[chbot] Stepper Motor Checking

Thu Jul 7 03:26:21 BST 2011

Your quoted excerpt makes my point: torque is measured in *ounce inches*,
not ounces per inch. Torque = force x distance, not force / distance.

Ounce(force) per inch would be a valid unit for stiffness, not for torque.

Simon.

On Thu, Jul 7, 2011 at 2:12 PM, Simon Chester <simonches at gmail.com> wrote:

> It's not incorrect: http://en.wikipedia.org/wiki/Torque#Units
>
> In British unit, "pound-force-feet" (lbf x ft), "foot-pounds-force",
>> "inch-pounds-force", "ounce-force-inches" (oz x in) are used, and other
>> non-SI units of torque includes "metre-kilograms-force". For all these
>> units, the word "force" is often left out, for example abbreviating
>> "pound-force-foot" to simply "pound-foot" (in this case, it would be
>> implicit that the "pound" is pound-force and not pound-mass).
>
>
> On Thu, Jul 7, 2011 at 12:07 PM, Simon Knopp <
> shrunken.apple.head at gmail.com> wrote:
>
>> I stopped reading the first link when I saw "...torque is usually measured
>> in ounces per inch". A whole page about measuring torque prefaced by an
>> incorrect definition. Oops.
>>
>> Simon.
>>
>>
>>
>> On Thu, Jul 7, 2011 at 11:43 AM, Mark Beckett <m.beckett at amuri.net>wrote:
>>
>>> Since there is a dgree of interest around steppers
>>> I found this while searching for something else.
>>>
>>> http://www.romanblack.com/stepper.htm
>>>
>>> I'm sure the members could improve on the glue it down approach.
>>> Also he is measuring the hold torque, which will be different to the
>>> rotating torque.
>>>
>>>
>>> For Robin
>>> He has a very interesting section on one wire
>>> http://www.romanblack.com/blacknet/blacknet.htm
>>>
>>> For those folowing the CNC he has this
>>> http://www.romanblack.com/cnc_good.htm
>>>
>>> Mark
>>>
>>>
>>> On 4/07/11 16:43, HARTLEY, ROBIN (ROBIN) wrote:
>>> > Hi,
>>> > I've looked at the trim routers and initially disregarded them as they
>>> are 1/4 chuck, rather than 1/8, and a lot heavier than a dermal.
>>> >
>>> > After destroying 2 home made spindles, 1 after 10 hours work cutting
>>> ali which I think was an air flow issue&  the next after 20 minutes because
>>> it was a cheap armature, I may well look at the trim routers again.
>>> >
>>> > The extra weight puts higher demands on the Z axis, which in my case is
>>> where I found out all about some uni-polar steppers not liking bi-polar
>>> drive with PWM.
>>> >
>>> > Due to my design I'm a bit limited on space&  I got another stepper but
>>> it has the same problem.
>>> >
>>> > There was a comment in this thread about speed control, here's my
>>> experience.
>>> > Most of these home made machines are routers rather than mills&  so cut
>>> with a very fine feed so you only need enough speed rather than managing a
>>> speed feed relationship of a mill where it produces chips.
>>> >
>>> > My approach is to do a test piece run and adjust the depth of cut to
>>> keep chatter under control, almost impossible with a plastic cased dermal.
>>> > I then ramp the speed up until I here the spindle start to load
>>> significantly, I can hear the speed drop, then set my G code to run up to
>>> about 50% of that feed rate.
>>> >
>>> >
>>> > With a home made spindle, which is basically a cheap dermal knock off
>>>  removed from it's case and ali blocks for bearing mounts, I can cut 2mm
>>> deep at about 150mm/minute feed.
>>> >
>>> > The secret to cutting ali is to keep it flooded with coolant. In my
>>> case I use lots of CRC. I basically stand there with a spray can&  keep the
>>> grove full of CRC.
>>> >
>>> >
>>> > For any one building a machine alignment of the feed screws is the
>>> biggest issue. What worked for me is to mount a bearing on the lead screw on
>>> the opposite end from the motor&  clamp the lead screw against for/aft
>>> movement and at the motor end I use a piece of rubber fuel line as a
>>> coupler. The modern reinforced fuel injection line has a lot of reinforcing
>>> that prevents twist.
>>> > For lead screws I use 8mm threaded rod, 1.25mm per turn,&  for the nuts
>>> I use a piece of plastic chopping board.
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>> > Regards,
>>> > Robin
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>> > -----Original Message-----
>>> > From: chchrobotics-bounces at lists.linuxnut.co.nz [mailto:
>>> chchrobotics-bounces at lists.linuxnut.co.nz] On Behalf Of Chris Hellyar
>>> > Sent: Saturday, 2 July 2011 11:03 a.m.
>>> > To: Christchurch Robotics
>>> > Subject: Re: [chbot] building CNC router - was Free stepper motors
>>> >
>>> > 'Urro...
>>> >
>>> > Given a dremel new is $120-150 ish...
>>> >
>>> > Trim routers like these:
>>> >
>>> >
>>> http://www.powertoolshop.co.nz/product_info.php/cPath/20_96/products_id/20
>>> >
>>> > For $119 with a full alloy body are a better bet.
>>> >
>>> > As I see it, it's cylindrical so it's easier to mount, no speed control
>>> > inbuilt so you can use a closed loop speed control on it for better
>>> > cutting in soft stuff.  It'll also have higher rotor inertia and a
>>> > better quality chuck.
>>> >
>>> > There are a few on the market.  When I last looked there were a few
>>> > options on the shelf at Bunnings/Mitre10 that looked good.
>>> >
>>> > I was specifically thinking dremel replacements for wood/plastic/alloy
>>> > cutting.  If you're looking for dedicated spindle ebay is probably your
>>> > friend..
>>> >
>>> > And, having said all that, my next project is going to be swinging a
>>> > water cooled VFD spindle.  I am sooooo over the noise of brushed
>>> routers!!!
>>> >
>>> > Cheers, Me.
>>> >
>>> > On 02/07/11 10:17, Volker Kuhlmann wrote:
>>> >> On Sat 02 Jul 2011 02:06:20 NZST +1200, Chris Hellyar wrote:
>>> >>
>>> >>> There are some very reasonably priced options rather than sticking
>>> with
>>> >>> a dremel.
>>> >> Can you elaborate?
>>> >> And are these options for a dremel replacement or a CNC spindle?
>>> >>
>>> >> Thanks,
>>> >>
>>> >> Volker
>>> >>
>>> >
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>>
>>
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>
>
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