MAINSHEET SYSTEM
DESIGN
KYLE ROSS s3433915
GRAP2578 ADVANCED KYLE ROSSPROTOTYPING s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
INTRODUCTION Our first and hardest task of the semester, for advanced prototyping was deciding what to make. My ideas mainly revolved around what I spend most of my free time doing, which is sailing, a class of boat called an International Moth. The main idea I had was to build a hydrofoil for my boat, however I did not want to spend hundreds of dollars on carbon fiber. When I knew it that would not work as well as my current foils, due my lack of knowledge in hydrodynamics. I decide to build a specialized pulley system for the mainsheet of my boat, this was because the block or pulley, is a fundamental product to any sailing boat and it was a good opportunity to put my have my onw take on designing one. The mainsheet is the central control system of the sail on a sailing boat. Once I had decided on building the pulleys (or blocks in the sailing world), I began to further explore what would be required of the blocks and how to design and manufacture a functioning set.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
RESEARCH As I have sailed since I was 7 and been in the moth class since I was 15, I have had a lot of experience in what would be required of the functionality, for each individual block in the system. It was applying this knowledge, to make a part that could be; manufactured, withstand the stress applied, and assembled with correct tolerances, that would be the challenge. It was through research of the materials, manufacturing processes and design, of blocks already on the market that I was able figure out the basic requirements and processes needed to build my blocks. While also identifying where I could improve upon to make a more functional block for my boat. Due to the lightness, relative strength and ease of machining, I decided I was going to make my blocks out of Aluminum. Each block would consist of three main parts; 2 sides and an inner rotating race. I also identified I would use the Haas CNC milling machine to cut the sides of the blocks and potentially the inner races. This would mean all my designs would have to be completely resolved on CAD before I could manufacture anything.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
CRITERIA The main sheet on a moth is usually a 4:1 purchase system, meaning I would need to design 4 blocks. To improve on the current options on the market and add functionality to the blocks for a mainsheet, the block were designed with these ideas in mind. -Optimize the blocks for 7-8mm rope, where 40mm blocks are commonly to small while 55mm blocks are excessively big and chunky. -Keep the attachment point located through the middle of the block to maximize simplicity, versatility and strength by looping the 2 ropes together, while most importantly minimizing the distance between opposing sides of the system, which is key to center the boom therefore trimming the sail correctly. -Have each of the four blocks designed for its exact function in the system. -On a moth, the mainsheet is constantly held in the hand for hours. With the knowledge that I can only hold and pull comfortably under 20kg (196.2N) vertically up (normally sailing conditions and body position). I can estimate the average force exerted on the first block in the system is 784.8N with the purchase system. Nevertheless this number could peak much higher at times.
Through the design process there were many restricting factors that became apparent with the ability to make these parts with the Hass CNC mill. -Due to the size and amount of parts I needed I would be restricted to the 3 axes of cutting. -The minimum internal radius would depend on the tools available and the depth they could cut with the 3mm ball nose being the smallest, there for internal radius could be no less than 1.5mm. -Since each part was unique in shape without being completely round or square they would need to be milled from rectangle block leaving the part in place held with fine tabs to be later cut out. In addition have enough material left, to withstand the force of the clamp. -Tolerances of the cutting would approximately be .01mm. -Due to time constraints the sides would have to be the same with no male and female locking mechanism, so that it would halve the amount of time needed for programing the code of the CNC mill.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
BLOCK 1 This is the Block I designed first and is the basis for all the following Pulleys. Block one is the starting point for the rope meaning it requires a becket or a second attachment point. Due to this it would have to be the strongest of the four blocks, as it would receive the most force at the starting point. This is why it has four bolts joining the two sides compared to the two in the other blocks. With these requirements in mind and using 3mm balls as an initial dimension to design around, I began my cad model with 2 basic revolves, one for the inner race and one the sides, working out the wall thicknesses and tolerances around the rolling balls. Later adding; thru holes, bottoming out tapped holes and also enclosed areas for the ropes to keep them in place. The design continually evolved as I frequently made changes to wall thicknesses, tolerances, radiuses on fillets and overall shape, as I spoke to Rafael and other engineers getting and idea of the limitations of the CNC mill and strength needed. After many changes I was able to find a compromise on the shape, with the side being able to be manufactured by CNC milling and the inner race would be CNC lathed with enough strength.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
BLOCK 2 This was the most complicated pulley in the system due to the fact it has a ratchet mechansim, meaning it restricts the internal race to spin in one direction. This is so that as the mainsheet is easier to hold in place by adding friction, when letting the rope out but being just as easy to pull in. Starting with the first blocks model the block was overall increased in diameter and width. The race’s, outer face is changed from a concave to wedge shape so the rope catches more, while the inner face has ratchet teeth added. The two bolts are moved roughly to the center of the block and between the faces is a arm held in place by a pin that torsion spring pushes into teeth on the race catching them in one direction, making up the ratchet mechanism.
