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  1. #1
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    Gantry construction: steel vs. aluminum?

    Hi,

    I'm working on spec'ing a new Chinese machine. 1100x1800 with a full table structure, hiwin rails, etc. I've also chosen ball screws on all axis for higher accuracy, but have now been informed that the gantry structure had to be aluminum instead of steel due to the weight and ball screws not being rigid enough.

    This seems odd to me since it's the bearings and rails that are taking the weight and all VMC's use ball screws (and are dealing with much higher forces). The design is supposed to be a full square tube structure on the uprights, but I had expected steel like in the larger format machines.

    We're not planning anything as heavy as done with a full VMC, but am going to do aluminum. What I wanted was the heavy structure of the large format machines but in a smaller package (therefore increased rigidity), but suggestion of an aluminum structure for the gantry has me worried.

    Thoughts?

    Thanks,

    -Gord

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    Re: Gantry construction: steel vs. aluminum?

    I can only presume it was lost in translation.
    Maybe he meant the Hiwin rails and bearings. What size have you ordered? 35mm? or 25mm?
    Do you have 2 balls screws on the long axis?

  3. #3
    Community Moderator ger21's Avatar
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    Re: Gantry construction: steel vs. aluminum?

    I've also chosen ball screws on all axis for higher accuracy, but have now been informed that the gantry structure had to be aluminum instead of steel due to the weight and ball screws not being rigid enough.
    Tell them to use the correct sized ballscrews.
    Gerry

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    Re: Gantry construction: steel vs. aluminum?

    Quote Originally Posted by ATMOS_Gord View Post
    Hi,
    I'm working on spec'ing a new Chinese machine. 1100x1800 with a full table structure, hiwin rails, etc. I've also chosen ball screws on all axis for higher accuracy, but have now been informed that the gantry structure had to be aluminum instead of steel due to the weight and ball screws not being rigid enough.
    Is this a tried and tested design, or are you paying someone to design a new one? Are they saying T-Slot aluminum? Or just Aluminum? Name of the company? Cost of the machine?

    Quote Originally Posted by ATMOS_Gord View Post
    We're not planning anything as heavy as done with a full VMC, but am going to do aluminum. What I wanted was the heavy structure of the large format machines but in a smaller package (therefore increased rigidity),
    1100mm x 1800mm = 43" x 71", is that cutting area or overall size? That's not a small machine. How fast is this machine supposed to move? What is the lead and diameter of the ballscrew? What kind of motors (stepper or servo size) and gear reduction?

    Quote Originally Posted by ATMOS_Gord View Post
    but suggestion of an aluminum structure for the gantry has me worried.
    Aluminum structure could mean lots of different things. You could have a big structure made from bolted plates with bolted internal ribs and filled with epoxy granite, and that would be awesome. But it wouldn't be light. It's the reason they're giving you that's the problem. It's some BS.

    Also based on the size you mentioned, a smaller diameter ballscrew (16mm) could have problems with whip, and a 25mm diameter ballscrew would be strong enough (2 driving the gantry?) unless you had some very very fast accelerations (in which case the gantry would need to be stiffer to accommodate those accelerations, so that doesn't make sense either). Is this being designed by an amateur?

    So how heavy is the aluminum gantry they are proposing, and how heavy was the gantry design they said was too heavy?

    Unless you can post some better info....pretty general statements you've made, not alot of detail about the company or the design.....then the short answer is to keep your money and go elsewhere. Have you already paid into this? If not, walk away. If so, you could have a problem.

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    Re: Gantry construction: steel vs. aluminum?

    Hi Everyone,

    Thanks for the helpful input. I should have provided more details.

    We are currently spec'ing this as a new machine to be built. The company is Acctek. I've researched quite a bit about them on here and was pleased with what I found. They have also been good to work with so far, very responsive.

