[DDM]

Ok people sound off what do you guys think is better for a multipurpose machine wood/Aluminum? Is having a moving gantry good for having less materials for a larger work area or is having a moving table better for the accuracy. I'm just talking about a moving table in One Axis Y I think. What I'm looking at is building a somewhat production machine out of extrued Aluminum and then having a mini mill head for Aluminum and a Router for the wood. Is a moving gantry going to be strong enough to handle aluminum or should I lean toward a moving table. I think a lot of the newbs like me on hear could benifit from this discussion.

Carl

[duluthboat]

Hi Carl,

I’ll make this short because I’m calling it a night. For me the bottom line for cutting metal is a fixed spindle where it only moves in the Z axis. (up and down) This allows the use of a beefy spindle to hold and drive the cutter.

Gary

[Chagrin]

Which is heavier - the table or the gantry?

(move the lighter one!)

[ynneb]

I have made mine moving gantry but I am thinking moving table would have been better.
Moving table takes up twice as much room though. The big dissadvantage with moving table is you need long linear bearings and that can come at a big cost. If your table is only going to be small then go for moving table

I feel because a moving table is closer to the bearings it would be much more stable. Also you can then make a really solid and weighty gantry and not have to worry about how heavy it is.

[svenakela]

I agree with Gary.
On my machine I'm making a compromise. The table will move in X, but the gantry in Y. I don't agree with the idea of moving the lightest one, move the object that causes less vibrations. If the spindle is mounted on a high gantry and the gantry is vibrating (and it will, right?) the vibrations will amplify a lot. Small movements will be big at the tip of the mill.

--Sven

[High Seas]

DDM - all good resposes so far for your question - Have you poked your nose into the "Design Center?" There's a link there to a site that sort of summarizes the styles of system design http://www.cnczone.com/forums/showth...&threadid=4080

If you're looking Big table - thats heaps of space to handle the footprint of the machine and motors to move the material - might consider a "low profile gantry" that moves with most of the mass close to the plane of the x axis rails. Sorta like "System2" in the photo gallery -
cheers - Jim

[duluthboat]

It really is a matter of making the trade offs required to do the job. With Z fixed and X/Y tables moving ( like most large vertical machining centers ) you get a very rigid machine. The foot print will also be the largest compared to the cutting area. With the fixed gantry and Z moving on the bridge you lose some rigidity but gain cutting area, and on it goes. It’s all about building the machine that fits what you want to do.

Coolant is another thing to consider when cutting metal. How do you contain the mist, fumes, or liquid?

What I’m trying to say is the product you wish to produce will strongly influence the way the machine looks.

Gary

[balsaman]

Moving Table is less complex and generally more rigid, but takes up more room.

Eric

[DDM]

Ok I've had this idea floating around in my head lately no matter what way you decide to build a machine using 8020 extruded Aluminum. The key to having a good machine is to have it rigid and in most cases that means heavy. What if a person was to fill the inner passages in the larger extruded Aluminum with Cement or something like it. This would help with the vibrations and it would help with making it ridged. Its just a thought.

The second part is kind of off topic from my origional post but it is along the same lines. What does everyone think of using a rack and pinion setup for the linear movement on at least the X and Y axis on a moving gantry style router. I've seen a few plasma cutters with this but the forces arn't there as they are with a router or a mill. My main concern would be that the gantry would kick sideways because there is nothing driving it on the other side. It would be nice for the speed but would it be a problem in the future.

[balsaman]

Rack and pinion can work. Usually you would extend a shaft accross the table so you drive at both ends of the gantry. Some problems can be too much backlash in the rack and pinion as well as in the reduction if a gear box is used. Timing belts can be used instead of a gear box.

As far as concrete is concerned I have no idea.

Eric

[j10stretch]

Has anyone used an old laser cutting machine? I was thinking of buying an old 4 x 8.Mazak laser machine and removing the laser head and all the internals that's not needed. Not sure if the bearing on the gantry would be strong enough for side loading of cutting. Ideas?

[awerby]

I'd advise against that plan. A laser cutter, while it may bear a superficial resemblance to a CNC router, is built to solve different issues. There's no resistance to cutting forces, so it doesn't need the rigidity that's key to a router's performance. Also, the Z axis is likely to be too short for many carving tasks. If you already had a defunct laser machine I'd say sure, give it a try, but going out and buying one seems like asking for trouble. Save your money and wait for a used router or mill to retrofit; you're more likely to end up with a machine that does what you want.

[wizard]

Ok people sound off what do you guys think is better for a multipurpose machine wood/Aluminum?

Better is relative. Even for aluminum only processing; after a while moving table machines become very large if you are processing aluminum sheet goods of large size.

Is having a moving gantry good for having less materials for a larger work area or is having a moving table better for the accuracy.

Either can be accurate, it is my opinion that a moving gantry machine requires a lot more effort and expense to achieve the same accuracy as a moving table design.

I'm just talking about a moving table in One Axis Y I think.

Well this is a discussion all of tis own. I would prefer that everybody references axises from the bottom to the top, (X,Y,Z) as it makes communications with all the differing locations a bit easier. However some them to think that the long axis should be the X axis, I disagree with that idea.

What I'm looking at is building a somewhat production machine out of extrued Aluminum and then having a mini mill head for Aluminum and a Router for the wood.

Reconsider extruded aluminum if you goal is primarily to machine aluminum. This especially on a machine of any size.

Now the problem here is what do you mean by machining aluminum. At some point you need a machine considerably stiffer than what is suitable for a wood only machine. The other issue is that if you are focused on machining aluminum you really need to consider a Lube system.

