This is my Mikini 1610L CNC Mill
So while getting ready to machine a model steam loco coupling rod (http://www.sprocketandpinion.co.uk/couplingrod/) i deceided to check the runout of the spindle and test the accuracy of the machine. All looking good but while indicating the bed to check of perpendicularity i identified some play in the left and right rear X trucks. I found this by being able to lift the bed in the back left and back right corners approximately 5 thou.
Heres a video showing the movement:
The play can be seen from 00:18 into the video.
It was suspected that lack of oil had caused the bearing to wear within the trucks and a strip down was needed to replace the trucks on the X axis.
How is the mill constructed
The mikini 1610L uses standard linear rails, trucks and ball screws on the X, Y and Z axis.
Now it seems to depend on the individual machine as to which manufacturers components are being used. For my machine (serial number 61-V20-291) it uses HIWIN components throughout the machine. However my fiend Ralph from the US has a 1610L serial number 45-V20-122 uses Hiwin HGR20 rails and xyz trucks.
Did they switch from Hiwin to AMT or vise-versa?
The X axis has inverted rails mounted to the underside of the bed. These rails slide into trucks mounted upside down on the top of the saddle. The bottom of the saddle sees mounted trucks and these slide onto the rails mounted on the casting. As shown below.
In the above pic you can see the X ball screw has been removed and the bed has been slid all the way to the left ready for removal. It is important to place a plastic holder into the trucks as the linear rails are slid off, this prevents the ball bearings to fall out.
Cabinet – The dissasembly starts with the removal of the left side of the cabinet. This is held in place with 8 bolts (with nuts on the back) around the waist part and then 3 bolts on the back and 1 on the front panel. With the left side removed the X-axis can be disasssembled and the bed slid out the side.
X-Axis – Start by removing the X-axis stepper from the right side of the bed, loosen 1 grub screw in the coupling and 4 bolts hold the stepper to the ballscrew bearing block, care taken as the stepper will magnetically attract any steel chips left in the machine, so it was wrapped in brown paper.
Next remove the circlip on the left hand ball screw bearing block, use of circlip pliers here and care taken to make sure the clip doesn’t ping off the pliers and gets lost. The ball screw bearing blocks bolts are then removed, 2 on the left floating end and 4 on the right stepper end. There are pins in the bottom face bearing blocks which locate the bearing blocks onto the saddle.
Next remove the 6 bolts which hold the ballscrew nut to the block on in the center of the saddle and can be seen in the picture above.
The left bearing block will pull off the ball screw and with the bed slid to the right, the ball screw can be removed out through the right hand side of the bed and out the right hand cabinet window.
Analysis of wear
Ralphs initial suggestion that the trucks had run dry can be clearly seen in the following pictures:
These pics shows a new truck:
Below you can see the back right X-axis truck, covered in rusty coloured sludge and clearly see ball bearings are missing. The play in the plastic rail protector is very obvious when compared to the front trucks which show no sign of rust of missing ball bearings.
Pic below shows the front trucks in relatively good condition.
The pic below shows the underside of the bed, front rail, very clean and smooth.
This below pic is the back rail in constrast, it shows surface rust transferred from the damaged truck over time. I dont know yet if this rail will clean up.
Pics below show close examiation of the ball screw nut, it looks in good condition despite not recieving any obvious lubrication
The nut spins very smoothly and there appears to be now laterial play.
The top of the saddle showing X axis trucks, lubrication feeds and ball screw block.
In part 2 i will continue to disassemble the machine by removing the Y-axis ball screw and the saddle. This will allow the X-axis trucks to be replaced, followed by cleaning, inspection, re-assembly and calibration.
“I would like to thank Ralph for all the help and encouragement he has given over the past weeks. Stay safe buddy.”
“I would also like to thank B’engineer for his help removing the Bed”