    What we are spec'ing (in more detail):
    -1100x1800 table, t-slot top
    -Full table structure with heavier steel (8mm)
    -Taiwan Hiwin rails (25mm)
    -Taiwan ball screws on XYZ (25mm on XY, 16mm on Z)
    -Taiwan servo motors, 750w on each axis
    -Rapids are only 4000mm/min
    -3.5kw air cooled spindle
    -dust collector
    -coolant mist sprayer
    -control is mach3 on a separate computer

    It will looks something like this machine:

    http://www.acctekcnc.com/uploadfile/...0095439723.jpg

    After communicating with them more, they have clarified that the gantry on these is cast aluminum. Unfortunately I don't have any better pictures of the internal structure. They have though said that a steel frame gantry using 3mm material (about 1/8") can be done for a small up-charge.

    I wonder which would be stronger? My guess would be the steel, but as you point out NIC, it depends on the details of the cast aluminum one.

    I don't know what gear reduction there is on the servos. Also there is currently only one ball screw driving the long axis Z. Given the span across is over 1m, does having a ball screw down each side make more sense to reduce twisting forces when cutting near the edges?

    Thanks,

    -Gord

    [Edit] Updated the ball screw size for Z, had originally written it was 25mm.

  6. #6
    Community Moderator ger21's Avatar
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    Re: Gantry construction: steel vs. aluminum?

    4m/min are very slow rapids, especially for a machine with 750w servos.

    I'd be specing 3232 ballscrews, with the appropriate reduction. You should want at least 10m/min rapids, which still isn't very fast, imo
    Gerry

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    Re: Gantry construction: steel vs. aluminum?

    Quote Originally Posted by ATMOS_Gord View Post
    Hi Everyone,
    They have also been good to work with so far, very responsive.
    Of course they are, they're making a sale. After the sale, when things go bad, that's the time to see how responsive they are.

    Quote Originally Posted by ATMOS_Gord View Post
    -Taiwan Hiwin rails (25mm)
    -Taiwan ball screws on XYZ (25mm on XY, 16mm on Z)
    Read this review:

    http://www.cnczone.com/forums/chines...6-forum-5.html

    He paid for the Hiwin rails, and got USED COUNTERFEIT bearing blocks (with missing balls)!

    He paid for Taiwan ball screws and got generic Chinese ballscrews.

    EDIT:

    He posted "Here is my story" in a thread about Acctek, but it looks like the company was XYZ tech, not sure if these companies are related, other than being in the same town.

    I still wouldn't recommend this company.

    Quote Originally Posted by ATMOS_Gord View Post
    -Rapids are only 4000mm/min
    That's only 157 IPM. That sucks. That's like buying a new car and being told it won't drive over 75 kilometers per hour.

    Quote Originally Posted by ATMOS_Gord View Post
    After communicating with them more, they have clarified that the gantry on these is cast aluminum. Unfortunately I don't have any better pictures of the internal structure. They have though said that a steel frame gantry using 3mm material (about 1/8") can be done for a small up-charge.
    That's like buying a new car and upgrading to a 50 HP engine. 1/8 inch wall steel tube? No self respecting machine would have less than 1/4", For the size of the machine, I'm guessing 3/8" with internal ribs would be appropriate. Upgrading to 1/8th inch wall thickness steel is a joke I'm afraid.

    Quote Originally Posted by ATMOS_Gord View Post
    I wonder which would be stronger? My guess would be the steel, but as you point out NIC, it depends on the details of the cast aluminum one.
    It's not about which one is stronger. It's about which one is stiffer. Steel is about 3x stiffer than aluminum, but alot of factors come into play. For example, you could make a larger structure out of aluminum that may have the same stiffness and weight as a steel structure with a smaller geometry. For the exact same geometry however, steel is much stiffer. Ask them for some pics of the cast aluminum gantry structure. I'm curious to see it.

