Re: [CAD_CAM_EDM_DRO] DIY Router Design questions ?

----- Original Message -----
From: <rab@...>

> My first thoughts are to use bolt together aluminium extrusions with
> linear slides, leadscrews and servos, but have a lot of questions.

Aluminum extrusions (i.e. 80/20) are nice but very expensive. They are
worth the price if you don't have welding capability. Steel box tubing will
produce a better router for less money and more work.


> In gantry style systems where the gantry is driven from both sides,
> what's the best way of synchronising both the leadscrews in case the
> gantry skews ?

Les Watts built a nice router using dual X leadscrews and a jackshaft. The
cost of precision right angle gearboxes outweighed the savings of using one
motor. Friction losses were also high - on the order of 500 watts.

> Does a rack and pinion have any advantages over a leadscrew ?

R&P is definitely less expensive and less sensitive to contamination. The
other, often overlooked problem with screws is shaft whip. Long screws will
buzz like a guitar string if you spin them fast. We are having problems
with a machine in my shop that uses a 1 inch diameter 6ft ballscrew at 400
rpm. The low budget ballscrews have quite a bit of drunkenness to them and
tend to excite easily. We are designing the 10 foot router table with
rotating ballnuts to get around this problem.

I would go with R&P if I had it to do over. The X axis screws and nuts were
about $900. The custom spindles for the ballnuts will have a fabricated
cost of about $300 each.

> Is it worth looking at linear motors ?

What is your budget?

> Given that each part would need use of a roughing and a finishing
> (fine detail) tool, I'm looking at ways of mounting two router heads
> to save tool-changing, has anyone tried this ?

We looked at a Colombo high frequency spindle and a six position ATC. The
toolholders alone are $170 each. The spindle was $5000. The ATC would have
been about $5000. Porter Cable routers are $130-$290 each and dirt cheap to
rebuild. I can mount four of them on a Z axis turret for little more than
the cost of four ISO-30 toolholders alone. The Colombo can cost $500-$1000
just to rebuild.

Doug