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Laff Riot
05-20-2003, 10:38 AM
I think the most intimidating thing about designing your first CNC machine is not missing something - but using a plan or assembly that will not work for our purpose despite how well we think it will. It's not like we all use our machines for the same thing so there must be some basic diversities in design and ideas.

So.. what are some of the biggest mistakes, black holes of cash and time that have been tried and proven to be to ambitious or costly for the hobbiest?

What did you want to cut with your settup but you just can't quite get it right?

balsaman
06-02-2003, 11:24 PM
The biggest mistake people make is trying to build thier first machine too large or too complex or too expensive. If you want to build a machine, keep it simple, cheap as possible, and not too large or complex. Your chances of finishing it go up huge if you keep this in mind.

You will make mistakes. There will be things you wish you did differently. Build a simple machine, learn from it, and if you feel the need, build another.

Eric

cbcnc
06-03-2003, 12:00 AM
Hi,

I think that it is important to stick to tried and true ideas and not try to invent the slickest, new, linear bearings. I say this out of experience because I tried to design a formica, UHMW, dovetail slide and ran into problems of uneveness and sticktion. They probably weren't insurmountable but I would have had to rebuild and I was getting tired of messing with it. So I am now going with something that has been done before. Just so I can get a running machine.

Chris

Laff Riot
06-03-2003, 10:34 AM
Ah the good ole days of grand ideas for that 5'x10'.. Pillow Blocks? whats a pillow block?.. anyways - and it will have dual individually controlled heads... G Code interpreter? And since it seems easy enough I will put in a 15 slot automatic bit changer.... Gecko? Why do I need a lizard? Maybe I will make it horizontal to save space... Limit switch? We dont need no stinking limits!... And maybe a 10 hp 1/2 inch collet router head.... Software? Cash? Oh.. well.. ahem... Honey how much can i spend this month?


Anyone for a nice 2x2 with rebuilt trim router?

dmoore3008
06-04-2003, 12:27 AM
I'm still building my first cnc machine...a 5' x 10' monster... it was only supposed to take, oh- 3 months at the most- HA !...2 years later and 75% percent complete (scrounging up parts from junkyards and industrial trash takes time and luck ), I often wish I would have started smaller, say 2' by 2' ? If so , I would at least have a little cnc machining under my belt by now. So I say this to all fellow newbies... Start small and enjoy...:rainfro:

JOE65
06-04-2003, 12:42 AM
You think you got trouble? check this out :D http://www.members.shaw.ca/dgray108/01140013.JPG

Start small and keep that E-switch handy

chuckknigh
06-04-2003, 01:20 AM
The high powered CO2 LASER I wanted to build for my first CNC machine just isn't panning out. I can't seem to make the necessary front surfaced mirrors with the equipment I have, and every time I try to buy a 10KW LASER commercially, they keep asking me what I intend to do with it! Can't imagine why... :-)

JUST KIDDING!

Seriously...my only real hangup at this stage is in building my own driver boards. I've got the chips, but my skill at circuit design leaves something to be desired. I've even intentionally limited the physical size of my design, so I don't have the 5' wide gantry problems in the previous messages...but the cheapskate in me wants to build my own boards.

Anyone care to help me out with the circuitry? I'm being quite serious in my request.

Allegro SLA7051M PWM unipolar translator / driver chips. I've only got 3 of them, so I need to get it right the first time!

-- Chuck Knight

FRAMEDNLV
03-11-2004, 02:18 AM
Chuck Knight,
Have you been able to get the driver working? I have been looking at using the same chip or the sla7052. Can you tell me how you went about getting the samples.

Thanks,
Chris

ynneb
03-11-2004, 02:45 AM
Yes I agree with balsaman there. Too big a machine for the first go. I am 6 weeks into this from new and have set out on building a 4 foot x 8 foot router table.

Already I realise I have bitten off a bit too much. But I have determined to finish it within 2 months even if I die doing so.

For any one else I would recommend a smaller project.

Oh and I could have bought plans for a fraction of the cost of the machine, but pride made me think I could work it out for myself. I will though,but for the sake of saving money now I am having to do it the hard way.

abasir
03-11-2004, 06:03 AM
Chuck,
Let me digest the datasheet for a while and see if I can be of assistance ;)

BTW, how do you intent to talk to the driver? Step/Dir or PWM?

owhite
03-11-2004, 09:02 AM
In contrast to the keep it simple folk, which is still very reasonable advice, I felt like my biggest mistake was to make life easier and just use steppers. The resolution sounded good at the time, but I really wanted to go much higher as soon as I saw what a circle looked like.

