-
Was about to get a toy- then I did some research...
...and now I seem to have myself a new hobby trying to put together my first ever cnc from scratch! I have no prior experience with cnc’s, but I’ve been looking at getting one for some while now. Mostly for various wood projects I’ve got going on from time to time, but also hoping to get my kids involved and interested in industrial design (I.e. to better understand what actually goes into making things).
Now, having spent countless nights looking at different kits online and ploughing through forums I’ve come to realise that all the kits within my budget come with compromises, many of which I wouldn’t be prepared to pay the asking price for. Luckily, I stumbled upon mycncuk which, to my mind, seems to offer the most helpful and on point advice of any cnc related forum I’ve visited. Actually, it’s the active members here that have (unknowingly) pushed me over the edge and got me worryingly excited about this.
Which brings me to what I’m doing here. I’ve lurked around the forum and stolen a bunch of great ideas which, in turn, has yielded a concrete plan of what I’ll get myself into. For anyone kind enough to drop me some critique, I’ll be posting my initial iterations in the build log thread (I hope that’s the correct one) and hopefully I’ll get started soon enough!
Other than that, cheers to all of you who actively and constructively share your views with us less experienced- I’ve already learnt a ton!
-
Re: Was about to get a toy- then I did some research...
Welcome and best of luck with your build.
-
Re: Was about to get a toy- then I did some research...
Cheers! I can't seem to get my design pictures uploaded (they're resized to requirements and I've tried three different OS) but will post my plans as soon as I get it to work.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
Cheers! I can't seem to get my design pictures uploaded (they're resized to requirements and I've tried three different OS) but will post my plans as soon as I get it to work.
What format are you using? Also you might need to make a couple more posts.
I am sure Lee (forum owner) will pop up and sort it for you
-
Re: Was about to get a toy- then I did some research...
I think they were png (I'm using the free version of shapr3d for rough sketching and it only allows for stl exports and screenshots).
-
Re: Was about to get a toy- then I did some research...
Welcome to the forum. You'll find plenty of help and advice here.
You have to make a minimum number of posts (10 I think) before you can upload pictures. have a look at the forum rules.
Kit
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
...
Other than that, cheers to all of you who actively and constructively share your views with us less experienced- I’ve already learnt a ton!
I’ve been operating my machine for a couple of years and if there is one thing I would tell anyone who is designing a CNC... think scenarios where things go wrong. How easy will it be to fix or adjust your machine.
For instance my Ox is great when it works... but when the belts come loose I have to disassemble a lot of the carriage if the Y axis comes loose and don’t get me stared on the holes for the tension adjust on the long rails.
You see you actually have to remove two inner wheel stacks just to get to the bolts that hold the stepper motor in place. It’s just bad design imho. Maintenance tasks like belt tensioning should be simple to do.
So imaging you crash your machine (don’t worry, we all do it). Your carriage is now skewed... how would you realign it to the frame.... I solved that for me by hitting the emergency stop, moving the carriage to one end where I have aligned two end stops... I push the carriage gently against the stops and the release the E-Stop... the motors come online and all I have to do then is run a homing cycle.
Oh yeah, you will need to install limit switches so you can run homing cycles. Definitely makes life easier.
Oh and these are just suggestions from CNC noob... I’m still learning every day... but loving every minute.
-
Re: Was about to get a toy- then I did some research...
Quote:
Oh yeah, you will need to install limit switches so you can run homing cycles. Definitely makes life easier.
Just to be clear for the benefit of new users.
limit switches and homing switches do two different things. Although a homing switch can be setup at one end to act as both. ie it is a homing switch when first run (homed) then the software changes it to a limit switch.
Limit switches are nearly at the end of travel on each axis to stop the machine from hitting the hard stops
-
Re: Was about to get a toy- then I did some research...
And soft limits are there to stop you accidentally crashing the machine due to any one of a dozen easy mistakes. But they only work only AFTER you have used the homing switches to tell the machine where it is.
-
Re: Was about to get a toy- then I did some research...
Welcome to the forum :)
Yeah... this is quite a time-sink (and potentially money-sink) of a hobby.... ;)
Based on your post title, I'm guessing you were thinking of grabbing one of those pre-made Chinese jobbies off ebay?
They get an awful lot of flack (from me too!) but I think they do actually have a place; as long as you're prepared for how pathetic their capabilities are, they're a reasonably inexpensive way of experiencing the CNC process and way of thinking, allowing you to start exploring what you might want out of a machine.
The Shapeokos of the world give the same lessons, but are more expensive to begin with, although probably allow a greater amount of time before you outgrow it.
My first CNC was a simple conversion of a 3D plotting tank (think 40x40x40 work area, but about as stiff as jelly). It taught me lots about GCode, CAD CAM and what I needed from a machine.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Kitwn
And soft limits are there to stop you accidentally crashing the machine due to any one of a dozen easy mistakes. But they only work only AFTER you have used the homing switches to tell the machine where it is.
