OXcalculator - Bill of Material and Cost calculator v1b006 (xls + ods)

Noob question... I'm planning my OX build and I plan to machine acrylic, aluminum, MDF, etc. But I often machine expanded polystyrene, which I'm hoping to achieve 500+ IPM. I'm using a GRBL controller w/ 24V 4A outputs and I want high torque motors for accuracy and fast acceleration, but I don't want high current/torque to limit my rapids.

So I'm using the Stepper+ calculator to help figure out the steppers for my OX build, and I've come to a conclusion that seems counterintuitive: With all other aspects of the motor being the same, lowering the Max Amps seems to increase the max speed of the motor. Can someone explain why this is? Why would a 2A motor move 2x the speed of a 4A motor with everything else being equal?

 

I'm no expert and, like you, I'm still struggling to understand the laws that are at work to answer your question. An often quoted source on the question (in my searches on the net) is www.geckodrive.com. They have a Step Motor Basics Guide. I'll admit it is beyond my attention span ... I just use the formulae as, surprisingly, I don't have to understand everything. This PDF seems to answer your question, maybe in the very first page.

 

Thanks @Serge E. Maybe I should post this question in the Openbuilds stepper section to get more feedback too. I'm not trying to get "theoretical" as much as understand if I'll be limiting my real-world speeds if I choose a high-current motor instead of a moderate current model. I see giant machines on YouTube moving at 1000+ IPM and I can't imagine that they have less than 1A motors, but that's what I'm seeing when I use the calculator. Anyone else with experience here?

 

Yes, do leave a post in the stepper section and even the controller threads for feedback as not all threads are being followed by all who could answer.

I use these Dual Shaft Nema 23 CNC Stepper Motor 76mm 1.9Nm 23HS30-3006D - US$ 21.38 for myOX, with a CNC xPro controller. They have been known (by accident I assure you, thus not often) to push (with the router) the clamps out of their way without breaking into a sweat. Kind of scary, especially when limit switches have no way of knowing about this. Of course, it was no where near 1000+ IPM, but fast enough that if it was a finger it would be gone !

What are the "giant" machines moving at those speeds ? One must consider speed, torque and forces, such as the tendancy of an object, especially if heavy, to want to stay on course rather than changing direction too rapidely ... The mass of these machines comes in play to help. Also, what material are they working on and with what kind of tool (spindle and bit) ? Are they cutting into "butter" or is it inconel ?? If they move a laser around, the load is fixed. If they are moving a spindle/router, one must add resistance as the tool cuts through material. Machines must also be very rigid so as not to flex under the many forces of swinging around anything at those speeds.

The OX and its many derivatives don't have the heft, or intentions, of moving much of anything at such speeds.

In other words, the stepper motor and its characteristics are just part of the equation.

 

Notice, as well, how they have a Nema 23 CNC Stepper Motor 2.4Nm(340oz.in) 1.8A 23HS41-1804S with nearly half the current load (amps) but 50% more torque ... It's also about 50% longer than the version I use (see other reply). At this stage, it's still all chinese/greek to me : bigger stepper motor, less current but more torque. Which, apparently, correlates with the formulae and your question ? Does it ?

 

Thanks for the additional info. I agree, there is a lot more to consider when trying to move at high speeds. I'm really only concerned with high IPM when machining EPS (styrofoam), which has very little cutter resistance at high speed. So, I guess I'm looking for motors that can move fast during low or no-load conditions, but still maintain good torque when milling wood/plastic/aluminum at much lower speeds.

I've put both of the motors you linked into the calculator and I realize that the speed is more of a factor between current and inductance. So the 340 oz. model you linked to has a max IPM of 277 because the inductance is much higher than the others. In this case, I would consider that motor a bit too slow.

I have a feeling that I'm overthinking it (as usual) and I'll be fine with whatever motors I end up using. Thanks again for your help and providing the calculator in the first place.

 

I appreciate all the work you have done on this spreadsheet, but would you *please* be willing to devulge the password to enable us to unlock the cells? I'm not asking because I want to change any values. I just want to be able to change the height of some of the cells so I can read them!

