On 4/21/2016 7:09 AM, Gene Heskett wrote:
> On Thursday 21 April 2016 04:04:16 Gregg Eshelman wrote:
>
>> Belt drive from the stepper? If there's enough metal in the pulley,
>> drill and tap three holes into the face then get six flanged rubber
>> bushings. Mill out a circle of metal with three holes. Put bushings in
>> holes, bolts through bushings. Screw to pulley. Hooray! A damper. :)
>>
> Chuckle.  Sounds workable Gregg, but its only a 17 tooth pulley in quite
> close proximity to the 42 toother driving the nut, so figuratively
> speaking, no room to swing that cat.  Besides its a double shaft motor,
> and it does have a spool of 1.75" fender washers with elastomer washers
> stacked about 2.25" high on the upper end of the motor shaft.  See best
> view of it at the sig's link + emc/36.html.  But thats not the same
> motor, that 252 was pulled and a 432 put in its place later.  It shows
> the whole new Z drive before it was installed on that toy.  Back up to
> about 29.html to see it installed.  Those dampers work very well, took
> the motor stall from about 9 ipm to around 34 ipm if everything is
> right. But the psu is only 28 volts, and I have a new 44 volter ready to
> go in at the same time as I put a 5i25 into that system.  Even with
> software stepping, I have carved a boat load of stuff on that little
> mill.
>
> But there is very little insulation in that building, so I only keep
> enough wintertime heat in it to keep it above the dew point so its off
> limits to this old diabetic for long enough to setup and do a job in
> cold weather.  I'll also need to round up a 5 volt wall wart to run the
> rest of the logic in that mills electronics box when I make the psu
> switch as the 28 volter has a 5 volt output its all running on now.
> I probably have a suitable one of those as I never throw out the wall
> warts even if the rest of the kit has died & been thrown out.
>
> But it looks like I'll need to chew up some 1/2" stock in the lathe,
> making anchors from the screen door springs that will do some counter
> weighting on the G0704. A 6mm Allen head cap screw with a 20mm long
> spacer, and a 1/8" deep and wide groove should make it a pull out the
> spring and drop the loop over it anchor point.  Easy to change springs
> if I should stumble over some wound from a larger wire.  These, at .052"
> are a bit lighter than I'd like, but they should help.
McMaster has a nice selection of 3' long springs of various OD's, wire 
diameters, and spring rates.  They seem reasonably priced (~$5-$10) in 
sizes likely used for this type of application - 
http://www.mcmaster.com/#extension-springs/=122u4yj.

I'm curious if anyone has compared moving mass (pulley/cable/mass) vs 
springs for counter weighting a G0704.  Other than ease of 
implementation, space requirements, etc., any real world 
advantages/disadvantages of either?  ie Z axis repeatability? Any 
thoughts on the "right" amount of counterweight?  1/2 the head weight, 
more/less?


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