That's not quite correct actually. Soft limits will work without a home switch by just hitting Home all, after which home will be where ever the machine happens to be parked. However, it's not advised because then you still crash the machine into the ends. But if your going to fit just home switches then you may as well make them move with the axis and have them double up as Homes and limits.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
....... However, it's not advised because then you still crash the machine into the ends.
Precisely!
I have one set of switches which double up as limit and homing switches. This is very easy to configure in LinuxCNC. Once the machine has homed itself the soft limits will prevent the limit switches from disabling the stepper drivers (most annoying!) even if I get the gantry out of the way by just pressing the LEFT button on the USB Nintendo game controller (er, sorry, meant to say "sophisticated manual pendant") until it stops.
As Hermione Granger (almost) said "Simple but effective".
-
Re: Was about to get a toy- then I did some research...
Wow glad to see so many replies!
Quote:
Originally Posted by
NeoMorph
I’ve been operating my machine for a couple of years and if there is one thing I would tell anyone who is designing a CNC... think scenarios where things go wrong. How easy will it be to fix or adjust your machine.
This, I'm def a fan of simple solutions. So I've done my best to keep my design free from unnecessarily complicated solutions. Sometimes it might come at the expense of top notch quality, but then again I'm here to learn!
Quote:
Originally Posted by
Kitwn
Welcome to the forum. You'll find plenty of help and advice here.
You have to make a minimum number of posts (10 I think) before you can upload pictures. have a look at the forum rules.
Kit
Good to know. Actually, I was lucky there is such a rule as it gave me more time to consider my design (which now is even more developed) :)
Quote:
Originally Posted by
AndyUK
Welcome to the forum :)
Yeah... this is quite a time-sink (and potentially money-sink) of a hobby.... ;)
Based on your post title, I'm guessing you were thinking of grabbing one of those pre-made Chinese jobbies off ebay?
Yup, something like that. And I'd probably been quite happy with whatever I would've got had I not dug into it. Nontheless I figure it won't be cheap anyway (time or moneywise) so I might as well make building one a hobby in itself + I'll have to learn the basics of electronics which I've never made time for!
-
Re: Was about to get a toy- then I did some research...
As I wait to break the 10 post limit so I can upload a pic of my design for public dissection I'll try posting a couple burning questions I have in this thread.
1. Partly related to neomorph's comment- in an attempt to keep things simple I've considered using fk/ff ball screw supports mounted directly on the end plates/gantry plates, but this would require the steppers to be mounted with spacers (in between the stepper and the other side of the plate). The other option would be to use bk/bf supports mounted some distance away (on the "inside") from the plates, leaving enough clearance for the steppers to be mounted straight on to the plates. Do both work equally well in practice?
2. This might be impossible to answer without more details, but I'll give it a go. I currently have planned about 150mm of Z travel which would make the gantry plates roughly 500mm in height as measured from the X (long) axis side mounted rails to the top (ie the plates would extend a further 100mm below the cutting bed). Does this seem OK or would it be advisable to give up some Z travel in favour of shorter gantry plates?
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
2. This might be impossible to answer without more details, but I'll give it a go. I currently have planned about 150mm of Z travel which would make the gantry plates roughly 500mm in height as measured from the X (long) axis side mounted rails to the top (ie the plates would extend a further 100mm below the cutting bed). Does this seem OK or would it be advisable to give up some Z travel in favour of shorter gantry plates?
You'll always get a stiffer solution with less Z travel, but I wouldn't have said 15cm is unreasonable. Also depends on if the bed is adjustable or not - if not you have to consider the clearance height of any clamps or vises you plan to use. Having said that, it sounds like you're implying a 25cm (500-100-150) tall gantry? Without seeing the design its hard to say, but sounds quite hefty!
-
Re: Was about to get a toy- then I did some research...
Sorry, I might have been a bit unclear in my description, essentially the gantry plates would be roughly 60 cm in total height. But what matters, I suppose, is that the gantry would be 18cm + two round linear rails mounted top and bottom adding a further 5cm or so to the overall height of the gantry. While the space between the non-adjustable bed and the bottom of the gantry (including the rail) is 20 cm, the free height from the tip of a typical router bit on a mounted spindle down to the bed is 15cm (when Z is in its top position). Hopefully that cleared thing up a bit!
-
Re: Was about to get a toy- then I did some research...
You should have very clear what you would like to do with that machine. But IMO the best machine for a starter is CNC mini mill. Smaller area but a real machine, not a toy. And will not lose resale value so much. And can make real parts. very good for learning.
Worse thing to buy is crappy Chinese machine and God forbid a belt driven machine.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Boyan Silyavski
God forbid a belt driven machine.
Here we go again.! . . . Have you ever built or used a belt-driven machine.?
