Re: [CAD_CAM_EDM_DRO] Leadscrews, PCB router experiment

Alan Marconett KM6VV wrote:

> Hi to the list,
>
> I have a pair of nice lead screws, with a fancy (recirculating?) nut. I
> have posted two pix, if anyone can help identify the manufacturer.
> These are smaller files! I promise!
>
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/SherlineCNC/AcmeLSnut2A.jpg
>
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/SherlineCNC/AcmeLeadScrew2A.jpg
>
> The leadscrew is ACME (the square thread), about 460 mm of 12 mm dia
> ACME thread, with a 10 mm dia surface (place for bearing?) on one end,
> and a 5 mm journal (?) on the other. The "nut" is about 38 mm long, and
> the brass flange is about 46 mm in dia. There are 10 threads in 30.0xx
> mm, or about 3 mm per thread. I don't want to take it apart, as it
> seems to be will adjusted, with zero backlash. Anyone recoginze it?

If it is "recirculating" that implies a ballscrew. If it has no backlash, then it
is almost certainly a ballscrew. Although there is a way to grind ballscrews
that looks much like an Acme thread, most have threads with rounded
bottoms. 3 mm lead is pretty common in the metric threads.

>
> Also posted is a PCB router table project, in which I used a similar
> pair of lead screws, coarser pitch. Uses 15 deg motors (24 steps), and
> 9:1 timing belt drive reduction. I intend to change these to direct
> drive, NEMA #23 motors, 200 steps, half/step drive. The X over Y is not
> what I really want, so I'm thinking of re-doing the whole thing, make it
> a "bridge" construction. The Z axis drive assembly I intend to use
> (well, I don't really know what it was) to hold a dremel tool.
>
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/SherlineCNC/Router7A.jpg
>
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/SherlineCNC/ZaxisDrive2.jpg

Yes, the mechanism you show probably does not have enough stiffness
for PCB drilling.

You ought to see an Excellon to see what the "Pros" think is necessary!
an 8" thick, 5' x 5' granite surface plate as the base, sitting two on granite
legs over a ton each, with a granite beam over the top with the drilling
heads mounted to it. The table floats on air bearings, with the X axis
a big granite beam glued to the table, and a second granite beam attached
to a slider riding the first beam for the Y axis. These machines can drill
.013" (.33 mm) holes all day.

So, in comparison, a few steel rods doesn't seem anywhere near stiff enough.
A gantry has to be stiffer than a stack of two axes of similar construction.

Jon