need help planning

[russell]

i am researching building my own cnc router and could use a little help

i would like to see a machine about 4ft by 4ft
i would mainly be cutting 3/4" soft wood
it would be running a 2 or 3 hp router
i would need a repeatability of around 1/32"
speed up to as fast as the router could cut

one of my biggest roadblocks is sizing the moters and ballscrew without being
an engineer
like saw for instance my gantry setup was 50lb?

would i be ok with steppers or should i go with servos
and how much would they cost

i would like to keep this inside of $6000 or $7000 total
i may be dreaming i dont't know?

any and all help would be greatly apreciated
thanks

by the time

[ger21]

Check out http://www.campbelldesigns.com and http://www.data-cut.com

[atifeh]

I am also in progression of the research phase to build my own cnc, therefore I might as well share my experience.
I started by gathering as much information as I could, visited each and every site and compared different machines, read a lot of tutorials and white papers, joined a few yahoo groups and persued the threads closely, changed my design quite numerously.
I found quite a lot of machines well thought and well designed which you could find them in this forum as well, but I came into this conclusion that I have to design it from scratch if I want it to be a fit-for-my-purpose, the hard way though, maybe even reinventing the wheel. But if feels good.
Anyway through reading a lot of materials I am summing them up into an Excel spreadsheet which will be added to gradually. The first part will be the determination and selection of stepper motors which will be ready in a couple of days and I will send it to you (I don't know if there is a file submission folder for general use in CNCZone like those in Yahoo groups? If there is, please inform me). The second part would be lead screw sizing, which will happen afterwards.
Since I intend to use Aluminum profile I have prepared a spreadsheet to calculate the deflection of different types and sizes under various loads, if it might help.

Nader

[Evodyne]

Hi Russell. Lance here. I'm very much like you-in the planning stages. One thing I did early on was to scour this site and look at the specs on machines others are selling. Take the time and go back through some of the old threads-just about every question I came up with had already been asked-and answered.

Gerry (Ger21) gave you a few links, but he pointed me to some pics of his machine that you may want to look at. He's done a good job making a very robust frame from wood. That is one way to keep the costs down.

If your diligent and know what you are looking for you can make out well on eBay. Research finished auctions to see what a thingy usually goes for. Also to see how often they come up. Then find out what it is worth new! That $300 ball screw sounds like it's too much until you find out it was $3,000 new and only shows up about twice a year at auction. All of a sudden it looks like a bargain-if that's what you need.

So is your $6,000-$7,000 machine a possibility? Just to give you an idea, here is what I've got in mine. I'll give you the actual prices I paid to date. I'm not trying to brag or show off, but to give you an honest appraisal of what you might be able to do.

Router-Craftsman 2-1/4 hp 8,000 rpm to 27,000 rpm w 1/2" and 1/4" collets
List $219, on sale for $199. Kept the router and currently trying to sell the case, fixed and plunge bases for $50. If successfull, $150 invested, new.

One box of seven supposedly bad Baldor DC servo motors. Part numbers MTE 2240 BLBCN and 2250 BCBCN. Roughly 40-50 VDC bus, 20 amps, and 5000 rpm for the small 2240s, more for the 2250s. With tachometers and 100 PPR quadrature encoders. Mislabeled by Baldor-the small motors read 30 oz-in of stall torque. Should have been 30 lb-in! I paid $210 for all seven. Six had nothing wrong with them, number seven had one broken solder joint on the tachometer. I fixed it and it works fine. I'm going to keep them, but if I wanted I could keep just three for my machine and sell four. The 2250's today list for $1,000 new. So say $100 to $300 each on eBay. But without selling anything I'm up to $360.

Three G320 step-direction Geckodrives for DC brushed servos: new from Mariss $114 each. So $342.00 for drives. Now I'm at $702.

A complete slide unit with 5-6 inches of travel. This will be the Z axis. This came with THK rails, an NSK ground ball screw, built in limit switches, NEMA 23 motor mount, brushless servo motor and an RSR linear encoder. Bought two for $275. Motors were bad, everything else was good. Don't need the linear encoders, so I'll sell them for $75-$100 each. I could sell off the second slide for $100-$125. But assuming I don't, I'm up to $977.

I wanted ground ball screws. Just because. I found some inadvertantly being sold as lead screws (much cheaper). Apparently no one else saw what they were-I got a 1-1/4" diameter ground ballscrew with 60" of threads, two coupled ball nuts, bearings, mounting blocks, and NEMA 42 motor mount for $300. He had more, so I picked up three others. The 50" long, 1" diameter ones were about $250. If I use one 50" and one 60" I'd be at $550 for screws. So $1,527 total.

