So here is how I'm getting there correct me if I'm wrong. If you look at the rating for the motor it is set up based on half stepping. So at full step this motor has 200 per revolution. This means that 1/2 stepping there would be 400 step per rev. Looking at the torque curve I chose 3000 PPS as my staring point. 3000 PPS / 400 steps = 7.5 revolutions per second. 7.5 rps x 60 =450 RPM. 450RPM x 8mm (lead screw produces 8mm per revolution)= 3600 mm per minute. 3600 mm per minute/25.4 (25.4mm = 1")= 141.7 inches per minute. If we follow the torque curve over from 3000 PPS it shows about 0.8 N-M...but that is at 24v input and 2.8 Amps...Guessing that I will really only be able to run my Gshield at around 2A I just called it about 60% of 2.8A. So 60% of 0.8 N-M is 0.48 N-M. I used a calculator I found online to convert N-M to in-oz and it shows it to be about 68 oz-in. So with 2A @ 24v with the stock lead screws moving at 8mm per rev based on about 141.7 ipm you would have about 70 in-oz of torque with this specific stepper. Honestly I have no idea if that is good math or not...but if it is good math then to answer my own question...if I'm cutting aluminum at around 50-60 ipm then I would have even more torque available at those speeds. (This post has been adjusted to reflect 8mm per rev on the stock lead screw...unless I missed something all the math should be updated)

 

With all this talk about the Dewalt 611 I though I might relay some info from my own build. I was concerned with the Dewalt in the supplied mount while cutting aluminum. I'm sure everyone has their opinion about how much precision to expect from this machine, I just wanted to tighten it up as much as possible. I looked at other options for a mount and settled on the mount that Chris Laidlaw produces and sells on eBay.

I was the second person to buy the mount from Chris that specified it was for the OpenBuilds PlateMaker using a Dewalt 611. When the mount arrived I could not find a way to mount it to the existing gantry plate with out drilling holes in the new mount plate. I emailed Chris and he promptly responded that I should just use 4 bolts and t'nuts. Knowing Chris supplies most of his mounts for OX units I figured he might not have a PlateMaker (PM) on hand, hence the reference to the OX mounting method. I responded with pictures and an explanation that the PM has a gantry plate that his mounts connects to directly. He immediately jump on the problem and created a 1 to 1 pdf file of a modified hole pattern for his mount plate. I printed out the template, taped it to the plate and drilled the holes.
After a few more exchanges, via text and voice, we got on the same page and he sent the final template which worked perfectly. I further suggested that I had an idea for an improved PM gantry plate and would like to hire him for the job. He graciously excepted. I sent him a crude drawing of my idea and with that Chris did a 3rd mod to his mount plate, making it function with the OX, the PM and my new gantry plate.

Can't tell you how refreshing it was to deal with a fellow of such integrity, willingness and abilities in the CNC world... Chris will get all my work if you guys don't keep him to busy. When the new gantry is finished and I get it for testing, I'll post the design to the OpenBuilds community and I'm sure Chris will produce them as required.

More to come on my build, seems like I modify it more than us it. I have a large commitment for "plate like parts" and I need to get my manufacturing time down to a reasonable time, that was the motivation to buy this kit to begin with.

Thanks for all the good tips,

FredQ

 

Rick I updated my post based on your correction. Based on my math at 140 ipm you would have about 70 oz-in of torque...now just want to figure out the guestimated torque at 60 ipm...can't be as simple as just doubling it....

Used 1000 pps which is about 50 ipm guessing at 60% of 2.8A being 2A math shakes out to be about 85 oz-in at 50 ipm

 

I believe you are leaving one important thing out. You'll notice on the torque curve the attainable PPS depends on the load. So first you need to know the force required to do the the milling operation you are checking for, then you need to translate that back through the lead screw and onto the stepper into torque. Only then will you know the attainable speed for your particular case. For example if you had very low load, e.g. moving, but not milling into anything, then the force is very low and your speed can be very high. However to mill into aluminum it takes a fair bit of force to break the chips away so the attainable speed drops. So it's not enough to arbitrarily pick a torque value like 68 oz-in in your example. You need to know the required torque if you want to solve this mathematically. The full math is a bit more involved.

 

Thanks Bob,
My calc for feeds and speeds with the bit I would like to use say for 16k rpm (lowest speed of the dewalt router) I need to be cutting at around 60 ipm to for a 0.002 chip load. I was hoping that I could work my way backward if I got a good idea of the torque these steppers will produce at my desired speed if someone could tell me if 85 oz-in of tq would be enough to run at those speeds. For .25" bit wih 0.025" step downs....Like you said the full math is more involved but beyond were I know how to go to get there

 

Even with knowing the chip load of 0.002 and all other relevant parameters including speed, I'm not familiar with the chart or equation that tells you the force required. (If someone knows this I'd be interested in seeing it.) The force (not torque) I'm referring to is that on the lead screw. If you did know the force required onto the lead screw (call it F), then it becomes easy assuming you know the nut efficiency. Use this equation:

required torque = F * D / (2 * PI * E)
where:
D = the lead distance (8 mm in our case)
E = efficiency fraction going through the anti backlash nut. I don't know what this is for us. For a ball nut it would typically be 0.9, but for our case it will be less efficient.

