accuracy of home made CNC machine

[spaltiel]

Hello,

I'm new here (is it the correct forum?) and I hope to build a nice CNC machine.

also I saw at:
http://buildyourcnc.com/yrailsandnut.aspx

machine which looks nice. however, does anyone can estimate the accuracy for this kind of machine?

I hope i can get 0.1mm (~0.0004") accuracy. (actually I know it is not accurate but it is good for me and I don't know if it is realistic for homemade machines)

According to your knowledge and experience is it realistic?

thanks

[awerby]

Originally Posted by spaltiel Hello, I'm new here (is it the correct forum?) and I hope to build a nice CNC machine. also I saw at: http://buildyourcnc.com/yrailsandnut.aspx machine which looks nice. however, does anyone can estimate the accuracy for this kind of machine?

[The accuracy of a machine like that would be low. It looks like they're going for the cheapest possible build, with the least equipment required, and the most easily sourced hardware. There's nothing wrong with that, but the amazing thing about it is that you can build a CNC machine that way at all, not its ultimate accuracy.]

I hope i can get 0.1mm (~0.0004") accuracy. (actually I know it is not accurate but it is good for me and I don't know if it is realistic for homemade machines)

[I think you're off by a decimal point, but even +/-.004" overall accuracy would be better than I'd expect from a machine like that. +/- 1mm (.04") is more like it. However, there are lots of things you can make that don't require great precision. If you want better specs, you'll have to go with higher-quality components - like acme screws instead of hardware-store allthread, precision linear rails and trucks instead of skateboard bearings riding on aluminum angles, and a metal frame instead of MDF. ]

Andrew Werby
www.computersculpture.com

[stevespo]

I don't want to sound negative, but .1mm accuracy seems very unlikely (impossible) with that design and components.

If you check the specs on even many medium and higher-end commercial machines (using expensive linear rails, ballscrews, etc) they never claim to have that level of accuracy. They may have that type of resolution, but repeatability is more like .001" to .004"

With 1/4-20 threaded rod, MDF, skate bearings, etc you're going to be limited. I couldn't say to what degree of accuracy, but (.1mm/.0004") seems unrealistic. Backlash, racking, staying square, etc. They are all going to be issues.

Steve

[dertsap]

.1mm accuracy on a home wood cutting router is probably not going to happen . wood working doesn't need that kind of high precision . I would recommend away from building that and look at joecnc plans or the jgro , these are better proven builds and are fairly straight forward to put together . if you do some searching around the forum you will see what the rest of us have done and maybe you will be able to come up with your own design that can work within your budget (if you have one) . regardless which way you go there will be plenty of help available to help you build a much better design if you ask for it

some plans to look at
http://www.cnczone.com/modules.php?n...warticle&id=24
http://www.cnczone.com/modules.php?n...warticle&id=71
and a few others http://www.cnczone.com/modules.php?n...category&cid=2

[stevespo]

Yeah, absolutely look around and see what fits your needs/budget. There are some great, proven designs that don't require much more (time, money) than the plans you're looking at - but could provide much better accuracy and performance.

What are you hoping to do with your machine? What types of materials will you be cutting? What types of projects do you envision? People may be able to offer more guidance based on what your goals/needs are.

Steve

[spaltiel]

Originally Posted by stevespo Yeah, absolutely look around and see what fits your needs/budget. There are some great, proven designs that don't require much more (time, money) than the plans you're looking at - but could provide much better accuracy and performance. What are you hoping to do with your machine? What types of materials will you be cutting? What types of projects do you envision? People may be able to offer more guidance based on what your goals/needs are. Steve

Hi,

I hope to be able of making 3D parts from plastic and wood
and maybe i need to be more specific regarding the accuracy.
I design parts in mm and I want that the mistake in the part size will be 0.1mm I hope. I thought that CNC machine are very accurate. Do these parameters change the ability to realize such a machine at home?

thanks

[dertsap]

Originally Posted by spaltiel Hi, I thought that CNC machine are very accurate. thanks

a $100,000 cnc is very accurate an mdf home built cnc won't be near as accurate , the precision that you are aiming for is far beyond what most manufactured parts are toleranced for aside from bores and other special features but for general metal machining + or - .005 inch tolerance is fairly common , .1 mm is equivalent to 1/9 of the thickness of a piece of lined paper , so without understanding what types of parts you plan to make I would have to assume that the accuracy that you desire is unnecessary for wood or plastic

[stevespo]

Actually, the original unit conversion was incorrect (we didn't notice).

.1mm = .0039" = .004" (4 thousandths of an inch, ~diameter of human hair, ~thickness of a piece of lined paper, etc)

That type of accuracy can be achieved with a DIY router, but depends heavily on the components, design, care taken, etc. It's not necessarily easy or cheap. An inexpensive router can have that much runout alone. Flex in the frame, backlash, endplay, etc.

You'll have to really understand all the variables involved and make sure the design has each one of them covered to reach and maintain that type of accuracy.

Steve

[LeeWay]

I do have that kind of accuracy on my shop built router now. Initially I had about .005" I think and now that I added double ball nuts, it cut that in half. My shop built mill is more accurate than that.
My router though does ride on skate bearings, but is made mostly of steel with a few thick aluminum plates thrown in. Not MDF. MDF will be part of your limiting factors. Threaded rod would be the other. You can get anti-backlash nuts for those too though, so then it really comes down to size and design.

I think if you threw just a little money at a very small machine built with these type parts, you could just get to .004" without too much trouble.

[spaltiel]

Originally Posted by stevespo Actually, the original unit conversion was incorrect (we didn't notice). .1mm = .0039" = .004" (4 thousandths of an inch, ~diameter of human hair, ~thickness of a piece of lined paper, etc) That type of accuracy can be achieved with a DIY router, but depends heavily on the components, design, care taken, etc. It's not necessarily easy or cheap. An inexpensive router can have that much runout alone. Flex in the frame, backlash, endplay, etc. You'll have to really understand all the variables involved and make sure the design has each one of them covered to reach and maintain that type of accuracy. Steve

Thanks

sorry for the mistake (accidentally I did type extra zero)

I do understand these parameters and I'll do my best to get good result.
I'll try to build the machine step by step and later I'll decide how and what to improve.

[spaltiel]

Originally Posted by LeeWay I do have that kind of accuracy on my shop built router now. Initially I had about .005" I think and now that I added double ball nuts, it cut that in half. My shop built mill is more accurate than that. My router though does ride on skate bearings, but is made mostly of steel with a few thick aluminum plates thrown in. Not MDF. MDF will be part of your limiting factors. Threaded rod would be the other. You can get anti-backlash nuts for those too though, so then it really comes down to size and design. I think if you threw just a little money at a very small machine built with these type parts, you could just get to .004" without too much trouble.

I don't understand why MDF is limiting factor.
My plan is to use aluminium L shape as rod and skate bearing as rider.
Is the MDF rigidity is the main problem? or something else?

[dertsap]

Originally Posted by stevespo Actually, the original unit conversion was incorrect (we didn't notice). .1mm = .0039" = .004" (4 thousandths of an inch, ~diameter of human hair, ~thickness of a piece of lined paper, etc) That type of accuracy can be achieved with a DIY router, but depends heavily on the components, design, care taken, etc. It's not necessarily easy or cheap. An inexpensive router can have that much runout alone. Flex in the frame, backlash, endplay, etc. You'll have to really understand all the variables involved and make sure the design has each one of them covered to reach and maintain that type of accuracy. Steve

oops
ya I agree that type of accuracy should be fairly easy to achieve with the right setup
you'd be far better off using steel angle than using aluminum angle , mainly for wear and strength