New build idea about Z axis - Any Problems?

[NIC 77]

I'm about to start a build of a 4 x 8 router. I will be using a driven uniguide from pbclinear mounted backwards for the z-axis.

I have designed the way my gantry attaches to my carriages in such a way that I can quickly (well, could take half an hour) re-bolt it much higher from the table top. The gantry will weigh at least 150 lbs.

I was initially planning on purchasing a uniguide with a stroke of 13.5 inches. Now I am thinking about purchasing a uniguide with a stroke of either 19.5 or 25.5 inches.

When routing parts from wood, the gantry height will have a clearance from the table of around 12 inches. Any more than this and I am concerned that the moment caused by the cutting forces could have detrimental effects.

However I would have the option of increasing the gantry clearance to 25 inches by moving the gantry upwards when routing a foam block. Also, I would now have 25 inches of useable travel.

This will also be helpful for more clearance from the table with the addition of a rotary axis, although in this case I may not need any more travel as the piece would already be higher off the table. It would be pretty neat to carve a 12 inch thick piece of foam with a rotary axis though.

The only drawback is that when using the router for wood I would have a whole lot more Z axis sticking up above the top of the gantry and my Nema 23 motor would be much higher (12 inches). I'm not even sure this is a drawback but perhaps there's something I'm missing.

So what does everyone think?

[awerby]

I'm about to start a build of a 4 x 8 router. I will be using a driven uniguide from pbclinear mounted backwards for the z-axis.

[That could work.]

I have designed the way my gantry attaches to my carriages in such a way that I can quickly (well, could take half an hour) re-bolt it much higher from the table top. The gantry will weigh at least 150 lbs.

[Don't try to change it over all by yourself...]

I was initially planning on purchasing a uniguide with a stroke of 13.5 inches. Now I am thinking about purchasing a uniguide with a stroke of either 19.5 or 25.5 inches.

[That's really long. There's a reason most routers keep the Z-axis short. The longer it is, the more leverage he cutting forces will have to deflect the tool.]


When routing parts from wood, the gantry height will have a clearance from the table of around 12 inches. Any more than this and I am concerned that the moment caused by the cutting forces could have detrimental effects.

[You're right about that.]

However I would have the option of increasing the gantry clearance to 25 inches by moving the gantry upwards when routing a foam block. Also, I would now have 25 inches of useable travel.

[Useable for what? How long is the longest tool you'll be running?]

This will also be helpful for more clearance from the table with the addition of a rotary axis, although in this case I may not need any more travel as the piece would already be higher off the table. It would be pretty neat to carve a 12 inch thick piece of foam with a rotary axis though.

[It would be easier to lower the rotary axis than to raise the gantry height.]

The only drawback is that when using the router for wood I would have a whole lot more Z axis sticking up above the top of the gantry and my Nema 23 motor would be much higher (12 inches). I'm not even sure this is a drawback but perhaps there's something I'm missing.

[How high is your ceiling?]

So what does everyone think?

[I think your gantry and everything it attaches to will have to be extremely heavy-duty if that long Z-axis is to be held steady, especially when cutting wood.]

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[NIC 77]

Originally Posted by NIC 77 View Post

I'm about to start a build of a 4 x 8 router. I will be using a driven uniguide from pbclinear mounted backwards for the z-axis.

[That could work.]

I have designed the way my gantry attaches to my carriages in such a way that I can quickly (well, could take half an hour) re-bolt it much higher from the table top. The gantry will weigh at least 150 lbs.

[Don't try to change it over all by yourself...]

[Good Point]

I was initially planning on purchasing a uniguide with a stroke of 13.5 inches. Now I am thinking about purchasing a uniguide with a stroke of either 19.5 or 25.5 inches.

[That's really long. There's a reason most routers keep the Z-axis short. The longer it is, the more leverage he cutting forces will have to deflect the tool.]


When routing parts from wood, the gantry height will have a clearance from the table of around 12 inches. Any more than this and I am concerned that the moment caused by the cutting forces could have detrimental effects.

[COLOR="Blue"] [You're right about that.]

However I would have the option of increasing the gantry clearance to 25 inches by moving the gantry upwards when routing a foam block. Also, I would now have 25 inches of useable travel.

[Useable for what? How long is the longest tool you'll be running?]