    Quote Originally Posted by ATMOS_Gord View Post
    I don't know what gear reduction there is on the servos. Also there is currently only one ball screw driving the long axis Z. Given the span across is over 1m, does having a ball screw down each side make more sense to reduce twisting forces when cutting near the edges?
    For this kind of set up you'd want a high lead ballscrew (as Ger21 mentioned). So with a servo driving it, yes, you'd want some kind of belt driven gear reduction from the servo. I assume "Z" was a typo, we're talking about your long axis.

    Quote Originally Posted by ATMOS_Gord View Post
    [Edit] Updated the ball screw size for Z, had originally written it was 25mm.
    16mm ballscrew on the Z? Cheap! Is there seriously a 750W servo attached to a 16mm ballscrew?

    Some more reviews here:

    http://www.cnczone.com/forums/chines...524-cnc-5.html

    Also I looked around at a few more threads. I'm convinced that some of the "good" reviews this company has received are fake. Many are from people with 6 posts or less, looked like some created an account for the sole purpose of giving a good review about Acctek, with a command of the English language that is reminiscent of Otto Frederick's coerced confession in North Korea.

    Not trying to be negative towards you in any way Gord. Just giving my honest opinion. I realize it does sound harsh. My recommendation is to stay away from this company.

    Quote Originally Posted by ger21 View Post
    4m/min are very slow rapids, especially for a machine with 750w servos.

    I'd be specing 3232 ballscrews, with the appropriate reduction. You should want at least 10m/min rapids, which still isn't very fast, imo
    I agree with you completely. But I don't understand why a customer would need to tell the manufacturer what is required to get good results. Again with the car analogy, you don't specify what kind of gear ratios are used on the drivetrain of the car you buy. It just works like it should.

    Perhaps if you put the onus on the customer to spec everything then you have someone to blame shift when the performance in inevitably crappy.

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    Re: Gantry construction: steel vs. aluminum?

    Quote Originally Posted by ATMOS_Gord View Post
    Hi Everyone,

    Thanks for the helpful input. I should have provided more details.

    We are currently spec'ing this as a new machine to be built. The company is Acctek. I've researched quite a bit about them on here and was pleased with what I found. They have also been good to work with so far, very responsive.

    What we are spec'ing (in more detail):
    -1100x1800 table, t-slot top
    -Full table structure with heavier steel (8mm)
    -Taiwan Hiwin rails (25mm)
    -Taiwan ball screws on XYZ (25mm on XY, 16mm on Z)
    -Taiwan servo motors, 750w on each axis
    -Rapids are only 4000mm/min
    -3.5kw air cooled spindle
    -dust collector
    -coolant mist sprayer
    -control is mach3 on a separate computer

    It will looks something like this machine:

    http://www.acctekcnc.com/uploadfile/...0095439723.jpg

    After communicating with them more, they have clarified that the gantry on these is cast aluminum. Unfortunately I don't have any better pictures of the internal structure. They have though said that a steel frame gantry using 3mm material (about 1/8") can be done for a small up-charge.

    I wonder which would be stronger? My guess would be the steel, but as you point out NIC, it depends on the details of the cast aluminum one.

    I don't know what gear reduction there is on the servos. Also there is currently only one ball screw driving the long axis Z. Given the span across is over 1m, does having a ball screw down each side make more sense to reduce twisting forces when cutting near the edges?

    Thanks,

    -Gord

    [Edit] Updated the ball screw size for Z, had originally written it was 25mm.

    Just specifying "aluminum" or "steel" doesn't tell you enough to gain the required level of comfort. There is an enormous difference in the properties of the various grades and alloys of both aluminum and steel.

    Aluminum 7075 T6 has strength that is very comparable to some steels and has superior rust resistance. It is unlikely that you would be getting the best and strongest grades of hardened stainless steel unless you specifically ask for it (and pay the extra costs).

    It is also worth noting that, while steel is stronger and stiffer inch for inch, the difference can be 100% compensated for by adjusting the part thickness like people do with epoxy granite. If the steel alloy was twice as strong as the aluminum specified, make it 2" thick instead of 1".