So make my recommendation for people starting up: take the plunge and use servos with fairly high resolution encoders on them you'll be happier with the final product.

owen

cnczane
03-11-2004, 06:04 PM
I started drafting in July, but didn't cut MDF until mid-September. I'm pretty well done with component pieces at this point, but still need a router head and platform.

There was this sinking feeling every time I thought of actually cutting that "expensive" MDF. (I actually remember thinking "$22 for one 4x8 sheet of 3/4 MDF is sure a lot to spend on this CNC machine..." :p I would not be surprised if my wife told me I've sunk $850 into it.)

I finally did get up the courage to make the cuts, and the next day realized the Y-axis should be done differently, but the gantry was already cut! (I finally used the pieces upside-down...)

In terms of "How to avoid mistakes," I'd say, "Be patient and gather your pieces slooowly." I bet most of us bought one piece or another in a state of "just-gotta-have-it-because-might-not-get-another-chance" and then it just sat there while more and better and cheaper went by us on ebay. (Mine was spending $80 for a power supply that wasn't quite what I wanted or wanted to pay months before I needed it.)

This morning I finally got my machine's base up onto the rolling cart I found at a surplus shop. "Gee, it would've been nice if I'd made it just-a-few inches narrower, so it could roll THROUGH the doors." but

Another occurs to me: No matter what, it's going to cost more than you figured. I don't think you're saving anything building your own, by the time you figure time and aggravation, but nothing beats the rush of YOUR beast coming off the paper and into life.

Still, it's kinda like marriage; I didn't know my wife had warts until we'd been married a couple years. Real machines sometimes have a few too.

pack rat
03-12-2004, 01:53 AM
I came to a tought that my mistakes are my best teachers and a gift that is offered to others.Can you imagine if all the people KISS the machine, we would end up with machine that is generic and unimaginative and impersonal. I like to improve things and yes, failures occur and I try not to repeat them. So let them come I Will Not Be Intimidated By Innate Object.(someone else said this) However my biggest problem is the constant improvement of ideas and not settling down. Indecisiveness is another.

kfong
03-12-2004, 03:18 PM
I really have to agree with this statement. The learning curve isn't building a CNC it's using one. Once you get your CNC machine going, you will find that it's the cad packages that will take all your time. 2D stuff isn't too bad, but wait till you try to do 3D.

Instead of building a mill, we bought a micro mill from Harbor Freight and just added stepper motors to it. Instant CNC machine, only took a weekend to do. We have been quite happy milling away, and will be using this little machine to make our big gantry mill. There are pics on our website under metalworking of the mill.

Kin Fong

http://www.embeddedtronics.com/


Originally posted by dmoore3008
I'm still building my first cnc machine...a 5' x 10' monster... it was only supposed to take, oh- 3 months at the most- HA !...2 years later and 75% percent complete (scrounging up parts from junkyards and industrial trash takes time and luck ), I often wish I would have started smaller, say 2' by 2' ? If so , I would at least have a little cnc machining under my belt by now. So I say this to all fellow newbies... Start small and enjoy...:rainfro:

kfong
03-12-2004, 03:28 PM
Hi Chuck,

Here is a micro stepper design we did for our CNC mill. It works great, the design is on line and the source code is free. Definitely go with a micro stepping board, runs much smoother. You think it was a servo motor at first. Look under Microstep on my web page.

Kin Fong

http://www.embeddedtronics.com/



Originally posted by chuckknigh
The high powered CO2 LASER I wanted to build for my first CNC machine just isn't panning out. I can't seem to make the necessary front surfaced mirrors with the equipment I have, and every time I try to buy a 10KW LASER commercially, they keep asking me what I intend to do with it! Can't imagine why... :-)

JUST KIDDING!

Seriously...my only real hangup at this stage is in building my own driver boards. I've got the chips, but my skill at circuit design leaves something to be desired. I've even intentionally limited the physical size of my design, so I don't have the 5' wide gantry problems in the previous messages...but the cheapskate in me wants to build my own boards.

Anyone care to help me out with the circuitry? I'm being quite serious in my request.

Allegro SLA7051M PWM unipolar translator / driver chips. I've only got 3 of them, so I need to get it right the first time!

-- Chuck Knight

kfong
03-12-2004, 03:36 PM
Oh, I did look at the specs of your chips. Not a choice I would make. Only full and half steps. Also, unipolar. We found stepper motor resonance to be a problem with full and half steps. Microstepping really reduced that.

Kin Fong

http://www.embeddedtronics.com/


Originally posted by kfong
Hi Chuck,

Here is a micro stepper design we did for our CNC mill. It works great, the design is on line and the source code is free. Definitely go with a micro stepping board, runs much smoother. You think it was a servo motor at first. Look under Microstep on my web page.

