The chuck for the spindle uses a tapered fit. As such, it can fall out as has happened to me twice already.

I was cutting a sheet of Balsa when the chuck decided to let go. Fortunately, I was watching and my hand was within a few inches of the ESTOP kill switch. I got it stopped before it did more damage.

This is a very good reason why you should NEVER leave you CNC machine unattended while cutting!

I guess I did not put it back in tightly enough after the first time it came out. I hope there will be no more repeat episodes like this one... I unscrewed the flex shaft and sandwiched the chuck and its housing between a couple of 1/2" sockets and rapped it pretty hard with a hammer this time. I used the sockets to keep from damaging the chuck or the bearings. Attached files

 

I used a sheet of 1/2" foam, but you could use FFF just as well. The half inch stuff is very soft and the balsa sticks to it very well and does not slip.

This was not a problem per se on my MK1.5 because it did not have the spring tension that this machine has.

I was able to move balsa with the top rollers down, but it pressed the balsa into the rollers so hard that the balsa got indentations all over it from the non-skid material, hence the reason for putting a carrier under it.

 

try putting a dab of loctite on the tapered section, that should hold it once you press it in good.

 

Excellent idea!