HUGE router table

[musicmkr]

I was showing off some stuff I did on my new CNCDremel at work and my boss decided that I need to build a router table to fabricate architectural aluminum composite panels. (Reynobond, Alucobond type panels, 4mm panel consisting of .03" alum, over poly, over .03" alum, you only mill out one layer of alum, and the poly layer, to allow panel to bend)

Heres the problem, the only machine I've ever built has a total working area of 8"x8"x3.5", and a machine for composite paneling has to have a working area of 12' x 5'.

Has anyone here done a machine for this purpose, or of a similiar size? My boss wants to do it on the cheap, like a few thousand dollars. I think this is possible since we only need about .03" accuracy. Could I get away with running Gecko's, and a rack and pinion setup? What size motors are we talking here?

I should have kept my mouth shut, but now I'm in it good. I'm sure I can do it, but this is quite a jump for a second machine.

[Cliff_J]

Here's a 4x8 machine done with Bishop Wisecarver bearings that seem quite reasonable in price and timing belts for action instead of rack and pinion (much better value from what I can find of R&P at mcmaster) so its one example of a way to do it. The bwc.com bearing rails are available to like 20' so they have your dimensions.

http://www.axxustech.com/Axxus4x8/axxus_4x8.htm

Although I have yet to build my second machine as well, I'm thinking of putting my THK rails back up on ebay and switching to the BWC bearings instead. They'll hold up better in the dust (no grease needed like THKs) and will cheaper in a larger size. So far just playing around with kevlar reinforced urethane timing belts from McMaster has been quite positive, so that seems to be my likely motion source too.

Here's also a couple places with plans, seem to be ok from what I've read on here but no personal exp.
http://www.machinetoolcamp.com/
http://www.inshorepowerboats.com/cnc.../CNCROUTER.htm

HTH
Cliff

[turmite]

musicmkr if all you are going to cut is the .030 alum and the poly I would use double stack 34 frame steppers, rack and pinion or timing belt. With a machine this size you will need to build a moving gantry and the aluminum extrusion would sure be a fast way to get the machine up and running.

If you are interested I have 3 or 4 of the double stack 300 oz steppers I would part with. I also have a drive pack to go with them but it is not micro step. These motors have been use very little as well as the drive pack. All the compontents are Anaheim Automation. If interested pm me. If not I will put them on the zone here first and then if no takers off to ebay.

Mike

edited to add: this really came off sounding like a hard core sales pitch. I would use the 34 frame motors whether I bought them from turmite or not!

edited again for spelling!

[musicmkr]

Thanks for the links, those are all similar to what I want/need to do. I had never seen the "V" bearing/track before, but it seems like it would work pretty slick for this application. They would probably work better than any other form of slide since I am looking to get a couple hundred IPM, and the bearings will get quite a workout. I had wondered about a belt drive system, but I didn't think I would be able to get good enough resolution, but it makes more sense after seeing it.

As for motors I figured I would need two large ones for the y axis, one large one for the x, and a medium sized one for the z. Do you think that 300 oz steppers would get the type of power I'll need to move & stop this amount of weight? I had been thinking about using motors somewhere in the 500 -700 oz/in, is this overkill?

The machine will most likely be Aluminum extrusion since I work for an architectural glazing company, and at any given time we have around a half million pounds of the stuff in stock.

[Cliff_J]

Well remember that steppers make peak torque at slow RPMs and torque falls off as RPMs go up. Servos have fairly flat torque curves all the way up to near their max RPM. Some servo motors go up to 4-5000RPM while most steppers have lost massive amounts of torque at 500RPM.

Also, the motors are geared down for the timing belt system much like a leadscrew offers an effective gear reduction to make rotations/inch (or the inverse at resolution) managable and to increase the force the motors are able to put to the machine. Again the faster spinning with torque at RPM servo seems desirable.

Someone more experienced with cutting 200ipm on a large gantry would be better to answer your exact question, but the extra expense of the servo would likely be worthwhile in your case where speed is a design criteria. Getting this large something like Gekko drives seem to be standard fare, so its only the difference in motor price that is yet one more decision to make....

Cliff

[HomeCNC]

Musicmkr,

You might find the original thread of Deans belt driven router a nice read.

Timing belt driven router - updated pictures

[musicmkr]

Thanks for all the link. I had never thought about belt drive but now it seems to be the most pratical for this application.

I am wondering, If I wanted to drive the gantry with only one stepper, I would still need two belts/pinion drives (one on either side of the gantry) right? Has anyone done a machine where the belt ends are clamped on to the gantry like this picture?

[chuckknigh]

I had a thought about your design.

Do you need a full third dimension, or just "cut/not cut" capabilities on your Z axis? Something akin to a plotter's pen up and pen down...

If the latter, you could just lift the entire Z axis assembly with a cam on each side...no big deal. Wouldn't even take a particularly big stepper, either.

KISS

-- Chuck Knight

P.S. Consider roller chain on a sprocket for your drive, too...there's a thread going on at the CCED list, about roller chain and backlash. The general consensus on that list is that, properly designed, it exhibits virtually no backlash, straight out of the box.

http://users.adelphia.net/~northeast...m/machine.html

[High Seas]

Your challenge is certainly a great leap from the first one you built.
By comparison these guys only made there second one 20 feet bigger!
http://www.janicki.com/envelope.html

That still only works out to 20-30% increase in size - you're leaping much more - relatively speaking - what say something like 120%+! Work that into your bonus/perks package for sure.

Cheers (and best of luck)- Jim
(mind you that may not be the biggest one I've seen - that was maybe at the (former) GD Plant (FtWorth) building wing box sections for the F-16 - AWESOME!

[anoel]

Make sure you estimate high so that you can come in under budget and there will be no... "Well, it's going to cost about another 2 greand than I first thought..... "

[ynneb]

Hey High seas, I went to that site you posted the link for. What I cant understand is why they are generally making the positives instead of the negatives of the items to be created. Whats the deal there?

[musicmkr]

What a great link, thats the coolest machine I have ever seen.

As for my project I am still coming up with designs, and getting prices for parts. The thing is my company doesn't want to spend too much on a new machine since every new faster tool we buy tends to not get used. I guess the guys in the shop want to keep as many positions as possible so for them faster doesn't always equal better.

Since all our work is in the field of architecture, and job site tolerances are pretty much plus or minus a brick, accuracy over 1/32" is just not required. To keep initial costs down on this machine I am going to cut some corners.

As I've been pricing stuff I have come to realize that the linear motion systems can easily cost more than the motors and drivers. I've looked into THK profile rails, (OUCH!), thompson supported shaft rails, and also the "V" bearing system by BWC that was mentioned earlier. Even the "V" track system is a killer when you need 14' long rails.

For my linear motion system (at least on the long axis) I am not going to use on of the above linear systems, instead I am planning on using aluminum angle as a "V" channel, and the gantry will run on somtihng similar to rollerblade wheels, shaped on a lathe. The aluminum channel will be accurate enough, and using hard rubber instead of metal will keep the track from wearing. Has anyone done somthing like this? If not then does anyone see any problems I may run into?