On my monitor, many of the cells that are full of text have text that wrap beyond the cell, requiring me to scroll up and down through the cell to read it. It's really annoying. FWIW, I'm using the ODS version and LibreOffice 4.3.3.2.

 

Sorry about that, I thought the cells would still adjust. I was off (to the South) for a while, so I'll catch up with things ... I will be converting the whole thing to a responsive web page as I integrate some of the future features mentioned early on.

By the way, you could always Google for the Excel macro which cancels out / resets ANY password of ANY xls/xlsx files (so much for Microsoft security, eh ?) I use it at work for people who forget their passwords ... The only good use for those passwords is to 'freeze' key cells/formulae, avoid accidental changes.

 

Thank you for the calculator. Shipping costs are a significant part of my expense, so I am wondering how best to run some what-if scenarios. Shipping costs are affected by both weight and dimensions (primarily the length of the longest pieces of v-slot). I will check my local sources (Grainger, etc.) for the v-slot to possibly avoid paying to ship that. I see Nema 23 and 17 steppers on eBay (sometimes with free shipping), and on Amazon (free shipping with Prime). I have many variables to consider. Ideally, it would be nice to have a weight column on the calculator, but I understand that I need to figure some of this out myself.

 

Hmm ... nice idea, having a weight on each item line. Some of them are "known" and can be defaulted - such as the V-slot. But most are going to need manual input. As you indirectly mention, the costing will need to account for the source : split the 'total' weight by source Unfortunately, some of the shipping cost might also vary according to dimensions not just weight. Some vendors also do odd things for calculating their shipping cost. However, I'll think about the whole concept as I might be able to make it a bit easier to budget a build ...

I am still working out (very part time right now) on how I will implement as a web version. I want it to handle just about "any" build, be it an OX or C-Beam derivative. Just need to define "modules" and how they relate to each other. Obviously, I would have to define the default "modules" ... I have OCD, so I tend to aim (way) beyond the obvious. Which means it can take a while before I deliver. Sorry.

 

TBH I dont think weight needs to be added. So many companies upcharge or add on handling fees. It was cheaper for me to buy my gshield from inventables for 45$ then to get it for 25$ from another site, because shipping was 9$ vs 50$.....................

 

Indeed, shipping cost is such a wild parameters it would be difficult to work it in by weight. Many order over time so shipping gets even more out of hand - avoid having to pay for everything at once but probably paying tons more in shipping ...

However, it might be interesting to get the weight in for a rough estimate of the machine's total weight ? More trivia than practical use maybe ?

 

I noticed that many of the OpenBuilds items on Amazon (wheels, bearings, M5, brackets) qualify for free shipping with Prime (which I have). That works for me.

The 80/20 V-Slot 1500mm Length is $30.00 + $4.49 shipping which is reasonable.

And another Amazon source has Nema steppers with free shipping.

Now for the plates ...

 

Good luck with those amigo
Im running a set from Blue Ox off of ebay, but **** are they expensive. Even more so once I got a quote from a local metal supply and the whole thing would've cost me only 75$ in aluminum plate and I could've probably have the machine time for 40$ from a local cnc mill. Oh well, what can ya do.

 

Don't forget the 'free shipping' with Amazon Prime actually cost you the yearly Prime membership fee (100$us/year). Is it just items shipped by Amazon (they warehouse for sellers) which fall under the Prime free shipping offer? So if you order often enough of those items, every year, it's a great deal. Otherwise, might not be so much of a savings ... I do a bit of ordering with Amazon, regular "free" shipping takes usually a week, no fees to pay. Just have to order 25$ or so to get the free shipping without Prime. Stuff which comes through China is sometimes with free shipping, but several weeks to receive. Vendors charging too much, with or without shipping is avoided. Patience usually pays.

 

Hello,

I just found the calculator this afternoon and it looks great ! But I am running into a problem. The file is locked and I cannot change any of the fields.
How do I get it unlocked? I put the link below where I downloaded it from.


Downloaded It Here

 

I have the same problem. I am guessing the OP stopped at version 1 and version 5 was only ever a dream

 

This video tells you how to unlock an excel spreadsheet.

https://www.google.com/url?sa=t&sou...BMAF6BAgGEAk&usg=AOvVaw2yEUzre3q5qHYU8PTU-XMA

Alex.