Is a moving gantry going to be strong enough to handle aluminum or should I lean toward a moving table.

You can build a moving gantry machine tool suitable for machining steel if you want too. The question is would it be economical. In my opinion a moving table machine is an easier machine to construct to a high degree of accuracy and is also easier to implement a stiff design.

I think a lot of the newbs like me on hear could benifit from this discussion.

Carl

Carl I strongly recommend reading through the stickies. Lots of good sound basic info there for somebody contemplating a DIY design. Especially consider the thread on gantry beam design to understand how various parameters impact stresses on a gantry beam. Ultimately you need to determine how large of a machine you want to build and then determine if a machine that large (and within your budget) can effectively machine aluminum. Actually the budget issue is key here, given an unlimited budget you can build a huge gantry machine that will do aluminum well.

So to get to the meat of your questions we need to know the following:

1. What are your expectations? Especially when it comes to alumminum removal.
2. What is the desired working area of the machine?
3. What is the budget? This is key as limitaiton here mean hard limitations on the machine.
4. What are your shop facilites like? A better equiped shop means lower costs and less contracting out of machining.
5. What is your local support like? Tha tis do you have local machine shops able to handle this sort of work if you need something done professionally.
6. How much space is available? This often answers the moving table vs. moving gantry question
7. What is your local ability to get materials and supplies? Having a local metals supplier, especially one that sells drops at a discoount can be a big advantage in a DIY machine build. Getting used stuff helps too. This comes back to getting the most bang for your buck.

In the end, until you define you goals and expectations it will be very hard to give you a lot of help. Start with the desired working area.

[wizard]

It really is a matter of making the trade offs required to do the job. With Z fixed and X/Y tables moving ( like most large vertical machining centers ) you get a very rigid machine. The foot print will also be the largest compared to the cutting area. With the fixed gantry and Z moving on the bridge you lose some rigidity but gain cutting area, and on it goes. It’s all about building the machine that fits what you want to do.

I don't agree 100% here, you can buy fixed gantry mills that are very stiff. Frankly at some point a gantry becomes the only way to span a long distance with any expectation of rigidity.

Coolant is another thing to consider when cutting metal. How do you contain the mist, fumes, or liquid?

This to me is huge and people seem to forget about it. Casual aluminum machining is one thing, you can sit there with a squirt gun. However anything that involves more than a hour of machining really requires a lube system of some sort. Event guys running Bridgeports resort to lube/coolant system software some sort.

What I’m trying to say is the product you wish to produce will strongly influence the way the machine looks.

Gary

Yep! We really need to have some idea as to how the machine will be used to comment much.

[wizard]

Ok I've had this idea floating around in my head lately no matter what way you decide to build a machine using 8020 extruded Aluminum. The key to having a good machine is to have it rigid and in most cases that means heavy. What if a person was to fill the inner passages in the larger extruded Aluminum with Cement or something like it. This would help with the vibrations and it would help with making it ridged. Its just a thought.

Water is heavy and it isn't to rigid, well except around here in the winter. Weight doesn't always translate into rigidity, you still need a good mechanical design to keep all the forces under control. It is very much a combination of things that lead to rigidity and low vibration intensity.

AS for aluminum don't put plain old concrete in it. Concrete will corrode aluminum. I'm not sure why you are already fixed upon 8020. I really don't like extruded aluminum for these sorts of applications. Especially for a gantry.

Now if you are talking about epoxy granite type fills then yeah it can help a machine, effectively impacting resonances. The fill may or may not help with rigidity though. If you want to learn more about filling tubing to enhance the performance of that tubing for machine usage there is a paper written by a guy named Bamberg that dives into the subject deep than you will likely want to go. I had a disk failure recently and sadly lost my local copy so the title of the paper escapes me, if you can find it it is very enlightening when it comes to using steel tubing for machine tool purposes.

The second part is kind of off topic from my origional post but it is along the same lines. What does everyone think of using a rack and pinion setup for the linear movement on at least the X and Y axis on a moving gantry style router. I've seen a few plasma cutters with this but the forces arn't there as they are with a router or a mill.

Rack and pinion is as old as the gear and frequently used in machines. The problem is backlash control.

My main concern would be that the gantry would kick sideways because there is nothing driving it on the other side. It would be nice for the speed but would it be a problem in the future.

At some point you need a connection to the other side that keeps the forces somewhat balanced. Sometimes that means a separate rack and driver system. For larger machines guys often drive each side of the gantry with ball screws. This is one area where a moving table can win because you can drive from the center of the table if the linear bearings are spaced far enough apart.

[j10stretch]

I'd advise against that plan. A laser cutter, while it may bear a superficial resemblance to a CNC router, is built to solve different issues. There's no resistance to cutting forces, so it doesn't need the rigidity that's key to a router's performance. Also, the Z axis is likely to be too short for many carving tasks. If you already had a defunct laser machine I'd say sure, give it a try, but going out and buying one seems like asking for trouble. Save your money and wait for a used router or mill to retrofit; you're more likely to end up with a machine that does what you want.

I can get it for less than what the materials for the table frame. And I know the rigidity if the gantry would be sufficient. The z axis would be around 6 inches, but I can manipulate that. I haven't seen it done and I can only find cnc routers retrofitted with lasers. Just curious if this would work....guess I'll try and see what I can do lol.

[bhurts]

I'm for the idea of using the old mazak laser. Unlike other lasers it looks to be better made and quite a bit more heavy duty then 99.9% of machines built on the zone for any purpose. According to the ones I found they also weigh about 25000 lbs. Probably a pretty cool project but the size is not practical for me.

Ben

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