4' x 4' x 8" Router Build

[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!

[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]

That’s a fair point, I’ll look at moving them through 90 degrees. Thanks!


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[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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[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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