New guy go easy

I have been running and programming cnc lathes and mills for almost 20 years now. I am fortunate enough to work for a company that allows me to make personal stuff after hours. Well it gets old staying until 12 or 1 in the morning machining my personal projects. I have decided to take on the task of building my own machine, I purchased the momus design plans and after drawing the machine in solidworks I am thinking it will not suit my needs. I am looking to machine aluminum and plastics so I need something with a little more accuracy and rigidity. After doing some searching I now know that I want to use linear slides and ballscrews with some hefty stepper motors. My question before I get started is should I go with two motors for the Y axis? Can I use any length ballscrew? I'm still unsure of machine size because I don't know if I am limited by the ballscrew length. Thanks for looking..

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My question before I get started is should I go with two motors for the Y axis?

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That really depends on the design, but for a typical moving gantry machine, two motors usually makes a more rigid machine.

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Can I use any length ballscrew?

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Typically, you either get a screw to fit the machine, or design the machine around a screw. It's kind of difficult to use a 48" screw in a 24" machine.

What size machine are you looking for? What materials do you plan on using to build it?

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After doing some searching I now know that I want to use linear slides and ballscrews with some hefty stepper motors.

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If by "hefty" you mean big, that's often a poor choice with steppers. On small to medium sized machines, smaller steppers will often outperform very large steppers.

Thanks for answering my questions. By hefty I mean over engineered, I don't want the machine jumping while cutting which I would have had with the belt drive machine. I would like a 24" x 36" cutting area and plan on building it with extrusion. I originally designed a machine built from solid 6061, that would have been very pricy. You would suggest one motor on either side of the gantry? I guess I will draw something up and then ask about motor sizes. Do you know of any plans that have already been made for a extrusion built machine with around the same cutting area? thanks again.

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Originally Posted by ger21

That really depends on the design, but for a typical moving gantry machine, two motors usually makes a more rigid machine.



Typically, you either get a screw to fit the machine, or design the machine around a screw. It's kind of difficult to use a 48" screw in a 24" machine.

What size machine are you looking for? What materials do you plan on using to build it?



If by "hefty" you mean big, that's often a poor choice with steppers. On small to medium sized machines, smaller steppers will often outperform very large steppers.

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Look at CNCRouterparts.com
But you'll need to modify thei designs quite abit for ballscrews and linear rails. You'd also want to beef it up quite a bit, if your main goal is cutting aluminum. A welded steel frame is probably a better choice, and much cheaper.

This was my original desgn, probably going to scale this down and go with something like this.
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Originally Posted by Beachcustoms

I have been running and programming cnc lathes and mills for almost 20 years now. I am fortunate enough to work for a company that allows me to make personal stuff after hours.

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That is fantastic as i gives you a leg up on others here that struggle with a home shop or have to involve a machine shop to get their builds done. Because of this access I'd seriously think about a more robust machine.

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Well it gets old staying until 12 or 1 in the morning machining my personal projects. I have decided to take on the task of building my own machine, I purchased the momus design plans and after drawing the machine in solidworks I am thinking it will not suit my needs.

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Well it is good that you recognize that the machine won't do the job for you.

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I am looking to machine aluminum and plastics so I need something with a little more accuracy and rigidity.

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I get a bit worried when I see comments like this, what is a little more accuracy? Further rigidity usually comes with a bigger up front cost to put more mass into the machine. Ultimately you may have to move away form a moving gantry machine to get the precision and rigidity you want.

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After doing some searching I now know that I want to use linear slides and ballscrews with some hefty stepper motors. My question before I get started is should I go with two motors for the Y axis?

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Generally (this is open to an extended discussion) the axis that moves the gantry is the X. If you go with moving gantry then two motors may be a good idea. There are alternatives especially with the smaller sized machines. The really question in my mind is: do you really want a moving gantry design if the goal is precision and rigidity? In the smaller sizes you are talking about here it is often easier to achieve these goals with a fixed gantry/moving table machine. I probably wouldn't go much bigger in a fixed gantry design but it is certainly doable in the size of machine you indicated.

