Re: rotary hand encoder wheels with detent

Hi Fred,

I've been trying these step sizes, too many?

0.200
0.100
0.050
0.020
0.010
0.005
0.002
0.001
0.0005
0.00025
0.000125

Although the Sherline and stepper motion hardware isn't accurate to the
smallest step size, it seems necessary if one wants to creep up to a
surface, to set a zero on a part.
Too many choices? I "rotate" through them with a push of a PB, or as a
menu, with the cursor keys. This list is used by both the pendant and
"cursor key" jogging (pendant and keyboard jog are NOT available at the
same time).

Currently I am playing with a 256 cpr encoder, because that's what I had
on hand. A Sherline knob pressed into service has 50 divisions, so I'm
thinking that might be a good choice. Now to work in the detents! I
have a "DigiKey" 24 cpr encoder (read by a PIC) on a "radio" project, it
has detents, but there is a fair amount of drag on it, doesn't spin, and
is not as nice as the 256 count encoder. More experimenting required!

Alan KM6VV


imserv1 wrote:

>
> --- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...> wrote:
> > Hi Fred,
> >
> > How about a 1, 2, 5 progression of jog increments?
>
> The jog increments are usually called out in relation to the smallest
> resolution that you would normally use in a program and which you
> could reasonable expect the machine to move. I have not mentioned
> any less than .001 because I am skeptical that home hobby machines
> are much better than that. .0005 maybe on a Bridgeport machine in
> very good condition, .0001-.0002 is very rare in a home made machine.
>
> If you think in terms of your intended movement it is easier to
> decide what values to shoot for. In my opinion, even though it is
> common on commercial machines, I don't think that 100 detents is
> needed. Most of the benefits of a pulse wheel can be had with a 10
> or 20 pulse per rev mechanism. You want .001 increments so 10 or 20
> times .001 is .010 or .020 per revolution. .01 increment is .1 or .2
> and .1 is 10 or 20. .1 is probably too coarse with only 10 or 20
> pulses and certainly is too much with a 100 pulse wheel and a 5 inch
> Y axis.
>
> This leaves you with resolutions of .001 and .01 which will probably
> give you 75-85% of the benefit of a 100 pulse wheel at 1/4 the cost.
>
> If you used an encoder like Sphero's you could use the push button to
> toggle off and on, or off, .001,.01, and just add a push button or 3
> or 4 position switch for the axis selection.
>
> > And what is a Vlier?
>
> A Vlier Pin is a set screw with a spring loaded plunger for a tip.
> The pressure can be adjusted by turning the screw. Hence a
> mechanical control for the feel of the detents. Since the plunger
> has a spherical radius(usually a steel ball), you can use a drill tip
> to make small dimples that work very nicely with a Vlier pin.
>
> http://www.vlier.com
>
> These are used in fixture design and building. They are carried by
> all the major industrial suppliers like MSC, J&L, and also by the
> fixture people like Reid Tool and Carr Lane.
>
> Since Reid gave me a catalog back in the 70's when I was an
> apprentice and since I still think they have some of the best gadgets
> in their catalogs: http://www.reidtool.com/pdf/188.pdf
>
> They cost $3-$4 each. Well worth not having to make a detent youself.
>
> Best Regards,
>
> Fred Smith
> IMService