Build Thread- My CNC Design...

[slickrick]

I have gotten my design to a point I would like to share it with all of you.

I welcome any and all suggestions from you guys.

I plan to use this on wood and aluminum plate and block. Speed doesn't matter as much as accuracy to me.

The Cutting area:
18" x 18" x 4" (EDIT: The table base will most likely be aluminum too. It looks liek wood because I put a wood material on it for contrast in the picture)

The base:
Made from 3/8" aluminum and 1" aluminum angle.
3/4" Dia. supported rails.
1/2" ACME rod (probably 1/2x10 2 start) centered under gantry
(4) 3/4" thomson open pillow blocks will support the Gantry. 2 on each side.
Guide rod span: 2'-5" (supported)

The Gantry:
3/8" aluminum along with 1" aluminum angle.
The Y axis will run along 1/2" guide rods with a 1/2" ACME rod driving it, centered.
It will have 4 closed Thomson pillow blocks supporting it.
Guide rod span: 2'-2" (unsupported)

The Z Axis:
Made from 1/2" and 3/8" aluminum
1/2" guide rods with 1/2" ACME rod centered.
The Z axis will have 2 twin Thomson closed pillow blocks.
Guide rod span: 9" (unsupported)

All axis' will have guide bearings on the rod end farthest away from the stepper, and will have thrust bearings on the stepper side of the rod.

I have not gotten to the point that I have figured out what size stepper motors I need. Nor have I figured out any of the electronics I will need to buy/build.

I am pretty confident structurally other than maybe being a little light on the thickness of the gantry pieces.

I'd like to hear what you guys think.

Oh.....money is pretty tight right now, so this may take me quite a while to build. Hope you stay with me.

Rick

[Thazul]

Hi slickrick,

It looks pretty good.
The one thing that screams out to me, and I'm not sure if it's necessary is stiffening the sides of the gantry.
I tend to like to over build things. I would probably extend the bottom of the gantry a little and either use some larger
angle to reinforce, or even better, something that runs vertical up the side.
I scribbled a little bit on one of your images to give you a visual of what I mean, have a look.

Looking good though, keep up the good work!

Andy

[slickrick]

Andy,

Thanks.........Not a bad idea. I'm thinking that the three pieces that make up the top of the gantry along its width should be enough to keep the bottom squared up, but that is a pretty good idea.

If anything, I could add length to the lower piece of the gantry to add gussets to it later.

[slickrick]

Some particular things I have questions about are the size of the supported rails on the base (3/4), and the size of the unsupported rails on the y and z axis (1/2"). Are these large enough?

Another is the size of the Acme rods. Is 1/2" enough?

[ahren]

Your 1/2" ACME rods are definitely sufficient for a machine of this size. Tons of people (including myself) have built successful machines with this size screw. In fact, the components I sell on my website are based around this size screw.

As for the rails, the supported ones should be fine. For the unsupported ones, you'll need to take a look at the load you expect on them. You can then use the MOI calculator and deflection calculator here:

http://www.engineersedge.com/calcula...re_case_11.htm

http://www.engineersedge.com/beam_be...flection_2.htm

Your 1/2" rods have a moment of inertia of about 0.003 in^4. Using double this (for two rods), with a 100 lb cutting load, you're going to get nearly 0.25" of deflection. I'd say those are not going to cut it. Going to 3/4" rods gets you 0.047" of deflection, which is much better, but still pretty bad. I'd either support the rods, or go with a different bearing system for the gantry.

Ahren
www.cncrouterparts.com

[slickrick]

Thanks Ahren, I'll look at those pages during my break at work tomorrow. I don't know what the amount of load I will be generating. Is 100lbs cutting load a standard I can use?

If I am cutting an aluminum block with a pass of say 1/8" would I be generating that much cutting load?

Tomorrow I will take a look at 1/2", 5/8" and 3/4" supported rails.
Thanks for the info.
Rick

[TOTALLYRC]

Originally Posted by slickrick I have gotten my design to a point I would like to share it with all of you. I welcome any and all suggestions from you guys. I plan to use this on wood and aluminum plate and block. Speed doesn't matter as much as accuracy to me. The Cutting area: 18" x 18" x 4" (EDIT: The table base will most likely be aluminum too. It looks liek wood because I put a wood material on it for contrast in the picture) The base: Made from 3/8" aluminum and 1" aluminum angle. 3/4" Dia. supported rails. 1/2" ACME rod (probably 1/2x10 2 start) centered under gantry (4) 3/4" thomson open pillow blocks will support the Gantry. 2 on each side. Guide rod span: 2'-5" (supported) The Gantry: 3/8" aluminum along with 1" aluminum angle. The Y axis will run along 1/2" guide rods with a 1/2" ACME rod driving it, centered. It will have 4 closed Thomson pillow blocks supporting it. Guide rod span: 2'-2" (unsupported) The Z Axis: Made from 1/2" and 3/8" aluminum 1/2" guide rods with 1/2" ACME rod centered. The Z axis will have 2 twin Thomson closed pillow blocks. Guide rod span: 9" (unsupported) All axis' will have guide bearings on the rod end farthest away from the stepper, and will have thrust bearings on the stepper side of the rod. I have not gotten to the point that I have figured out what size stepper motors I need. Nor have I figured out any of the electronics I will need to buy/build. I am pretty confident structurally other than maybe being a little light on the thickness of the gantry pieces. I'd like to hear what you guys think. Oh.....money is pretty tight right now, so this may take me quite a while to build. Hope you stay with me. Rick

