Hi all,

It's about time I got out of the dark ages when it comes to drilling my boards and I wish to build a CNC machine. While I understand how the drill info is sent to the machine which steps motors to get to the right place I am unsure about which motor to go.

Just about in every project I have seen the large square stepper motors but I saw these:
http://www.ebay.co.uk/itm/5X-Steppe...al_Components_Supplies_ET&hash=item4181122453

Are these acceptable for a small light weight machine? I know that torque might be an issue which is why I would make the axis and table as light weight as possible. Could these be used?

All the best,
Robin

 

I wouldn't they will be slower than molasses and probably not have allot of torque.

 

To reduce friction and backlash you are probably going to need the ball type lead screws which are fairly expensive. I understand the desire to build rather than buy but you may be better off starting with one of those cheap CNC "engraving" machines off ebay which has all the mechanics fabricated for you.

 

Second sirch, unless you have access to a machine shop you'll never build one cheaper or as good as the ones pre-made. Doubt if you can even get the materials for the price of one of the finished ones that will work right out of the box.

If you do decide to build one, go with at least a NEMA 23 size. For just a drill a single stack would be OK, but for any milling a double stack would be better.

 

No matter which stepper you choose to use for your project, you're going to need to "close the loop"
I've been working with steppers for 25 years now, and I can tell you that they're VERY prone to miss steps when used for production purposes. You would need to program your controller to reset the machine's axis position very often if you don't want the steppers to start "drifting" over time, possibly ruining valuable pieces you've been working on.
I strongly suggest you consider adding encoders to your design, or get these steppers from Oriental Motors... they're quite expensive, but I've been using them for almost 15 years now and I can tell you they're a slice of heaven... almost as good, if not better, than most servos with the same power rating, and less expensive too.

 

Most of the hobby'ist CNC crowd use steppers because of price, servo's are a superior way to go, but usually a little more tuning involved as well as the cost.
You may want to check out the dedicated site to CNC hobby at CNCzone.com.
I went into the CNC business from the commercial systems and servo's end, so I am biased in favour of the servo, I did have a short flirtation with steppers but was disillusioned with the comparison in performance, so we mutually parted ways, but there are many out there that are using them successfully.
http://www.cnczone.com/forums/index.php
Max.

 

This is an old problem that has already been solved, and stepper motors are not likely to be part of the solution. If you want a CNC machine to do production work, then get a CNC machine to do production work. Ask yourself what is the best use of your time. You will spend years on the learning curve of building your own machine.

 

This is an old problem that has already been solved, and stepper motors are not likely to be part of the solution. If you want a CNC machine to do production work, then get a CNC machine to do production work. Ask yourself what is the best use of your time. You will spend years on the learning curve of building your own machine.

Right... but in my case I already spent 25 years doing just that... ha ha ha...

But I'll grant you this:

• The software I developed is not capable of continuous contouring
• It really only works in 2-1/2 axis
• It can work in up to 4 axis, but cannot do tool offset calculations

On the other hand:

• One of my machines has been working nonstop for 20 years now, with no major repairs needed
• I have complete control of spare parts, cabling, connectors and circuitry
• Some parts requiring special processing can far more easily be made in a specially designed machine

But as you say, the truth is, that if you're not planning on making a living with this sort of work, then yes, it's probably much better to simply buy a commercially available.

 

that if you're not planning on making a living with this sort of work, then yes, it's probably much better to simply buy a commercially available.

There is also a few kits around and ready built aimed at the home shop rather than for Industrial use.
Max.

 

When I built mine, I used NEMA 23. Homemade L297 and L298 controller. LinuxCNC.

 

sorry for my bad grammar... I intended to end that last sentence as "... a commercially available machine"
English is my second language, and although I do proof-reading and try to polish my phrases before posting, every once in a while either an orthographical error or a small diction no-no slips through...

 

sorry for my bad grammar... I intended to end that last sentence as "... a commercially available machine"
...

Known as 'implied but not stated'
Max.

 

For a small PCB drilling/milling machine NEMA 17 steppers would be fine and the minimum I'd recommend.

And you can easily build one for less than the cost of most "commercial/ebay units".. Just takes a bit of creativity but there are plenty of designs out there that require little to no machining.

And steppers work just fine for a CNC machine like this. The only time you start missing steps,etc... is when you push the steppers beyond their limits or they are under powered. When used properly you can have very good repeatability assuming good mechanical design/low backlash,etc...

 

For a small PCB drilling/milling machine NEMA 17 steppers would be fine and the minimum I'd recommend.

And you can easily build one for less than the cost of most "commercial/ebay units".. Just takes a bit of creativity but there are plenty of designs out there that require little to no machining.

And steppers work just fine for a CNC machine like this. The only time you start missing steps,etc... is when you push the steppers beyond their limits or they are under powered. When used properly you can have very good repeatability assuming good mechanical design/low backlash,etc...

I hadn't payed close attention to what the OP said he wanted in the first place, which was drilling his boards... somehow the word routing slipped into my mind, I don't know why... So yes, I'm going to agree with you in everything you've just said. My only advice then would be for the OP to consider the value of his own time when designing, programing and assembling his own machine, unless he's also doing it for the fun of it, of course.