REVISIONS REV.
4
5
7
DESCRIPTION
8
6
DATE
3
1
2
Top View
Exploded View
Front View
ITEM NO. PART NUMBER 1 RB2-002P 2 RB2-004P M4x12 socket 3 screw low head 4 RB2-001P 3mm G5 Silcon 5 Nitride Ball 6 Torsion spring 7 RB2-006P 8 RB2-007P
Right View
Process Specific Tolerances
Laser Sheet Laser RHS Machined Saw Cut
±0.25 ±0.3 ±0.2 +0/-2
General Fabrication ±0.5
GENERAL TOLERANCE UNLESS SPECIFIED ISO 2768 - MK LINEAR DIMENSIONS 0.5<t 3 3<t<6 6<t<30 30<t<120 120<t<400 400<t<1000 1000<t<2000
±0.1 DRFT'D Kyle Ross ±0.1 ±0.2 DRAWN Kyle Ross ±0.3 ±0.5 CHK'D ±0.8 ±1.2 APPV'D
Ratchet Block 2
2
2 80 Leaver 3.0mm pin Spring 2mm Pin
1 1 1
DO NOT SCALE DRAWING DATE 16/4/2015
MATERIAL: Various
16/4/2015
ANGULAR DIMENSIONS t 10 1° 10<t 50 ±30' 50<t 120 ±20' 120<t 400 ±10' 400<t ±5'
QTY. 1 1
THIRD ANGLE PROJECTION
UNLESS OTHERWISE SPECIFIED: DIMENSIONS ARE IN MILLIMETRES NAME
DESCRIPTION Rachet Block inner race Rachet Leaver
WEIGHT: 29.91 g
MAX QTY PER PALLET: DATE CREATED: Thursday, 16 April 2015
DESCRIPTION: Rachet Block 2
FINISH: Assembled
DEBUR AND BREAK SHARP EDGES
PRODUCT ID: SCALE:1:1
RB2-003B SHEET 1 OF 1
A3
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
BLOCK 3 Block 3 being the first turning point for the rope, itâ&#x20AC;&#x2122;s only function is change the direction of the rope with as little friction as possible. With the exact same inner race as block one. The design is the same besides the balls are channeled thru a bridge reducing the contact points with the moving race, and therefore in theory removing friction. This change in the design meant only two blots were used and relocated roughly in the middle. Another company has done this and given how well it worked I was inspired to try a similar design, but without many prototypes to get the tolerance perfect I was reluctant to believe it would reduce the friction.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
BLOCK 4 Since block 4 is the last pulley the rope goes thru it only really needs to redirect the rope to where you are in the boat from the ratchet block. This mean it has to rotate easily and be versatile, requiring a samller diameter. The inner race is significantly reduced in diameter and is set into the sides so the rope doesnâ&#x20AC;&#x2122;t slip over the sides.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
SOURCING MATERIAL With the majority of the design done, the list of materials needed were as follows. -5x160mm lengths of 10x100mm 6060T5 aluminum plate, for the sideâ&#x20AC;&#x2122;s easily sourced form the aluminum trade center for $45. -1x 150mm length of 60mm diameter 2120 aluminum round solid, again from the aluminum trade center for $24. -10x M4x10mm low head socket screws from united fasteners. -300x 3mm Ceramic (Silicon Nitride) balls sourced online at AliExpress from china at $105. -Small torsion spring with ID of approximately 1.7mm made from a micro clothes peg, as sourcing this single spring was impossible without spending over $100. -10mm length of 3mm and 1.5 Stainless steel rods found at home.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
CNC MILL At the end of week 6, I had all CAD models of the 4 blocks finished and was ready to start milling the sides and internal parts. Each length of aluminum plate was used to make two sides of a block with the last length used to mill the two internal parts. Since each part had detail on both sides the plate would be milled form once side then flipped, lined up and then run the second program from the other side. With each cut taking over 1.5 hours and a total of 10 cuts, this equated to over 4 days of milling.
