Re: DRO

Art,

I didn't find any of those bearings at the goldmine. What
do you use them for--are they holding the idler pulleys in
your setup? If this is the case I guess the dimensions are
not critical, and another bearing would do just as well. Or
am I missing something?

"A. G. Eckstein" wrote:

>
> From: "A. G. Eckstein" <axtein@...>
>
> Joe,
>
> Lets start from the botto, I also felt the same way when I started this
> project. However I am using a "cable" that appears to be plastic coated
> multi-strand wire. It is the stuff that is used on a parrallel bar for a
> drafting table. Its tough and so far, does not appear to be slipping.
>
> Check the diameter of the shafts on you encoders as mine were advertised at
> 3/16", but are actually 5mm. Makes a big difference when you order the
> drill rod for the shaft and try to stuff it in the hole???
>
> So far, on the two axis that I set up using this with the 5mm shafts (no
> diameter reduction), I am getting a consistant 0.000177" resolution for my
> units to count by. On the z axis, I am attempting to grouve the shaft to
> reduce the diameter so I can get that magical 0.0001 resolution; but will
> settle for 0.000125. I am afraid of the slippage problem at such small
> diameters along with the possibility of bending the shaft due to tension of
> the cable. It appears we are talking physical diameter of the shaft in the
> bottom of the grouve on the order of 0.0988" ! But I had to buy a 3'
> length of drill rod so I guess I can afford to try as I don't see any
> additional projects in the near future that will use 5mm rod for anything
> and I use only about 2 1/4" of rod per set of axels.If I start having
> problems with this type of wire, may try some of the heavier guitar strings
> (don't ask what note, I ain't no musician;_) )as it appears these have a
> circular wrap around a central core thus giving the effect of a "tire
> track" which would be parallel to the axis of the shaft rather than the
> strands that are perpendicular to the the shaft.
>
> Hey, I'm just a country redneck that is doing this for fun and the fact
> that the numbers on the computer screen are eaiser to read than the ones on
> the dial and I have trouble trying to read a scale even with a loupe! So
> even if I am off a thou or so, that is still at least 20-30 times more
> accurate than I can do with a scale and a scribe!!!!!
>
> All fun aside, I want it to be as accurate a I can make it. Considering
> what I am starting with:
>
> 1 An oriental mill/drill which we all know has its problems in the accuracy
> department.
> 2 Acme thread screws that have a ton of backlash in them.
>
> Yes, I desire positional absolute accuracy, but more often than not a
> higher desire is to have relative accuracy. For instance, if I want to
> mount a motor with a bolt circle fastening pattern, I want the central
> mounting hole and the bolt holes to be really accurate. If it is off-center
> of the plate I am machining by .050, big deal. In the case of the blocks
> being machined for the DRO project, it is important to have consistant
> accuracy between the bearing hole and the mounting holes etc. Exactly how
> far from the edge of the block is of minor importance.
>
> Another point on the encoders; when I ordered the encoders, I also got some
> bearings they had advertised. Well, I ordered 10 and destroyed one of the
> motors in trying to see how everything was put together. Got down to the Z
> axis, and needed another bearing...Had run out of the loose bearings so I
> went to dig the one out of the encoder end of the motor I destroyed. It has
> a different OD than the one in the nose of the motor which was the same
> size as the loose ones that I ordered. So If you are planning on useing
> those bearings, please be aware of this small problem.
>
> Art
>
> At 09:08 PM 02/23/2000 -0800, you wrote:
> >From: Joe Landau <jrlandau@...>
> >
> >Art,
> >
> >I am starting to build a DRO for my mill--have bought motors
> >and encoders from Goldmine, and am planning the setup. I'm
> >curious how your wire loop worked out, --what path did you
> >use, and what kind of wire. I remember reading that Steve
> >was worried about slippage. Have you experienced any, and
> >how have you prevented it?
> >
> >Intuitively, I'd think a steel wire on a very small steel
> >shaft could slip very easily.
> >
> >--Joe Landau
>
> OLDER THAN DIRT
>
> Country Bubba
>
> (Actually the inventor of Country and Bubba)
>
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