4' x 4' x 8" Router Build

[JAZZCNC]

This is where I'm at:

x-axis:
2010 x 1480mm ballscrew geared down 2:1 from 4Nm NEMA 23 motor
2 x 20mm x 1450mm HIWIN rails + 4 x HGW20HC2R carriages

y-axis:
2 x 2010 x 1750mm ballscrews geared down 2:1 from 4Nm NEMA 23 motors
2 x 20mm x 1900mm HIWIN rails + 4 x HGW20HC2R carriages

Why are you gearing 2:1 if using a 10mm pitch.? It's not required and would actually be detrimental to the machine as it will be slow. If you are trying to lower the screw speed then go with a 20mm pitch and then use the 2:1 ratio, this will give the same travel velocity as 10mm but with half the screw speed.
If not lowering the screw speed just go with a 1:1 ratio with a 10mm pitch.

I'm at the point now that I really need to tie down some key components so that I can finish detailing everything and have a few questions for the hive mind:

Motors - Are the CNC4YOU 4Nm NEMA 23s the way to go for all 4 motors? Electronics is definitely not my strong point, I'm going to need a lot of help to get through that part of the project!

Yes, they will work but if you are going to this trouble then I would go with Closed-loop steppers as the price difference isn't massive and they are much more accurate.
Also, it's not just the motors you need to decide on, the drives which control them and the voltage you run them at are important. Don't go with any drives that are rated, 50Vdc Max. To get the best from 4Nm motors you'll want to be running them around 60-65Vdc or 50Vac if the drives support AC voltage which many do these days. You also need a safety margin on the drive's Max voltage or around 10%, so if using 60Vdc you want drives with a max voltage of 70Vdc or more.

Pulleys - are HTD5 the ones to go for? I've modeled up 14T & 28T (copied from Joe's amazing design) and there are a couple of things I'm not so happy about. Firstly the motor shaft is not long enough for the pulley when using one with a boss, it overhangs the end which doesn't seem ideal. The alternative is to use a pulley where the grub screw is on the toothed part and it seems like that will munch through the belt as it rotates - anyone got experience of this pulley type? My second concern is fitting the smaller pulley onto the 20mm ballscrew - the shaft is nominally 12mm which looks too big for the pulley to fit, turning the ballscrew down to 8mm or so seems like it might be too weak? The alternative to this is increasing pulley sizes which will make the motor pulley quite large.

HTD 5 x 15mm wide is perfect for this job.
Regards the grub screws then turn the Boss inwards so it's on the shaft if possible, if not then it's ok to drill between the teeth provided you remove any burrs. However, you say you are putting the small pulley on the screw.? You have this the wrong way around, you want the small pulley on the motor and the large pulley on the screw if you want 2:1 ratio.

Cable chains - What size do I need (I'll be using a water cooled spindle)? Should I use the same size for all 3 chains or should they get progressively smaller?

Larger is better, the worst thing you can do is use too narrow cable chains and have the cables rubbing against each other, worse still if your running noisy cables like the spindle cable with signal cables like limits, etc, which you will be.
You also don't need 3 chains, on the machines I build I only fit chains on X-axis and Y-axis, the Z-axis which is mostly just the spindle cable and water pipes, I run thru flexible conduit.
The energy chain I supply has internal dimensions of 25 x 58mm.

This pic shows the flexible conduit and energy chain, there is the same chain at the rear of the gantry.

[JonnyFive]

Hi Jazz, thanks for the reply, I appreciate the help.

I thought I'd read about gearing the motor / ballscrew to lower the screw speed to prevent whip whilst keeping the motor running at it's most efficient speed? Maybe I've got it all wrong. So 1:1 is the way to go is it?

As I mentioned the electronics side of things is really not my strong side, the more I read about it the more lost I get. Could you point me in the direction of some suitable closed loop steppers? I've had a look but they seem to be around £200 each? I had been thinking of going with a UCCNC ethernet controller, is this a good option? Do closed loop steppers need a different controller & drives?

I had put the big pulley on the motor based on what Joe did in his video: https://www.youtube.com/watch?v=gQz9G_Dlv3w about 45 seconds in.

The cable chains I have modelled are 50 x 17.5 internal - I'll increase this to 25 x 58mm as you suggest.

