09 August, 2014 Page 1

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Jeremy Riley
5 years ago
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AutoCAD Design of Avionics Stack Top Cover Plate 09 August, 2014 I ve settled on a hybrid method of designing and fabricating most of my sheet metal and milled components for my second Helicycle.

1 AutoCAD Design of Avionics Stack Top Cover Plate 09 August, 2014 I ve settled on a hybrid method of designing and fabricating most of my sheet metal and milled components for my second Helicycle. I start by laying out the part using AutoCAD. It s not cheap at around $1200. I acquired a legal copy from work before I retired and it served me well for years. Unfortunatley I upgraded my PC to Windows 8.1 and half my old applications stopped working. I now have only a few days left on my demonstration version before I have to shell out real money to unlock it. But that s another story I like AutoCAD because it is dimensionally perfect. It uses vectors and doesn t care whether you re designing an aircraft carrier or a microscopic part. You can add as many different layers as you want and each one can be a differeent color or line type and you can turn them on and off as needed. Once I have the part looking the way I want it on the screen I print it out on an inexpensive laser or inkjet printer. All the printers you see at the local office supply are digital and use stepping motor technology, and they are very accurate August, 2014 Page 1

In this one I made two lines that are 0.010 apart and the paper bled them together but you can still see that the printer resolved the two lines.

2 Here s an example using the cheapest paper I could find. The printer is also the cheapest laser printer I could find. They pretty much give these things away and then hit you with the ink or toner cartridges. Comparing large prints of eight to ten inches with my dial caliper I can t see any dimensional errors. In this one I made two lines that are apart and the paper bled them together but you can still see that the printer resolved the two lines. Maybe with better paper I would see a slight improvement. The next step is to cut the paper out to the exact size of the piece I m going to make and tape it down carefully. Then the material and the paper are clamped on my mill s table. I m using a scrap piece of plywood as a backing so I don t scratch the sheet metal. At first I was dimensioning the drawing so I could use the calibrated dials on the mill to move the work based on the dimensions, but that s very tedious and I have to account for any slop in the feeds. I abandon that method and used a mechanical center finder to position the quill directly above each hole. That s faster and accurate enough for what I m doing August, 2014 Page 2

Of course getting the sheet metal blank cut to the correct size and having it be a

my Harbor Frieght combination metal sheer, brake, and roller I tossed out the

spot-on and runs all the way to the blades.

3 Of course getting the sheet metal blank cut to the correct size and having it be a nice rectangle and not a trapazoid took some practive and a few minor improvement to my Harbor Frieght combination metal sheer, brake, and roller I tossed out the original guide for the sheer which was way off and made my own My new guide is spot-on and runs all the way to the blades. In this picture I have my precision square in position and you can see that it look pretty good August, 2014 Page 3

Here I ve cropped the previous picture to just show the brake portion. It consists of a 90-degree chissle blade at the top that presses into a 90-degree V slot at the bottom.

for the brake as there is for the sheer.

To line up the material so the bend doesn t end up at an angle I carefully clamp my square on the bottom side of the material to be bent.

4 Here I ve cropped the previous picture to just show the brake portion. It consists of a 90-degree chissle blade at the top that presses into a 90-degree V slot at the bottom. The trick is to figure out what the offset is from the edge of the bottom die piece to the inside of the bend, and also to position the material so the bend is not at an angle since there is no guide for the brake as there is for the sheer. It took an afternoon of working with thin strips to nail down the offset, so now I can mark a line that goes next to the outside eddge of the die and have the bend come out where I want it. To line up the material so the bend doesn t end up at an angle I carefully clamp my square on the bottom side of the material to be bent. Then I slide the piece up against the side of the die so that the square is flush, and start the bend. Once it gets started nothing is going to move so I can remove the square and complete the bend. This works out perfectly. Now that I ve gotten in some practice I can usually hold about or less across the length of one of these pieces for the dimensions of the material cut and also the accuracy of the bend. Again, that s good enough. Incidentally, good enough is a concept that is hard for a lot of engineers to come to grips with. Trying to make anyting perfect cost a fortune and is never quite achieved. The real art of engineering is knowing where good enough is. If you error on one side the part will fail and if you error too far on the other side the part will be too costly to manufacture. Of course, if I had a CNC mill I wouldn t have to do any of this and I could go directy from the CAD drawing to a machine file and the mill would make me the part. I d still have to cut the sheet, position it, and change bits a few times, but the rest would be automated. Sweet! Ah Ha! The tool I was waiting for just arrived. It s a laser center and edge finder. You stick it in a collet or a chuck, turn it on, and put the dot where you want it. Since it s a laser and well collumated, the laser can be as far as a foot away from the work surface. Below is a tight shot of the printed center marks with the dot in the middle. Remember that those lines are about.004 wide based on the picture on page-2. Looking at this blow-up I can see that I m off about the thickness of a piece of thin paper, but my eyes can t resolve that without a magnifier August, 2014 Page 4

5 Equipped with these tools: AutoCAD or another drawing package that can create accurate drawings Any cheap laser of inkjet printer A center/edge finder (I like the laser much more than my mechanical one) A verticval milling machine You can do some very accurate machining with a minimum of fuss. It works for me August, 2014 Page 5

AUTOMOTIVE ALTERNATOR CONVERSION FOR N750G TRANSMISSION DRIVE PULLEY MODIFICATIONS

AUTOMOTIVE ALTERNATOR CONVERSION FOR N750G TRANSMISSION DRIVE PULLEY MODIFICATIONS In this section I ll describe the modifications I made to the transmission pulley. The first thing I did was to remove all the electrical cables from the engine and drop it to expose the transmission and