Re: [CAD_CAM_EDM_DRO] re:worm drive -> rack and pinion

Ballendo;
the all thread rod with the normal gear bit wont work very well ,the gear will touch
only on two points at the rod also to find a gear to mesh with the available threaded
rod will be almost impossible pcd, no of teeth modul etc., the worm wheel made with
the tap will work as the tap has the same pitch as the threaded rod,I know it
as I have used some system.,just few months ago I suggested this same
setup on this list regarding a large plasma cutter
regards
mariano


ballendo@... wrote:

> Lawrence,
>
> Interesting thought. And the quick/slow (responding post) is
> something I'll remember for later...
>
> Now, as to your question:
>
> Many things CAN work, but compared to what?
>
> I'm understanding "ready rod" to be what I would call "allthread".
> (standard hardware store threaded rod).
>
> If so, the gain from this technique will be the cost difference of
> ready rod vs. rack. Also, Rod may be easier to "mount", esp. in short
> lengths (just "stretch" it between two holes appropriately
> positioned). However, this will be offset by:
>
> 1)The time to make the "pinions".
>
> 2)The fact that worm gears are not designed to be rack/pinion. This
> means the thread form (vee) will not carry anywhere near the load of
> the acme rack, and the alignment between "worm" (pinion) and "gear"
> (ready rod) will need to be MUCH more precise than std. 20 degree
> pressure angle rack/pinion. And Loads will tend to "push apart" the
> two pretty easily since the angle involved is 30 degrees.
>
> (It's worth noting here that if you are designing a rack/pinion
> machine, alignment(to eliminate backlash) will be helped by using the
> older standard of 14.5 degree rack/gear)
>
> 3) The poor quality of most ready rod threads. Pitch variations/ bad
> plating/ etc. (there's a REASON these things are cheap!
>
> So, with the multitude of other options (rack/pinion, leadscrews,
> belts, chains, cables, etc) you have available, I'd let this one sit,
> unless you are looking for the fast/slow of that other post. Even
> then, I'd think hard first. For the reasons laid out above.
>
> On the other hand, if "ready rod" was acme threads... and I used
> an "acme" gear (no real need to have the "worm style wrap-around"
> threads, but you COULD) this would, IMO, be worth looking into. What
> is the cost difference between acme "threaded rod" and "Rack"???
>
> Hope this helps.
>
> Ballendo
>
> >I was wondering if anyone has tried making smaller diameter wheels
> >that could be used as a pinion running on a threaded rod "rack". I
> >am thinking of something in 1" pd wheel that would mesh with a 5/8"
> >piece of ready rod...
> >Lawrence Glaister
>
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