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

[norggan36]

Hello and welcome.

[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.

[Juranovich]

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...

[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).

[Juranovich]

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?

[AndyUK]

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!)

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...

[Juranovich]

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! :)

[Boyan Silyavski]

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

[JAZZCNC]

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.

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.

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.

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.

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.

[JAZZCNC]

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.

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. . .

Chill out Boyan, I still Luv ya Dude, and it's only for the sake of others we do what we do.!