Introduction: Spinnaker Pole Track Slides

I race on an Express 37 in San Francisco Bay.

These are unique boats designed and built in Santa Cruz, California in 1984 and in 1985 won 1st, 2nd, 3rd in the Transpac Race.

We race them in a one design fleet on the Bay where one mistake can cost a race.

The boats are over 30 years old and some of the parts are hard to find or non existent.

In our case the inserts for the spinnaker pole no longer existed and our track slider was an early version that was not compatible with the modern off the shelf track sliders.

The pole is used as an extension of the boat, and anchors (tacks) the windward clew of the spinnaker, where as the leeward clew is controlled by the sheet and used for trimming.

The outboard end of the pole attached to the sail is moved depending on the point of sail and wind dynamics. This puts a very large load on the mast end of the pole.

The mast end of the pole is articulated vertically along the pole track.

The part that I will be showing you how to make is the sliding bearing section of the pole track slider car.


Step 1: Measure Current Solutions

The Captain, Bartz came to Pier 9 and dropped off two samples of the insert that doesnt fit in our car but is in production, and another black molded plastic insert that had flanges on both ends but was at least an inch or more short in length. The result was non of these sliders worked for our track car.

The first task is to measure and CAD up the to be slider.

A - wall thickness side a

B - wall thickness side b

C - part height

D - channel depth

E - part width

L- part length

The white plastic:






L- over 6 inches ,153mm estimate.

Molded black plastic:






L-102.3mm 4.029"

Step 2: 3d Print

The original goal when making these parts was to CNC them from Delrin, Teflon, or Garolite.

Unfortunately, days passed quickly and Rolex Big Boat Series was a day away.

I set the Fortis in the 3d Print Lab at Autodesk Pier 9 to make 2 sets in Black ASA

I didnt have time to put them in the bath so for one set I used pliers and a dental pick to clean out the support material.

In the others I was able to extract the support by slightly bending the part after fiddling with the support a bit. I thought I was crafty and tried this technique to the 4th and final part. It snapped...

3 Parts. 1 full set. 1 back up slide.

7 Races. 4 Days of Racing.

Lets hope for the best. What could happen? they could snap under the load of the pole. The could break up and jam in the pole track if they dont fit correctly. The importance of the pole sliding up and down is in order to change points of sail going down wind. In a gybe the pole at the mast is raised, and the outboard end is lowered so that it can be detached from the sail and switched under the forestay and to the other clew. switching the windward and leeward clew. The pole must be able to slide!

The interesting thing is I never measured the pole car. only the slides that didnt work, and a length measurement from Bartz of 4.5"

After printing. The installation would be the final integration, there was no chance of iteration Day 1 of racing.

Here are the measurements of the 3 Parts Compared.

The white plastic: A-1.58mm B-1.42mm C-6.26mm D-4.68mm E-8.56mm L- 153mm estimate.

Molded black plastic: A-1.52mm B-1.45mm C-6.44mm D-5.04mm E-8.12mm L-102.3mm 4.029"

3dprinted black plastic: A-1.48mm B-1.48mm C-6.72mm D-5.10mm E-8.22mm L- 14.56mm 4.512"

Step 3: Install and Operation

In the morning before the race the foredeck, Andrew and I removed the screw at the bottom of the pole track and slid the car off the track. The 3d Printed Parts fit PERFECTLY!! what! I was a little surprised. I mean proud of course, but very first fit check! Ok. Time to Race!!!!

After the First Day both slides were still operational in their position.

Through Day 2 the slides functioned perfectly, or did it?

Step 4: Failure Analysis and Redesign

On the morning of Day 3 I was handed a fractured slide.

It was found on the deck in the evening of Day 2. I was not aware of this, so for some reason I didnt have the replacement with me. It was not fractured along a 3dprint grain, but it was fractured a little distance from the flange, so it indicated that It was not torque on the flange. What was it? I used a glue and tape to inject silicon glue into the back side of the broken slide in the morning. It worked for the first race of Day 3, but then fell out. In the middle of the two races I modified one of the old slides. I used a knife to "drill" holes in the slide where worn out pins would be pressed into. It worked just long enough to finish the day. On Day 4 I showed up with the replacement. Both the 3d printed parts lasted for 1 Race. On the way back to the dock I was handed a broken slide. We figured out what was breaking the slides. The car stop on the bottom of the track was a hard stop. When the pole came sliding down the track into its "stowed" position it was slamming! The slamming was breaking the part.

Did the part need larger flanges? maybe not. that could help.

Did it need to be stronger? I could try to print using Poly Carbonate.