Looking good so far. Unfortunately, you will need speed to cut wood without burning. I don't meen lighting fast but it needs to go as fast as you would move a router by hand. I would guess at least 40IPM on the low end without loosing steps.

Originally Posted by Thazul Hi slickrick, It looks pretty good. The one thing that screams out to me, and I'm not sure if it's necessary is stiffening the sides of the gantry. I tend to like to over build things. I would probably extend the bottom of the gantry a little and either use some larger angle to reinforce, or even better, something that runs vertical up the side. I scribbled a little bit on one of your images to give you a visual of what I mean, have a look. Looking good though, keep up the good work! Andy

Going with what Thazul has scribbled on your drawing, you can go with the thin side pieces you were concerend with. If you build it stiff to start with you will never regret it. It will be easy to test for flex with an indicator when you are done. Set up the indicator and push in the direction of the y axis travel. If you can get it to "rack" you need to add stifness.

If I get a chance I will test mine and see what I get for a flex reading. Just make sure the cleanex is ready because I am not sure I want to know.

Originally Posted by slickrick Some particular things I have questions about are the size of the supported rails on the base (3/4), and the size of the unsupported rails on the y and z axis (1/2"). Are these large enough? Another is the size of the Acme rods. Is 1/2" enough?

I'm with ahren on this one, go with the supported rails for at least the y, I have seen a lot of the Z's built this way. The loads that the z will se are different than the x or y.

Originally Posted by slickrick Thanks Ahren, I'll look at those pages during my break at work tomorrow. I don't know what the amount of load I will be generating. Is 100lbs cutting load a standard I can use? If I am cutting an aluminum block with a pass of say 1/8" would I be generating that much cutting load? Tomorrow I will take a look at 1/2", 5/8" and 3/4" supported rails. Thanks for the info. Rick

100lbs sounds like a good figure to me. You can lean on the machine and easily exert that much force if you are as big (fat) as I am.

It depends on the size end mill you are using. It also depends on how long your lever arm gets to be. If that endmill is in the end of a spindle/router and it is hanging down 4" to give you working room, the force seen by the gantry is higher than the actual force seen by the cutter. I guess that the proper term is torque. Not only will you get linear flex but twist as well.

Just think about how much vertical force you can put on a 1/8" drill when using it by hand, 50lbs?. If you are drilling 1/8" hole in aluminum you don't want the whole machine flexing all over the place. On the smaller bits the load is less but the likelyhood of breaking goes up if you are not going in straight or are flexing.

Sorry for rambling.
Mike

[ger21]

Unless you go with 1" or larger, you'll probably be unhappy with unsupported shafts on the Y.

[slickrick]

Ok, well I checked out the website to see what the deflection would be, but does that site really pertain to rod? They say beam, but that could be quite a few things. I beam, square tube or rod? They all would have different deflection rates. Maybe I'm missing something on the page saying it is for rod.

I tried plugging in the numbers Arhen used and I never was able to get the same ones he got. If you look at the formulas, to get the maximum deflection at load, you need to know the modulus of Elasticity.......hummm....I don't have a clue what that would be. It would depend on the type of rod used.

Anyways, I decided to stick with the 1/2" on the y axis but support it along the back.
My gut instinct is giving me a wierd feeling that supporting it this way will help but not maximize the amount of deflection it could by changing the way it supports the rod.

What do you guys think about supporting the Y axis this way? Will supporting it this way eliminate deflection caused by torque forces from the router cutting the material?

Mike, I'm not sure how quick this machine will be able to cut yet. I haven't even started to figure out what steppers I need. The electronics are my weakest area for this.

I assume that if I couldn't even get that speed, i could reduce the depths of my cuts.
Right now, speed is not the priority as much as accuracy and the knowledge I am gaining by designing and building it.

Gerry, 1" is pretty large for this small machine. Supported rails it is...hehe

Thanks everyone for the input.
Rick

EDIT: Forget the first paragraph.....I understand M.O.I. now. Still looking up Modulus of Elasticity.

[ahren]

"Beam" is a generic term that doesn't specify cross section. The particular calculator I sent you to was for a round cross section, which is what you have. The modulus of elasticity is determined by the material, and is a measure of stiffness. The default value of 30,000,000 psi is about the elasticity of steel, so it's a good general number to use. You need to make sure everything is in pounds and inches in this case.