For a small router, (or even a basic large machine) then belt drive is a very good solution with high efficiency and low backlash that's reasonably cheap and easy. Yes, maybe not ball screw good but much better than other methods like R&P or cheap lead screws if done correctly. . . . .Don't knock it until you've tried it.!
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
1. Partly related to neomorph's comment- in an attempt to keep things simple I've considered using fk/ff ball screw supports mounted directly on the end plates/gantry plates, but this would require the steppers to be mounted with spacers (in between the stepper and the other side of the plate). The other option would be to use bk/bf supports mounted some distance away (on the "inside") from the plates, leaving enough clearance for the steppers to be mounted straight on to the plates. Do both work equally well in practice?
Yes either works fine. Also consider attaching the motors to the screws with belts as it provides a few advatages. It Lowers resonance, allows a ratio and gives flexabilty in location so can turn motors inwards and keep width narrower.
Quote:
Originally Posted by
Juranovich
2. This might be impossible to answer without more details, but I'll give it a go. I currently have planned about 150mm of Z travel which would make the gantry plates roughly 500mm in height as measured from the X (long) axis side mounted rails to the top (ie the plates would extend a further 100mm below the cutting bed). Does this seem OK or would it be advisable to give up some Z travel in favour of shorter gantry plates?
With out seeing your design then yes it's not easy to say but 150mm Z travel is standard on router machines I build and 500mm length plates is about right so your not far away.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Here we go again.! . . . Have you ever built or used a belt-driven machine.?
For a small router, (or even a basic large machine) then belt drive is a very good solution with high efficiency and low backlash that's reasonably cheap and easy. Yes, maybe not ball screw good but much better than other methods like R&P or cheap leap screws if done correctly. . . . .Don't knock it until you've tried it.!
100% agree.
Double belting reduces a lot of the stretch too. I glued my lower belt to the aluminium and it really improved the accuracy too.
It all depends on what materials you want to work with. Woods and plastics and cast aluminium (yeah, ALWAYS go with cast if you don’t want to get tons of aluminium welding to your endmills) then belt driven machines are great for learning the ins and outs of CNC... plus it’s cheaper to fix if you have a horrible crash that would warp the screws and ways of a non-belt driven machine.
I had one incident where a glitch decided to rapid in the long axis (X axis on my machine) at crazy speed and it slammed into the limit sensors (thank god I put them in spring mounted blocks) before ramming the hard limits. Then it was skipping gears before the limit switch went “eh what.. WHAT THE F???” Before shutting the machine down.
That’s not so say it was slow to respond... it was just that the incident developed so darn fast that it accelerated into the stops like a crash test dummy machine. If it had been a screw driven machine I would be looking at stripping the whole thing down due to warp... and the cause? A glitch in the gcode plus me messing with the X max rate and inputting 1500000 instead of 1500.000.
CNC baby steps. Belt driven machines are good to learn on as replacing belts is cheaper than replacing ball screws. Now imagine that crash happening to a screw driven machine???? 😱🤯🤬
Butttttt... don’t think that the eBay machines are good value unless you are ready to possibly throw away all that money. Better to buy a machine from a reputable seller in your country who can help.
It may cost a little more but if anything goes wrong they are there to help. I had a bad CNC xPro controller which was exchanged after trying to get it working with the supplier. No cost to me... and sorted FAST!
-
Re: Was about to get a toy- then I did some research...
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Yes either works fine. Also consider attaching the motors to the screws with belts as it provides a few advatages. It Lowers resonance, allows a ratio and gives flexabilty in location so can turn motors inwards and keep width narrower.
Originally I was a bit hesitant to this idea (for sake of simplicity), but it grew on me as I considered my design from different angles.
Now, I don't want to go into to much detail before i break the 10 post threshold and can post pictures, but considering I'm planning to make the frame 1000x800mm (effective working area approx. 750x600mm), should I use 1605 ball screws on all axis, or is it better to use 1610 on X and Y (and possibly 1605 on Z)? With belts, I guess, it doesn't matter as much since I could always gear it to suit the purpose, but am I unnecessarily restricting myself if I choose one over the other? I'm thinking of using nema 23 2.4nm steppers (in case it's relevant info) and mainly work with wood (hard and soft) and occasionally soft alloys e.g. aluminium.
In relation to the above, I'm thinking of using base 30 60x120 extrusions for the long axis (for easy mounting of 20mm round linear rails) and 3 cross beams (along the short axis) of 60x60 extrusions mounted flat with the top side of the side extrusions. Essentially the frame would rest on the side extrusions and I'd have an even bed extending over the whole 1000x800 surface. I could also use 60x120 for the cross beams (which would undoubtedly make the frame more rigid), but that would force me to move the belt driving steppers outside the gantry plates (instead of hiding them under the table) which defeats the purpose of keeping a compact design. From your experience(s) would the 60x60 cross beam solution suffice or should I play it safe with 60x120 all around? Mind you, I'm constantly trying to balance performance with costs, hence, I'm inclined not to overbuild just because I can.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Boyan Silyavski
You should have very clear what you would like to do with that machine. But IMO the best machine for a starter is CNC mini mill. Smaller area but a real machine, not a toy. And will not lose resale value so much. And can make real parts. very good for learning.
