Re: [CAD_CAM_EDM_DRO] Smallish CNC Miller

Ian Haynes <ian.c.haynes@...> wrote:
Hi Terry,

Thanks for the info. Taking all the replies together it seems that the
Bridgeport is at the top end of steppers and unless something big can be
found servos are the way to go. Thanks for the link to the surplus DC
motors, could you advise on a suitable encoder and source or at least what I
should look for in the spec?

///"US digital" makes a very good inexpensive encoder and they are great to deal with also. The Geckos require an encoder 5V with less than 50 mA current draw if you are going to power them right off the Gecko. Most encoders exceed this. However you can use an external power supply, and if you arent sure of the draw use an external supply. The best bet is just buy some new ones from USdigital they can be had for as little as $30 each. An important consideration regarding encoders is the resolution. Depending on the software you use. If you use Mach2 or Mach3, The pulse train is limited to 45k steps per second. Sounds like alot but a high res encoder will eat that up rather quickly especially driving 3 or more axies simultaneously. This also effects drive selection. The 320 is the standard drive and the 340 has a built in step multiplier to increase the number of steps to the servo. You'll need to calculate ballscrew pitch, ratios, software pulse speed, and desired rapid to really
determine the encoder resolution. I use 200 cpr's with 2.5:1 reduction, Mach2 and Gecko 320's on Bridgeports and they work great.

Ron

////



There are some encoders on Ebay and I had a
look at the specs but I don't know enough to know if they are what I need.
My plan would be to use Gecko servo drivers.

I got the Chris Bruno drawings and they are a great start.

Thanks again

Ian

----- Original Message -----
From: "Blue"
To:
Sent: Friday, April 29, 2005 12:48 AM
Subject: Re: [CAD_CAM_EDM_DRO] Smallish CNC Miller


> Hi,
>
> I'm sure there are some on this list who will disagree with me but here
are
> my thoughts as I'm also UK based and doing the same job on my Bridgeport
> clone.
>
> 1) Mach2 is a good choice
>
> 2) Forget stepper motors as those needed to move the slides on a
Bridgeport
> need to be in the order of 1400 in/oz and probably Nema 42 frames, these
are
> expensive. The ones you have indicated are not big enough. Go with Gecko
> 320's and servo motors, if you want to say some money and play at making
> them yourself buy permanant magnet DC motors and stuff an encoder on the
> ends. There has been some discussion about these :
>
>
http://www.surpluscenter.com/sort.asp?UID=2005040516484640&catname=electric&
> keyword=MBDD
>
> Item #10-1573 but I think item #10-1783 may do as well, anyway I have
> ordered the latter.
>
> The encoder could be obtained from a small surplus servo or bought new
from
> USDigital.
>
> 3) Ballscrews are availble at not too much cash, around �50 each, from
> ebay.co.uk. There is a company advertising nearly every week selling 25mm
x
> 5mm lead ballscrews of various lengths.
>
> 4) My machine does not use the combined leadscrew mounting banjo that the
> Bridgeport uses and there is no reason why you could not make the
mountings
> for the ballscrews yourself before you take your machine to pieces and you
> have access to a lathe.
>
> 5) I am planning on using the knee as the Z axis but will also ballscrew
up
> the quill. I bought some plans for doing the quill off the web but can't
> remember who from, I think it was Chris Bruno @ Sliderule Racing. It was
> only about �10 and worth the money.
>
> Regards,
>
> Terry
>
>
>
> > Hi Folks,
> >
> > Firstly thanks a lot to all the people who replied to my first post.
> > I learned a lot from the replies and a lot more from all the other
> > traffic in the group, thanks again.
> > I may regret this decision but based on the info I have gleaned I am
> > going to attempt a conversion of my Bridgeport.
> > The strategy is to firstly get hold of some software for a play.
> > Based on what I have read and seen I conclude pragmatically that
> > Mach2 looks a good choice, the manual alone is a great piece of work.
> > Step 2 is to get some servo motors working on the bench. Gecko 210s
> > seem to be a good choice for the drives but I could do with a bit of
> > guidance on stepper motors. Nema size 34 motors look like the right
> > choice for the X and Y motion (might hold off on Z until X and Y are
> > installed) but there seem to be options within this spec. I am UK
> > based so any suggestions for suitable suppliers and more specific
> > spec would be welcome. Radio Spares do motors 2.5V 4.5A with a
> > holding torque of 2200mNm (part 440-470), Mclennan have other options.
> > What do you think about a break out board between the PC and the
> > Geckos? Not strictly necessary I understand but useful?
> > With things working on the bench I plan to start work on the machine
> > conversion. I have purchased Chris Bruno's (what a helpful guy!)
> > manual which looks like a great place to start and like the idea of
> > still allowing manual operation. Conversion to ball screws seems
> > essential especially as my Bridgeport is a little tired and I am
> > following this up with a UK supplier. I have not managed to find a UK
> > supplier of a ready made conversion kit and may yet fall back on
> > Rockport assuming they are willing to ship at a sensible price.
> > So there we are, the journey has started, my data file is filling up
> > and the hunt for hardware is on.
> > Any other words from the wise would be most gratefully appreciated.
> >
> > Ian
> >
> >
> >
> >
> >
> >
> >
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> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
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subjects, that are not allowed on the CCED list.
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> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
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