Thread: CNC TTU Build

Originally Posted by John H

So will the 387s have enough torque for my application?

Also, as I'll be running four steppers, will the 8.3A power supply have enough grunt?

For the 425s, it's a total of 11.2A and 14A for the 387s

There is enough torque with either motor it will just depend on the gearing and the speed you want.

I believe the 387's will be able to attain a faster speed but because I have not done any real world tests I cannot be certain.

About the PSU, you can wait 5 weeks and I will have some 10A PSU's or I could supply Dual PSU's.

Originally Posted by rodm

Hi John,
I have my doubts. I have 497 but have doubled up on the pulleys to get a speed advantage effectively lifting the screw to 10mm pitch. Steppers deliver their torque down at low revs so I am taking advantage of that but at that ratio it brings the motors to ~250 oz on the screw less losses for friction.
If you are following the same design then 387 will be the equivalent of 194oz. I'm not an engineer so I can't quantify it for you but gut feeling is it might be a bit light on.

I originally thought he was gearing it down. Hmm only thing is I would be thinking the 387 can hold more torque down the line than the 425.

BTW I am no pro in this area. Rods been building machines for yonkers so he's probbaly right

Chris,
These things can get very technical and lot of variables such as length of screw, weight of gantry, allignment, etc can all play their part.
I think the best advice that can be given is a generalisation based on previous experience. I don't think anyone expects you to guarantee performance with your motors given you are an agent and not the manufacturer. If you did your prices would have to reflect that.

John,

You know your X4, well i suspect they have at max 120oz/in steppers in them. My machine screams and I've never had it torque stall on me yet.

Now, i also have ~500oz/in steppers on my gantry. These are geared 4:1 and so far it runs the unit quite well. Keep in mind, i've not cut wood with it.

I believe you will end up with 2 power supplies to allow for your stepper setup. So 2 of the 8 amps would probably be better suited. You can load these between the motors.

What I think you need to consider with the 387's is how heavy is the gantry going to be, how well do you think it will run on the bearings and what type of acceleration/speed to do you want out of it. Now for most cutting 500mm/min would probably suffice as a maximum.

If all this concerns you, i suspect you need to try and source some bigger stepper units to be safe.
This would mean understanding the currents, load, etc on the G251's all again.

Food for thought

/Michael

Hi Mike,
I am sure that the X4 would have larger motors than 120oz. Seig's KX3 has 600 and 850oz Nema34's. I have 497 and 640 on my converted X3. I can't find specs on the Syril KX4 motors but it would be a big ask to move cast iron riding in dovetails with a 120oz motor.
With these new Chinese spindles 500mm/min is slow. I used to cut around those figures with a die grinder but now cut conservatively at 2000mm/min in wood and plastics and about 600 to 1000mm/min in ally. A mate runs his machine at 6m/min in ally but he is a thrill seaker.
I would be aiming at a minimum of 3m/min rapids for a machine with one of those spindles. I do agree with what you were implying that speed is not the most important feature and can be compromised in a non industrial application.

Well, the collection of parts has started. Nothing too exciting picture wise, but the Cast Iron Castors (man, those things are heavy duty), bearings for the ballscrews, and Gecko 251s

Hi John,
I'm glad you got the castors - they are ideal for our machines and really good value. I have about six sets of them now.
Well you are committed to the project now so that is a good thing.
Did the 80/20 come in cheaper than the Item quote?
cheers,
Rod

The 8020 quote was slightly cheaper (Kevin provided a discount on the extrusions in the quote, otherwise it would have been more expensive).

But they have different size profiles so the Gantry beam would have to be 80x160 (compared to the ITEM 120x80) and the side supports would be 120x40 (compared to the ITEM 160x40).

This would mean I would have to have the Gantry higher off the side rails and the gantry itself would be heavier. I want to keep the gantry as low as possible to the side rails while still having a reasonable Z clearance.

At this stage I'm still learning towards the ITEM system, but I'm still playing with the design so I will see how it goes.

I was having a play with Adobe Acrobat 3D. I'm not sure if this will work, but I've attached the pdf of my router plan so far.

John,

All looking great. I flicked back through the thread, but did not pick up on the way you were going to drive the X axis. Am a bit dopey tonight ... been chain sawing down the back of the farm all afternoon and a bit pooped.

I was just a bit concerned at the way the gantry loads are being transferred to the main side beams. The size of your overall machine is not dissimilar to mine and I know that my gantry weighs heaps. The way it is shown is that the load is offset to the centre of your beam by a cantilever plate on the gantry and then an angle on the side of the beam. Would it be possible to move your rail to the top of the beam? That's why I was looking at how you were going to drive the axis, as you may have some cunning way to utilise the angle on the side of the beam!

I have attached a couple of sketches which indicate what my concerns were.

Also where are you going to fit your cable chain for the Y axis? If you look at my thread, you will see I have fitted a couple of fancy brackets to the top of my gantry sides to hold a cable tray & cable chain, but they were only afterthoughts and I should have incorporated that provision into the gantry sides themselves!

If you are ever on the highway between Sydney & Queenbeyan, feel free to drop in and see my table which should be finished any year now!

Cheers,

Alan

Hi Alan,

I've based my design based on Rod's Morphy CNC build. The concept is to keep the rails and ball screws away from the dust as much as possible. The X Axis is going to be driven by twin ball screws with a pulley arrangement on each. Here is a pic of Rod's which explains it better.



Thanks for the offer of showing your table. If I'm every up that way, I'll drop you a line.

Another part arrival today.

This one is a Hailea ACO 009 air compressor to blow the chips away from the cutter.

Hi John,
I think it was Greolt that put us on to these some time back and I have been using one for a couple of years. They are great and quiet as well.

John,

If your design is following Morphy, then let my ramblings about load and bending moments go through to the keeper!!

Did you get your air pump off ebay or somewhere else. That I think is the last item I have to buy, except maybe for a better solution to my vacuum pump for the vacuum table ... my vacuum pump that I am using on my Widgitmaster sends off an enormous oil plume, which I currently have piped out of a window, but my new Alpha Zoot machine is going to be well away from walls etc, so no option of ducting it out of the window! Got a price for an oil plume filter in excess of $200 which seemed somewhat over the top for a cheap vacuum pump.

Cheers,

Alan

I think you should buy that $200 plume filter.

Then disassemble it and show us what is in it.

I have tried a couple of designs so far with little success.

Greg