Was about to get a toy- then I did some research...

[Kitwn]

....... 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".

[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?

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.

[Desertboy]

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.

I built my CNC after building a Rep Rap it really helped get my head around how it all works.

Hiwin's and ballscrews but the core principles remain the same.

[Juranovich]

Wow glad to see so many replies!

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!

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) :)

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!

[Juranovich]

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?

[AndyUK]

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!

[Juranovich]

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!

[JAZZCNC]

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.

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.

[Juranovich]

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.

[AndyUK]

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).