Re: Stepper Size Selection

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet" <thom@...> wrote:

> This does not have a simple answer. Everything in the equation is
> dynamic:

Agreed ... thanks for your response. It's pointed me at the things I
need to consider.

> What kind of milling are you going to do (steel, alum, light

material?)

Steel, aluminum

> What is your leadscrew TPI and what speeds do you want to 1.) cut at;
> B.) rapid at.

Leadscrew is 10 TPI. As for speeds ... don't really have the
experience, but I'm not looking to build a super-fast, top of the line
machine. Cost is a definite consideration and I'd trade speed for that.
It's will be a purely hobby setup - not commercial - so cyle times are
not super important.

> What is the torque required to move the empty table?

The static torque I measured at the handwheels is approx 30 0z.in

> Do you have room to mount 34 frame motors? How about toothed pulleys?

Yes and Yes

> If you give more detail about your mill then others that have
> retrofitted that type or similar units can chime in. As it is it's
> difficult because the description of "large minimill" doesn't mean
> much to us.

Yeah, it was a bit vague I guess. It's just that the Sieg X2 seems to be
the most ubiquitous machine described as a "minimill" and mine is a bit
bigger. In fact it's the Weiss WMD20 show here:

http://www.weiss.com.cn/products/wmd20v.php
<http://www.weiss.com.cn/products/wmd20v.php>

> Pure guessing would have me suggest 740 to 900 oz-in motors with 1:1
> coupling BUT that only gets you within a REAL rough estimate. The
> leadscrew pitch will change the equation. If you use ballscrews the
> backlash will be less and the force to turn the leadscrew less.

As much as that eh? I was hoping for something more like 250 oz.in (but
what do I know ... that's why I'm here). For cost reasons, I wouldn't
want to convert to ballscrews at least initially.

> It most cases emphirical numbers from testing or from others that have
> tested are the only way unless you know all of the numbers down to the
> size bits and material you plan on using.

I was coming to that conclusion. Problem is my mill doesn't seem to be
all that common (which is a pity because it beats any X2 I've seen head
and shoulders for quality). It does approximate an X3 so that might be a
guide.

> Sorry but if you can post better information then you will get better

Point taken, Tom. Hopefully some of the above will help.



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