Counterweight planning

Page to collect notes and references for the head counterweight system. The head weighs around 100Kg, which translates to a lot of permanent down-force that the Z axis will have to contend with. A bigger motor is the easy way around this, but there is also the issue of wear on the screw. I am looking at this now so that I can plan ahead while I make the last mounting plate for the top of the column.

Thomas Powell's solution using gas springs and garage door pulleys.





http://imageevent.com/tppjr/mill/rf45dovetailmill/zaxiscounterweight?p=0&w=1&z=2&c=4&m=-1&s=0&y=1&b=10&l=5

The machinetoolswarehouse cnc version of the RF45 which doubles as a training machine for body building ;-).   Its actually pretty serious: Hiwin linear slides, servos, better spindle bearings, VFD 3phase motor etc. All this can be yours for ~$12k... ...which is why I'm doing this the hard way!




I'm not completely convinced by the garage door pulleys, but the gas springs seem more elegant to me. So chain and sprockets plus gas springs it shall be.

Mcmaster idler sprocket:

35

3/8"

20

0.640"

2.59"

0.72"

__

6663K23

21.95

Above drawing doesn't show the Pitch Diameter. List of said measurements:

http://ablproducts.com/35-chain-sprocket.html

Update 2012 9 26

The counterweight project can no longer wait! I installed the Z axis with the column on the work bench to make things easier; way more pleasant than perching on top of a ladder. As soon as I was done I put the column back on the base and the head back on the column. As I was letting the tension off the chain block I discovered that the head will now turn the screw under its own weight - so without power the stepper the head will crash into the table!

Couple of 3/8" threaded stainless studs with flats and holes for #35 chain connectors.

As a temporary fix to get up and running I threw together a couple of pieces of plywood and some sprockets with 1/2" bolts and rod for axles.

The trouble is that I don't have anything heavy enough in a convenient form factor to act as a counterweight. The bucket-o-scraps just isn't going to cut it!