DIY Chainplates – Cutting and Drilling

13 Mar
In my last post I talked about the process of choosing the material for making your own chainplates. Today we’ll cover the machining process and then I’ll follow up with my polishing techniques. The material that I ended up using was 2″ wide, 1/4″ thick stainless steel barstock which I had cut into 18″ lengths. It looked like this when I picked it up:
Actually I’ve already done some polishing on the top one, the bottom one is as I received it.
This is hot-rolled 316 stainless steel barstock. Cold finished barstock would have been a better choice (explained in my last post). From this rough stock to a finished chainplate there are four steps: cutting, rounding the edges, drilling, and sanding/polishing. Each step has its own challenges and on each I made at least a couple errors before I nailed down my technique. I couldn’t find any DIY bible along the lines of This Old Boat (Don Casey) or The Boatowner’s Mechanical and Electrical Manual (Nigel Calder) which covers construction of your own chainplates so the internet was about all I had to turn to. There is a decent amount of information on chainplate construction out there but like any DIY source (including this one!) these are often techniques which worked for a certain person in a certain situation and are not always repeatable. There was also the question of which tools I had available and whether it made more sense to feel out my own technique with the tools I already had or expend more of my budget buying tools to do things the ‘right’ way. 
Another option would have be having a machine shop do the work. A shop with a CNC water jet cutter can do all the cutting and ‘drilling’ in a matter of minutes and with the precision of a computer. This should actually be comparable to or less than the cost of doing the cutting and drilling oneself depending on the tools and skills at your disposal. If you have a similar project I would start by calling a few shops for a quote. No need to mention it’s for a boat. Plus if you’re having a shop cut your material even the sanding and polishing could be avoided if you can find an affordable source for polished stainless plate.
As for me, for better or worse I insisted on doing all the work myself.  I’m happy that I did because I’ve learned a lot in the process but this is the first boat project where I would actually have saved money had I outsourced some of the work. As usual I did it all with tools that I already had or could buy cheaply, meaning I sometimes fudged things a bit. Here is my ‘machine shop’:
Not pictured: the most-used tool, a basic 4-1/2″ angle grinder
 The 1950’s Delta drill press was a Katrina flood rescue and the bandsaw is Harbor Freight’s cheapest metal-cutting model which I bought used. I would say the drill press is a necessity and the bandsaw a huge convenience.
I started out by marking my barstock using a compass and measurements from the chainplate sizing table in Skene’s Elements Of Yacht Design. Once this was traced out in marker I went over it with a scribe- a tool which scratches the metal. This ensures you can still see where you’re cutting when the cutting oil wipes away your markings (Yep, figured that one out the hard way. There are few things more frustrating than having to call off a whole night’s work because you’re missing some little $5 tool…). 
My new Dynex rig uses clevis pins so I needed to round the tops of my chainplates and for looks I decided to do the bottoms as well. For this I had to make a little cutting table to turn my horizontal chopping bandsaw into a vertical free-form one. This was an intended modification for the saw so it wasn’t too difficult to do with a bit of aluminum plate from the scrapyard:
That yellow and black thing at the very bottom of the photo is my scribe
The radius of my rounded ends is a bit smaller than the saw is intended to cut so I had to make the cuts a section at a time. Some of them were rougher than others. To finish the really messy ones I marked the radius again and used a bench sander with 80 grit paper to round them off.  Unfortunately I was on my own for most of this so I wasn’t able to get a lot of photos but I’ve saved one chainplate for last. A friend and I will use it to making a video of the process from start to finish which should be up in a week or two. The advantage to using a bandsaw for this as opposed to a grinder, plasma cutter, or some other ‘hot’ tool is that the bandsaw is a cold-cut saw, meaning it produces little heat. If you heat stainless too much it weakens the stainless properties by pulling extra carbon to the surface of the metal so it pays to be careful about this.
With the bars rounded off I moved onto the drilling process. Each plate needed three 3/8″ holes for the bolts and one 1/2″ hole for the clevis pin. It proved to be a bear of a task. The trick to drilling stainless steel is to keep the material as cool as possible. It isn’t much of a heat conductor so it will get hot very quickly and work hardens when it reaches a certain temperature. This means each time you don’t do something quite right it work hardens and gets progressively harder to drill. To do it right you take a bit the full size of the hole you want (no step drilling – it work hardens your material) and drill through in one pass at a very slow speed and with a great deal of pressure.
On an antique drill press with a bit of wobble in the quill and only a few speeds this is easier said than done. After destroying more drillbits than I care to admit I gave up on using my (old)new tool and did the last of the holes on the nicer press at the bike shop where I work (Gerken’s Bike Shop). Even with the better drill press I had trouble getting through my 1/2″ holes on a single pass but I found that with care I could drill a little at a time without hardening the material. It is important to use a lot of cutting fluid or coolant when drilling stainless with the ideal situation being a tool or second set of hands dribbling a constant flow onto your work. I also found it helpful to mark my holes with a center-punch, a tool which makes a small indent to help start the drillbit. Regardless, they were not all quite on center.
When stainless gets too hot it becomes an oily blue color and then a scorched brown.
The shaving on the left stayed cool while the one on the right overheated. This hardens 
the steel and chews through drillbits.
Here we are with some chainplates cut and drilled, ready to be polished. Another technique is to do most of your polishing before making any holes but I wouldn’t want to do this unless I knew I could rely on my drill press to give nice clean edges – mine did not.
Next time I’ll talk about my polishing process and then some time soon we can wrap up this whole chainplate business with a short video and some pictures of them on the boat. Can’t wait for that day!

