Re: RoboFac / Stewart-Gough Platform / Hexapod Milling Machine

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Simon Arthur <chroma@m...>
wrote:

> Wayne C. Gramlich wrote:
>
> >Whenever I read one of these CNC articles in a magazine,
> >the first question I ask is "How accurate is the machine?".
> >To date, the Robofac article has not discussed accuracy.
> >For the amount of money he spent building the thing, I
> >suspect he could have purchased a Sherline/Taig table top
> >unit and done a quite straight forward CNC conversion.
> >Again, it is hard to tell because he does not discuss
> >prices to any level of detail.
>
> Any suggestions for measuring accuracy?

Just tell us if the unit is holding .01", .001",
or .0001" accuracy.

By way of comparison, people regularly mill items
to .001" on Taig/Sherline.

> Does Sherline or Taig make a 5 axis machine?

Net yet. Many people who are building robots
(which is the overall thrust of Servo magazine)
will be perfectly happy with a 3-axis machine.

> I suspect my hexapod has a larger work envelope.

Both Sherline and Taig publish the work envelopes for
their machines. What are the dimensions of your
work envelope? (I didn't notice the work dimensions
published in your article.)

> I have spent less than $1000 on RoboFac. I didn't
> include a price list, as many of the parts are
> scrounged, including the controlling computer.

It makes it hard to compare prices doesn't it?

> Some of the more expensive parts that I paid for were:
> metal for the frame
> sheet metal bed
> stepper controllers
> stepper motors
> anti backlash acme nuts
> motor power supply
> router

If people are willing to scrounge a little, they
can buy a new CNC ready Sherline and probably
put to gether a fully functional system for a
similar price range -- certainly well less than
the $2000 you mention in the article.

> >I don't want to come down too hard on his work, since
> >it really is quite a challenging project. But in the
> >end, the question is whether or not he is able to build
> >useful parts or not with his creation. So far, I have
> >my doubts.
>
> It's not for everyone. I have done some useful work with RoboFac,
> including milling aluminum. Have a look at the CNCZone thread:
> http://www.cnczone.com/forums/showthread.php?t=7467&page=4

Please post some more pictures of your useful work.

-Wayne