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cheap cnc dos and don\'ts

by:QY Precision      2019-11-25
CNC is a hot topic on this website.
I have built one and I want to take a moment to share some of my thoughts on this issue with those who want to be independent.
There are countless different diy cnc machines on the internet and they all look cool.
But many of the same machines have basic design and decision-making flaws.
The focus of this article is on the low-end market.
If you have the money to buy THK linear rails and Staples then this is not for you!
For others with a more moderate budget, please read on. A fair question.
I made a CNC machine myself.
I should add that I also do machines that I think are quite capable.
None of my first or second attempts have happened.
The third time is not a charm for me.
But this one here is the fourth machine I made and it works very well. How great?
Well, I travel at 174 inch kilometers per minute.
I also wired a printed circuit board on it.
For a machine with such a low cost, both are very impressive.
How much might you ask?
I\'m not on the record, but I guess there\'s about $200 in total for this machine.
This includes the cost of the computer and the router spindle.
Machine frames, mechanical components, electronic equipment, each nut and screw.
But I found out a lot of material or bought it.
Someone can make the same machine and spend a lot more money than I do.
Tell us, the wise old Saint, how did you do this feat?
Read on, and that\'s what this article is about. Maybe so.
I haven\'t told the whole story yet.
Although the machine I made is fast, powerful and precise, it does not have a large working envelope due to its physical size.
This is because I had to make a design compromise due to the cheap linear guide I used.
That\'s the drawer slide.
Yes, this is a drawer sliding CNC machine tool.
However, I had almost nothing in a yard sale and succeeded in getting some high quality Accuride full extension bearing slides.
I bought two pairs for five dollars.
The new slides are easily a pair of hundred dollars.
They are really good.
Cheap Big Box Shop drawer slide can work?
I don\'t know. I never tried it.
From the cheap slides I \'ve seen, it looks really good.
So this is the first question.
Purchase quality slides at a reasonable price.
Mine came out of some kind of device.
They have an interesting lip on them and must have turned over the sheet metal drawer.
The slides in the photos are not my slides and I have never taken a picture of them.
So I took a picture from the Internet.
I kind of like the dollar notes in this picture.
I think it has a deeper meaning.
Cheap slides may work anyway.
I\'m sure they will.
No drawer slider is a good linear guide for CNC machines.
But by the way, they\'re OK.
Next, I will discuss how to use mine correctly.
There are certain limitations that need to be recognized when you build a budget CNC machine.
Some compromises need to be made.
The bottom line is that you end up wanting a machine that works.
I\'ll tell you now, forget the design of a moving gantry.
If you don\'t have a decent linear guide, the moving gantry will fail.
Fixed gantry, moving table is the way to fly.
If the structure is static, it is much easier than moving.
I can\'t even believe I have to say that, but that\'s what it is.
In this step, I put a few photos of the CNC build I did before, a machine that ended up not working properly.
It is a double drive mobile gantry type skateboard bearing structure.
I am sure it will succeed. It didn\'t.
It was almost successful.
But almost only the palm of the horse and grenades.
This is not the case with CNC machines.
So CNC is hardly counted.
If the fixed gantry is so big, why don\'t you do that?
Well, there are some shortcomings in the fixed gantry machine.
They take up the space of how many work envelopes you have.
To some extent, moving a huge table is also a challenge.
The X trip on my machine is only 14 inch and a half.
This is a bit limited.
But not as limited as I originally thought.
When a machine is accurate to a thousand parts, I find that complex small objects become the main focus.
If you look at what a lot of people do with their CNC machines, they often do some small work.
Although some people do like to cut parts off the whole piece of paper.
4x8 CNC machine tools are generally not within the budget.
You are going to open your wallet and bleed for one of them.
All full forms of the wind type can now be left.
This article is not for you.
Just looking at the picture of how I connect the slide of the linear guide drawer may not show up immediately.
So I will discuss it here.
On the x-axis, they are inside the box frame, and the x-axis table frame is pre-loaded between slides.
I mean I have a table frame member (
Wooden frame under the table)
It was very tight there.
That is to deal with any sewage that may be available on the drawer slide.
Now, on the y-axis, my design doesn\'t have the same blockage and I can choose.
Well, I could have, but I chose to fully support the strategy.