[Usable for something like this

[nomedia="http://www.youtube.com/watch?v=EbnoXMyUapM"]YouTube - ‪CNC Router 4 axis machine Shaping Foam‬‏[/nomedia]
[nomedia="http://www.youtube.com/watch?v=TSRGe5N9hVg"]YouTube - ‪2010 24 enero 012.mpg‬‏[/nomedia]
[nomedia="http://www.youtube.com/watch?v=0qmZMq8bbn4"]YouTube - ‪Time-Lapse CNC Milling Part 2‬‏[/nomedia]
[nomedia="http://www.youtube.com/watch?v=3qOnCNhTHmM"]YouTube - ‪Frezarka CNC w Zakładzie Obróbki Odlewów w Drawskim Młynie #2‬‏[/nomedia]

You can see the bit lengths they're using in the vids. I'm guessing the longest bit length would be around a 8 inches long]

This will also be helpful for more clearance from the table with the addition of a rotary axis, although in this case I may not need any more travel as the piece would already be higher off the table. It would be pretty neat to carve a 12 inch thick piece of foam with a rotary axis though.

[It would be easier to lower the rotary axis than to raise the gantry height.]

[The rotary axis will be attached to the table top. It will therefore not be possible to lower it]

The only drawback is that when using the router for wood I would have a whole lot more Z axis sticking up above the top of the gantry and my Nema 23 motor would be much higher (12 inches). I'm not even sure this is a drawback but perhaps there's something I'm missing.

[How high is your ceiling?]

[About 8 feet high - but good point]

So what does everyone think?

[I think your gantry and everything it attaches to will have to be extremely heavy-duty if that long Z-axis is to be held steady, especially when cutting wood.]

[I don't intend to cut wood with the gantry in the high position, just foam. Are you saying that having a longer Z axis extending above the top of the gantry will effect cutting wood when the gantry is in the low position? For the gantry a piece of 3 x 3 Aluminum T-slot with a piece of 1.5 x 3 steel rectangular tube bolted to the back of it, an additional piece of 1.5 x 3 steel rectangular tube bolted to the bottom of it and and double width aluminum IVT rail bolted to the front of it.]

[awerby]

Originally Posted by NIC 77 View Post

You can see the bit lengths they're using in the vids. I'm guessing the longest bit length would be around a 8 inches long][/COLOR]

[Good luck finding one - it's very rare to see a bit longer than 6 inches.]

This will also be helpful for more clearance from the table with the addition of a rotary axis, although in this case I may not need any more travel as the piece would already be higher off the table. It would be pretty neat to carve a 12 inch thick piece of foam with a rotary axis though.

[It would be easier to lower the rotary axis than to raise the gantry height.]

[The rotary axis will be attached to the table top. It will therefore not be possible to lower it]

[Since you haven't built this yet, you can mount the rotary table so the axis center height is at the level of the table. You can cover the gap with a removable panel when doing 3-axis work, and pull it out when you're using the 4th axis. This would allow you to maximize the useful travel of your Z axis without having to raise the gantry.]

So what does everyone think?

[I think your gantry and everything it attaches to will have to be extremely heavy-duty if that long Z-axis is to be held steady, especially when cutting wood.]

[I don't intend to cut wood with the gantry in the high position, just foam. Are you saying that having a longer Z axis extending above the top of the gantry will effect cutting wood when the gantry is in the low position?

[Maybe a little, but the main problem comes from having it hanging down 2 feet or so with the spindle at the end.]

For the gantry a piece of 3 x 3 Aluminum T-slot with a piece of 1.5 x 3 steel rectangular tube bolted to the back of it, an additional piece of 1.5 x 3 steel rectangular tube bolted to the bottom of it and and double width aluminum IVT rail bolted to the front of it.]

[This is hard to picture without a drawing or anything, but it doesn't really sound massive enough for what you're talking about. I'd think you'd want a beam about a foot high by 6" thick for your gantry, with a couple of linear rails mounted parallel to effect the Y axis motion. ]

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[NIC 77]

[QUOTE=awerby;955353][This is hard to picture without a drawing or anything, but it doesn't really sound massive enough for what you're talking about. I'd think you'd want a beam about a foot high by 6" thick for your gantry, with a couple of linear rails mounted parallel to effect the Y axis motion. ]

This vid at 1:55 shows a uniguide mounted backwards:

[nomedia="http://www.youtube.com/watch?v=QrPEpDmbXeY"]YouTube - ‪CNC Gantry Solutions in Motion‬‏[/nomedia]


A piece of 3 x 3 Aluminum T-slot with a piece of 1.5 x 3 steel rectangular tube bolted to the back of it, an additional piece of 1.5 x 3 steel rectangular tube bolted to the bottom of it and and double width aluminum IVT rail bolted to the front of it.