I actually stumbled upon another thread where I think you were involved and this idea came up. It's actually not a bad idea as a) I'd have something to learn the basics on b) I happen to know of a (apparently) decent used mill that's for sale c) I'd be able to machine my own alu plates. As of now I'd probably have to have the majority of them made for me...
On the other hand, that would entail spending money on two machines instead of just one...
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
Now, I don't want to go into to much detail before i break the 10 post threshold and can post pictures, but considering I'm planning to make the frame 1000x800mm (effective working area approx. 750x600mm), should I use 1605 ball screws on all axis, or is it better to use 1610 on X and Y (and possibly 1605 on Z)? With belts, I guess, it doesn't matter as much since I could always gear it to suit the purpose, but am I unnecessarily restricting myself if I choose one over the other? I'm thinking of using nema 23 2.4nm steppers (in case it's relevant info) and mainly work with wood (hard and soft) and occasionally soft alloys e.g. aluminium..
Either could work - and there are builds showcasing both - which you lean towards depends on what you want to cut. For woods + plastics, you'll want to lean towards the 10mm pitch screws on that size of machine. If its more fine detail work and metals (in which case you might consider building a mill rather than a router...) you'd want to lean towards the 5mm pitch screws. Its not about how quickly you want the machine to finish jobs, its about cutting at the right speed for the material.
Belts offer some flexibility with ratios, but there are a few things to consider. First, your pitch defines how fast you can go before screw whipping becomes an issue. Look at the following page, and click the blue link at the bottom to open a calculator:
https://www.zappautomation.co.uk/ecalculators.html
A 1605 or 1610 screw will have a root diameter of ~12mm. Using a BK BF setup, a 1000mm screw can get to around 1500rpm before whipping is an issue. That limits our rapids to 7.5m/min on a 1605, or 15m/min on 1610.
Typical stepper motors will be falling off in torque dramatically above 1000rpm = 5m/min 1605 or 10m/min 1610. This is where your belts come in, its about allowing the motor to stay at appropriate RPMs for the speed (or torque multiplication).
Now, I'd personally aim for rapids in the 7.5-10m/min range for a wood router, which suggests 10mm pitch screws, but some people are happy with the 5m/min.
As for the Z axis, the travel is massively reduced so large rapids arn't an issue. A finer pitch should give slightly higher accuracy and holding torque at the correct Z location, so I'm all for fine pitch Z screws. 1605 should be fine.
Those motors sound a little weak to me. You should use the motor calculation sheet to determine what you need. Mines a similar size, and I use 2x2010 X screws (2x4nm low-inductance nema23 steppers) and a 1610 Y screw (3.1nm).
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
AndyUK
Those motors sound a little weak to me. You should use the motor calculation sheet to determine what you need. Mines a similar size, and I use 2x2010 X screws (2x4nm low-inductance nema23 steppers) and a 1610 Y screw (3.1nm).
I'm at that stage where I think I've figured out the basic mechanics of a CNC, but I now start to realize all the intricacies of the fine details. So thanks for pointing me in the right direction. I suspect I'll go for 1610 on X and Y to avoid whip and keep the 1605 on Z for precision. As I decide on the final gantry design (and the associated weight) I'll get back to the motor calc to figure out the steppers needed. Just one question though, if I have two steppers driving the long axis, should I input half the total weight of the gantry in the calculator?
Also, you don't happen to have any comments on the frame?
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
If I have two steppers driving the long axis, should I input half the total weight of the gantry in the calculator?
Good question. It's a topic worth discussing. My personal view is that you should double the screw inertia (you have two screws to spin), but also double the motor torque (two motors, after all!)
Quote:
Originally Posted by
Juranovich
Also, you don't happen to have any comments on the frame?
Keep posting and I'll comment when you've posted some pictures of your design :) I'm quite a fan of extruded aluminium profiles, it makes the whole thing a lot easier - my gantry went together in hours, my steel and epoxy X axis took weeks. I don't think you can 'overbuild' though...
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
AndyUK
Good question. It's a topic worth discussing. My personal view is that you should double the screw inertia (you have two screws to spin), but also double the motor torque (two motors, after all!)
That sounds much more logical than my suggestion as the weight is naturally not disappearing anywhere... I'm now lacking a homer simpson "duh" emoji for my question! :)
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Here we go again.! . . . Have you ever built or used a belt-driven machine.?
For a small router, (or even a basic large machine) then belt drive is a very good solution with high efficiency and low backlash that's reasonably cheap and easy. Yes, maybe not ball screw good but much better than other methods like R&P or cheap lead screws if done correctly. . . . .Don't knock it until you've tried it.!