Under full support policy, each drawer slider starts on the other side of the y-axis.
In this way, the y-axis has solid support throughout the range of motion.
This is also good for me.
Two puzzles annoyed me when I was making my machine.
They are all related to the way the drawer slides are screwed down.
Drawer slide manufacturers want you to be able to pull out the slide and get into the screw holes.
Yes, this is not the case with CNC machines.
They are bound and controlled. Problem!
I ended up solving the problem in a different way on the x and y axis.
On the x-axis, I will first install each slide to an angle.
Then I screw that angle into the frame of my machine.
This angle hangs down from the slide and I can make holes anywhere I want to go.
Right outside. It was easy.
Before I put the angle/sliding component into the frame as well, I also installed the pieces of the table rack onto the drawer slides.
On the y-axis, I just put a hole in the frame and I can reach the screw hole through this hole.
The overall theme of all this is easy and feasible.
Or at least as easy as it actually works.
Because part of this is hard enough.
At least the frame of the machine itself should be touched.
I made my frame with building Wood.
Not because it\'s great, but because it\'s cheap.
Cheap and easy to buy.
I went to the big box store I was not very friendly and just bought it.
I think I used three 2x6 and four 2x4?
The length is all 10 feet.
Then I put all the wood through my thick planing bed and leveled all the wood.
Yes, put it all together.
I can\'t stress that anymore, everything has to be as square as possible.
I \'ve been talking about how my machine is accurate to a few parts per thousand.
This is not a miracle.
I precise my whole machine to a few parts per thousand.
Take the time to be careful and do it well.
Be extra careful.
You do CNC machines, not country benches.
I actually use the digital card clamp and the volume block to set the y-axis cross frame component.
I was extra careful to make sure they were as close to the plane and the table as possible.
I made many adjustments.
Attention to detail pays off in terms of precision and performance.
If your frame is not parallel, your axis is bound.
You have to do it right.
It is not necessarily beautiful, but it must be right.
Once I got my machine tired of the docking I was doing, so I decided to make a rabbet joint.
This is a mistake.
Because it makes the square a lot more difficult than it should have been.
I don\'t think that adds any strength either.
The butt joint is the simplest geometric joint for accurate production.
If the length of the part is appropriate and cut into a square, the joint work can be adjusted.
Very simple, very simple.
On the base you will notice that I just used the bolt.
They are not beautiful, but they are strong.
This is what I have been looking.
The spell of the frame is strong and square.
Everything needs to be aligned with the universe.
This is the foundation you will build.
If you get this wrong, you will bring endless troubles to yourself.
So, take it slowly and do it well.
What are the linear actuators you might ask?
It is the mechanical position that makes things move on one line.
In my case, it\'s the lead screw.
There is a place here. I suggest you go to the middle of the road.
The cheapest one is not good enough.
All rebar bars are stored by hardware. Don\'t use that.
I used half a dozen acme screw bars.
This is something you can\'t buy at your local hardware store, but it\'s worth a try.
60 degrees all threads are designed to bind and become tight.
This is exactly what our linear actuators don\'t want! No we do not.
We want to turn rotating motion into straight motion with a little efficiency.
The efficiency of the Acme screw is about 40%.
The average old hardware bar is more like 10%. It sucks. Don\'t use it!
The efficiency of the ball screws is 90%.
But I told all the spiral ballers were lost.
My machine is more expensive than my machine.
Could another viable option be chain drive?
I didn\'t go that way myself, but I won\'t get a discount here.
The chain drive has some decisive advantages over the lead screw.
You can get higher fast motion with lower motor shaft speed.
When you have your CNC machine running, you will understand why this is so ideal.
But let me say that in order for my machine to run 200 inch per minute, my screw has to rotate 2000 RPM.
It\'s a little fast.
I said my machine could reach 200 IPM but I didn\'t say I was running it at this speed all the time. I don\'t either.
Speed is ridiculous.
I don\'t want to go to the grid.
Return to the acme lead screw.
Acme works fine, but the tip is a weird thread.
Taps for Taps are also rare.
Expensive too.
So I didn\'t buy it. I made one.
I wrote an article about how I did this.
Because I made high density polyethylene plastic screw nut myself.
High Density Polyethylene is elastic, so it is naturally resistantbacklash.
