Denford Starmill - how to remove spindle drive belt?

Dear all

I am in the process of refreshing my Starmill by gutting all electronics and replacing belts.

I have not been able to remove the spindle drive belt because it is trapped by the Z-Axis leadscrew as per photo below.
Attachment 20342

View from the top. for the life of me, i cannot see how this castellated nut is holding the leadscrew in since it is locked unto the leadscrew itself. I am tempted to undo the nut to see what happens but at the same time i am reluctant since it appears that this might be pre-loaded and i do not know how much the pre-load is when i reassemble it.
Attachment 20343

Appreciate your help and advise.

Kind regards
francis

You'll need to remove the castellated nut, and then knock the leadscrew downwards out of the casting. The nut is what sets the preload on the two bearings that control endfloat, whereas the bearing at the opposite end is just to provide support.

You may need to remove the column, as there may not be clearance in base casting to let the ballscrew/support bearing to drop out.

Thanks m_c for your reply. Will try that out. From the technical drawings I just downloaded, I think you are right that the ballscrews comes out from the bottom =(

This is one of those things, where the "if it's not broke, don't fix it" methodology may be very appropriate.

i would agree with you on that but my drive belt is pretty old and also i am putting in a new motor with higher hp. the starmill came with the earlier 200w motor. hoping to stuff a left over >1kw servo motor that i have sitting unused into the column. i have done trial fitting and it fits with good clearance and stuff but i would like to change the belt to a tooth belt and hope to do rigid tapping in the future. i still have multiple of these 1-1.5kw spare servos and drivers sitting around so its a case of might as well.

I have not taken to replacing the old spindle motor belt as yet. Instead I have fitted a new servo motor in place of the old motor because the old driver board died and also i want to get more power. I made a simple adapter plate to hold a Nema34 1kw servo motor in place. There is enough space to put in a 1.5kw motor if you are so inclined. The 1kw motor is shorter than the original Baldor motor so I actually gain some Z travel (the 1.5kw motor is about the same length as the original Baldor motor, so this swap will not reduce Z travel).

Since you've fitted a servo, it may be worth considering the bit extra effort and fitting a toothed belt, as that opens up the possibility of rigid tapping.

I wouldn't worry too much about reducing Z travel by fitting a longer motor, as the bigger problem is usually lack of Z height. My old Novamill, the Coventry EasyChange holder would just about hit the table before it ran out of travel. Certainly with a tool holder in, it would hit the table. If had kept it, I would of fitted a column raising block.