Best intentions

[Laff Riot]

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]

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]

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]

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]

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...

[JOE65]

You think you got trouble? check this out

Start small and keep that E-switch handy

[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

[FRAMEDNLV]

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]

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]

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]

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]

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..." 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.