That aside, supporting the rails should fix you up nicely. This effectively transfers the load into your whole gantry, which has orders of magnitude higher sectional modulus than the rails. This is due to the fact that sectional modulus is a function of thickness cubed in the bending direction. That's why ger suggested 1" rods -- though they are twice as big in diameter, they have ~8 times the resistance to deflection (caveat -- I haven't gone through all the math for a circlular cross section, but this is true for rectangular beams). Supported rods are even better, because you get to count the thickness of the supports plus the thickness of your gantry.

Ahren
www.cncrouterparts.com

[TOTALLYRC]

What do you guys think about supporting the Y axis this way? Will supporting it this way eliminate deflection caused by torque forces from the router cutting the material?

Supporting the 1/2 inch rod will make a huge difference like ahren said. It is probably an order of magnitude stiffer.



Mike, I'm not sure how quick this machine will be able to cut yet. I haven't even started to figure out what steppers I need. The electronics are my weakest area for this.

The electronics is the "easy part" because there are so many ready made packages available today.



I assume that if I couldn't even get that speed, i could reduce the depths of my cuts.
Right now, speed is not the priority as much as accuracy and the knowledge I am gaining by designing and building it.


Reducing depth of cut can help in many situations but there is a certain minimum speed that you need to go or you are just gnawing away at the material and not really cutting. Plus what you then do is just wear out the end of the cutter. If you are doing something with a profiled cutter in wood then you will need to take a full cut to get the best results.

Here are a couple of points in no particular order.

1. Don't skimp on the Z axis motor.. The weight of the Z axis slide plus the router/spindle going against gravity is significant.

2. If you are using 1/2" x 10tpi acme screws, you will be able to go fast enough as the length of the screw is short enough to not wip on that small of a machine.

3. For a beginner, going with steppers is the easier and most cost efective way to go.

4.Go with the fastest stuff you can afford(without getting silly), even if it means waiting a few more weeks to purchase parts. On my machine which was bought off of ebay and was my first cnc, They skimped on the power supply and motors.

Of course now that I know a little more I am upgrading the power supply and have aready had to upgrade the Z motor and screw. A 20 tpi with a motor too small for the load was depressing to say the least. I could go 60 ipm with the x and y and would loose steps above 25 with the z. When you have to drill 100 holes it would take forever. Just with the motor and screw upgrades the Z will now go 50ipm and the feed of the drill is the same but just the increased rapids have decreased the time for the same part by 30% or so.

5.I would recomend a package based on the G540.This is a 4 axis motor drive with a breakout board and 0-10v to drive a VFD for and 3phase AC motor or a AC input DC motor controller built in. Plus the drives morph from micro step to full step on the fly which in laymans terms you will get maximum speed from your motors and still have micro stepping at low speeds which retains the fine resolution. The G540 also minimizes the number of wiring connections, great for the first time installer/builder.
It is tremendous bang for the buck. I have several gecko products and highly recomend them. Read the manual from Gecko's website. It will answer the first 20 questions you will have and some of it applies to
non-Gecko products.

www.kelinginc.net has this package.


G540 4 axis package (1PCS G540 +4 pcs KL23H2100-30-4B (3/8” Dual
shaft with a flat) 382 oz-in + 1 pcs KL-350-48 48V/7.3A 110V/230V
power supply): $549.95 It may sound like a lot, but you will very happy.

There are other suppliers and packages but this is a for instance.

6.If you need more I/O, get the G251's (which are basically inside the G540) and the CANDCNC breakout board. It has port stretching and the ability to use 2 pports if you need it. www.candcnc.com

7. There are other systems out there and if you want to buy the parts piecemeal, make sure you do your home work.

When picking out the electronics, take what I call a "total systems approach". This means that the motors, drivers, and power supply interact and need to be considered together. If you start with cheap, unknown motors, chances are you will wind up with a less than optimum system.

8.Don't just take my word for it. Search the Zone for more info.
I will only tell you about products that I have used, purchased or at the very least have had good experiences with the supplier/manufacturer. I have used or at least own all of these and I am very happy so far. I have the g251's and the candcnc breakout board and will be installing them this winter on something. I just couldn't pass up the introductory price when they came out a couple of months ago. I actually had to up my cc limit but I feel it was well worth it.

9.Read as much as you can, I have learned a lot from reading the "Zone" and it has saved me from some basic mistakes.

[slickrick]

Hummm......that package sounds a little more expensive than I want to spend right now.

I'm trying to get this project going with little impact to the household fiscal budget...hehe.....I sleep next to the treasurer, so basically this means extra money from ebay or computer side work.

So I know I have quite a bit of reading to do. I have many questions about the electronics.
Down and dirty, I need to learn to figure out what size steppers minimum I need, and what will be too large.
Driver boards......I know little to nothing.
Power supply....well...I know what it does....hehe..sizing is a different story.

If anyone has a good link to a page that explains everything, I'd love to check it out.
I think I have some bookmarked from my travels around here...I'll check those out first.

So thanks again for everyones help. I appreciate it.
Rick