looks like for 2nm nema23 steppers it is about £40 stepper plus £20 driver vs £80 for closed loop motor and driver, so maybe extra £20 per axis well spent. Where will I see the benefit besides getting error rather than inaccuracy due to missed steps?

Depending on which you get then the main differences will be smoothness and speed/torque.

The smaller closed-loop motors (<=3nm) all tend to be 3 phase and the motors use 0.9Deg step amount or 1.2 rather than 1.8deg found on typical hybrid steppers. This gives a smoother action but requires more pulses from the controller to get the same speed. But controllers like AXBB or UC300 etc have more than enough frequency so this isn't an issue.

Being 3phase they provide more torque and allow higher rpm's. Typical RPM where torque starts to drops away is 1000-1100rpm for hybrid stepper motor. With closed loop it's around 1500Rpm, but this does depend on other factors like quality and voltage etc. But in genral they are faster and stronger.

Larger (=> 4Nm) Closed-loop motors can be found either in 3phase or two phase versions.

But still all down to the design, so guess I need to fire up Fusion360 and start designing. Plan to start from the Z-axis and work out axis by axis. The Z seems a simple matter of sandwiching 15mm linear rails and 1605 ball screw between two plates and getting the heights and clearances right...we shall see.

Don't use 15mm for the Z-axis as it makes more difficult to build regards clearances and they are fiddly. 20mm cost very little extra and make for a much stronger and easier to build Z-axis.
Whatever you do don't cut corners on the Z-axis, it's THE one area you don't want to get wrong because it holds the tools so if it flexes or vibrates this will be seen in your work.!


Below are 2 machine designs, both can be single or twin screws and placed under the bed for protection. The larger one will extend past the end of the bed and the side, it also adjustable length 4th axis.

Edit: also a larger version with extended side rails for more front extension.

[Andrewg]

Your way way over thinking this.!! . . .

That is what I need - Keep me focused on the real issues


Yes this is what I aspire to:Neat, clean, capable looking machine!
From your previous posts I am assuming I am looking at
- 45x90 extrusions on Y axis with two for the L gantry.
- 12mm Plate for ends and gantry sides
- 20mm linear rails all axis
- 1610 ballscrew, 1605 on Z driven via belt and pulleys so steppers can be tucked out of sight, 1: 1 gearing? is it worth added parts?

A little worried about the X/Z carriage getting complicated. If rails on front face and ballscrew on top, then couldn't it be a single plate again?

I am assuming this design cannot cut beyond the table, but by removing the gantry sweep back and maybe mounting the rails on the face of the gantry (and removing the control panel) I could create sufficient over run.

The smaller closed-loop motors (<=3nm) all tend to be 3 phase

The ones I was looking at for price were like these appear to be just steppers with encoder and therefore not 3phase though these look similar but are described as 3phase and are £40 more so guess your advantages of 3phase closed loop will cost a little more. Know little about steppers besides frame size (NEMA) and torque (Nm) plus a vague idea that inductance needs to be worried about.

Don't use 15mm for the Z-axis as it makes more difficult to build regards clearances and they are fiddly. 20mm cost very little extra and make for a much stronger and easier to build Z-axis.

Again feedback from real experience appreciated. How much should I be worried about keeping Z axis weight down? I was assuming that on a small machine, I want to keep the weight being flung about to a minimum to ensure good acceleration and performance whilst allowing modest (lower cost) motors and drivers to be spec-ed.

Working on a Z axis, need to upgrade the rails to 20mm!

[JAZZCNC]

From your previous posts I am assuming I am looking at
- 45x90 extrusions on Y axis with two for the L gantry.
- 12mm Plate for ends and gantry sides
- 20mm linear rails all axis
- 1610 ballscrew, 1605 on Z driven via belt and pulleys so steppers can be tucked out of sight, 1: 1 gearing? is it worth added parts?

Yes 45 x 90 with 10mm slot Bosch Rexroth or equivalent with this style of machine. This is type and size is required to allow easy fitting ball screws because the slots match up with Bk12 bearing blocks so no extra plates are required.

12mm could be used for the end plates but I wouldn't use it for the gantry sides and Z-axis. Normaly I would use 15mm for the end plates and making motor mounts etc and use 20mm for the gantry sides and the Z-axis.

A little worried about the X/Z carriage getting complicated. If rails on front face and ballscrew on top, then couldn't it be a single plate again?

Well yes and No.
Yes could be done but with this design, it compromises the machine in other ways. Rails on the front face only mean the distance between the rails is narrow so there's less support to the Z-axis rear plate.
Next the ball screw on the top means extra plates will be required so the bearings can be mounted, this means extra work and it also raises the screw high up the Z-axis rear plate causing an imbalance in how the forces are applied.

I am assuming this design cannot cut beyond the table, but by removing the gantry sweep back and maybe mounting the rails on the face of the gantry (and removing the control panel) I could create sufficient overrun.

No, it can't, well it does but not by much. This design doesn't suit cutting past the front. If you want to cut past the front then use a gantry design like what's used on the other machine along with a slightly different base frame for rail placement.

That machine uses ITEM style profile 120 x 80 with an 8mm slot. It makes a very stiff gantry and if you look closely you'll see one rail is on the front face and the other is on the top.

If you like I could quickly knock you up a model of how it would look.?

The ones I was looking at for price were like look similar but are described as 3phase and are £40 more so guess your advantages of 3phase closed loop will cost a little more. Know little about steppers besides frame size (NEMA) and torque (Nm) plus a vague idea that inductance needs to be worried about.

Those would work reasonably ok even thou 2 phase. The more important spec to look for is the voltage the drives can be run at. I
inductance is important but it goes hand in hand with voltage and I won't get too deep into why now, let us just say more volts allows higher rpm's and negates slightly if inductance is on the high side.

Now those drives allow Max 60vdc but that is the maximum and you never want to run at or near the maximum so we allow roughly a 10% tolerance on the voltage. So the ideal voltage for those drives is 54Vdc which will still allow the motors to give decent RPM.

However, if I was going with 2phase these are what I would use. The extra Nm means you can push the machine harder but more than this the extra Voltage range allows for higher speeds. Another advantage and money saver is that they will run on AC or DC so if you run on AC you only need a transformer. Whereas with DC you need to build the PSU with capacitors and bridge rectifiers which costs more money.

https://www.aliexpress.com/item/3279...69e73421AESKcL

Again feedback from real experience appreciated. How much should I be worried about keeping the Z-axis weight down? I was assuming that on a small machine, I want to keep the weight being flung about to a minimum to ensure good acceleration and performance whilst allowing modest (lower cost) motors and drivers to be spec-ed.

With 3Nm with 50+ Vdc or the motors, I suggested then for normal woodworking conditions with a typical 2.2Kw spindle, etc you don't need to worry at all.
Only if you have special needs or are going to use the machine for work like 3D which has lots of high-speed positional moves and attach a heavy spindle-like ATC spindle will you need to consider weight or fitting higher rated motors that can handle it and give you the speeds you need?

[Andrewg]

If you like I could quickly knock you up a model of how it would look.?

If you have the time it would be very helpful!

So the X/Z carriage with rails top and bottom and ballscrew behind, ends up being an inverted G rather than C - do you have a picture of the back?

Lichuan 5.5N.m closed-loop step motor
Ok those are seriously stronger motors than I was thinking off, but I guess it is good you are revising my expectations for when I finally try and calculate what power I need/can afford! I wont worry about weight then, as I can see you are directing me toward a seriously solid solution.