Sunday, September 26, 2010

Job For An Acquaintance

Few days ago, I was waiting for my wife to pick me up after an appointment which was near Mike's place (  Decided to pop over to see if Mike was around.  Unfortunately, he wasn't.  When I was looking into his shop with full glass to see if I can spot any new tools or idea, I met Robin, who happened to be there looking for Mike.  We had a chat and exchanged name cards.  Learned that he is into scale modeling business and owns a Unimat SL.  He was telling me about some kind of plastic he created which doesn't melt when being machined.  I showed him a couple of my novice work and left when my wife arrived.

I got a call from him a couple of days back asking if I could help him machine a part in aluminium.  Though I was excited about being able to do some CNC work on my lathe, I daunted on the quantity.  He wants 6 pieces of the same part.  As a hobbyist, I am not into production of some sort.  Doing the same stuff for 6 times can take the fun away, turning it into work.  I obliged nonetheless.  Maybe the repetitive job can help me understand how to set things up once and make many parts.

I received 2 pics at night and started with the CADCAM in BobCad.  Not too difficult a job for a novice but I realized that the first 2 I machined came out undersized by 0.35mm to 0.40mm overall.  Could it be backlash?  I've to find out.

Anyway, the pics as usual.  The video can be watched here: Can't seem to upload it here for whatever reason.  Maybe the file is too big.

This was one of the two pics sent to me.  The rounded portion was based on my guesstimate as Robin said the dimension wasn't critical.

The first task was to draw up the part in BobCadCam and assign machining features to it.
The part being simulated in Virtual CNC that came with my BobCadCam purchase and subsequent upgrades.

The gcode generated in BobCadCam being loaded into Mach3.  There seem to be some glitch in the graphical representation in the toolpath window but it cuts ok.

Onto the lathe.  The 22mm aluminium stock was mounted in the 3-jaw automatic chuck and supported by the ball bearings steady rest.  Really love the improved steady rest!

The result.

Drilling the 5mm hole about 45mm deep.  The travel of the tailstock ram is only about 35mm or so.  What I did was to drill to almost the max travel of the tailstock, push the drill with the tailstock further into the hole and contiue drilling from there.

Time to part off.  The part off tool was fed into the stock slowly by surely.  No major issue.  The biggest I parted off was a 40mm stock for the die holder.  The experience on that previous job gave me confident to do this on the smaller diameter of 20mm.
First piece done! It was 0.4mm undersized.  So I sent Robin an email asking about the required tolerance. He replied saying that the 0.4mm is acceptable.

This was just part of the mess produced.  For the fun of it, I flattened and folded them up :-)
I wanted to stop here as I ran out of smaller diameter stock.  The urge of wanting to figure out what could have contributed to the undersized part got the better of me and I started work again using a piece of 40mm stock, which I've only 2 pieces left.

To prepare the stock, I clamped it in my Matchling Screwless Vise supported by a piece of Proxxon Vee- Block I bought from Mike.  Flycutter was used to clean up the 2 sides.

It was then held in a 3-jaw chuck and turned down to about 30mm.  I did that to also zero the x-axis after turning it down. I'm able to hold the stock in the chuck better after the flycutting.

2 pieces done.  The 2nd one is undersized by about 0.35mm  The only thing I did differently this time was to trim the stock to smaller diameter while zero'ing the x-axis.  Z axis was also zero'd after a light face cut.
I need to buy some smaller diameter aluminium stocks to cut short machining time and avoid wastage.  All in all, I'm quite please with the result I get..  2 down and 4 more to go.

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