Re: [CAD_CAM_EDM_DRO] Re: Stepper Size Selection

Yeah, that's a bit smaller than I think Tom was thinking of. I'd say
that 250 oz-inch motors might be a little small, but 350 or 400
oz-inch motors, directly coupled, would probably be pretty reasonable.
I'd give a conservative ballpark estimate of 15-20 IPM cuts in
aluminum and 40-60 IPM rapids. Alot of your max speeds will be
determined by your top spindle speeds, which at 2200 rpm is pretty
low. For comparison, my Taig CNC mill (which is alot smaller) has a
spindle that tops out at nearly 11000 rpm, and most CNC routers have
10-20k rpm spindles. You don't need such high speeds on manual mills
because the feedrates are usually much lower.

On Sat, Jun 14, 2008 at 6:04 PM, dnaman43 <mevagissy@...> wrote:
>
>
> --- 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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>
>