[Kammo1]

Hi all, just would like to ask a few questions before I start my journey into the world of CNC. I would like to build a moving gantry style router and so far have the electrics sorted it will be the Xylotex 3 axis package and linear motion will be skate bearing and pipe design.
The thing that is puzzling me at the moment are leadscrews and what to use I have heard of allthread,acme and even trapezoidal but what do I go for ?, I remember Joe saying he used threaded rod that fitted into a skate bearing which acted like a thrust bearing at the end of the leadscrews but what size. Also I would like to keep the cost reasonable with the leadscrews so cheap isn't always going to be the best. Also I live here in the UK so any fellow Brits that would like to share any links I would greatly appreciate, many thanks to this wonderful forum and the wealth of knowledge is immense.

[chuckknigh]

The hole in the middle of skate bearings is 8mm. An 8mm threaded rod will fit it perfectly.

Converting to Imperial measurements, 8mm is .3149" which is very close to .3125". 5/16" threaded rod. No, it's not a *perfect* fit, but it's close enough. And, you can shim it to perfect size by filling in the gap with something like wire, if desired.

-- Chuck Knight

[Kammo1]

Thanks Chuckknigh for the reply, that seems to make sense and now I can see the wood for the trees I knew it was something like this but couldn't narrow it down. My actual cutting area is going to be 30 inches X 16 inches and the Z axis will have a clearance from the deck to router tip of about 3 inches, would the 8mm or 5/16th threaded rod be adequate for this size router table or should I go with something larger and have the end turned down to fit the bearing ? Also if I use the 8mm threaded rod what speed can I expect safely with the Xylotex driver and power supply. Sorry if it seems like a million and one questions but I would like to plan ahead and make as few mistakes as possible.

[andy_ck87028]

I believe acme and trapezoidal are imperial and metric equivalent of the same product respectively.

Andy

[chuckknigh]

I'm in the US, so I think in Imperial measurements. 5/16" rod is usually 18 threads per inch. That means that you have to turn the leadscrew 18 times, to move your carriage 1 inch.

30 inches in your longest axis -- to jog (high speed, no load) from one end to the other, you'd need 30 inches per minute, assuming 1 minute is "fast enough" for you. That translates into 540 rotations of the screw...540 rpm. 9 rotations per second.

That's pretty fast rotation for a stepper motor.

If 2 minutes from end to end is sufficient, it'd be 270 rpm...4.5 rotations per second. That's more reasonable.

-- Chuck Knight

[Kammo1]

Chucknigh and andy,many thanks for your replies they are greatly appreciated.You guys sure know your stuff about CNC and it is nice to know you share your knowledge with us "NOOBS!!! he,he. I think for my first machine I am going to go with the 8mm threaded rod as it is available everywhere and once I have gained the knowledge and understanding of how CNC stuff works I can upgrade to better leadscrews but then again if it works fine weel I'll leave it alone.
Another question if I may, once the machine is built and electrics are ready to go what software can you recommend that is easy to use and to get started on straight away ?? Also how does the software recognise what leadscrews I have and for it to move exactly where I want it to and at the right distances say to cut a 4 inch X 4 inch square with 8mm rod or 1/2 10 acme?

[paulC]

TurboCNC or MACH2/3. Both are available for evaluation.
TurboCNC will work on any old PC.
Mach needs a higher spec machine but I would recommend it as the better product.
Configuration is simply a bit of math. You basically give it steps per mm or steps per inch.
Paul

[Kammo1]

TurboCNC or MACH2/3. Both are available for evaluation.
TurboCNC will work on any old PC.
Mach needs a higher spec machine but I would recommend it as the better product.
Configuration is simply a bit of math. You basically give it steps per mm or steps per inch.
Paul

I pressume you do this in the software ???

[paulC]

Yes.
Both have very good documentation so recommend you start by downloading this and reading.
http://www.artofcnc.ca/
http://www.dakeng.com/