    The only area you can't compensate for the difference in properties is on the rails and ball screws where the steels higher surface hardness makes them more abrasion resistant.

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    Re: Gantry construction: steel vs. aluminum?

    Hi NIC, Gerry,

    Thank you for the honest feedback. It's not harsh, it's just looking at things in a critical light. And it un-covers interesting things.

    For example, I have found that this machine has the servos connected directly to the ballscrews (1:1 ratio). The specs for the Delta servo motors show that this is then in-line with the rapids values that have been quoted.

    However on another vendor we have talked to, they are using a similar spec servo, also directly coupled, but they are quoting rapid values of 2x as much (8000mm/min)! Hmmmm, that math doesn't work.

    This other supplier is using a steel construction gantry, but 4mm thick material. I'd like to see construction pictures too, I'll see what they say.

    I'm beginning to think that this is all there is going to be in this class of machine (and price point). We've checked on Taiwanese offerings and things are going to be $30-50k and up. But it's quite obvious the difference in the machine, those are much more substantial. Just look at the difference in weight!

    I'm not actually too concerned with rapids values like these for what I'm doing. It could be made faster with different gearing, but that then reduces the force the motors have (or you go to stronger motors) and if things are not as structurally rigid as ideal, making things faster isn't going to be helping anything.

    So what do you all think in terms of what should be focused on? My feeling is the structural rigidity and precision of the movements. Obviously honesty and integrity of the supplier too, and as I've mentioned above that one can vary significantly.

    Any suggestions on good examples of this that people have seen?

    Thanks again,

    -Gord

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    Re: Gantry construction: steel vs. aluminum?

    Quote Originally Posted by Goemon View Post

    Aluminum 7075 T6 has strength that is very comparable to some steels and has superior rust resistance. It is unlikely that you would be getting the best and strongest grades of hardened stainless steel unless you specifically ask for it (and pay the extra costs).
    It has nothing to do with the either the yield strength or ultimate strength of the material, because you aren't designing for strength. You are designing for stiffness, so modulus of elasticity is the factor that is important. There's no point in using a more expensive grade of aluminum (like a 7000 series) on a CNC because it's stronger when it has the same modulus of elasticity as a less expensive grade. The only advantages you might get is if you have to drill and tap any holes it will be harder to strip the threads, and it may be easier to machine than some other grades. Of course, steel is stiffer still, and less expensive. Very heavy gantries are OK for properly geared and designed CNC machines so saving weight isn't a huge factor on most industrial designs.

    Quote Originally Posted by ATMOS_Gord View Post
    For example, I have found that this machine has the servos connected directly to the ballscrews (1:1 ratio). The specs for the Delta servo motors show that this is then in-line with the rapids values that have been quoted.
    Totally unacceptable to have a nice 750W servo direct connected to a fine lead ballscrew for such a long travel. What a waste!

    Quote Originally Posted by ATMOS_Gord View Post
    This other supplier is using a steel construction gantry, but 4mm thick material. I'd like to see construction pictures too, I'll see what they say.
    I'm curious too. I'd like to see some pictures. I want to see if they have ribs, etc, or if they are simply using a tube. 4mm is also quite thin, IMO, for a gantry tube. Steel isn't that expensive, so I don't understand why they would scrimp in this way.

    Quote Originally Posted by ATMOS_Gord View Post
    I'm not actually too concerned with rapids values like these for what I'm doing. It could be made faster with different gearing, but that then reduces the force the motors have (or you go to stronger motors) and if things are not as structurally rigid as ideal, making things faster isn't going to be helping anything.
    I hear you, but also, the really slow speed is an indication that they don't know what they are doing. Based on the lack of a good design for the drive system, I suspect that the rest of the machine would also suck to the same degree.

    Quote Originally Posted by ATMOS_Gord View Post

    So what do you all think in terms of what should be focused on? My feeling is the structural rigidity and precision of the movements. Obviously honesty and integrity of the supplier too, and as I've mentioned above that one can vary significantly.