Use the proper units for F and D to get the units of torque you need. The (2 * PI * E) factor is unitless.

Once you know the torque then you can see if the torque chart indicates if you are within the limits for the motor.

But I don't know how to get at the value for F. As Sonkid said it depends on many factors. From a practical perspective it would be safer to go by what others here have attained with the spindle you plan to use.

 

Aluminum and Aluminum Alloys

 

look at the examples in the file tab aluminum
; Generated by SketchUcam V1.2b1
; File: SketchUcam Aluminum Examples.skp
; Bit diameter: 3.175mm
; Feed rate: 800.000mm/min
; Plunge Feed rate: 250.000mm/min
; Material Thickness: 6.500mm
; Material length: 250.000mm X width: 250.000mm
; Overhead Gantry: true
; Multipass enabled, Depth = 0.500mm
; RAMPING at 4.0 degrees
; Optimization is ON
; www.PhlatBoyz.com
; Loaded profile CBM_Alum1-4

800mm pm is pretty quick. you can watch the video and see it does a good job.

Don't over think this.

once you start using the machine you will get a feel for the speeds and feeds your machine likes....
Bob

 

That's some cool data. But it's still very dependent on the tool itself. I agree with Bob. Trying it yourself will yield more accurate data than the theoretical values since there's too many places to get the calculation wrong. It's not trivial.

 

Main thing was just wanting to know at the right cutting depth if 60 ipm is a reasonable cutting speed for this machine.

 

if you are talking about aluminum 60 is most likely too fast 30 is closer with a .020 depth of cut...
hope that gives you an idea....
oh almost forgot those figures are for a 1/8" 2 flute endmill....

 

OK cool thanks

 

I've been cutting lots of 6061-T6 aluminum lately using a .125 single flute cutter. Running at 30 IPM with a .0313 DOC and I can't imagine running at twice that speed. At these settings the first couple of passes really shake the machine but the finish comes out nice. The holes are as they came off the machine the edge I deburred with a file.

 

As a reference what router/spindle did you use, and how many RPM?

 

Same question... As a reference what router/spindle did you use, and how many RPM?

 

I use the Dewalt 611 at its lowest speed on the dial.

FredQ

 

I think low speed on that router is 16k.

 

That's what they advertise but I have no way of measuring it, yet...

FredQ

 

Yeah just have to take it at face value. Using feed speed calc app says with your set up you should be going a little slower at 20 ipm...might help with the shakes. Please post more pics of finished pieces if you can ... Using FSWizard app for Android BTW.

 

those feed speeds are with my ox and it's a harbor freight spindle 26000rpm

 

Yes I started out at 20 but found that I could get up to 30 and still get good results. I think the shakes is more the chip load coming off the long side runs. It makes some cool looking chips. I think I tried 50 when I first started and that was not going to work because I had the DOC real light.
Still looking at the super-pid as a potential improvement.

More pictures as requested.

FredQ




first attempt at engraving text...

 

Hey guys,
New to the CNC world. It has always been an interest for me. I've got the machine all assembled and really like how it's turned out. Went with the Dewalt611. Got a screaming deal on it.
Using a 24 V power supply, KL-4030 steppers, and a C10 driver. Working on getting everything setup.
Just have a wiring question about the wires from the Nema23's. I have a red, green, blue, and yellow. Trying to figure which one goes to A+, A-, B+, and B-
All the diagrams I've found have different colored wires. Any help would be greatly appreciated.

 

those are open builds steppers?
red and green pair
yellow and blue pair
double check by touching one of the pairs together and see if it gets harder to spin the motor...
so close bet you are excited!!

 

FredQ thanks for the pics! I was thinking of mostly using 1/4" bits but looks like feeds have to be very high for router speeds and 1/4" bits. It's painful having all the hardware sitting here and no time to build!!!

 

Fred and Bob (and anyone else that wants to chime in), for your aluminum cuts are you using AlTiN coated bits?

Also would be interested in knowing where you've found your bits. I search and found this place which looks good...
End Mills |Carbide End Mill Store|

 

I have used many different bits these cheap one seem to just as good of a job as the more expensive bits.

3.175 mm 12mm CEL 2 Flute Carbide End Mills Router Bit

I have also used this 1/4" bit only because they sell them at home depot.

Freud Tools | 1/4" (Dia.) Up Spiral Bit

 

I'm mostly using solid carbide single flute bits, mostly bought on amazon. All are 1/8" dia cutter of various length. All are designed for Aluminum and plastic they say. Amana 51474 cut all the posted pictured parts, engraving done with Amana 51406 1/16' ball mill. I have some Onsrud that cut well also as well as some Micro100 bits.

FredQ

 

OK I'm back. Sorry for disappearing for a few months. Finally got hired and am no longer a temp with a staffing service. Full time maintenance. So I am still kinda digging out of the financial hole I found my self in after working at minimum wage for radio shack for almost a year. Looking forward to the holidays over time check first of the year. I am building that bigger high power rocket I alluded to back in September so some of the big check is going towards that project but next on my list is the C-beam machine. Then perhaps a 3D printer of some kind.