Friday, August 12, 2011

A2Z Z-Axis Leadscrew Upgrade - Nut Mount Top

I was home alone while my wife was attending a workshop at church. Though feeling tired, I urge myself to start working on the long overdue leadscrew upgrade at the home workshop.

Not trusting that the split vise is clamped flat to the mill table, I've to cut the stock for the top piece of the anti-backlash nut mount to fit my favorite Matchling 3" vise, leaving about 10mm on top of the actual dimensions. The markings were done using the height gauge on the surface plate. I was then stuck with my first problem for the session; the bandsaw gave some trouble when cutting off the excess stock. The blade was rather jerky and didn't sit properly in the bearing guide. But I managed to rough cut the stock to size.


Facing was done next to smoothen down the sawn sides. Though I don't need the 4 sides to be perfectly square, I took the opportunity to practice squaring up stock. The Japanese-made engineering square was put to use against the mill table and the best side of the stock. After going round the stock, I've an acceptable piece; the best almost squared stock I ever achieved.

Next came facing of the top to the required thickness of 6.5mm. I gathered that this is not a critical dimension from looking at Tang Kee's drawings. The gcodes was done using BobCad with a 1/2" HSS 2-flute endmill. The target depth to face is 2.98mm at about 0.25mm per pass. Step over was set at 40% of the cutter diameter.

The whole process took over 1 hour to complete! Midway, I realized that I was actually climb milling... The cutter was going from left to right, from front to back. No problem encountered.


I also observed that there were steps created every time the cutter stepped over the programmed 40% of it's diameter! What a pain!!!

This is how it looks under normal light:


I applied filters to exaggerate the surface:


I've tried my very best to tram the mill and yet... Sigh... I can even feel the ridges running my fingers across the surface.

Anyway, a short video of the run midway through:

YouTube Video

Anyone can suggest solution(s) to this?

- Posted using BlogPress from my iPhone

7 comments:

Anonymous said...

I think you should try to use Fly-cuter for surface finishing!MC Quek

metalAddict said...

Interesting. How depth was the finishing pass? What about using a smaller diameter endmill and thus reducing step over?

Wongster said...

No finishing pass. 0.25mm per pass throughout. 12.7mm endmill already more than an hour for total depth of merely 2.89mm.

I've flycut the piece. Biggest error - 0.04mm.

Regards,
Wong

Anonymous said...

I think your machine is not align. The ridge is due to the end mill cutter not perfectly square to your table. A simple way to check is to cut your metal with parallel y-axis lines instead of parallel x-axis lines like you do now.

Wongster said...

Hi,

Name? Thank you for your comment.

I would think so. But... I just trammed it not long ago and this was the first job after tramming. Something I've not done right...

I was thinking about it, it came about when I was clamping the parts down in the vise. I'd to tap the stock down quite a few times to have the stock pressing against the parallels. Could that be the source of the misalignment? I kept having the feeling that the squareness of the sides would affect the stock alignment in the vise when tightening. I may be wrong.

Regards,
Wong

Gadget said...

Wongster,
your tram adjustment is off.all that you should see on a mill stepover is a witness mark-change in swirl pattern from moving the bit to the next cut path. You may have to shim the mill head or the colum to make this work-this is sometimes a very tedious task. you can make your own tram tool on the lathe or buy the "nano-tram" tool. I used my dial gauges and got my mill to .0003 in 4" movement (z).
I always check and adjust the tram and lash movement after alot of cutting (my last milling machine, so Im used to the process.
good luck
gadget47

Wongster said...

Hello Bob,

Good to have you on my blog. Hope things are well and good with you and your work.

Wow! you're able to get to 0.0003" in 4"! amazing!

I just square up the mill yesterday and did some flying cutting. I'm now at about 0.02mm in 100mm, which is within my expectation.

Like others said in the Sherline group, make more chips than keep trying to square things up. I'm back on the z axis leadscrew upgrade :-)

Keep in touch Bob.

Regards,
Wong