I’m taking a break from the CNC Project, since I keep losing steps, and I’ll probably need to open, adjust, and clean the whole thing. I may even have to mill the gibs.
So, I started working on the NTN – 600 fiberglass (deep v) hull I got a while ago. I ordered a water cooled brushless motor (Turnigy AquaStar 2842-2800KV) and an ESC (HobbyKing 50A Boat ESC 4A UBEC), an adjustable stinger drive (55 mm – Black), an aluminum water cooling outlet, and a pair of turn fins last week from Hobby King. I’m waiting for their arrival. I already have various shafts and props, a good quality aluminum rudder with water intake, some servos, and some LiPo batteries (7.4V – 5800 mAh) in stock.
CNC props (38 mm and 35 mm) that require no sharpening or balancing. Their shaft holes (3 mm and 3.25 mm) from left to right) need to be enlarged to 4 mm.
Brass prop attached to 4 mm flexshaft (in brass grease tube and Teflon bushing), with a drive dog and a prop nut.
675 mm hull.
Long transom extension.
As the two-part rudder bracket was holding the rudder too far from the transom, I decided to replace one of the parts (the mounting part) with my own (leaving the hinge part as it was). The width of the new part would be 30 mm as in the original, but since the rudder mounting extension on the hull’s transom is 17 mm thick, the mounting section of the part would have to be 7 mm shorter than the original piece. I would still have to make the extruded and slotted part 24 mm long, to be able to hold the rudder hinge part firmly.
I designed the part on SkecthUp since I still need to learn a real solid modeling CAD program.
The result was a bit different than what I actually designed.
Here’s what I managed to do on FreeCAD. It keeps crashing and messing up on me
A mixture of what I had in mind (no center hole in the slot) and what I ended up with (no double holes in mounting ears).
I had a 15 mm thick machinable aluminum piece laying around, and it took me more than half an hour to cut out a suitable piece with a jigsaw. After that, I squared the piece to 30 x 24 x 15 mm (width x height x depth) on the mill.
Cutting this piece took me about 30 minutes with a jigsaw.
Block Squared to 30x24x15 mm
Later on, I milled off the sides of the slot section (9 mm wide, for a 3 mm slot with 3 mm walls) down to 5 mm using 8 mm and 6 mm end-mills.
Milling the pockets with an 8 mm end mill.
Rudder with the incomplete bracket.
I decided to drill the holes while the work piece was still thick and solid. However, I messed up on the mounting holes, since I was supposed to reduce the height of the mounting section of the part (5 mm thick) from 24 mm to 17mm first, and then decide on the location of the holes.
I drilled the wholes prematurely (too wide apart), before milling off the 7mm from the mounting sides.
Reamed the wrong holes.
Eventually, I had to mill off 10 mm instead of the actual 7 mm to get rid of the useless 2 holes (actually the larger countersunk area), leaving me with a 14mm tall area and only 2 holes for mounting. You can see the old and the incomplete new bracket in the picture below.
Still incomplete bracket (middle) with the original bracket parts (right).
Later on, I drilled a third hole in the middle of the slot for a better hold, and enlarged that part of the slot to a 5.5 mm hole, to be able to fit the 5.2 mm bolt head there, also countersunk the bottom hole to avoid blocking the slot.
I also messed up the holes on one side of the slot. I drilled 2 x 2.5 mm holes on the side of the 9mm wide extruded part which would later form the slot, so I could cut threads in them with a M3 x 0.5 mm tap. After milling off the 3 mm slot in the middle of the 9 mm extrusion, I tapped the threads for the holes on one side, and enlarged the holes on the other side to 4 mm instead of the actual 3mm. Since threaded holes were ok, the hinge piece has 3 mm holes, and the countersunk holes hold the 3 mm bolts fine, that was no big deal, really.
Still incomplete, but the holes were countersunk. Hole in the middle needed a cylindrical guide in the slot.
Three 3 mm mounting holes seen from the back.
I gave the part its final shape with my belt sander and files, and polished it with my Dremel Tool to a mirror finish. The chuck came off twice due to vibration (I’m no machinist, and I don’t make parts everyday) and marred some small regions of the part. I think I need less fluted end-mills for machining aluminum. I don’t really mind, I’ll do better next time.
Here’s a table of the weights of the parts and some notes about those parts.
||Adjustable and nice looking.
||Add 45g weight to balance with ESC on the starboard side.
||To be centered parallel to transom on adjustable slide.
|Motor + Coupler
||Motor mount centered in hatch opening.
|Shaft + Prop + Tube
||These easily go below battery.
|Cables + Hoses +Pipes
||Silicone hoses, brass tubes, aluminum tubes.
||50A 4A UBEC
||New bracket milled to get the blade 20 mm closer to the prop.
||I need to make some from L profiles and 1 mm stainless steel sheets.
||They are also on their way, 40 mm length is probably too small.
I also finally bought myself a workbench, a tool cabin, and a tool shelf rack. I’ve been busy with rearranging the stuff and cleaning up. I’ll finish it all today and start working on the boat on the new workbench soon.
Final status of the workbench side.