    Any suggestions on good examples of this that people have seen?
    I have no idea what it is you want to make with this and use this for. That limits feedback. For example, if you were cutting MDF all day long, I might say that a good dust collection system is essential.

    You mentioned cutting aluminum. So how thick and how fast (MRR?) and how often? This is for a business or a hobby? You mentioned "we" so that makes me think this is for a business?

    Also, what is your budget?

    That being said, in your shoes, and on a budget, and you mentioned you want to cut aluminum, I would be looking to buy a good used machine instead of a new one, especially if this is for a business. Like a Biesse or a Multicam or a Thermwood. New, those would be out of your price range it sounds like, but you know what, I saw an add for a used Biesse router for a couple grand in the past year, and I should have snapped it up but I had no where to put it. Deals can be found. The only thing is you have to check what kind of power requirements the machine needs, and may have to retrofit some parts of it if you can't provide the requisite power. You MIGHT be able to find a good used industrial quality machine for the same price as a new crappy import.

    What part of Canada are you in?

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    Re: Gantry construction: steel vs. aluminum?

    Hi NIC,

    Good points about looking for used higher end machines. There are deals to be had but often availability is the issue.

    We also have some unique challenges with our location and physical access. Can't get anything wider than about 69" through the door. We have 3-phase power available, but apparently not enough amps on the current breaker for any of the larger consumption machines (without spending a couple grand to upgrade that). So we're trying to stick with 220 single phase.

    We have an ok budget that we could use for this (let's say $20k), but you have to be getting something for that. If it's a lower capability machine/design, I'm not willing to keep adding for improvements that aren't of value (to us). For example, an ATC would be a useful feature, however researching people's experience with them in this machine class, I'm not convinced that they are reliable enough in the long run to make that worth it. Again at this level of equipment.

    And on what we are doing, it's a bit of a range of things. There'll be some wood, but mainly for jigs and fixtures to hold other work. The bulk is to be either plastic (PVC, ABS, acrylic, etc.) and aluminum. Speed isn't an issue for the aluminum since it's low volume, R&D type of work. Honestly something like a Tormach would be great for what I need to do in aluminum except for the working envelope being too small. We really need to size (area) more for layout of the work so the machine can be kicked off and work it's way over many pieces. That's mainly for the plastic stuff, the aluminum are small volume, one offs. Aluminum pieces could be 1" thick, but the work is milling out pockets, drilling holes, single form threading, etc.

    We're in the greater Toronto area, but luckily out the city! And you?

    Oh and we got some pictures from them on the gantry construction. Only for the cast aluminum pieces though. They're better looking than I expected. No dimensional info though, but appears to be thicker than what they said they would do with steel (3-4mm). I'm not sure which would be better now, although on possibility could be to look at reinforcing it later ourselves.

    Thanks,

    -Gord
    Attached Thumbnails Attached Thumbnails 171110102558458.jpg   171110102621349.jpg  

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    Re: Gantry construction: steel vs. aluminum?

    Quote Originally Posted by ATMOS_Gord View Post
    Hi NIC,

    Good points about looking for used higher end machines. There are deals to be had but often availability is the issue.
    I found this one:

    https://www.machinetools.com/en/for-...od-c40-routers

    If you could get it through the door somehow and get the power set up, and it's in good working order, a machine like that could cut aluminum all day long. And do it well.

    Might cost a few grand to get it moved, I think you'd need some professional help. No idea if the controller has issues on an older machine. You could do a conversion to mach 3, that might cost a few grand also, but if the current control system is working fine, and compatible with whatever CAM software you use, then there's no point. The problem is that if it breaks down, replacement parts and service might be hard, and you might need to do a mach or other conversion at some point.

    I'm not saying to buy that specific machine, but I am saying that it is in an entirely different performance class, and it's probably the same as the Acctek router would cost. A new high quality ATC spindle would cost more than that machine.