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder


  1. Petar

    Im going through the same stuff and I have few comments. Water gun with abrasive media will erode the hole and leave rough finish. This is not what you want for inner surface of a chain plate. It might be fine for the 3/8″ bolt holes. Ideally, you would want nice square whole and flat (shiny) surface of the inside of chainplate hole so the clevis pin does not have point loading and hole elongating. Good way would be to have CnC shop drill 1/16″ smaller hole and you just finish it with a nice slow drill press with finish hole diameter.
    As far as one time pass with single drill bit, it might not be what I’m finding. I agree that the key The key is to keep the speed down. However, the less metal you take away less friction and less heating. So stepping the bits does help to lower generated heat and keeps you away from work hardening and glowing bit flutes. I bought a drill doctor sharpening tool that I’ve been using to restore drill bits. it works great.
    Some of my holes are 5/8″ and few are 3/4″ on a 1/2″ thick stainless, Tayana 51 (FD-12). So whole drilling is a daunting task, but speed is everything. I have a drill press that can be stepped down to 600RPM. That is theoretically good to 3/8″ into stainless with cutting oil. But its all relative, if you’re not making progress it will work harden even at 600RPM with the smallest of bits like 1/8″ that i start with. Drilling fast and adding oil, with 600RPM setting, i was able to get the holes to 1/2″ without work-hardening stainless. But it required multiple drill bits (5) and re-sharpening of drill bits. To go up from there I am finding that i need a drill press that can go as low as 100-200RPM. Also HP of drill press is critical. 3/4″ hole roughly needs 3/4HP motor. Keep in mind that if you lower RPM you are increasing your developed torque. For a motor Torque and current in the winding are directly proportional. So for instance we smoked the AC motor winding on my buddies 1/3 HP drill press when we went to lowest speed setting because its so easy to induce large torque at low RPM. This was as we went from 1/2″ to 7/16″ and then to 5/8″ (apparently too big of a step up from 7/16″ to 5/8″ for 1/3HP motor). Lesson learned there is 1/3HP at low RPM will smoke the motor very easily as you try to apply force. So i’m trying to find a used 3/4″HP drill press to finish remaining holes. Yard sales and craigslist are best.
    Also, I’m still trying to find modestly priced chamfer bit to round the edges of a 3/4″ hole. The most reasonable thing was to use 7/8″ drill bit and drill a tad bit to introduce a small bevel. But its not coming out nice a smooth.

    Polishing is a whole other beast. I’m getting throughout quite great with two 4.5″ angle grinders. One rests while the other works. Lots of flap wheels from ebay or amazon(60, 80, 120, 180, 240 and 320 grit) and then a 5″ polishing pad with 320/400 and 600 grit wet/dry automotive adhesive disks. From there its wet sanding by hand in a cross pattern with higher grits (800, 100, 1500) and then rouges on a sisal and buffing wheels. its an exercise in patience, and attention to detail. In this fast -paced world, not too many folks now-days have the patience for it. Some resort to electropolishing which helops but is no match (IMHO).

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