Re: [CAD_CAM_EDM_DRO] "metric" ballscrews? , and other misc. was Re: Pulse Gen

600 IPM is obtainable even using the "artificial limits". The secret lies
is in the mechanics, not the electronics.
Start with a faster pitch lead screw and work from there.

Smoke

-----Original Message-----
From: ballendo@... <ballendo@...>
To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
Date: Wednesday, December 06, 2000 9:24 PM
Subject: [CAD_CAM_EDM_DRO] "metric" ballscrews? , and other misc. was Re:
Pulse Gen

>Alan wrote:
><snip> and a few pairs of what I think are 8tpi. x 3/8". I think
>>they may possibly be metric, as the shaft end was not a simple
>>English dimension, and some of the 3/16" (?!) hardware associated >
>>with them turned out to be metric!
>
>Alan, Keep in mind that MOST bearings are metric, so the leadscrew
>ends would be sized to fit. Also that a lot of "motion control stuff
>comes from Germany, Italy, and other European countries, accounting
>for the hardware.
>
>8tpi is .125; 3mm is .118, which is 8.46tpi. I'd guess its 8tpi
>imperial!
>
>>200 IPM! In my current mindset, 20 IPM is fast!
>
>And the signmakers, plastic fabricators and woodworkers would like to
>see 600ipm rapids! This is one problem with CncPRO.
>It places "artificial" limits on the top speed attainable. It seems
>to change its' "opinion" of "top speed" based on order of entry of
>parameters; or something! It's very frustrating to KNOW the machine,
>computer, and drives can go faster; others have said CncPRO will put
>out 20K steps/sec, but because of something internal to the program,
>it "decides" on a ridiculously low top speed... Doug???
>
>>What steps/in should I be shooting for? And what's realistic?
>
>5tpi,400spr(1/2 step)or 5tpi,200spr(fullstep) 2:1 ratio, is/was an
>industry standard; so 2000 spi (.0005 increment) will cover a lot of
>older machines.
>
>You want your SPI to be DOUBLE your smallest expected accuracy need,
>as a minimum. So the drive setup in the paragraph above should be
>good for a plus or minus .001 system. Four times smallest expected
>increment will suffice for MOST systems. In reality, as long as all
>parts of the system can handle it, more is better.
>
>A fun exercise is to draw some circles, lines, and arbitrary shapes
>on graph paper. Now using ONLY the "points" where the lines cross,
>duplicate the shapes you just drew as nearly as possible. This IS
>what the CNC control is doing! You may find that a "circle" is an
>octogon! Or even a square! When you then realise that each square is
>one "step", or "least increment", you start to see the CNC thing a
>little differently, IMO. Try a VERY shallow taper! or "mill" a 9/32
>hole with a 1/4 inch endmill...
>
>The real limit to this has been the programming side of things. Until
>recently, 16 bit long integers were the best compromise of size/speed.
>Since 2 to the 16th power is 65536, with a 2000 spi system, you ran
>out of travel at about 32 inches of axis travel. The new "magic
>number is 2^32 or about 4.3 billion. If we start in the "middle" of
>this number to allow for positive and negative travel, we have about
>2.14 billion "steps" available.
>
>So, take your desired travel and multiply by your desired spi, and
>you'll see what sort of calcs the computer is going to need to do.
>Next look at your desired top speed "times" your spi, divide by 60
>and you'll see how many steps/second you need from the pulse train.
>
>Find the "balancing point" between the two equations (based on your
>system and programming needs/capabilities) and you'll have your
>answer to how many steps per inch "should" I have...
>
>Hope this helps. Keep in mind it's just one persons' thoughts. As in
>most CNC issues, there are many paths to fulfillment...
>
>Ballendo
>
>
>
>
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