    What I am saying is to have a better look around at what is available locally.

    Quote Originally Posted by ATMOS_Gord View Post
    We also have some unique challenges with our location and physical access. Can't get anything wider than about 69" through the door. We have 3-phase power available, but apparently not enough amps on the current breaker for any of the larger consumption machines (without spending a couple grand to upgrade that). So we're trying to stick with 220 single phase.
    How many amps 3 phase? How many amps single phase? Even the less expensive Chinese spindles are 3 phase. The phase conversion is done by the VFD. You can get 1 phase to 3 phase VFD's, and it is my understanding that you can use just about any VFD to do the phase conversion, but unless it is specified as 1 to 3 phase, the VFD input current spec needs to be oversized by a factor of 1.73 (about double).

    No idea how much power the vacuum table might need.

    For my own build that I am working on now I am using an 11kW spindle from a Biesse Rover, no idea if it was a good or bad idea yet. It's a 380V spindle but I will be derating it to 220V instead of limiting the current excessively and using a transformer. I'll be using the VFD to do the phase conversion. These spindles have a constant V/f curve, so up to around 6500 RPM the spindle would never even see more than 220V even if it was hooked up to a 380V VFD. I still need to find an appropriate VFD. For the axis, Nema 34's off 120V.

    Also, I have a small room in the basement to work on this, so my entire machine is bolted together in sections so I can move it up and down the stairs . Yep, it's a pain.

    This will be my 2nd CNC build. My first one wasn't very good at cutting aluminum, which is what I'm trying to rectify here. It takes forever. It would be so much better to buy a good used machine (and not too much more expensive) as to build a good one, if you have a shop to put it that doesn't involve stairs.

    My point is simply that there are some ways around power limitations to get a machine working, perhaps not as well as it work work otherwise, but working nevertheless.

    Quote Originally Posted by ATMOS_Gord View Post
    We're in the greater Toronto area, but luckily out the city! And you?
    I'm also in Ontario. A few hours away from you.

    Quote Originally Posted by ATMOS_Gord View Post
    Oh and we got some pictures from them on the gantry construction. Only for the cast aluminum pieces though. They're better looking than I expected. No dimensional info though, but appears to be thicker than what they said they would do with steel (3-4mm). I'm not sure which would be better now, although on possibility could be to look at reinforcing it later ourselves.
    That looks better than I expected also. I can't really figure out how it goes together exactly. I wouldn't buy a new machine with the idea that it needs to be reinforced. What is the cost of this thing including shipping if you don't mind me asking?

  13. #13
    Community Moderator ger21's Avatar
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    Re: Gantry construction: steel vs. aluminum?

    You might consider looking at a CNC Router Parts Pro kit.
    They are designed to run on 220V single phase, and a complete kit should be in the $10k-$12k range I think.
    They have a lot of customers cutting aluminum with their machines.
    Gerry

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    Re: Gantry construction: steel vs. aluminum?

    And with the CRP kits, you have zero problems getting it through any door. I think it would fit your needs pretty well. Plug and play electronics kit, a nice plug and play spindle system and a few other items are a great value if you are wanting closer to finished machines. The mechanical parts of the machine itself go together rather quickly. One weekend. Two tops would get you a completed machine. They are built much closer to home. You know exactly what you would be getting. Customer service is outstanding. The only thing I want on mine that is not offered by CRP is the auto tool changer.
    They are around though and cost nearly as much as this machine or much much more depending.
    Lee

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    Re: Gantry construction: steel vs. aluminum?

    Quote Originally Posted by ger21 View Post
    You might consider looking at a CNC Router Parts Pro kit.
    They are designed to run on 220V single phase, and a complete kit should be in the $10k-$12k range I think.
    They have a lot of customers cutting aluminum with their machines.
    $10-$12K USD is $12.7K to $15.2K Canadian. That's getting pricey.