Here we go again, my first machine was belt driven and aint nothing bad with it, just learn how belt stretches on each material and each temperature... Of course you will say if properly calculated will not happen and i will tell you that for same price it could be ball screw.
Why don't you relax and stop supervising me what i say, it's just an opinion. I am not pretending like you to be the final word on everything
-
Re: Was about to get a toy- then I did some research...
Andy I'm quoting you but please don't think I'm having a pop at you or knocking what you said. I mostly using the quotes to point other factors out and clear some things up.
Quote:
Originally Posted by
AndyUK
A 1605 or 1610 screw will have a root diameter of ~12mm. Using a BK BF setup, a 1000mm screw can get to around 1500rpm before whipping is an issue. That limits our rapids to 7.5m/min on a 1605, or 15m/min on 1610..
Ok well forget this because it's not that simple, there's too many factors involved which make these calculators of much use to a real-world DIY machine. I've built machines that use 16mm dia 10mm pitch screws at 1100mm that will happily reach 25+Mtr/min without whipping. How they are aligned and ball-nut mount fixturing etc all kick in and screw these calculations up. Similair is true of the Motor calcs as well, I've seen them things spit out stupid numbers.
Quote:
Originally Posted by
AndyUK
Typical stepper motors will be falling off in torque dramatically above 1000rpm = 5m/min 1605 or 10m/min 1610. This is where your belts come in, its about allowing the motor to stay at appropriate RPMs for the speed (or torque multiplication).
Belts can be used for this reason but it's not the main reason why I use them.
There are two main reasons why I use belts.
#1 Is to allow me to use a higher pitch screw and apply a 2:1 ratio which then lowers the screw speed by half so whip is lowered. Torque is doubled due to ratio but is offset because the linear torque of higher pitch is lower, one cancels the other in effect. I mostly use this approach on longer machines.
#2 Is to lower the affects of resonance on the motors/drives. This gives a much smoother running motor and often allows higher RPM because the drives are not having to deal with resonance issues. Don't underestimate resonance and how it can affect a stepper motor, it can literally cripple a motor and half it's RPM.
Quote:
Originally Posted by
AndyUK
Now, I'd personally aim for rapids in the 7.5-10m/min range for a wood router, which suggests 10mm pitch screws, but some people are happy with the 5m/min.
Now, this is where it gets sticky and motor/screw selection becomes very important.
For a balanced machine your better to size motors and screws not for rapid speed but in such a way that your cutting with the motors at an RPM that gives good torque while cutting.
Ideally, you'd use the Motor Torque/speed curve graph to help select the right screw pitch to give the feeds your most likely to cut at for the materials your cutting mostly. But most Stepper manufacturers are about as trustworthy as politicians so you can't believe any of the bull shit they show. Plus lots of other factors come into play like voltage they are being run at and how wired etc.
So we know through experience that a typical NEMA 23 motor wired in parallel with voltage in the 60-70v region above 1000rpm torque starts to drops off and above 1200rpm drops quickly to about 1500rpm then stalls can occur.
Now for a router cutting mostly soft materials or man-made boards using a carbide cutter and extraction for chips, will be between 6-10 Mtr/min. Now the higher end won't work with a 10mm pitch because the motor would be spinning at 1000rpm where torque is low and dropping away. So we need a higher pitch or motors that spin faster with torque ie: servos.
So keeping with steppers then we need to change the pitch, the next common pitch would be 16mm. This gives 10,400mm/min at 650Rpm which is a little too low rpm at this speed, 750rpm would be a nicer figure but this gives 12,000mm/min. So here's where a small ratio on the belts would kick in and allow us to balance the machine up. Reclaim a little linear torque and lower screw speed. Plus the added advantage of better resonance handling.
So a 1.25:1 ratio would be like a 12.8mm pitch which at 750rpm would give 9600mm/min which is a nice area with good amount of torque. With rapids in the 15Mtr/min range at 1200Rpm and without getting too close to the stall point, which on a stepper at 70vdc is around 1300-1500rpm dependant on alignment etc. However, because of the ratio, the screw speed would be around 960Rpm so we are still ok regards whip. We have also gained back a little torque from the ratio.
So it's winner, winner chicken dinner and we have a nice balanced machine. That will fly like the wind and cut at correct feed rates with good amount of torque left.
However at DIY level most don't cut correctly or with carbide tooling or chip extraction so they manage with 10mm pitch and just cut slower. However, if they ever decide to cut correctly or with carbide tooling etc then they will struggle or fail. The balanced machine above will cover all bases with only real loss being slightly less resolution.
Quote:
Originally Posted by
AndyUK
As for the Z axis, the travel is massively reduced so large rapids arn't an issue. A finer pitch should give slightly higher accuracy and holding torque at the correct Z location, so I'm all for fine pitch Z screws. 1605 should be fine.
