breakout board suggestions?

i will soon convert a knee mill to cnc with linuxcnc using steppers, i plan to use gecko drivers (not sure which yet) and will purchase a mini itx motherboard with parallel. on thing i want to eventually do is add spindle feedback for adaptive feed when tapping and would like to hook up some kind of pendant for jogging and setup. what is a good breakout board and should i look into a mesa card for more i/o?

i will soon convert a knee mill to cnc with linuxcnc using steppers,

Well that is what I did. I do not think you stated if you were going to use the knee as an axis or just use Z .
You would be fine for x,y,z with steppers.
For my knee I only use it to position work so speed is not important so I used a stepper and a 10-1 gearbox. Slow but works fine with stepper.
I use John's Simple Remote Pendant joypad with incremental moves added to it to "touch off" my work.

Rick G

thanks for the replys.

i'm aware of the concerns for steppers but if i go servos the costs add up and i may as well buy a used cnc at auction. this i can do for right at about $1000. any more power and i wouldn't want to be using r-8 collets and tool holders and more money could put me in the range of a used machine at auction. machines from the early 80's still have good hard parts but the controlers didn't get friendly and sophisticated till at least the late 80's. if i look long enough i can find something that out lived it's usefulness but can be brought back to life with linux cnc. but this is to be cheap, quick and fun. after i start making money with it i can save for a serious machine.

if a usb pendadnt is ok maybe i'll search e-pay and see if i can find something with a handwheel. if not i guess i can use a game controller if there is a way to switch between continuous and step by step jogging. i may also want to built a tool measurer and a touch probe but dont need to use them at the same time and i guess that only needs 1 i/o line.

well i guess i can go with any old breakout board for now since i don't need a ton of i/o initially.

as for the g540 it's nice but it's too small. i'll need 6amps and 80v. but their drives that handle that are all pretty similar.

just to alleviate concerns for the steppers here is a spreadsheet i found with some numbers plugged in. i just guessed on the cutting forces as i haven't had to do horsepower calcs in a while and didn't have the machinists handbook on me when i did this but i think i picked a liberal number and i should be able to cut at 60ipm and rapid at 100 with ball screws and a 200% margin of excess torque.

edit: doesn't look like attachments are working. i may be too new, not sure what the forum rules are...

well i have a day job. but there are a few items i see a need for. and i think this will do the job. i'll probably sell carburator spacers to local engine builders and i also have an interest in electric guitar and guitar aficionados will pay pretty good $ for anything. not enough to get rich i know but if i can find a used machine with a toolchanger i think this can make me just enough to buy it.

i'm well aware that i won't likely need 60ipm. just making the point that this should do well enough if things are well lubricated. but with a 3-flute cutter or multi flute arbor mounted mills doing light facing 60ipm isn't out of the question.

BigJohnT wrote:

My BP Series 1 knee mill has a Kwik Switch spindle which means I can load each tool and touch off to the tool table. It doesn't have a tool changer (I'm the tool changer) but I can run programs with multiple tools. I've seen the spindles on flea bay before and the tool holders as well. Just another thought.

A 3" diameter face mill with 5 inserts and using a 0.005" chip load and 600 SFM is 765 RPM and 19 IPM... a 3/4" 3 flute using the same chip load is 3056 RPM and 45 IPM. A 1/4" 3 flute with 0.003" chip load is 9167 RPM at 82.5 IPM so usually you run out of RPM on older machines before you get any speed going.

When choosing a stepper ignore the holding torque number it is pretty much meaningless as it only indicates how hard it tries to not move... get the RPM torque curve for the stepper at what ever voltage you are using and use that to calculate your ratios and speeds.

John

ive seen similar on a series 2 with bt40 tooling. never on a series 1. i didn't know it existed.

my machine is made by induma. it is similar to a bp and may accept a j head but i'm sure the actual spindle parts are different.

i don't have a full torque curve for the steppers i've selected but the spreadsheet assumes a "corner speed" on other parameters and gives the predicted torque at speed mainly based on the inductence. they are low inductance nema 42 motors. the low inductance is the key and is what gives them good high speed performance. there should be a very good margin. www.mycncuk.com/forums/faqs-problems-sol...-need.html#post10046

using the spread sheet i put in 150kg for the mass, 1.1 friction coefficient, 5mm thread 25mm diameter, 20 minor diamter (didn't want to take time to look up acme thread specs, this part is just for inertia, it's close enough) 500 newton cutting forces... motor specs are 5500 g/cm^2 inerita, 12 nm holding torque at 6 amps, .30 detent torque, and 6mh inductance.

i will also point out that i'm not driving the knee i will drive the column so my z travel in the programs will be limited. although i do have an idea to fix the issues with torque to drive the knee by supporting some of the weight with an air bag or air piston and regulating the pressure which is something i saw on clausing mills my shop had when i was in the airforce. it seems to me that driving the knee is just problematic and would be too limiting as far as speed goes if i want to do 3d cutting not to mention mounting a motor on the knee is just awkward it being at a weird angle. though if i later feel i can get it to work and decide to live without a a hand crank i can directly couple it rather than belt drive it.

the quick change adapters are interesting. i will look into those. you've all been very helpful with ideas.