Moving Table vs Moving Gantry; Dremel vs Router

[chuckknigh]

For a homebuilt unit, which is a more robust design? I can see benefits to both approaches...

My understanding of them is based, primarily, on photos of other people's machines, and of Cranky's 7th Sojourn and Routezilla designs.

Both look well engineered, and both would be excellent designs to emulate. (OK...copy) But which, for someone starting with a "blank sheet of paper" is the better design to emulate?

I *like* Routezilla better -- something about it appeals to me. But, my concern is the potential for the gantry to rack while the machine is under load.

Is this a real concern, or is it more of a theoretical thing? I'd be using twin rails -- one on each side with fully supported homemade linear bearings -- and a screw drive mounted in the center.

THANKS!

-- Chuck Knight

P.S. For the cutter head, would it be better to go with a Dremel/RotoZip, or a small router?

I already have both a Dremel and a trim router, so it's not a matter of using "what I already have."

And then there's this router:
http://www.harborfreight.com/cpi/cta...emnumber=44914

I've seen it on sale for $20 from time to time...a truly exceptional price. Something cheap that I could dedicate to this project, next time it goes on sale.

[anoel]

I built the 7th Sojourn and liked it well. The table was a bit small for my specific needs. With a little help from John I just finished up the mechanicals for a Routezilla sized machine. It's more of a hybrid of the Routezilla and Pheonix as I migrated the X and Y axis from the 7th to a moving gantry style machine. So far so good. I've not cut anything with it yet because it's going to need some faster speeds to cope with the large size of it. It's got a 28"x16" cutting area. I'm moving to 4v steppers and a 24v power supply in the next few days, which should prove to be much more powerful than what I've been using. I hope to get slightly better than 25" per minute with it. I cut all of the plastic parts and the gantry uprights with the 7th Sojourn and alignment was extremely good on this one. I can turn the lead screws very easily with my fingers and move any of the axis with less effort than I could on my all hand cut 7th. I'm pretty stoked. I can't wait to get my power supply. Where's that damn UPS man?

[HomeCNC]

I never liked the moving table because the screw under the table is exposed at times, and it requires a larger floor/table space.

[chuckknigh]

Why does it need higher speeds? Is it just a matter of practicality vs patience, or is there an actual reason to have the higher speeds?

To start out with, I'm thinking of getting "whatever" steppers I can find, adapting them through pulleys/gears to the torque I actually need, and then upgrading as better parts come available.

By driving it from a smallish shaft to a larger pulley, I should be able to increase the effective torque and resolution of "whatever" I can find. And, it doesn't seem to be too hard. It might make the machine painfully slow, but it should work...and suffice till better parts can be had.

I'm going to use that braided air hose coupling trick that was mentioned on the board -- good tips on here, and on the RC forum. I've already mocked up one of my screw drives, and it works just fine. Support bearing on each end, air hose coupler design, etc. Works great, even if it is only 6" long at this point. Like I said -- it' a mockup.

I have a computer flea market event coming up next weekend -- it's obvious what types of things I'll be hunting for. There's usually at least 1 guy down there with steppers and otical components...and another with broken LASER printers and Xerox machines. Both should prove to be good sources for steppers.

-- Chuck Knight

[anoel]

Is'nt "Just because" the excuse our parents alwas gave us?

The need for speed is the fact that I need to route soft and hard wood. Too slow Feed rates cause the wood to get burn marks. 6 inches per minute on a 28 inch long axis would be dreadful, think about it. It'd take over 4 minutes to go from one end to the other. 12 inches per minute is almost as bad. I'll accept full length travel in a minute though, anything less would be like watching paint dry.

[chuckknigh]

:-)

Anyway, seriously, I always wondered what the big deal was about speed. While there is a practicality aspect (1/2" per minute would be painful!), almost any speed is still workable.

In my case it's the precision, and not the speed that I'm interested in.

Having said that, though, I'll be overjoyed if I find some 450 oz-in steppers at that sale this weekend. :-)

Any particular devices I should look for, for scavenging big steppers? Big printers, old IBM typewriters, LASER printers, mainframe tape drives, copier machines. Anything else that would be a good choice? Last month I turned down an old IBM mainframe for $5. I'd have taken it for eBay, had I had any way to arrange for shipping. I'm telling you, *ANYTHING* technological can (and does) show up at this sale.

-- Chuck Knight

[WOODKNACK]

Anoel,
Your machine looks very good! You did a nice job..

Did you use 1/4-20 threaded rod or something different?
You might be able to get a little more speed out of 1/2-13 threaded rod.

[anoel]

I used 5/16" - 18Tpi threaded rod. It was the easiset to deal with without finding someone to turn the ends down. I did need to grind one end down to 1/4" to fit the motor coupling, but that was easy because I just needed to grind it down just till the threads were gone. Ginding down a 1/2" rod to a centered 5/16"/22mm to fit the thrust bearing would have been a bit more risky and if done wrong would cause binding and vibration. If everything works well I might jump in again and try 1/2" and have someone turn it on a lathe.

[WOODKNACK]

I was thinking about turning some 1/2 rods down. Lucky for me I have acces to a lathe. What are you using for a board? John's board? I can't wait to hook my new xylotex board to a machine. I have to get the lead out of my a_ _ and get working on it. With spring here there is much to do around the house.. Sucky...

[anoel]

Yeah, I'm using John's board. (or a 3 axis clone of it at least.)

[WOODKNACK]

Well keep up the good work and keep us posted. Would like to see something you cut on that machine. Again nice looking machine....

[WOODKNACK]

Anoel,
What size is the foot print of your machine? How much room does it take up?

HEY CHUCK,
I looked at that router at HF. Looks like an easy one to adapt to a machine with that square base on it. I wonder if you can get different collets for it. Like say a 1/8 collet so you could use dremmel tool bits.. You could buy a route speed control at say Wood Workers warehouse to control the speed of the router!!