First Machine design - your ideas pls

[Moondog]

Hello.

Only a recent member and I have gained so much information from reading the advice on this forum. It has given me the confidence to 'take the plunge' and build. I must thank Ynneb for getting me this far, his help has been invaluable.

I am building a CNC router, table size 3000mm * 1500mm. The main use will be to cut Marine Ply sheets.

I am not looking for the fastest machine, just some grunt...

With Ynneb's help I am choosing Reliance servos (800oz) 1750rpm and the X axis will be driven by a belt system.

When I am looking for lead srews etc I keep getting asked what pitch, what speed etc.. I don't have a clue and would appreciate this forums help for this and other things.

This is the Gantry side view of what I propose.

[Moondog]

Another pic showing the gantry design front. Please excuse the quality of the drawings. I need to get a better CAD program.

[ynneb]

Hey Moondog, could you please post the ebay link to the servos that you are going to get. I think some people here might be able to comment about them.

I too am considering buying the same servos for my next machine.
I have also recommended that he use the rutex drives for this system.

Any comments or suggestions would be appreciated.

[Moondog]

This is the link to the Reliance servos that I am looking at.

Your advice, comments etc welcomed.

http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

[Hobbiest]

Pitch on a lead screw refers to the threads per inch. Generally, pitch is refered to when talking ball screws-don't know why- and TPI when dealing with ACME, allthread, etc.

[Moondog]

Thanks Hobbiest.

My big dilema is to find out what size/thread/pitch do I need for my application. can anyone help.

thanks

[chuckknigh]

OK, look at it this way.

1/4" threaded rod has 20 threads per inch. That means you have to turn it 20 times, to move the table 1 inch.

If your steppers have 200 steps per revolution, that means to move it 1 inch, you have to supply it 20 revolutions x 200 steps/revolution = 4000 steps.

4000 steps per second is not a difficult number to reach, even for my old 486 ThinkPad notebook. That means you would be able to move your machine 1 inch every second...that's 60 inches every minute.

60ipm is not too shabby.

Just work out the numbers! To get an idea of your maximum pulse frequency, just run TurboCNC on your intended computer. It'll show you, in the first screen, the calculated number of steps you can provide, from its parallel port, per second. Then work backwards, and see what kinds of numbers you come up with.

It's not hard...just a little bit tedious.

-- Chuck Knight

[jeffs555]

This site has several calculators for figuring leadscrew sizes. http://www.nookindustries.com/acme/AcmeCalculators.cfm

The sizing depends on how long the lead screw is, how it is supported at the ends, how many rpm it needs to turn, and how much force it needs to push. You need to at least calculate the column strength which determines how much force you can push before the leadscrew bends, and also the critical speed which determines how many rpm the screw can turn before it resonates and starts whipping.

Jeff