Those motors sound a little weak to me. You should use the motor calculation sheet to determine what you need. Mines a similar size, and I use 2x2010 X screws (2x4nm low-inductance nema23 steppers) and a 1610 Y screw (3.1nm).
Spot on, on both accounts, except using the motor calculator. The key to speed is low inductance motors with plenty of volts wired in parallel.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Boyan Silyavski
Here we go again, my first machine was belt driven and aint nothing bad with it, just learn how belt stretches on each material and each temperature... Of course you will say if properly calculated will not happen and i will tell you that for same price it could be ball screw.
We do agree that ballscrews are better and not much more money. But I don't agree with telling someone NOT to use them with a statement like "God forbid a belt driven machine." because they are not that bad when done correctly with correctly sized belts. It's a perfectly good route for a first time builder on a budget who doesn't want to get into importing ballscrews etc from China.
Quote:
Originally Posted by
Boyan Silyavski
Why don't you relax and stop supervising me what i say, it's just an opinion. I am not pretending like you to be the final word on everything
I don't pretend to be the final word on everything.! . . . .I AM THE FINAL WORD. . . :joker::joker::hysterical:
Chill out Boyan, I still Luv ya Dude, and it's only for the sake of others we do what we do.! :beer:
-
Re: Was about to get a toy- then I did some research...
Another thing to think about is I am 100% guaranteeing that any machine you design and build will end up getting modified in some way after you get your first cut chips.
I think I spent the first year either pulling my machine apart and making minor alterations like packing the interior of the extrusion and bolting the gantry beams together to increase rigidity and reduce harmonics, to bigger alterations like removing the old Z axis and replacing it with a stronger C beam and replacing the aluminium gantry uprights with strong steel ones. This reduced a LOT of design problems with my original build yet I’m still not 100% happy.
What I mean is, until you get some experience under your belt it’s hard to know what you want from what you NEED to make your machine do what you want. I’m still very much a novice yet have managed to improve my machine a lot over the last few years.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
So a 1.25:1 ratio would be like a 12.8mm pitch which at 750rpm would give 9600mm/min which is a nice area with good amount of torque.
[...]
Spot on, on both accounts, except using the motor calculator. The key to speed is low inductance motors with plenty of volts wired in parallel.
Just to get my head around this- if 1m/min and 750rpm are good values for general wood working, what would be the sweet spot for detailed work (eg 3D engravings in wood) or the occasional aluminium job?
With regards the stepper size- what would be the optimal torque rating for the machine to be balanced (considering the consensus seems to go against 2.4nm)?
On a side note- thank you for the detailed discussion, since I’m new to this it sometimes feels I’m designing blindfolded as I don’t even know what parameters I should be aiming for!
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
NeoMorph
What I mean is, until you get some experience under your belt it’s hard to know what you want from what you NEED to make your machine do what you want. I’m still very much a novice yet have managed to improve my machine a lot over the last few years.
I hear ya! But isn’t it lovely to overthink things especially when you don’t yet know anything? Even though I constantly pull myself out of that rabbit hole, I keep falling in...
Quote:
Originally Posted by
JAZZCNC
.I AM THE FINAL WORD. . . :joker::joker::hysterical:
Also- I AM THE LAW!!!
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
Also- I AM THE LAW!!!
No No No I'm most definitely more THE OUT LAW.!!
Quote:
Originally Posted by
Juranovich
Just to get my head around this- if 1m/min and 750rpm are good values for general wood working, what would be the sweet spot for detailed work (eg 3D engravings in wood) or the occasional aluminium job?
Well not sure where your getting 1m/min from but giving specifics for sweet spots for things like 3D work isn't really possible because it's material and cutter dependant, plus 3D work requires a slightly different machine setup to get the best from it.
3D work tends to be lots of really short fast moves with very light depths of cut, so you tune the machine differently and biased more towards acceleration than speed if doing lots of 3D work.
Velocity is not so important for 3D because the moves are very short so even if you had a High feed rate set you'll never actually reach that feed before your at the end of the move and onto the next. So to increase the feed rate it's actually better to lower velocity and increase acceleration. So now the machine can accelerate faster and reach a higher feed rate before the next move comes around.
Because of the nature of 3D jobs being made up of lots of short moves a properly setup machine can shave hours off a job. The simple rule is that you can't have both high acceleration and high velocity, setup is always a trade-off between the two.
Aluminum on the other hand just requires correct feeds and speeds based on the tool and material type and machine setup don't really play much part because the feed rates are so low compared to wood or soft materials there is plenty of torque available with a machine set up for a balance of speed and acceleration.
For instance, I have 2 different profiles one for general work with a balanced setup of speed and acceleration, the other set biased towards acceleration just for 3D work. When doing 3D work I just load the different profile and I'm set up for 3D work.
Now if you want me to make this simple for you then here's what I would use in the machines I build for general woodworking/aluminum use.