You find that hard to picture?

Here's a picture from MetalHead's build thread of the IVT rail if that helps. My T-slot that bolts onto it is twice as wide.

http://www.cnczone.com/forums/attach...5&d=1305405783

Standard V-groove bearing carriage. That's a flat plate with V-groove wheels. Nothing special.

How the gantry is adjusted up and down is not relevant. That's not my question.

Also, my gantry is just as stiff as most of the 8020 gantry builds here, so for a normal length z axis it's not an issue.

The questions are:

1. Are difficulties going to arise from having an extra foot of Z axis sticking upwards from the top of the gantry when routing wood (when the gantry is at a normal height)? I can't see how it will be any different as far as the forces are concerned but perhaps I'm missing something.

2. Are difficulties going to arise from having the gantry raised 6 to 12 inches higher when routing foam?

For question 2, I think it comes down to what the cutting forces are when routing foam compared to routing wood. Does anyone know the typical differences? If the distance of z travel is double and the forces are half then the moment is the same or perhaps I'm missing a variable. Obviously cut speed and depth effect that equation. I plan on doing fairly fast and aggressive cuts in the foam.

If there are problems I doubt they would arise from gantry stiffness. Probably moments put on the v-groove wheels or the z axis it's self, so good thing I clarified what I'm using.

Does anyone out there have any experience with this?

[zool]

Is it realistic to ask one machine to do so many operations, which operations have such differing requirements with respect to both the machine itself and the various components; i.e., tooling; sizing of machine components [overkill in one instance and insufficient in another]; mechanical portion of motion control; electronics portion of motion control; and software portion of motion control. Also what the operator is capable of ??

And in asking so much from the machine, are there going to have to be too many compromises that will then need quirky and unstable work-arounds.

I say all this because I am worse than you in this area!

I am finding, and painfully and frustratingly so, in the actualization of my original Shop Droid design, that I have stymied progress by asking/expecting too much of the machine, and then having to take the time to reassess constantly is disheartening and has actually slowed progress to those goals.

For instance: It has taken a month to reassess and reevaluate software and control hardware. And though I now know more than I ever thought possible about these items, more or less I ended up almost where I started.

And I have not even addressed the issues you raised in your insights of my Shop Droid design, which are serious and do need to be addressed before production begins.

Where I have ended in the software/hardware/electronics search is this: Be here now, and do not let planning for the future distract.

With your built is might be: Focus on what is important in near-term production needs and in accumulating the skills needed to meet them, and face concerns about additional capabilities, both mechanical and skills, when, and if, they arise.

Also, for some of your production needs, it might just be more efficacious, both in terms of time and economics, to out-source those to someone who specializes in that type of production.

[And the above really shows how a consultant's mind operates relative to a engineer's mind!!!]

[NIC 77]

Zool,

I don't think it's as complicated as all that. The tooling is the same. The same router, just change the bit. The drives are the same, just leave enough slack in the cables to raise the gantry. The gantry is already designed to be adjusted up and down, I'm guessing it will take 20 min to half an hour to do it.

I'll make a separate profile in Mach 3. As far as I know that's not hard to do. I'll have to set the z-axis zero but you need to do that when you change bits anyways. The software is the same.

The only thing changing is the distance from the gantry to the table! The Z axis just isn't moving to it's full potential when the gantry is mounted lower, but it's still there.

If I focus on short term production needs I will inevitably end up shooting myself in the foot 6 months from now. I already know that this is a capability that I want. I'm venturing into an area of versatility that I have yet to see on these forums, but I'm going to make it work!

I need to be the guy who is outsourced to, not the guy who does the outsourcing!

I understand your frustrations. I have been experiencing quite a few of my own. For the past two weeks I've been saying to myself I'm going to be ready to order my major parts tomorrow and then tomorrow comes and I realize my design can be improved in some way.

So I'm working out all my bugs now as much as I can in the design stage to get EVERYTHING I want. I can't afford to do this wrong or twice. It's just taking longer than I want.

