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machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment.

Tag: V Carve pro

Turkish Bombard. The Barrel Script

Well, I bought a pair of NSK bearings for the Z axis of my CNC mill, and removed the old ones and inserted the new ones.  Cost $AUD 200.  Plus 2 or 3 half  days of  dirty heavy work.    And the problem persisted!!@!@

OK.  Time to get an expert opinion.  Here comes the cavalry.  Thank goodness for my expert friend Stuart T.

Very puzzling.  Even for Stuart.  There was some unwanted movement in the Z axis (about 2mm), despite being apparently properly installed.  Not a problem with the ballscrew or ballnut.  Even Stuart was puzzled.

“have you got any left over bits and pieces?  Is it all installed the way it was before?”

To cut the story short, we installed a thicker washer below the locknuts, and it seemed the problem was fixed.  Or was it?

Today I did another test run of the bombard mouth Arabic script.  Worked fine.  OK.  Time to finish the bombard.

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Here is the finished result, ready for painting.  I have used a 20 degree engraving carbide bit with a 0.2mm flat end.  There is some loss of fine detail but it is I think, adequate.  When it is painted, the filling putty above the pin screws (the white circles) will be invisible.  The engraving took a total of about 60 minutes, at 500mm/minute, 15,000 rpm.

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The setup.   A large angle plate clamped to the table.  The work clamped to the angle plate.

The translation of the Arabic script is “Help O God the Sultan Mehmet Khan son of Murad. The work of Munir Ali in the month of Rejeb. In the year 868.”

Turkish Bombard. The Arabic Script.

A little unfinished business on my model bombard is the Arabic script and floral decoration around the barrel mouth.

bombard-mouth

XIX.164 / 19-00164 Detail of muzzle of a great bronze gun. Turkish, dated 1464 Royal Armouries Museum, Leeds LS10 1LT Transparency tr-1185 Imacon Flextight Precision II

This is what I have managed so far….

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It is a practice run in scrap wood.

Some of the detail has disappeared because I used a milling cutter with an end width of 0.5mm.  Next time I will add another step using a cutter with a sharp point, and a lot more of the fine detail will appear.

That pattern took a total of 80 minutes to CNC mill, with the feed rate set at 500 mm/min.

Unfortunately my CNC mill developed a problem with the Z axis, probably due to a worn out end bearing.  I am hoping that it is not the ball screw nut.  Now in the process of removing the bearing. A heavy, awkward, dirty job.

When the mill is working again I will mill the actual bombard model and post some pics.

Computer graphics is not my strong point.  To get the CNC mill to cut that pattern I did the following..

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  1. Enlarged the photo, outlined the tracery and the script, then traced the outline onto tracing paper.  That 550 year old pattern is worn and hard to define in many places.  Quite a bit of guess work.  Lucky that almost no-one can read ancient Arabic script these days.
  2. Scanned the tracing and loaded the scan into Corel Draw
  3. Used Corel Draw to smooth the curves, and make 3 copies in an array of the floral design
  4. Converted the drawing to bitmap file (bmp)
  5. Used V Carve Pro to convert the bmp file to vectors
  6. Used V Carve Pro to generate the CNC G codes
  7. CNC milled the scrap wood at 16000rpm, using a 3.2mm carbide cutter

Making the Lathe Spider

Drawing the chuck, the bore, and the 3 spider components.

Drawing the chuck, the bore, and the 3 spider components.

Using CAD to measure the dimensions.

Using CAD to measure the dimensions.  The main requirements are that the 3 components are identical, and the 30/120 degree angle.  (360/3).

Transfer the dimensions to Vcarve pro, to generate the G code. (not essential to use Vcarve pro. This simple shape could have been entered directly into the CNC mill)

Transfer the dimensions to Vcarve pro, to generate the G code. (not essential to use Vcarve pro. This simple shape could have been entered directly into the CNC mill)

Simulation of the process, using VCarve pro. Again, not essential, but it is fun. I use an iphone App called FS Wizard to calculate the feeds and speeds.

Simulation of the process, using VCarve pro. Again, not essential, but it is fun.
I use an iphone App called FS Wizard to calculate the feeds and speeds.

Milling the components.

Milling the components.

The sacrificial holding plate, and the components. I tried a wooden sacrificial holding plate, but it was just not adequately rigid, and the finish was poor.

The aluminium sacrificial holding plate, and the components. I tried a wooden sacrificial holding plate, but it was just not adequately rigid, and the finish was poor.  The aluminium plate worked well.  It will now join the growing pile of sacrificial plates from other CNC projects.  You can also see the result of an extra milling step which removed the rounded fillet, allowing the spider to sit snug against the chuck jaws.

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