16mm Dia x 10mm Pitch screws for machines under 1000mm length with 1:1 ratio using belts to connect to motors. 20mmDia x 20mm Pitch with 1.5:1 Ratio for machine up to 1600mm.
NEMA 23 4Nm for 16mm and 20mm with twin/screws motors. For 20mm with single screw then 6Nm Nema34. Both with coils wired in parallel.
Look for motors in the 2- 4Mh inductance range when wired parallel.
50Vac or 80Vdc Digital Drives with 68Vdc PSU for Nema 23. NEMA 34 with 80Vac or 100Vdc drives. Both using Toroidal Transformer based PSU.
These are proven specs used on machines I build which are used for cutting materials ranging from cardboard to Aluminium and Brass on a daily basis working 12hr plus days 7 days a week in some cases.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
I hear ya! But isn’t it lovely to overthink things especially when you don’t yet know anything? Even though I constantly pull myself out of that rabbit hole, I keep falling in...
Also- I AM THE LAW!!!
My problem is when I overthink, it develops feature-creep in any of my designs and a simple rowboat turns into the Titanic (with associated problems included). 😳
If there is one piece of advice I could give it is if you are aiming to make mainly wood and soft material things GO BIG... as in get as big a footprint for your XY as possible. If you are aiming to make parts out of aluminium and steel... then GO SMALL as smaller equals more rigidity. As most hobby CNCers can’t afford a cast iron bed or have the skills of people like This Old Tony then a small mini-mill is actually better.
What threw me about bed size was how much you lose to the gantry and the dust boot. As I put mine into an enclosure I also wish me from the future had turned up and convinced myself to make the enclosure taller to give the dust extractor hose and router power room to move easier (I found keeping the mains lead away from the other wiring stopped any spurious signals getting onto the limit switch wiring... before I had the thing triggering random alerts all the time).
I also put onto isolation into the limit switch lines. I can’t remember the last time I had a spurious signal get through and trip the alarm.
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
50Vac or 80Vdc Digital Drives with 68Vdc PSU for Nema 23. NEMA 34 with 80Vac or 100Vdc drives. Both using Toroidal Transformer based PSU.
These are proven specs used on machines I build which are used for cutting materials ranging from cardboard to Aluminium and Brass on a daily basis working 12hr plus days 7 days a week in some cases.
*DRRRRRRRROOOOOOOOOL*
I would love drives like these. Unfortunately not everyone can afford drives and controllers that can handle them.
I’m disabled person who had to take medical discharge in my late 20’s because of a deformed gene causing something that is now known as Hypermobility Spectrum Disorder.
So I basically live on a disability pension. Saving up for my Ox took me two years before I could order it... but I’m glad I did. Ooznest manuals are simply the best (especially when stoned on morphine 😂).
-
2 Attachment(s)
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Well not sure where your getting 1m/min from but giving specifics for sweet spots for things like 3D work isn't really possible because it's material and cutter dependant, plus 3D work requires a slightly different machine setup to get the best from it.
My bad, meant to say 10m/min... effects of nightly writing...
Quote:
Originally Posted by
NeoMorph
I also put onto isolation into the limit switch lines. I can’t remember the last time I had a spurious signal get through and trip the alarm.
Of what I can see online non-isolated wiring seems to be quite an issue. Luckily, the electronics part is still some time away as that is the part I'm the least competent in (or more accurately "incompetent") and will probably be the most frustrating bit :)
Moving on to great news (for me at least) I’m finally able to post pictures of my design which is heavily based on ideas stolen from this forum! I planned on doing it in the build log section, but seeing the attention this thread has got I figure I might just keep it here (please correct me if I’m doing this wrong!).
So the basics:
- Total dimensions of the frame is 1000x800mm and gantry height 650mm as measured from the bottom of the frame to the top of gantry beam.
- The Z carriage is roughly 450mm high (extending some 150mm above the top of the gantry beam) and 200mm wide with 150mm travel (bearing blocks 300mm apart in the Z and 200mm in the X direction)
- frame consists of 60x120 alu extrusions on the sides and 3pcs 60x60 extrusions across (easy mounting of 20mm round linear rails ;) )
- gantry beam also 60x120 extrusions in L shape
- gantry plates and Z axis made out of 20mm alu, the thinner end plates/stepper mounts are 5mm alu
- the bearing blocks on the gantry plates are 250mm apart
- as discussed above 1610 or 1616 ballscrews drive X and Y, while 1605 will suffice on Z
- NEMA 23 (perhaps 4nm) on all axis as well as 20mm round linear rails
- Haven't decided on the spindle just yet, but should be able to carry something like a 2.2kW spindle (i.e. 5kg or so)
NB! All mentioned dimensions are not precise to the mm, but gives a good indication of the general size. Neither is everything perfectly aligned. I’ll anyway sort out the details as I make the final drawings in fusion. Also- I’ll model the final (balanced) version of the gantry plates as the gantry beam/Z axis design is finalised. Also2- stepper mounting plates will require adjustable fastening slots.