CNC LATHE With the sides being Milled, the inner races were designed however I wasnâ&#x20AC;&#x2122;t exactly sure how to manufacture them, since they could not be on the milled due to the concave shape on the outer ring. I was able to out source the manufacturing of these parts to the Advanced manufacturing precinct of rmit who did it free of charge on their CNC lathe. The back up plan if this wasnâ&#x20AC;&#x2122;t going to work, was to turn the parts on the lathe in the workshop and mill the racket teeth after on the Haas.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
HAND FINISHING Once the mill had cut all parts, they were still in their housings attached by 4 tabs each side. Firstly while the sides were in the housings I used this opportunity to tap the holes that need it. Unfortunately I ran into a problem, as I was using a tap that had the tip cut of to create a bottoming tap. Along with my lack of technique and no grease, I managed to snap the tap inside one of the holes. Unfortunately we were not able to remove the fractured tap still stuck in the part. The solution was to CNC another part. After learning my lesson and applying proper technique I was able tap the remaining holes without any issues. Also Before cutting the ratchet block sides out their housing I need to use the hand mill, to measure and drill all the holes on them, due to the asymmetrical hole positioning of the rods. The mill is not as accurate as the CNC mill and when being assembled the holes were pulling the sides out of alignment. I over came this problem by drilling out a single hole to be 0.5mm bigger in diameter, which was enough to correctly position the sides.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
CUTTING AND SANDING The tabs keeping the parts in their housings were easily cut using a dermal and then filed to match surface of the part. This took quite a bit of practice and patience to get right and is an area of my parts that could be slightly improved upon. The rest of the part was then sanded using a micro motor starting at 600 grit to remove machining lines then moving to 800, 1200,1500 and finishing the parts with 2000 girt sandpaper.
ANODIZING With All parts completely sanded I had them anodized over 24 hours for $95 at Collins Anodic Treatment; with sides in clear, the inner races in a grey and the inner race of the ratchet block in black. The inner races were made out of 2120 aluminum, which is good for machining but not for anodizing resulting in the dark spots due to its high copper content.
ASSEMBLY With all parts ready all that was left to do was assemble each block. This proved to be no way near as hard as I was expecting it to be. Using a water-based grease (easily washed out) the balls wanted to stay in position and it was just a matter of position the balls the Bolting two the sides together.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING
CONCLUSION Overall I am very happy with how my mainsheet system has worked. All of task two went according to plan with only one or two slight setbacks in the manufacturing process. Each block functions the way it was suppose to spinning better than expectations. Also I was very happy to see, all those hours on solidworks trying to get the design perfect, be transitioned into real life using Haas CNC milling. Since it was my first time using a CNC mill I was surprised how accurately it worked and learned a lot using it. Having said this once the blocks were assemble a error in the design did become apparent, the attachment point and depth of the concave need to be slightly altered in block 3 so that the rope wants to sit in itâ&#x20AC;&#x2122;s correct position further. This error may have been avoided using more hands on prototyping before manufacturing however due to time constraints and budget, I was not able to explore this as much as I maybe should have.
KYLE ROSS s3433915
DESIGN GRAP2578 ADVANCED PROTOTYPING