Re: [CAD_CAM_EDM_DRO] Accurate spindle for light miller (was "Hiya. New to thread.")

stan wrote:

> Thanks, I'll look into using a router. The larger diameter tooling will be a
> bonus too.
> The nicest thing about the dremel was the speed control, I'll have to try and
> implement the same thing with a router. The controller needs to keep track of
> the spindle rotation position so the two should go hand in hand.
> While a router will be ideal for cutting and small drilling with the materials
> the machine is intended for it will still need something for drilling larger
> diameters. The plan here was to pilot with the high speed spindle, then
> change to an electric drill for drilling above 3mm, tapping etc.
> While that will work ok it would be nice to use something accurate for low
> spindle speeds. Any thoughts?
> cheers

Thoughts (oh, no!) on spindles:

* How much "Z" travel do you expect to need,? Remember the point of
a 1/2" bit can use up 1/4" or more!

* Router bits (or center cutting mills) may be more accurate and
require less "Z" movement, but will require a rigid spindle.

* There are inexpensive variable speed routers. Some have been used
on CNC machinery because they are cheaper than the maintenance for
high speed spindles and the costs of frequent replacement are
offset by the costs of high speed spindles and either the downtime
while the spindle is rebuilt or the costs of a spare spindle.
Spares cost as much as the first one. Cheap routers with 1 year
warranty will often run for a year and getting replacements under
warranty if they won't is often an option.

* An encoder, magnetic pickup or photocell can keep track of spindle
rotation and position. Many shafts have a keyway which makes a
good 1 pulse per turn reference.

* Hand drills are not very good as spindles, most are not rigid
enough, I have *never* seen one with an encoder on it.

* For a real spindle, a "miniature" milling head can work (like the
ones from an old Rusnock or a Seig minimill.)
* Commercial spindles are expen$ive
* Making your own DIY spindles is not as simple as you think, nor is
it as bad as it appears.
* Just the duplex bearings needed will hurt the wallet. ;-)
* Moving the motor will add much mass to the spindle, not moving a
motor is more difficult. Look at a drill press, the motor is
stationary, but the spindle drive is complex.

For a friction drive, the driving element can isolate the motor from the
spindle, but it isn't as easy as it appears.

So there you have it, it will not be cheap in any case. Finding a
disassembled minimill with a blown motor is probably the cheapest way to
go. The bigger Bridgeport style heads are way too heavy.

Homegrown spindles are pretty simple, but you need a lathe and some
engineering to do it right.

Sealed bearings (for slow speeds) are pretty cool, but for high speeds
oil mist is better, but messy and tricky to keep clean.

Ceramic bearings imply deep pockets, but if they are properly set up
they are much more long lived.

In other words, find help before trying to use a hand drill as a spindle!

--
David G. LeVine
Nashua, NH 03060



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