Thanks again

[JAZZCNC]

I thought I'd read about gearing the motor / ballscrew to lower the screw speed to prevent whip whilst keeping the motor running at it's most efficient speed? Maybe I've got it all wrong. So 1:1 is the way to go is it?

I had put the big pulley on the motor based on what Joe did in his video: https://www.youtube.com/watch?v=gQz9G_Dlv3w about 45 seconds in.

Yes this correct but the way you had it was doing the opposite, this would double the screw speed not half it.

The reason Joe used a large pulley on the motor with a small one on the screw was to increase the speed because he only had 5mm pitch ball-screws. So he needed the 1:2 ratio to get the extra speed but in doing so he doubled the screw speed which increases the chance for the whip.

As the above demonstrates, Be careful with blindly following someone else's component choice or build thread if you don't fully understand what or why these have been used.?
It's very easy to select the wrong components and end up with an unbalanced machine or worse completley unusable machine.!

As I mentioned the electronics side of things is really not my strong side, the more I read about it the more lost I get. Could you point me in the direction of some suitable closed loop steppers? I've had a look but they seem to be around £200 each?

You can get them cheaper than that, but if you are not in a rush I can supply you with 4.5nm and drives from Lichuan that I fit on machines I build. Unfortunately, at the moment I only have enough stock for the machines I'm building, however, I have an order being produced at the moment and will have new stock in about 10 weeks' time.

I had been thinking of going with a UCCNC ethernet controller, is this a good option?:

Yes, it's very good, I use it on the machines we build and fit the AXBB-E ethernet controller. Again I can supply you with UCCNC and Controller if you want to PM I will give you prices.

Do closed loop steppers need a different controller & drives?:

They don't need a different controller but they do need drives that are matched to the motor/encoder. They are often sold in matching sets.

[JonnyFive]

I think part of the problem is I don't have the motor performance curve, I have worked out the ballscrew critical speed is about 1000RPM (end fixity type C - right?) but not sure what speed the motor should be going.

I'd definitely be interested in motors, drives & controllers - I'll PM you. I won't be ready for them for a few months yet so no major hurry on my part, I just need to know what size to design brackets to at the moment.

[JonnyFive]

I think I've remebered how I got confused with the 2:1 gearing, think I read somewhere about using 2020 ballscrews and then gearing them for lower RPM. 2010 seems to be the norm for a 4' machine so will go with that.

I've made a bit more progress on the design......

I have removed the gear reductions, now the x & y axes are geared 1:1 with 20T pulleys and the z is direct drive. I am still working with the 4Nm Nema 23s on all axes.

I have also tidied up the end stops and proximity sensors.

The x & y cable chains now have inner dims of 25 x 57mm (I couldn't find 25 x 58mm).

Think I'm nearly there with the mechanical design, soon be time to concentrate on the electronics - not looking forward to that one!

[Clive S]

I personally would turn the Z axis sensor the other way round ie. fit it on the back plate. This will make the cable neater.

You could just drill the back plate.

[JonnyFive]

I personally would turn the Z axis sensor the other way round ie. fit it on the back plate. This will make the cable neater.

You could just drill the back plate.

I like the sound of that! Thanks.


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[JonnyFive]

I like the sound of that! Thanks.


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Thinking about it, I think the reason I didn’t do this is because the sensor would have to be where the lower target thingy is now and there isn’t enough depth to fit it between the gantry and z plate. Unless I’ve misunderstood what you’re suggesting?


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[Kitwn]

Looks good to me. The only thing I would point out is that you have the proximity sensor end-on. There's very little room for deceleration between detecting the gantry and being smashed by it. A safer option is to have the sensor pointing uipwards so that it detects the gantry riding above it. You already have a non-smashable mechanical end-stop in case that fails.

Kit

[JonnyFive]

Looks good to me. The only thing I would point out is that you have the proximity sensor end-on. There's very little room for deceleration between detecting the gantry and being smashed by it. A safer option is to have the sensor pointing uipwards so that it detects the gantry riding above it. You already have a non-smashable mechanical end-stop in case that fails.

Kit

I haven’t looked at the data sheet for the sensor but. I’d assumed that it would be triggered 2 or 3mm before contact and I could then have the hard stop almost flush with the sensor z. How much overrun should I allow for? I guess when it’s travelling at speed something like 5-10mm would be better?


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