New Machine Build- How crazy is this idea for an X2 "staged" CNC conversion?

[mhackney]

Ok, I bought a new Micro Mark mini mill (X2) a few weeks ago. After spending time tuning it, I have the X and Y backlash down to .005" on both and the slop is in the nuts. I am going to do a split nut with adjustment to take out some of the slop (http://www.cnczone.com/forums/showpo...6&postcount=28).

Now, I want to do a CNC conversion but I would like to do it in stages so 1) I can see some success and get some use out of the tool quickly 2) to learn as I go and 3) to determine exactly what is acceptable for what I need.

Here is what I had in mind:

1) First, I want to keep the stock screws for the X and Y (after doing the split nut mod) and do a 2 axis conversion. I plan to use a Gecko G-540 and 387Oz Nema 23 steppers (probably buying from Keling, they have a 3 axis package with the Gecko and 3 387 Oz steppers).

Once that is up and running I can do some basic 2 dimensional stuff.

2) Update the Z axis with something - not sure what yet, maybe a ball screw - and add a 3rd axis.

See how this goes with the stock X and Y

3) if necessary, update the X and Y with ball screws.

4) add a 4th axis on my rotary table.

Does this make sense for the reasons I mentioned?

Cheers,
Michael

[Crevice Reamer]

Hi Michael! Yes, I think that is a VERY sensible way to go. Spend as little as possible, convert the mill in stages, learn CNC, and then when you are ready convert to ball screws. In fact, I'm beginning just such a conversion myself on one of my old X2s.

CR.

[mhackney]

CR, I've seen you recommend KL23H276-28-4B 270 oz motors for X & Y in several other posts rather than the 387Oz that I was going to use. I thought a step up in force might be good with the stock screws and the anti-backlash modification. It also turns out that Keling has 3 of these 387Oz steppers packaged with the Gecko and a 48 V 7amp powersupply for less than buying the components individually.

Cheers,
Michael

[Crevice Reamer]

Originally Posted by mhackney CR, I've seen you recommend KL23H276-28-4B 270 oz motors for X & Y in several other posts rather than the 387Oz that I was going to use. I thought a step up in force might be good with the stock screws and the anti-backlash modification. It also turns out that Keling has 3 of these 387Oz steppers packaged with the Gecko and a 48 V 7amp powersupply for less than buying the components individually. Cheers, Michael

Wow! A whopping $11 savings. I see John has finally started giving a little discount on his packages.

IIRC, you intend to go 4th axis at some future time. With three 387s, your 7.3A PSU is maxed out and will not support another motor. You might want to consider upgrading to the KL 5010.

The 387s will run slower than the 270s and require 5V more than 270 for best performance. Actually, with stock 16 TPI ACME screws, the motor is geared 3 times lower than with 5 TPI ball screws, and thereby ALREADY stepped up in force, so you will need all of the speed you can get--just another reason to go 5010 and get that couple of extra volts.

CR.

[mhackney]

CR, do you think the 270s have enough umph to turn the stock screws on the X and Y? That was really my only concern thinking about the 387s for the X and Y.

It turns out that Keling takes $10 off the Gecko 540 with a purchase of other items, so there really is no significant savings on the "package".

Perhaps I should pick up 2 of the 270s and the KL-350-48 power supply. That should get me started I think.

cheers,
Michael

[TOTALLYRC]

Originally Posted by mhackney CR, do you think the 270s have enough umph to turn the stock screws on the X and Y? That was really my only concern thinking about the 387s for the X and Y. It turns out that Keling takes $10 off the Gecko 540 with a purchase of other items, so there really is no significant savings on the "package". Perhaps I should pick up 2 of the 270s and the KL-350-48 power supply. That should get me started I think. cheers, Michael

In this case more is not better, especially when it comes to stepper torque ratings I just went from nema 34's down to nema 23's which are smaller and have less "holding torque". But what the "holding torque doesn't tell you is what is the torque at speed. I was able to increase my ipm by 40%. This is because with a 50v power supply, the motors are a better match. The nema 34's that I had really needed to be run at 80+v to really go anywhere.

With a 16tpi screw, you will find that motor rpm's are what you need to get a decent rapid speed. I define a decent rapid speed as one in which you can't finish lunch before the machine gets from one side to the other. All kidding aside, if it takes 1 minute for a machine to go from one end to the other, and we are only talking ~12" here,it doesn't take long for you to start pulling you hair out. On my taig, the 425 oz motors are so mismatched with the 30v power supply and driver that it isn't funny. I actually am using the 425's on my router, and will be putting the 270's or something simialar in their place.