It is also self-lubricating.
Would you trust me if I told you that high density polyethylene tastes good and the filling is small?
This may not be true.
But I still like high density polyethylene. I melt my own.
Remember when I said I bought two drawer slides?
This made me lose one shaft on a 3 axis machine.
So I made the Z axis with my own melted high density polyethylene.
But this is the story of another day. Ah electronics.
The love of my life.
But I bet a lot of people hate these things and think it\'s a terrible monster.
Things they don\'t understand
We are afraid of what we do not know.
But don\'t worry, because CNC is basically plug and play right now.
There is now a single board solution.
I don\'t recommend any of them though.
They are high in price, low in performance and severely limited in versatility.
But they are easy to use.
This could be a big part of their appeal.
If you want to get the ultimate in a stingy show, you have to order here.
The picture of this step is my control box.
There are many things there.
Our power supply is in the upper left corner.
It goes to the power supply in the upper right corner.
Its output is switched by a relay (
I have a remote control panel with a control relay switch-
After using my machine for a while, I decided what I wanted).
There is also a pedal under the power supply.
This is a distributed power supply of logic.
Then in the middle of the left is my homemade rest board.
You can buy it now for $5.
Then the prospect in the box is a line of motor drives.
I recently upgraded some TB6600s.
It\'s really nice to drive.
I think they paid me $8 and changed each one. Well worth it.
I run Linux CNC and I will not use Mach if you pay me.
Because I won\'t run Windows if you pay me.
I said.
CNC needs an RTOS (
Real-Time Operating System).
Windows is not a real-time operating system.
The disguise of Mach.
Linux CNC is the real deal.
Linux CNC actually uses the RTOS kernel.
Do you need to be a Linux Master to use Linux CNC? No.
Linux CNC is distributed with real-time images.
This means that the operating system is integrated with the application.
You just need to start the image to run.
To make it easier, I have to show up at your door and start your computer for you.
I won\'t do that.
There is a lot of information about Linux CNC here. Get it. It\'s free.
I can add more details.
There is more to be said.
But I talked about the main points of this article.
I know people don\'t agree with me at this point, but you are all wrong.
If you don\'t agree with the point I made here, write an article of your own.
You can argue with success, but don\'t expect me to be happy to put up with fools.
The first image of this step is the first job I generate G code for the machine and run it on the machine.
It\'s a plot (
I like drawing on my CNCit is so quiet)
Using a ballpoint pen, when you look at it, I realize I don\'t know what I\'m doing when I make this file.
So my machine ran three times per line.
I guess I have some sort of progressive depth cutting setting in the software I\'m using?
I don\'t even know now.
I think it\'s interesting, though.
Each line you see draws a line and then redraws it.
This should let you know what my CNC machine can do.
Repeatable accuracy.
It does the same thing with the spindle.
Because my machine is strong and strong.
The second image is that I dial in the PCB isolation wiring.
I was not exactly right the first time I tried.
I have a bent bit in collet, so it cuts very wide because the tip of the bit describes a circle on the job (
But I used that board anyway).
On the top floor I pulled the drill straight and made more trial cuts.
So this machine is quite capable if it runs correctly.
Others say the wide cut is due to the fact that my machine is not hard and shaking.
This is obviously not the case.
They were wrong.
I don\'t even use the height sensor software.
Some people have commercial machines that cost many times as much as I do and cannot isolate routing boards.
That\'s what it is.
If you make an informed choice, you can build a CNC for something that is not working well.
But you must have realistic goals and be careful at work.
All in all, this is a very long topic, but it is very complicated.
I hope someone can find some value from what I wrote here.
If you want to make a cheap CNC machine, make a cheap CNC machine.
This means not trying to make bad versions of expensive CNC machines.
Use basic cheap machine design, as I outlined here.
Fixed gantry, mobile workbench.
If the machine does not work, it is rubbish.
This design works.
If you want one of them, you need a decent linear guide.
More expensive than this whole machine.
This also does not mean the round rod without support.
Those things don\'t work.
There are so many cheap CNC machines on the Internet that should be taken back, shot and out of pain.
Don\'t let one of them have a live abortion that is almost impossible for 12 times.
Make a machine within your ability.
You can dream, but you need reality when you act.
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