    I have nothing bad to say about CNCRP, in fact I think they are much better machines than you would get from Acctek, based on what I have read. For plastics I could see them being used for a business, but for aluminum, I am not convinced that they are more than a hobby machine. People cut sheet metal on them but are they really appropriate for hogging out 1" thick aluminum plates? Again, not trying to knock on CNCRP, in fact I thought of suggesting them until I was reminded of what the total cost might be. Honestly, the cast gantry pics look better than a T-slot option to me but the poor design of the drive system and the horrible bad reviews and questionable good reviews of Acctek leave alot to be desired.

    This is an industrial thermwood router with ATC spindle for $7500 Canadian dollars. LOL! I'm just surprised no one commented on that.

    https://www.machinetools.com/en/for-...od-c40-routers

    And there are a few more industrial quality machines I've seen in local classifieds that you could get for perhaps 15K. But perhaps the effort to move it and get it set up isn't worth the extreme performance gain you would get in return? Gord, do you know what you are going to do? I'm simply curious how this will turn out.

    Perhaps all of these conundrums are the reason why many of us just build our own.

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    Re: Gantry construction: steel vs. aluminum?

    NIC, Gerry, Lee,

    That's good input. I've seen those "component" machines before and like the idea of being able to roll your own. And yes, no access issues in that case. However, I'm not convinced that these would be more solid (or even as solid) as the better ones from China. We actually have a machine like this in a much smaller size that I play with currently. It's made from extruded aluminum and is a solid little machine for what it is. But, ours is only 30x40cm (12"x16"). Very different scale!

    NIC that's a good find on that Thermwood. Too bad it wouldn't fit into our unit without knocking a wall down.

    I had to look again at some of our power specs, but we have 3-phase, 600v 40amps with the current hardware. We have far more power than that available at the unit, it's just the components currently installed are only this heavy. But to get some of the 380v options that are pulling a lot of power (like that 11kw spindle you have), it will require some major changes to the power hardware. Right now we can just plug in to 220v single phase and run anything up to 40amps on a single circuit.

    I'm not sure what we are going to do right yet. Local used high end machines would be ideal (even if overkill), but I just don't think we are going to find anything that will fit through the door. While this Chinese machine isn't perfect, it does have a lot going for it and some elements of it look pretty decent. And a machine like this is only in the $6k range.

    It's funny, with inquiring about all of the upgrades and asking if they can spec certain parts higher, they came back and asked if we were building a tank! For things like this, I don't actually believe there is overkill. Overkill is really "just enough".

    I'll keep posting as things go. If we go with this machine I'm thinking to go for their cast aluminum gantry rather than something fabricated from steel, mainly because I don't know how such a thing would look design wise and I'd rather go with what I can see.

    Thanks again for the valuable feedback!

    -Gord

  17. #17
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    Re: Gantry construction: steel vs. aluminum?

    Here's a thought. Order whatever size machine you can afford that you are comfortable with. Then hire someone to open up that wall. As much as we like to think so, walls on buildings are not permanent structures.
    They can be modified. You can have it widened permanently. More costly due to different doors and extending jambs etc. Temporarily the wall section can be removed and sealed again afterward. I would much rather stare at a resealed crack around a doorway than a machine I had to settle for.
    Lee

  18. #18
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    Re: Gantry construction: steel vs. aluminum?

    Quote Originally Posted by ATMOS_Gord View Post
    NIC that's a good find on that Thermwood. Too bad it wouldn't fit into our unit without knocking a wall down.
    They typically sell for over 20K used. Definitely worth checking out.

    I'm not convinced it couldn't be made to fit through the door. I'm sure the gantry and table can be removed. Perhaps there are some movers who can turn this (or something like it) on it's side to get it through the door. That would require some custom gear that could handle many thousands of pounds, but you never know, some specialty moving company might have that gear and be able to do it for you. You mentioned the door is 69" wide. On it's side it might fit. Sure it would be a major PITA, and it would take up more space inside the building.