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Can I use any length ballscrew? I'm still unsure of machine size because I don't know if I am limited by the ballscrew length. Thanks for looking..

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For the size of machine you are talking about you can implement a ball screw solution, that is no big deal.

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Originally Posted by Beachcustoms

Thanks for answering my questions. By hefty I mean over engineered, I don't want the machine jumping while cutting which I would have had with the belt drive machine.

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Over engineered can lead to excessive expenses. However rigidity in your design should be a primary focus if you want to do a variety of work in aluminum.

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I would like a 24" x 36" cutting area and plan on building it with extrusion.

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If you are talking T-sloted extrusions you run into a cost problem where the materials will set you back a bit. This especially if you focus on making the machine rigid.

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I originally designed a machine built from solid 6061, that would have been very pricy.

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Steel tubing is your best bet if money is a concern, you can leverage square and rectangular sections to suit the application. for many working with the tubing is a problem but you do indicate access to a shop. It might pay to describe what tooling you have access to in that shop.

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You would suggest one motor on either side of the gantry?

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That is one way to solve the stiffness problem in a moving gantry machine. However a gantry supporting a 24 inch wide cut isn't impossible to drive from two lead screws and a single motor. Your chosen machine size actually makes possible a range of drive arraignments that might not work well for larger machines.

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I guess I will draw something up and then ask about motor sizes. Do you know of any plans that have already been made for a extrusion built machine with around the same cutting area? thanks again.

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There are plans out there. It really isn't my place to comment on them as I've never used any of those plans. Your needs as i understand them are somewhat generic so there are probably more than a few suitable designs. Your best bet is to search for CNC router DIY plans on the internet. You will come up with many designs including the likes of this machine: Building the KRMx02 CNC — Kronos Robotics. In the end you will have to make your own decision but I will be honest and say I'm not a big fan of most extrusion designs out there. it depends upon what your needs are of course but when you say "accuracy and rigidity" you really need to get a handle on just how accurate you want the machine to be. Because there is a huge difference between using off the shelf parts and getting the accuracy they deliver vs actually building a machine to tight specs.

Frankly I'm of the opinion that if you want to go tot he expense of profile rails you need to also absorb the cost of the precision machining required to deliver decent results with those rails. In other words expense add up quickly if you want really good accuracy.

Thanks Wizard, I still plan on sticking with the extrusion gantry design. I Have started to redraw the machine and so far like the design. I didn't quite make it big enough to achieve the cutting area (I down sized so I could use all standard size materials)I was looking for but it still has more than enough. I have access to 3 12" haas cnc lathes and one Haas vf3 mill,the mill is pretty much my machine. I do all of the tool design and tool making for our shop so I don't see machining the pieces accurately being a problem. When I said I wanted it to be accurate I was thinking repeatability of .001 which I think is very possible. I am making custom covers and pool cues so if I can get it to repeat with in .001 I will be very happy. When I say I want it rigid I meant I don't want it to shake and shutter while its cutting. I know I wont be able to take big cuts with it but should be able to make a few passes and get the same results.

Motor question, can I use the Nema 34 460oz motors? I plan on buying the G540 kit and would rather go with the larger motors if I can (I know I can just want your opinions).

This is my design so far.
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I still need to add all the gussets and brackets that will stiffen the design up. Once I figure out which motor I will go with I will add them in along with the screws, nuts, bearing blocks and finally add all the holes for the dowel pins and bolts. The top of the table will be aluminum which will be bolted down to the extrusion, I plan on putting the aluminum on one of our large surface plates then bolting the frame and gussets on. this should help keep everything flat and parallel. If you see a potential problem please let me know.

