[chbot] CNC design

Thu Jul 7 00:48:02 BST 2011

Even better for those of you how already have some printers

http://www.romanblack.com/lini.htm


Mark

On 7/07/11 11:43, Mark Beckett 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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