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- Feb 1, 2015
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A year or so, I bought a set of metric drills, 1.5mm to 13mm by .5mm. It didn't come with a drill index so for the last year, they have just remained in a bundle. To make them easier to access, I decided to make a stand for them. (Details below)
I had delayed the project because of a lack of suitable material for the base. I needed a block about 4" x 4" x1.5" and wanted to use a plastic of some kind. (I prefer not to use wood because it attracts moisture causing swelling and possible rusting.) A check on likely sources of a suitable plastic proved unfruitful as the material cost was excessive. I decided to try to cast my own, using recycled plastic. My choice of materials was polypropylene as it has fairly decent mechanical properties and a fairly low melt temperature.
I selected a can from tomato sauce from the recycle bin for a mold as its diameter was almost 4". I heated the can to burn off the epoxy coating on the inside of the can. I calculated that I would need about 10 oz. of material for the raw slug. For a heat source, I used my hot air gun set at 390ºC and broke up the material and melted it bit by bit until the material was completely added. When the slug cooled, I peeled the can away.
Using the lathe, I turned the slug to 3.5" diameter and faced it to a thickness of 1.25". The next step was to drill the pattern for the drill bits. My design criteria for the pattern was that the drills be arranged in two concentric circles with the largest bit at the center. For stability and ease of access, the larger drills would be on the inner circle. Drills would be arranged in a descending order and the spacing between adjacent drills would be constant. This presented a fairly complex mathematical challenge which could be addressed in a spreadsheet but was fairly easily done in SolidWorks.
SolidWorks was able to position the required holes and could spit out the coordinate of each hole. However, transcribing the coordinate of 25 holes and keeping track of them while drilling is a highly susceptible to user error. A simpler approach for me was to export the model to SprutCAM and use it to drill pilot holes. With the click of a few buttons, the hole locations were set and the machine op of spot drilling the hole locations was run and posted to G code.
G code loaded into the Tormach, I set my x & y zero in the center of my blank and touched off the #2 center drill on the top of the blank. No need for precision here. Two minutes later all 24 holes were spotted. The work was moved to the mill drill for drilling the holes. Drill sizes were chosen to be slightly larger than the prospective tenant but not large enough to accommodate the next larger drill. This gave a .5 mm or .020" window for selecting an appropriate drill. The DRO was zeroed on the top of the blank and holes were drilled to a depth of 1" for each drill. I started with the smallest hole and worked my way up. To keep track of where I was, I inserted a pin in the hole after it was drilled.
The enclosed Excel spread sheet contains a table of drill location coordinates and a table of suitable holes sizes for each drill. The drawing will help to visualize the locations of each hole. A text file provides the G code for CNC drilling. Some modification may be required to adapt to your specific CNC mill.
I had delayed the project because of a lack of suitable material for the base. I needed a block about 4" x 4" x1.5" and wanted to use a plastic of some kind. (I prefer not to use wood because it attracts moisture causing swelling and possible rusting.) A check on likely sources of a suitable plastic proved unfruitful as the material cost was excessive. I decided to try to cast my own, using recycled plastic. My choice of materials was polypropylene as it has fairly decent mechanical properties and a fairly low melt temperature.
I selected a can from tomato sauce from the recycle bin for a mold as its diameter was almost 4". I heated the can to burn off the epoxy coating on the inside of the can. I calculated that I would need about 10 oz. of material for the raw slug. For a heat source, I used my hot air gun set at 390ºC and broke up the material and melted it bit by bit until the material was completely added. When the slug cooled, I peeled the can away.
Using the lathe, I turned the slug to 3.5" diameter and faced it to a thickness of 1.25". The next step was to drill the pattern for the drill bits. My design criteria for the pattern was that the drills be arranged in two concentric circles with the largest bit at the center. For stability and ease of access, the larger drills would be on the inner circle. Drills would be arranged in a descending order and the spacing between adjacent drills would be constant. This presented a fairly complex mathematical challenge which could be addressed in a spreadsheet but was fairly easily done in SolidWorks.
SolidWorks was able to position the required holes and could spit out the coordinate of each hole. However, transcribing the coordinate of 25 holes and keeping track of them while drilling is a highly susceptible to user error. A simpler approach for me was to export the model to SprutCAM and use it to drill pilot holes. With the click of a few buttons, the hole locations were set and the machine op of spot drilling the hole locations was run and posted to G code.
G code loaded into the Tormach, I set my x & y zero in the center of my blank and touched off the #2 center drill on the top of the blank. No need for precision here. Two minutes later all 24 holes were spotted. The work was moved to the mill drill for drilling the holes. Drill sizes were chosen to be slightly larger than the prospective tenant but not large enough to accommodate the next larger drill. This gave a .5 mm or .020" window for selecting an appropriate drill. The DRO was zeroed on the top of the blank and holes were drilled to a depth of 1" for each drill. I started with the smallest hole and worked my way up. To keep track of where I was, I inserted a pin in the hole after it was drilled.
The enclosed Excel spread sheet contains a table of drill location coordinates and a table of suitable holes sizes for each drill. The drawing will help to visualize the locations of each hole. A text file provides the G code for CNC drilling. Some modification may be required to adapt to your specific CNC mill.
