Thursday, February 9, 2012

Bearing Thrust Collar for Y Axis - Rectification

I was given 3 days medical leave from yesterday to Friday and decided to stay a day more at home to nurse the swell.  But I will return to office on Friday to clear my work; I've a client coming by tomorrow noon to sign our offer.  Come to think about it, unless its school holiday, I rather be at work.  Its strange, I know, but... got to learn how to let go.

Anyway, spent some time in the morning trying to find ways to rectify the error in my calculations.  I was looking at Graham's drawings on the Z axis mod and saw that the mounting holes he is using were slotted to allow adjustments.  So I went back to my 3D CAD file and put on the slots to derive the locations and the amount of material I need to removed.

The part was put back in the vise and tapped down.
After clocking the part to find the centre of the bore and edge from the flat surface, I dialed to the new hole location and start off with the bigger slot mill to cut the counterbore.
Lots of chatter during the cut. I was feeding the tool very slowly to form the slots after milling to 6mm deep. The 5mm slot mill was used next to mill the through holes.
Slot done - the ugliest around...
From another view.
I tap the mounting hole deeper to avoid having to shorten the #8-32 capscrews, taking the opportunity to clean up the holes.
If you enlarge the pic, you can see that I cut the right slot a little too long.  No harm done.
The thrust collar is now ready to accept the handwheel.
You can see that either I had the leadscrew adaptor a little too long or the thrust collar a little too thin, the handwheel couldn't seat in properly causing huge amount of backlash.  Two thick washers were employed to see how much I missed.  Looks like I've measured the length of the leadscrew adaptor that extends out of the thrust collar wrongly...

I went back to measure the amount of adaptor protruding from the stock thrust collar.  The difference was about 2mm.  Time to go back to the lathe...

I carefully trimmed off 2mm from the end. The wall of the counter-bored hole is rather thin. I was worried about it going out of shape.
The micro boring tool was up next to increase the depth of the counter-bore by the same 2mm.
I brought the table forward to avoid alignment problem later. Time to see if the shortened adaptor works.
Beautiful!!! The handwheel turns free and smooth.

I went ahead to tighten up the anti-backlash nut till the wheel is hard to turn and slacken it a little.  The handwheel still turns smoothly.  Finally... I DID IT!!! (giving myself a pat on the back...).

From the exercise, I know what I've gone wrong and what I need to take note of for future projects.  This has been a very rewarding learning experience for me.  The bearing thrust collar for the X axis is up next.  The hole locations are the same as the Y axis except that they're upside down.  I'll be starting with the thrust collar first before working on the leadscrew adaptor as the length of the adaptor depends on the thickness of the thrust collar.  This will give me some room to play after boring the small recess for the flange bearings to seat in.  Not sure if I want to start working on it today.  I've slight discomfort (not amounting to pain. kind of sore...) at the place the dentist operated on.  It can be a little distracting especially when counting handwheel turns.  I started over twice this morning when dialing in the distance after finding the edge.  Maybe I'll just rest a little while and read the George H Thomas' "The Model Engineers Workshop Manual".

I've Mike Kong of SG Tooling ( to thank for teaching me the centering method used in the bore. It works really well.  I dare not say that I'm right on centre but I should be very close.  Thanks Mike!

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