Monday, August 24, 2009

Cutting Thick Material Guidelines

I was asked about some tips on cutting thicker material.  The following are the points I mentioned to look for.

 

·         Always do a few test cuts of the different sections of the part at the speeds you expect to cut at.  So take the part and look for inside corners, outside corners, radii etc, then make a small part that will have all these features and program it and cut it so you get an idea as to how these will look on the finished part.

·         Write down the home position.

·         Practice some job interrupt as you may well need to do this in a long cut. 

·         Decide where you will pause the program if you have to in the middle of the cut.  In other words, is there a section of the part that is not critical to tolerances.  In your case of the gear, the very inside and tip of each tooth will never come into contact with anything and hence will be in fresh air.  As a result this would be a good place to pause the program and do any tests.

·         Once you have the part on the table, run the full program with water only at a high speed. This will mark the material and confirm that the part will fit on the piece of material and your set up is correct.

·         If you have to stop the program or you get a power failure do not rely only on the home position you wrote down.  Rather start the program and run the first part with water only and check that it follows the cut that you have already done.  You may also want to move it to another portion of the program and check that it still lines up there too.  I am always concerned that when restating a program you could be a few to several thousands of an inch out of position and this might not be good.

·         As you cut through the part, take a hack saw blade and grind off all the teeth so you have a  thin long gauge that will fit down the kerf that has been removed.  Let’s say the material is 6” thick.  Put a mark on the blade at say 6.5”.  Then take the blade and insert it into the cut and with the bottom of the blade sticking out the bottom, slide the blade along the tool path and check that the material is cut all the way through.  You of course have to make allowance for grates.  But this will give you a good guide as to the status of the bottom of the cut.

·         Make sure your abrasive is calibrated and set.

·         Use the coarsest hard rock garnet you can with your orifice nozzle combination.  In your case try to use 50 mesh hard rock with a 40th nozzle. 

·         Make sure the pressure is correct.

·         Ideally put in a diamond orifice as this is a much more reliable way to go especially when the material you are cutting is costly.

·         Check the condition of the nozzle.

·         Make sure the cutting head is vertical as if it is not the tolerances of the part will be compromised.  To do this line up the head or pierce a small hole in thin material. Then raise the cutting head up and the stream should go through the hole.  If the head is not vertical it will ‘walk’ out of the hole and the direction of the cut will tell you how your cutting head needs to be adjusted.

 

When we were a job shop we did a lot of heavy work with 4 heads simultaneously and the guidelines above helped.

Rich

 

 

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