[50chevy]

I have been looking and researching this site for a whilenow and I think I have a good idea on what I would like to build.

I am in the planning process of build a stationary gantrymilling table.
I would like to use all ½” or ¾” steel plates weldedtogether, but lately I am leaning toward the aluminum after looking at KatranCNC (thank you Katran for the build thread and inspiration)
The minimum work envelopthat I would like to get is 24” X 24” X 12” (X, Y, Z)

Ball screws 2505 -5 with double ball nuts fromlinearmotionbearings2008 from EBay.
HIWIN linear guides HGR25 with HGH25CA carriages
Hertz spindle HMB42 (2.2 KW, 3.0HP, 18000 RPM)
NEMA 23 590 for X, Y & Z
Later on I will be building a 4^th axis rotaryfixture with a 6” or 8” lathe chuck (that’s the reasonfor the long Z axis)
I need it to be ridged to cut aluminum at a reasonable depthper cut and maybe light cuts in steel.
What do you guys think is it possible or am I just wastingtime?
What should be changed and what is acceptable?

[wizard]

I have been looking and researching this site for a whilenow and I think I have a good idea on what I would like to build.

I am in the planning process of build a stationary gantrymilling table.
I would like to use all ½” or ¾” steel plates weldedtogether, but lately I am leaning toward the aluminum after looking at KatranCNC (thank you Katran for the build thread and inspiration)

I wouldn't even consider aluminum if you are going to build a welded up structure for machining aluminum. For one thing Aluminum is a pain to weld, more importantly you lose considerable strength in a welded aluminum structure. The idea that you would want to do some steel takes aluminum completely out of the picture for me as you would want a much heavier and stiffer structure.

The minimum work envelopthat I would like to get is 24” X 24” X 12” (X, Y, Z)

That is very doable size for a built up structure but I do hope that you have access to a machine shop to work all the mounting surfaces after welding and stress relieving. It might help to detail what you have easy access to as that has a big impact on what is feasible machining wise. For example the uprights and your gantry beam are of good design if you can machine all the surfaces after welding up the structure, if you can't a different approach would be required. That being said you should pay special attention to the rigidity of the gantry beam itself as that will be exposed to the long lever arm of the Z axis.

Ball screws 2505 -5 with double ball nuts fromlinearmotionbearings2008 from EBay.
HIWIN linear guides HGR25 with HGH25CA carriages
Hertz spindle HMB42 (2.2 KW, 3.0HP, 18000 RPM)
NEMA 23 590 for X, Y & Z
Later on I will be building a 4^th axis rotaryfixture with a 6” or 8” lathe chuck (that’s the reasonfor the long Z axis)

An alternative is to build support for the rotary into the frame of the machine, but that only really works for short pieces. It would help to understand what you expect to be doing with the rotary. The other bad thing on a fixed gantry machine is that there is only one place you can really build a rotary axis into the frame and that is directly under the Y axis, so maybe you don't have much of a choice here.

I need it to be ridged to cut aluminum at a reasonable depthper cut and maybe light cuts in steel.

You probably already know the long Z works against this thus requiring very stiff components for the Z assembly. This isn't impossible but you do need to design it in and have the ability to actually manufacture the components.

What do you guys think is it possible or am I just wastingtime?

Thought is never a waste of time and in most cases questions aren't. It really looks like you have a nice concept here. One concern is the upright gusseting that is on ether gantry / z axis side. You will want your spindle, Z axis and any potential cutters to be able to clear those upright gussets. For example will a fly cutter ram into those gussets if you should happen to use one. More importantly it is a very good idea to have enough Y axis travel to be able to over travel the table by a good measure. In an ideal moving table machine you would want enough travel to be able to completely machine the table of any fixturing mounted on it.

What should be changed and what is acceptable?

Well you are off to a good start!

As noted above I'd be concerned about clearance around the uprights supporting the gantry. You will want to be confident that nothing will ever crash into the uprights. Take into consideration that it is probably a good idea to make sure the Y axis over travels the table by a bit.

I'd make sure all of the tubing is internally braced throughout the machine. This to prevent parallelogram movement in the tubing. However it doesn't hurt as far a support of the tubing walls under the rails.

I'm not a big fan of making machines randomly heavy but mass does help when machining steel. Put the initial mass in the right places with heavy walled tubing and plates. It may pay though to leave access for filling the tubing with mass (epoxy granite most likely). Basically use your thick plates and tubes to build a stiff machine (your box sections) and then fill them to add mass if it becomes an issue.

Now here comes the other gotcha, many of the spindles on the market don't have much in the way of low speed performance, in fact many aren't even rated below 6000 RPM. This does't expect a lot of horsepower for machining steel anyways. You would either need a two speed spindle (gear reduction) or a separate spindle to be able to remove steel at a high rate. That is a rate that may demonstrate weak points in the machine. In other words I don't see you checking a 3/4" mill in a router spindle and carving out a piece of steel with it. if machining steel is expected to be a major use for this machine, i'd look closely at the spindle chosen to make sure it will have the torque to machine steel the way you imagine the machine will. Once past the spindle you will need to consider the rest of the machine as everything including table thickness will impact the quality of the machined surface when doing steel.

Generally I recommend that people put steel out of their minds in router type machines. For the most part I think that is good advice. However you seem to have a good sense of proportions here and are building a machine that will have at least some capability to handle steel. Im just not certain it will meet your needs whatever they are.