When you talk about oomph, how much oomph do you apply by hand???? Not much in most cases. If you refer to having to put oomph in buy hand, you would probably feel that something is wrong.

I have heard many people say that speed is not important because they are not in a hurry. But what they forget is that there is a minimum speed that you need to go in order to cut and not just rub. I also find that when doing a g83 chip breaking drill cycle, that the extra rapid speed can make a huge difference on a deep hole or lots of small holes. My router used to have a rapid speed not any faster than the feed rate at which I was drilling my holes. When doing a sheet of fiberglass parts with a total of 100+ holes, it makes a huge difference in cycle time. These are not production runs, but just a 36"x 36" sheet of parts that I do once or twice a year. In the past moth I have gone from 40v to 50v power supply, then changed to the 425 motors from the taig and then used a g251 to replace the blown g201(my fault) and in each case have seen the speeds go up. I can now reliably rapid the z axis at 200 ipm on a 5 tpi ballscrew. It will actually rapid faster, but during my testing, it would stall out somtimes and I need to be reliable, not the fastest machine out there.

I guess the purpose of my going on for so long is to emphasize that you need a motor that is matched to the load the you are moving, the screw and power supply that you are using, and not go with the bigger is better mentality that has permiated diy cnc for so long.

Best of luck,
Mike

P.s. CR knows what he is talking about. Like me, when his is not 100% right, someone will step in and offer their opinion. ( notice I didn't say wrong )

[hoss2006]

Looks like Keling has a new motor in production thats perfect for the G540,(no add to cart button yet)
KL23H2100-35-4B (1/4” Dual shaft with a flat) 318 oz-in
3.5 Amps and 54Volts.
Funny they have the 318's in a g540 4 axis package available though.
You'll need more torque than that for the Z axis when you get to it though,
the Z doesn't need to move all that fast but it needs to move a lot more mass.
You COULD get by with the 318 if you give it some help with a counter weight, air spring and/or higher pulley ratio.
If you want to add a 4th axis later, a 318 will be plenty for a rotary table type but if you want a lathe/4th axis type,
you'll need a motor with much more holding torque.
Hoss

[mhackney]

Thanks for the info guys.

Hoss (or others), how do you determine the volts for a stepper? I looked at the datasheet linked to and see the 3.5A rating but the rated voltage is 2.55.

Cheers,
Michael

[tooManyHobbies]

Originally Posted by hoss2006 You'll need more torque than that for the Z axis when you get to it though

What do you recommend for the Z?


Michael: We've been using this equation to determine motor drive voltage:
32 * square root(motor inductance in millihenries, mH)

For the KL23H2100-35-4B it's 32 * (2.8)^0.5 = 53.546, or 54 Volts.
(For the non-math nerds, square root is the same as raising a number to the 0.5 power).

tom

[mhackney]

Thanks Tom.

I would like to get my order in today before I get stuck in analysis paralysis! I would like to order from 1 vendor to save shipping and aggravation.

After doing some calculations and checking specs on the G540 and various steppers and power supplies, I think I have a better handle on the trade-offs, etc.

Might it make more sense to use individual drivers - like the Gecko G251 - so I could start with 2 and add as I go. Wouldn't this also allow me to use a separate power supply to power the Z or a future 4th axis stepper if I needed more current? The G251s are $69 each and would require a BOB and some extra wiring that the G540 doesn't but might give me more flexibility for future. This would also cut down my initial costs a bit too for a 2 axis conversion.

Cheers,
Michael

[Crevice Reamer]

Originally Posted by mhackney Thanks Tom. I would like to get my order in today before I get stuck in analysis paralysis! I would like to order from 1 vendor to save shipping and aggravation. After doing some calculations and checking specs on the G540 and various steppers and power supplies, I think I have a better handle on the trade-offs, etc. Might it make more sense to use individual drivers - like the Gecko G251 - so I could start with 2 and add as I go. Wouldn't this also allow me to use a separate power supply to power the Z or a future 4th axis stepper if I needed more current? The G251s are $69 each and would require a BOB and some extra wiring that the G540 doesn't but might give me more flexibility for future. This would also cut down my initial costs a bit too for a 2 axis conversion. Cheers, Michael

You can do as you please, but you will save pennies (if not pay more) and gain nothing but complication--In fact you will LOSE All of the G540 protective circuits and speed morphing, Spindle speed controller etc.

To equal the G540 High tech BOB, you will have to spend at least $100.

CR.

[mhackney]

Thanks CR, I was thinking that going the individual route would gain me additional flexibility downstream. But there is a lot packed in to the G540 and it is convenient. I think I will stick with it.

Michael