    These guys moved this through a 36" door, although I'm betting it's a few thousand pounds lighter than the thermwood. Safety first, don't get squashed!



    You're on the ground floor (concrete) and not overtop a basement?

    Quote Originally Posted by ATMOS_Gord View Post

    I had to look again at some of our power specs, but we have 3-phase, 600v 40amps with the current hardware.
    That's a huge amount of power! 600 x 1.73 x 40 = 41.52 kw! What's the problem?

    3 phase step down transformers can be found on kijiji for pretty cheap to get you to whatever the machine needs as input. I was just looking at a different thermwood c40 add, it said 3phase 460V 40 amps max. And that's only if you max out the inputs, which you probably will never do as you may never push the spindle and all motors to their max at once. And including a monster vacuum pump and dust collection system, which is probably half the power requirement.

    When you step down the voltage via a transformer, the available current goes up. IMO, you have more than enough juice to run anything you could buy without any derating.

    Quote Originally Posted by ATMOS_Gord View Post

    I'm not sure what we are going to do right yet. Local used high end machines would be ideal (even if overkill), but I just don't think we are going to find anything that will fit through the door. While this Chinese machine isn't perfect, it does have a lot going for it and some elements of it look pretty decent. And a machine like this is only in the $6k range.

    It's funny, with inquiring about all of the upgrades and asking if they can spec certain parts higher, they came back and asked if we were building a tank! For things like this, I don't actually believe there is overkill. Overkill is really "just enough".

    I'll keep posting as things go. If we go with this machine I'm thinking to go for their cast aluminum gantry rather than something fabricated from steel, mainly because I don't know how such a thing would look design wise and I'd rather go with what I can see.
    You're not building a tank. The industrial machines are many thousands of pounds heavier. People are usually far far more optimistic about how the less expensive, primarily diy machines they buy will cut aluminum. I made some very intricate aluminum pieces on my first build out of large solid aluminum blocks, but it was always a PITA and I had to be very careful about the bit types I used so it didn't gum up the bit, and I had run times of 20+ hours in total. It's not the kind of a thing you want to leave unattended, so for a business, the employee wages are a factor also when considering run times, even if it's a machine that isn't being used all the time.

    I've never CNC'd any plastics, just aluminum and wood, but I assume whatever you buy will be good enough, although reduced run times may again justify something better.

    I don't know exactly what you should do, and am certainly not telling you what to do, I'm only making suggestions based on my experiences and things that I have read and videos that I have watched. Perhaps the thermwood is too much machine for you, but in your shoes I would be looking for a used industrial grade one, perhaps a smaller one if you can find it.

    Please do let us know what you decide and how it turns out, I'm very curious to know what happens at the end of the day and how satisfied you are with the results.

  19. #19
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    Re: Gantry construction: steel vs. aluminum?

    Quote Originally Posted by LeeWay View Post
    Here's a thought. Order whatever size machine you can afford that you are comfortable with. Then hire someone to open up that wall. As much as we like to think so, walls on buildings are not permanent structures.
    They can be modified. You can have it widened permanently. More costly due to different doors and extending jambs etc. Temporarily the wall section can be removed and sealed again afterward. I would much rather stare at a resealed crack around a doorway than a machine I had to settle for.
    I tend to agree with you!

  20. #20
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    Re: Gantry construction: steel vs. aluminum?

    While big, old machines can be a very good deal, they can also be a lot of problems.

    Spare parts may be either not available, or incredible expensive.

    If they don't run, and need a new control, then can be very complex to retrofit.

    The exact type of machine makes a big difference as well.

    We have a $150,000 router in our shop. I wouldn't even think about using it for doing aluminum work, as it's just not that rigid. Even though it can fly through particle board and plywood at 1200+ ipm. And it weighs well over 5000 lbs.


    And a machine like this is only in the $6k range.
    Is that delivered? I've heard stories of unexpected $1000-$1500 customs and duty fees on chinese machines.
    Gerry

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