Newbie questions ?

[Calico]

I would like to build CNC Router about 1 meter by 1,5 Meter size with 50cm Zdepth cutting, Mostly cuts wood and Epoxy/fiberglass.
Precicion / backlash about 0.1mm required.

questions:
1. Can I use Stepper motor ? what size ? is Servo better ? how ?
2. What is bearing/leadscrew required for this ? minimum diameter ? what type ?
3. Does Gecko drive or Hobbycnc drive enough for this accuracy I need?
4. http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW
what about this item on ebay ? too small or too much ?
5. can I ask more ? later...
.
rud

[Nonoriginal]

1 yes. 275oz/in at least or set-up with gear reduction.
2 doesn't matter. You need to figure out how fast you want to cut/jog/etc... You already know that ballscrews are the most precise...so, go with them.
3. yes.
4 looks good to me...maybe I'll out bid you ...LOL
5. I guess, these question are easily answered if you search and read a little bit.

[kevlar129]

Hello Calico,

I am presently running my machine with direct drive 5mm pitch ballscrews from Techno-Isel. My machine is almost exactly what you describe. In my experience, my machine will max out (stall) at approx. 125 inches per minute. It presently has an accuracy of .00098" at full step. Here is the quick math for this...
5mm screw pitch / 200 motor steps = .025mm... .025mm * .03937 = .00098"
This is a tad bit overkill due to the fact that I run a plasma torch or a Porter Cable 3.25 HP router on the toolpost. I am re-designing my machine for a 4:1 reduction with belts. I am way excited with the prelim. drawings and speeds. With a 20mm total pitch, I feel it will be a perfect mix between speed and accuracy. I would be more than happy to send you my dwg file so you can check it out. It is a solid model, therefore you can look at it from any direction (the ONLY way to verify any machine collisions). If you have a way of viewing a dwg, let me know...you won't be sorry! This post is based on an actual working machine, already built and proven, with the exception of the belt reduction. I can provide you with actual part numbers for all of the parts needed. It is currently running Techno-Isel screws and extrusions, Hiwin linear slides, Gecko drives, Mycom/Nyden steppers, and Mach2 software. The machine extents are X=49", Y=98", Z=9". Hopefully all of my ramblings have not confused you in your quest! By the way, Techno-Isel does have 20mm screws...perfect for your application...and mine! Hindsight's 20/20!!!
Good luck and happy machining...
C

[H500]

Kevlar, can you tell me what the linear slides cost?

[kevlar129]

H500,

It's been a while since I bought mine. I'll have to look it up for you. In the meantime, I do recall speaking to the Hiwin rep out of Los Angeles, I believe. His name escapes me now, but if you look on their site, I think you can find an 800 number for them. As for the linear slides themselves, when I was designing my machine...(5 years and 2 wives in the making!)..., I researched virtually every manufacturer out there, and none of them even came close to Hiwin, in the bang-for-the-buck category. I have been completely satisfied with mine, as I am certain you will be too. If I can assist you in any way, please let me know. I am more than happy to help out a fellow DIY'er. By the way, the linear slides I am running are the LGH-25CA series...more than strong enough for even the most demanding aluminum milling operations.
Happy machining
C

[gregmary]

Kevlar,

I want to understand your math. You say you would like to use a 4:1 reduction gearing. Does this mean that you will have 1/4 the speed and 4 times the torque, or is it the other way around? If you go from 5 mm pitch to 20 mm pitch is seems your speed goes up by 4 and your torque is decreased by four.

I am currently running 200 oz/inch motors on a 18tpi lead screw (about 1.5 mm pitch I think) and it is too slow. I am thinking of going to a 3/8-10 which is a pitch of about 2.5 mm pitch, half of what you have today. To complicate comparison between our machines I am using ACME precision lead screws instead of ball screws which are about 1/3 as effeicent as yours (eat up a lot of power).

Anyway I wanted to understand what you considered the "perfect combination of speed and accuracy" was before I go off and invest in some more lead screws.

Thanks,

Greg

[ger21]

Greg, you might want to try the 1/2-8 2 start acme from MSC. It's only ~$25 for 6 ft, so you won't be throwing a lot of money away. 4 turns per inch, with around 65% efficiency.

[kevlar129]

GREGMARY,

Yes, you are absolutely correct in your assesment of the speed/torque trade-off. As I expressed in my previous post, my machine currently stalls (runs out of torque) at 125-150 inches per minute...way too low, wouldn't you agree? Therefore, with the sacrifice of "human hair" accuracy, I will allow the motors to spin well within their "torque bandwidth", with reasonable feedrates of 250 IPM. That being said, you are correct that I will have a theoretical 1/4 torque, but, when I had no torque left at an acceptable feedrate to begin with, I think I'm in a win-win situation. I must admit that I have substantially more torque on tap than I gather you do. My X is 950 oz in, Y is 1450 oz in, Z is 490 oz in. With a 200 oz in motor like you have, I can certainly see your concern for my design...my bad, I should have provided all of the relevant info in my first post. Thanks for the question, I hope I didn't confuse matters any further.
Happy machining...
C

[kevlar129]

GREGMARY,

Sorry for the back to back posts, but I did neglect to mention that motor torque needed is "directly" proportional to what your intended machining plans are, as well as the "dead weight" of your machine itself. If you are doing non-contact machining, you could probably get away with a smaller motor. I do both, so I am sure many people would agree that my gantry is way over-cooked for NC plasma cutting, and just about right for contact machining with a heavy Porter Cable on board. Hope I helped.
Happy machining...
C

[gregmary]

Kevlar,

Holy smokes, 1450 oz in on Y! What are you using? A Briggs and Straton lawnmowing engine?

I was poking around on ebay today and found a couple of "buy it now" ballscrews, one for my x and one for my z. Kind of an impulse buy you might say. So I hope to get more power to my cutter--contact machining as you say. It is always fun to get things in the mail.

Greg

[kevlar129]

Hey Greg,

Yep, over-cooked eh! Check out clickautomation.com for awesome deals on steppers and such. Best source I have found so far. Good luck on the Ebay items.
Happy machining...
C

[Calico]

Kevlar,
thanyou for the reply,
yes I use Solidworks if I can explore your CNCdrawing on that.

The difference between your's and my plan is the Z travel, I need about 60cm travel.

send me your file to auahlap@gmail.com

regards
ruddy