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Originally Posted by Beachcustoms

Thanks Wizard, I still plan on sticking with the extrusion gantry design. I Have started to redraw the machine and so far like the design. I didn't quite make it big enough to achieve the cutting area (I down sized so I could use all standard size materials)I was looking for but it still has more than enough. I have access to 3 12" haas cnc lathes and one Haas vf3 mill,the mill is pretty much my machine.

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Access to such machinery is fantastic and should make fabricating some of your parts a snap.

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I do all of the tool design and tool making for our shop so I don't see machining the pieces accurately being a problem. When I said I wanted it to be accurate I was thinking repeatability of .001 which I think is very possible.

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Repeatability and accuracy are two different things, given that you should be able to do fairly well. Moving gantry designs though are not extremely rigid though much can be done to improve the average design out there.

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I am making custom covers and pool cues so if I can get it to repeat with in .001 I will be very happy. When I say I want it rigid I meant I don't want it to shake and shutter while its cutting. I know I wont be able to take big cuts with it but should be able to make a few passes and get the same results.

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Well here is where you want to be careful in your design. For example many moving gantry designs pay no attention at all to the vertical supports for the gantry beam and this suffer when the thin plate supports vibrate like springs. So you need to do something that enhances the stiffness of the vertical supports, this can mean the use of tubing or extrusions to stiffen the design. In your case with access to a machine shop you have more options, you could machine the supports out of much thicker plate, design a screwed together box section, cast a support with gusseting built in or even weld up a custom design. The idea being to leverage what you have available to avoid a common pitfall on these moving gantry machines.

The other thing important here is the gantry beam itself which should be big enough to avoid deflection if you want to realistically do precision machining.

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Motor question, can I use the Nema 34 460oz motors? I plan on buying the G540 kit and would rather go with the larger motors if I can (I know I can just want your opinions).

This is my design so far.

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Nice pics! The biggest concern I have is the use of what looks like thin plate for a good part of the gantry mechanism. I'm a strong believer in box sections and where needed gussets. Of and the saddle that rides on the X rails should have its bearings spaced out a bit to counteract the tendency to rack or twist. Dual leadscrews are often used to take care of twisting in one plane but they do little to resist twisting in the vertical plane. Of course there is a trade off here in that more spacing reduces travel or forces you to build a bigger machine. It all comes down to how accurate you really need to be. Someplace a few threads back a guy posted a spread sheet that will help with some of these deflection calculations. In any event this spacing of the bearings on the X axis saddle is probably the second most common short coming with these moving gantry machines.

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I still need to add all the gussets and brackets that will stiffen the design up. Once I figure out which motor I will go with I will add them in along with the screws, nuts, bearing blocks and finally add all the holes for the dowel pins and bolts. The top of the table will be aluminum which will be bolted down to the extrusion, I plan on putting the aluminum on one of our large surface plates then bolting the frame and gussets on. this should help keep everything flat and parallel. If you see a potential problem please let me know.

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Well I highlighted my concerns about the gantry, I would worry about everything from the gantry beam to the X bearings. The problem being if you want sub 0.001" accuracy the gantry has to be rather robust as a system. It isn't clear to me how the Xaxis rails will connect to the table assembly but I would look for far mining material that is at least 3" in cross section and really would prefer to see you go to 4". I'm actually less concerned about extrusions here than in the actual gantry beam, the table can be assembled as a ladder type frame with lots of reinforcements a gantry just hangs in free space. Add enough rungs on the "ladder" to make sure the table top doesn't deflect significantly in the middle and you should be good.

Al the pieces for the moving gantry are made from 3/4 6061, I can go larger with the Y axis beam but im not sure it will be needed as I plan to add two 3/4 x 1 1/2 aluminum to all the pieces in a T to make them more rigid I just haven't gotten around to that yet. The x axis will run on v groove bearing which are spread apart 6", plus I have two bearings that will be mounted on both of the gantry uprights. this should eliminate any side to side movement (that's what the aluminum beams are mounted on the table top for.