Attachment 27119
Attachment 27120
So to the specific questions I have in mind, I'll leave out the ones already previously discussed:
- Frame; I quite like the 60x60 extrusions across the frame as they give me clearance below the table (eg for X axis steppers), but would it be too flimsy? Looking at it now, I have quite some weight on the gantry vs the frame. Maybe worth beefing up the frame with 60x120 instead, or at least the two furthest to the front, leaving clearance at the back for steppers...?
- Gantry/end plates; online consensus seems to dictate 20mm gantry plates, but what about Z mount? Is 20mm overkill and would 15mm do in a machine this size? The end plates/stepper mounts are 5mm (as commercial stepper mounts seem to be in that range). As they're not subject to any excessive forces in my design I suppose 5mm is enough. Essentially they're only carrying steppers and the odd limit switch as well as providing additional stability in the corner joints of the frame.
- Other comments/critique?
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
NeoMorph
*DRRRRRRRROOOOOOOOOL*
I would love drives like these. Unfortunately not everyone can afford drives and controllers that can handle them.
I hear what you are saying but £40-45 isn't a massive amount of money for a good drive. I've used lots of these low budget machines they are great value and work great. They cover a large range of motors including Nema32 upto 8Nm.
https://www.ebay.co.uk/itm/2DM860H-2...72.m2749.l2649
-
13 Attachment(s)
Re: Was about to get a toy- then I did some research...
Going to show you some machines I've built that are all the same design but slightly different in size or Z-axis type/length etc dependant on usage but all share the same profile size. 45 x 90.
These machines were designed solely for woodworking and range in cutting area size from 600x400 to 1300 x 700 with a mixture of single or twin screws. However, all of them will happily cut aluminum as you'll see from a couple of pictures sent to me by customers.
Now I'm not showing you these and saying this is how you should build your machine but what I am showing is that this kind of profile size will easily do what you need so don't go stressing about if your 120 x 60 is strong enough or not. What's more important is how it's used ie: L shape gantry bolted together etc.
Some of these machines are used for business and running 12hr days 6 day weeks and have been doing so with minimal maintenance for several years.
Can I also strongly advise you to drop the round rail and go with profiled Linear rail. It's much much better and far less hassle. Don't spoil a potentially great machine for a few Euro more. You'll also get the extra back when you come to sell it as you'll be able to ask more for the machine and it will appeal more to those who know what to look for.
Also, move the ball-screw on the gantry to the top and motor below to keep the length of the drop plate to the shortest possible. Another thing you need to be aware of and one of the reasons why I use the Bosch Rexroth style profile with slot spacing at 45mm is that it suits BK/BF12 bearing bolt spacing. This means you won't have to make mounting plates or mess around drilling the profile.
It's these little details that can easily screw your ideas up or make things much harder than they need to be.!!
Attachment 27132Attachment 27131Attachment 27130Attachment 27129Attachment 27128Attachment 27127Attachment 27126Attachment 27125Attachment 27124Attachment 27123Attachment 27122Attachment 27133Attachment 27134
-
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Going to show you some machines I've built that are all the same design but slightly different in size or Z-axis type/length etc dependant on usage but all share the same profile size. 45 x 90.
[...]
Can I also strongly advise you to drop the round rail and go with profiled Linear rail. It's much much better and far less hassle.
[...]
Also, move the ball-screw on the gantry to the top and motor below to keep the length of the drop plate to the shortest possible. Another thing you need to be aware of and one of the reasons why I use the Bosch Rexroth style profile with slot spacing at 45mm is that it suits BK/BF12 bearing bolt spacing. This means you won't have to make mounting plates or mess around drilling the profile.
It's these little details that can easily screw your ideas up or make things much harder than they need to be.!!
First off- those are some slick looking machines! Also, I never considered using a cross beam under the frame for dual stepper set-ups.
The round vs profile rail debate is one that has had me torn the most. Undoubtedly profile are superior in theory, in practice, however, I've been somewhat put off by the many worst case scenarios people have posted about when ordering the Chinese kind (which I strongly suspect is the only kind my budget allows). Second, being a first timer, I was hoping to get slightly more parallel mounting tolerance with the round rails (bc self alignment), and they provide more room for mounting ball screws on the same face (although that could also be achieved by spacers on the profile carriages). I'm curious though, in what way do you find profile to be less of a hassle?
Considering cost, downsizing to 45x45/90 extrusions might free up some funds that could be used on profiles... I might just have to bring out the famous abacus!
With regards the bk/bf12, I thought bolt spacing was something like 46mm in which case standard t-slot nuts wouldn't work? Or is it merely a case of using good ol' force?
I long favoured flipping the ball screw and stepper positions, but figured ball screw placement as centrally as possible relative to the gantry rails took precedence over drop plate length.