Re: [CAD_CAM_EDM_DRO] small spindle ?

On 05/02/2012 07:10 AM, turbulatordude wrote:

> I would like a spindle like a Dremel Flex shaft, alas, a friend burnt through half a dozen over a year. was he just unlucky ? is there a problem cooling or should he have oiled the bearings ?

Probably one of the worst choices possible! Dremel flex tools do not
work well in continuous use. While I don't know, but MAYBE something
like a Foredom TXH
<http://www.ottofrei.com/store/product.php?productid=19414> (over $400
list) might work acceptably.

> This will be for a very light duty machine. weight is an issue, I do not want to use anything as big and bulky as a dremel. and I would prefer to not make one.

Consider that the spindle is critical to operation. A flex shaft (like
a Dremel) has excessive end play and can give poor results.

> that is what I would like... now the reality has to come in. any suggestions ?

Yup, make one with a small motor which is light enough and plan to
replace motors regularly. You will need a small fraction of an HP, say
120 Watts, and a 24 Volt 5 Amp motor is either small or long lived.
Weight, size, cost or life, you usually get one or two of four.

An aircraft "outrunner" or "inrunner" motor with a controller may better
fit your needs, but you are getting into the expensive range. These
motors can run from $10 to over $100 based on HP ratings, etc., some run
into the 2,700 Watt (over 3 HP) range. A compatible controller will
cost $10 to over $200! However a microprocessor controllable, 32 Volt,
80 Ampere (continuous!) motor controller is not a trivial part.

Look at any 3 HP VFD to get an idea of the comparable prices.

Let's assume 120 Watts and a 12 Volt, 10 Amp controller with a 10 Amp
continuous motor. That will cost on the order of $20 for the controller
and $20 for the motor (an inrunner in this case.) Add cooling (they get
hot!) and a home made spindle with a 5200-ZZ bearing (about $10) on the
nose and a 6200-ZZ bearing on the tail end (about $1) in a hunk of DOM
(see
http://www.speedymetals.com/ps-3457-204-1-516-od-x-120-wall-dom-steel-tube.aspx
for an example.) Put a belt drive from a sewing machine on it, a fan
blade set for cooling (or use a muffin fan) and you are all set. All
you need is a means of retaining the bearings and a shaft with a hole
machined in the end and cross slit, use a one piece split collar
<http://www.amazon.com/dp/B000IL8328/ref=biss_dp_t_asn> to clamp the
bit. Note that the shaft will be metric at this point, that is why the
10mm collar. DO NOT USE A SET SCREW COLLAR! It will seriously
unbalance the shaft!

Since we are all seriously unbalanced already, adding more would just be
silly. :-P Be sure the spindle is well balanced or it will vibrate the
machine to death in a hurry.

> the machine is going to be made of 1/2 inch plastics. I got am getting a lot of scrap that I can put to use.
>
>
>
> Dave

Sounds like a great project. Good luck.

Dave 8{)

--
/"Political Correctness is a doctrine, fostered by a delusional,
illogical minority and rabidly promoted by an unscrupulous mainstream
media, which holds forth the proposition that it is entirely possible to
pick up a turd by the clean end."/
(quoted from http://www.wattflyer.com/forums/showthread.php?t=30060)

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