Slides for the X and Y axis. This probably doesn't apply as I got an absolutely fantastic deal. I picked up multiple sets of 80" long THK HSR 20mm rails with two HSR20-TR blocks each for $150 per pair. That isn't a realistic price. I sold the ones I didn't need for $200 per rail or $400 a pair. Even that is a good price. Since it is more in line with what one might pay on eBay, let's use the latter pricing. Two pairs of 6'-8" rails for $800. So our total is $2,327. Shorter rails are proportionally cheaper, as are the lesser quality grades (RSR, etc.)

I still need a power supply for the servos. Haven't a clue, but $300 sounds about right (in reality I've got loose parts and will build my own-$0). Frame materials, wire, misc electrical parts, etc, and we might get to $3,000 even.

Remember, I've got four extra servos and a slide I could sell off to lower this drastically.

The PC I have, and Mach II software in demo mode is free-and that's a price you can't beat.

Others will say I'm a fool and that a good machine can be built with less fancy parts. It's a matter of personal choice. Go with home made bearings, rolled ball screws/lead screws/rack and pinion and you can trim a ton. And if built well these can perform wonderfully.

In my opinion you can get exactly what you want for much less than your projected budget-especially given the 1/32 repeatability and the reasonable dimensions. Bargain shopping time!

Good luck and sorry if this was too long. I hope it helped.

Lance

[ger21]

I'd stay away from craftsman routers. For the same price Lance paid you can get a PC 892, which is a really nice router. But if your'e spending $6K-$7K, the smallest router I'd use is the PC 7518. A little more than $300. The next step up from that will be at least $2K

[russell]

thanks for your help
i was wondering where i would find these routers you are talking about

[ger21]

http://www.porter-cable.com/index.asp?e=547&p=2810
http://www.amazon.com/exec/obidos/tg...&s=hi&n=228013
http://www.amazon.com/exec/obidos/tg...&s=hi&n=228013

[Evodyne]

Gerry,

Ouch! My router = poo-poo? The selection in my town for routers was pathetic. My criteria was over 2 HP and variable speed. That was about all I could find.

Can you elaborate a little on why the units you referenced are better? I may go for a return and upgrade. I take it that the "PC" is Porter-Cable, or am I all washed up there too?

Any help is greatly appreciated. Thanks in advance.

Lance

[ViperTX]

The Hitachi router is 3 or 3 1/2 horsepower....I've got one and it's better then the PC. It's also nicely priced on Amazon.com....about $160 or so...last time I looked.

[Evodyne]

Thanks Viper. Have you actually used both to be able to say that the Hitachi is better? I'd ask you the same question I posed to Ger21: what makes one "better" than the other if the parameters like speed and power are the same. Conversely, what is to be avoided? (...well Lance, so long as you DON'T use the Craftsman, your fine...) Arghhh!

Lance

[ger21]

Correct me if I'm wrong, but the Hitachi is a plunge router, which makes it difficult to mount. The Porter Cable 7518 and a Milwaukee model are the only 3HP fixed base routers available in the US, I think.

Lance, I don't buy Craftsman power tools. I haven't used one in a very long time, at least 10 years. They may be better now, but typically they just don't last as long.
There is a Bosch and Makita that are comparable to the Porter Cable 892, but both cost a little more. And I happen to have 4 Porter Cable routers, so I stick with them.

A friend has a Hitachi, and he likes it.

I'd recommend the following brands at the top, not in order. Porter Cable, Bosch, Makita. I buy different brands for different types of tools. Makita cordless drill. Bosch jigsaw and belt sander, Porter Cable routers, laminate trimmers, and sanders. I have a Bosch laminate trimmer as well.

Dewalt and Hitachi are pretty good, but I don't much experience with them. Do have a Dewalt 12" miter saw, though. It currently has a broken switch. Newer models have a redesigned switch.

Was this any help, or just a bunch of rambling?

[ViperTX]

Originally Posted by Evodyne Thanks Viper. Have you actually used both to be able to say that the Hitachi is better? I'd ask you the same question I posed to Ger21: what makes one "better" than the other if the parameters like speed and power are the same. Conversely, what is to be avoided? (...well Lance, so long as you DON'T use the Craftsman, your fine...) Arghhh! Lance

Lance, yes I've used most of them at one time or another. I designed the first microprocessor based router for Craftsman back in the early 80's. What you find with of routers is that the universal motors that each uses are a bit different in characteristics and for under $200 Hitachi seems to be the best, we'll see in a few years of use how well they hold up.