As far as your design goes, I think you will be able to stiffen it up quite a bit. That was my original design to stiffen up the shopdroids design so I have spent many hours thinking about it and drawing diagrams on paper etc. The deflection vs unsupported span equation, as I'm sure you know is not linear so by adding steel brackets along the length of your long axis, I think that will work for you. The T-slot is already there to bolt into. For the gantry axis you may loose and inch or two in gantry clearance, but even if you did something as simple as bolting a .5 by 3 inch length of steel plate into the T-slot on the back of your IVTAAG as high as it will go without interfering with your gear rack it might just do the trick for you there as well. That might even work well for you on the long axis.

As far as the answers to my questions in this thread go, I have realized that by going through the process of typing out my questions and making this thread I may have already answered at least some of my own questions. It would be nice to hear from someone who mills large pieces of foam though.

In the video here:

[nomedia="http://www.youtube.com/watch?v=EbnoXMyUapM"]YouTube - ‪CNC Router 4 axis machine Shaping Foam‬‏[/nomedia]

which I posted a link to in one of my earlier posts in this thread, clearly shows the gantry for that system is either a single piece of 3030 or 40-8080 T-slot with some stuff bolted onto the top and bottom of it, kind of like my design, so I shouldn't have any problems milling the foam as far as my gantry is concerned.

As far as the V-wheel carriage, Z-axis, and managing the extra length of the Z axis over the top of the gantry are concerned I'm still open to hearing feedback, concerns, friendly warnings, and tips that could make my life easier.

I'm feeling much more optimistic about this idea than I did this morning.

[CarveOne]

I can't see that having a lot of Z travel above the gantry is going to cause problems unless you are expecting to run high accel rates and the dead weight swinging around up there may cause some flexing issues in the Z assembly or gantry. It will have some lever effects even though that end isn't cutting anything.

CarveOne

[zool]

Here are some serious soft-material multi-axis CNC machines

Tarus Products, a World Leader in Machine Tools

[NIC 77]

I can't see that having a lot of Z travel above the gantry is going to cause problems unless you are expecting to run high accel rates and the dead weight swinging around up there may cause some flexing issues in the Z assembly or gantry. It will have some lever effects even though that end isn't cutting anything.

CarveOne

Thanks for mentioning that. It got me thinking. Depending how far down the router is it may act as a sort of counterbalance as the router end will be the heavy end, but then again the Nema motor will weigh at least a few pounds not to mention the other parts.

I'm more concerned about the effect the increased moment from moving the heavy gantry up an extra foot will have on the V-groove bearings. My current design has the carriage plates for the long axis horizontal as opposed to vertical. I've been looking around and I can't find one single example of a machine using V-groove bearings that has a carriage plate mounted horizontally, although there are several examples of a heavy gantry mounted at least a foot above the carriages with vertically oriented carriage plates.

The cncrouterparts design has it's carriages mounted horizontally but it does not use the V-groove bearings.

What does everyone think?

I could mount the carriage plates vertically on my design easily enough, and add a second removable table top that is lower to mill the foam. It doesn't look like I'll be ordering my rails today.......

On a bright note, I just found out about a place about an hour's drive from me that has a whole bunch of used heavy duty bolt together pallet racks. I'm going to need to have a look at them before I make any more design changes. That could make things a whole lot simpler.

[NIC 77]

Here are some serious soft-material multi-axis CNC machines

Tarus Products, a World Leader in Machine Tools

Those machines sure have a long reach! Looks like some of them are for for metal too. They probably cost more than a house.

I found this post last night:

http://www.cnczone.com/forums/diy-cn...m_milling.html

That's pretty neat!

[PaulRowntree]

My current design has the carriage plates for the long axis horizontal as opposed to vertical. I've been looking around and I can't find one single example of a machine using V-groove bearings that has a carriage plate mounted horizontally,

What does everyone think?

I have only used V-groove bearings on my Z so far, but it seems like using them with a horizontal carriage (with the bearing axes vertical) would be fighting gravity, and the preloading of the device would be changing the vertical position of the carriage relative to the rails. Everything would move, while with a vertical carriage, nothing moves as you adjust the preload with the bottom rollers. Think of the assembly process. Even though Max Webster sang that we should 'Forget that fear of Gravity' in the mid seventies, I try to build things that work with it instead of against it.

Free advice is worth every penny.