Should I CNC for the next set of Races? um... YES!!!!! Time for the HAAS.

Step 5: CNC on the Othermill

Oh no! no HAAS. well.. I could do it on the HAAS, but because of the coolant used its not advised to use plastics, and the clean up process is intensive.

For a long time I looked towards the Othermill, inspired by the toaster oven sized milling machine.

What could I do with this machine powered by a quadcopter motor?

I'll start with the end, like every tool. Unless you know how to use it, you will probably make crap.

Ok. Time to start with the othermill. First I need to make the CAM.

The first round of CAM I made was thinking that I was going to do multiple flip operations.

This was clearly not practical with both the materials and the machine.

I resolved to make the part with a single flip operation.

Lots of things have to happen for this to come together even in the CAM software.

I need:

a Tool Library, Othermill Post Processor, Milling Tools, Part Reference, Part Workholding Strategy and Stock.

Maybe a lot of stock.... ;)

Step 6: Setup and Test Milling

There are a couple of really nice things about the Othermill

They use the tool as a probe.

If you use the "bracket" as a reference there is an automatic ref sequence.

I used strong double sided tape to secure the part against the corner of the provided bracket.

If things seem off you can pause and re-home in case there was a collision.

The tool libraries and processors for Fusion 360 are on the website and available within fusion.

I was really encouraged that it was all going to go great!!!!!!!!!!!

umm. so that did really happen.

I cut two pieces of stock, two became 6.

What happened.

Well at first I was using adaptive clearing tool paths at high precision.

From my last project I ran into issues with the simulation from not running the g-code at a high enough precision.

I used this same number in this project.

For about 8-10hours.

Pieces after piece the tool path would work great and then at some point, sometimes after the flip it would drift like it was totally lost.....

Each new piece of stock I tore apart I would try a new tool path strategy that got simpler and more brute force. For example I stopped using adaptive paths and used 2d contours with controlling heights with each tool path.

In my very last attempt, the end of the night, my last piece of stock. I reduced the tolerance to a crude number... haha not really, 0.1mm. I figured I didnt care about this because I could always finish the part with sand paper or a file..

Oh my goodness!!! after wasting an entire day running around being a bad robot user. I got the part I needed!! whew.. I would blame this all on user error, not on the machine. I think its important because I know a lot of users would not battle with it in the totally neurotic way that I did.

The final task was to clean up!!

For the entire day I had made plastic snow all over the place.. it took me another 2 hours to clean the machine and surrounding areas to a level worth leaving with Zero Guilt.

In summary I think the othermill is awesome.... but I need to try again and see if my lessons learned allow for rapis use next round. I dont like voodoo machines.

Step 7: Installation and Operation for Express 37 National Championship

The parts were milled.

The Othermill was cleaned.

11pm. SF Pier 9. I got home at midnight. At 6am the next morning I drove to the boat to install the new parts.

During my battle with the Othermill I think at 6pm.. I went into the 3D Printing Lab and set up a Fortis Machine to make 2 sets of Poly-Carbonate Slides. An exact copy of the Black ASA slides that I used during the Rolex Big Boats Series.

It was a back up in case no parts were CNC'd

When I went to fit check the CNC parts they were just a little too tight to go onto the track. They fit in the cars, but not also onto the track.

Honestly after they came out of the mill I spent about an hour with a razor blade cleaning up the burrs, but without the car measurements, or track measurements I could not ensure that the part would integrate.

We installed the Poly-Carbonate Sliders in the track for the first race.

On the way out to the race course the foredeck alerted me that one of the sliders was already broken.

While the PC was stronger, it was also more brittle. One slam against the pole track stopper shattered the slider.

We raced the first race with one slider, it lasted to the very last leg of the race.

During the break between races, I went below deck and retrieved both sand paper and a file.

I also grabbed a box cutter.

Luckly conditions changed enough that the 2nd race was delayed and I had enough time to clean both parts up to what I thought would allow them to fit.

We installed them in the track slider.

Two really great qualities. The plastic I used was soft. This did not shatter when it impacted the track stop.

The parts operated with no troubles through the rest of the 3 Days of racing.

The other boats in the fleet are interested in track sliders, as they all have the same problem as we did.

Did. ;)

The turn around for the first 3d printed parts was less than 24hrs.

The turn around from design, cam, cnc fabrication to installation and operation for the 2nd set of parts was also less than 24hrs.

It is amazing to me that everything fit as well as it did. I was very careful to measure, and reference the parts.

I think that the track sliders installed in Expeditious will be there for many seasons.

Im excited to use the Othermill for more projects.