Kin Fong

http://www.embeddedtronics.com/

kfong
03-12-2004, 03:47 PM
Hi Owen,

I can't say I agree with this statement. The only advantage servo motors have is speed and feedback. Other, than that stepper motors work very well. You must be using full or half steps, have you looked into microstepping? With the latest stepper motor designs, even the speeds are increasing. I have no problem milling perfect circles with my mill. You can see pics posted on my site.

Kin Fong

http://www.embeddedtronics.com/


Originally posted by owhite
In contrast to the keep it simple folk, which is still very reasonable advice, I felt like my biggest mistake was to make life easier and just use steppers. The resolution sounded good at the time, but I really wanted to go much higher as soon as I saw what a circle looked like.

So make my recommendation for people starting up: take the plunge and use servos with fairly high resolution encoders on them you'll be happier with the final product.

owen

FRAMEDNLV
03-12-2004, 04:41 PM
Back to the question about the allegro sla7052 or sla7051. Does anyone know about the circuit for this chip? It looks straight forward on the reference sheet.

Kin Fong,
I glanced over your site. Some of the numbers really look good. I'll have to look some more at it.

Chris

abasir
03-13-2004, 11:37 AM
I still could not figure out the purpose of SYNC :(. Can I just connect it for async mode? Anybody can help? The rest looks straight forward for direct connection to any parallel port.

FRAMEDNLV
03-13-2004, 12:51 PM
My guess is that if you don't use a circuit for sync then you would want to ground the sync. This would have the chip use the "asynchronous PWM operation". If you had logic on it would be "synchronous operation". The use of synchronous operation during normal stepping is not recommended because it produces less motor torque and can cause motor vibration due to stair-case current.

So I guess ground the sync and It should work but it will be noisy when the motors are not moving.

I still would like to know where to get the chip. I have been looking for about a month now. Where did you get your?

Chris

Jan
03-13-2004, 12:56 PM
Kin
I see you have an iopener displayed on your site.
I also have one and was wondering if the iopener had enough guts to run a cnc mill, I don't recall
if the parallel port is/was available.
Any thoughts?
jerry

kfong
03-13-2004, 01:12 PM
Hi Jerry,

We only use the I-opener as a remote display. The Dell computer shown on it's side is what is running EMC. It's at the bottom of the cabinet. As far as using the i-openener by itself, it should be possible as long as it's dedicated to the milling operations only.

For EMC you need a minimum of
An old P133 with 16-32Mb RAM, a 500Mb IDE hard drive, and a CDROM drive that can be booted from. If you want good performance from stepper motors, a Pentium 233 or better is recommended.

Kin Fong

http://www.embeddedtronics.com/


Originally posted by Jan
Kin
I see you have an iopener displayed on your site.
I also have one and was wondering if the iopener had enough guts to run a cnc mill, I don't recall
if the parallel port is/was available.
Any thoughts?
jerry

kfong
03-13-2004, 01:15 PM
You know, I don't recall a parallel port on the I-Opener.

Kin


Originally posted by kfong
Hi Jerry,

We only use the I-opener as a remote display. The Dell computer shown on it's side is what is running EMC. It's at the bottom of the cabinet. As far as using the i-openener by itself, it should be possible as long as it's dedicated to the milling operations only.

For EMC you need a minimum of
An old P133 with 16-32Mb RAM, a 500Mb IDE hard drive, and a CDROM drive that can be booted from. If you want good performance from stepper motors, a Pentium 233 or better is recommended.

Kin Fong

http://www.embeddedtronics.com/

Jan
03-13-2004, 01:57 PM
Kin
yes, it has a parallel port, just checked, but seem to recall some discussion on the iopener forum about the only
printer that was capable of use was some specific brand.
I'll have to go back and look this up.
Thanks
jerry

kfong
03-15-2004, 10:04 AM
I don't think you need to worry about that, I believe it's just a standard parallel port.

Kin Fong

http://www.embeddedtronics.com/

abasir
03-17-2004, 08:46 PM
Originally posted by FRAMEDNLV
I still would like to know where to get the chip. I have been looking for about a month now. Where did you get your?
Chris

You could ask for samples from www.allegromicro.com
Unfortunately, they don't send to my country :rolleyes:

lsfoils
03-28-2004, 12:29 AM
Yes, if you loose track of what you are doing, by thinking about the furture (in my case) you may have to backtrack a bit.

http://www.cnczone.com/forums/showthread.php?s=&threadid=1357&perpage=15&pagenumber=2