[mmoe]

Speaking as someone who has a 4 or 5 ton 4'x4' stationary gantry router, made of 1/2" plate steel with flanges of 3/4" plate, I can tell you that there are some problems with the idea of machining aluminum and steel as the primary application with this kind of machine (and mine is likely much heavier duty than what you are planning). First, coolant is a huge factor in machining aluminum and steel. If you are using a router on plastics, wood and some aluminum plate, you can get away without using much in the way of coolant and cutting aluminum dry for those times when it needs to be done. Power is not an issue and aluminum would cut nicely with what you propose. It will still tend to require more bits than if you had coolant, which means more expense to cut aluminum than if the machine were more of a metal specific machine in terms of design (I would say what you have is not really metal specific beyond being stout). If you are machining a block of aluminum, it tends to heat soak enough to make your tools wear out something fierce no matter how well you match feeds/speeds with the tooling and material. Forget using a mist for cooling, it tends to cause carbide to crack if it's not perfectly stable in cooling. Swings in temperature from insufficient cooling tend to microfracture carbide in my experience and you're better off cutting either dry or wet, not in between. HSS will fry without coolant, period. That's just the aluminum side; all that is more severe with steel. Accommodations for coolant would be needed, including a way to contain the coolant and recycle the coolant. FYI, routers throw coolant much father and in more of a mist than coolant coming off of a milling spindle. What you spec'd has a fan on it from what I can tell, so you can guess what kind of mess will happen. Mine does not have a fan, but requires are moving over the surface of the spindle via the dust collection system, so whether you are collecting dust or not, the dust collect must be pulling air through the head. Similarly, you can imagine what kind of mess your dust collection system ends up like if coolant is pulled through it. Clean up of coolant on a machine not made for coolant is a long process that makes you reconsider ever using it again.

3hp router spindle is not going to cut steel worth beans. I have two 10hp industrial spindles (they weigh more than a person can lift, each one of them). When you run at the lower RPMs that are needed for the feeds/speeds that work best for steel, you are cranking up the amperage required to operate the spindle at those lower speeds due to lower voltage coming from the VFD to the spindle. Low RPMs will equal tons of heat in the head as compared to doing the same amount of work at high RPMs (and higher voltage). I suspect you would burn those heads up often working with steel.

12" of Z axis seems like it would be long, but in order to be able to process a sheet using a 1/8" bit right at the table surface, while also being able to mount a Kurt vise with a 6 inch block of Aluminum, or the 4th axis you were talking about, you need to have a bit more than that in my opinion. What's the longest bit you would need and when would you need it? I find that the longer bits I use tend to be needed when I'm machining thicker stock, no surprise there. However, thicker stock usually also coincides with using a vise to hold the stock down. Now that 6 inch block is 8 inches off the table. If your head can come within about 1 inch of the table (useful for using small bits on thin material), then that means you have just a little over 4 inches of clearance for the head above your 6" block of aluminum mounted in your Kurt vise. Unfortunately, you won't be able to reach the bottom of your material while also being able to bring a tool long enough to do so above the clearance plane of your stock. In my opinion, you need to double the maximum height that the thickest stock you expect you might use could be, including the fixture you would mount it into or on. If you thing 6" thick stock on a 2" tall vise base is a possibility, I would be looking for a 16" Z axis. The advantage of a stationary gantry is that the Z axis can be made extremely sturdy, so you may as well make use of that.

Most stationary gantry machines (if I haven't scared you off of making one yet) are designed with more of a modular build. The base is one component, which gets machined after stress relieving, etc. Many have columns that are machined at the top and bottom like risers, using a flange mount both ways. The gantry then can mount to the riser making each component easier to produce because they are smaller and more modular. However, this costs quite a bit to have done. I would venture to guess that the typical stationary gantry router available today is in the neighborhood of $100-$200k, while moving gantry machines of similar quality (not necessarily sturdiness) are half as much. I think that is because stationary gantry machines just have significantly more materials in them, along with significantly more machining on them. I could get specific, having owned a few different kind of machines over the years, but my observations have been that stationary gantry machines are the least economical when it comes to space and production resources to create it, but the payoff in quality of machine seems to be worth the extra expense and floorspace.

If I were looking at a machining envelope around what you are describing, and planned to cut primarily aluminum and steel, I would focus on finding a used machining center with a bad or outdated controller and good mechanics. You can often find these for a decent price, then invest some time and money in them to bring them up to date. Most have a lot of Z axis height, likely for the reasons I stated, and many have most of the size of the table you are looking for (usually smaller one way, but bigger the other than what you spec'd). These would already have provisions for coolant and spindles that are made for what you want to do. The precision will be better than a router style machine as well. While 25mm profiled bearings are strong, they don't take the shock of machining metal as well as boxed ways that you'll probably find on most machining centers. The result is a better cut from less vibration on boxed ways. Downside to machining centers is that they are heavy, like my gantry machine. But it seems like you were OK with something that you don't really move around much, so maybe that isn't an issue. Food for thought!

[50chevy]

Wizard and mmoe thank you very much for your input that was helpful!!

Wizard,
It looks like I am leaning toward steel structure.
The only access I have to a machine shop is if I paid for it.
I would like to be able to remove the rotary from the table when needed so building it in the table is not an option.
The Z axis is what I am struggling with when it comes to it being ridged enough. I may have to go back to the drawing board on that one.
I do like the idea of Epoxy Granite; I would have to do some research on it. If you did use it would you go with a thinner steel material or stay with the same thickness?

Mmoe,
Man that machine that you have must eat up a lot of you floor space.
Yes I am struggling with the spindle. I don’t know if I should use a mini-mill or a table top mill head instead to be able to get the speed and torque. What do you think?
No you did not scare me yet ….I do like the idea of modular build. I have to draw something up for that and see what I can do.
It sounds like coolant is a must I would have to see what I can do about that.
I believe that the deepest cut that I would need is around 2” mark.
I did look at some used machines but the money and mostly space is not available.
So if this is a 12” on the Z axis realistically I can cut about 6”?
Did you build your machine?
Do you have some pictures for it?