Adding Setscrews to Stanchion Bases

[ebb]

ebbdon'tknowitall here,
but like you, probably, I've ruined a bunch of bits making holes in stainless steel..
A google search shows that you and I aren't the only ones.

Not sure what material your stanchion bases are. If they are bronze, there's no problem.
If they are s.s. there is a problem.

First of all, what is that hole that already exists in the stanchion base that goes all the way through?

If it goes all the way through the stanchion-base wall, in and out the other side, why not use a clevis pin - or hero cotter pin. A no thread deal like that would be much prefered! Actually it's a great idea!!! Even #8 or #10 machine screws with a nyloc nuts would get away from nasty cotterpin tails.

If you insist on going the set screw route, here are some resources:
First go to McMasterCarr (pg3072) to see what kind of set screw you might want. For instance, you can go with a cup point that you drive in and will engage the tube without dimpling because the cup has a sharp edge. But you might like a cone point, for which you would dimple the tube so that the cone insets slightly. This has better holding. If you have to enlarge and re tap the stanchion base for a larger set screw, you can chose a set screw with an extended smaller tip that could engage the tube with a smaller or the original hole in it.

If you have to drill a hole in the tube, you have a challange. Sailrite sells a $49 "drill steady" that clamps around 7/8s-1" tube that allows you to drill a 1/8" inch hole. You could probably make the hole larger, if wanted, with a hand drill. Any drilling in stainless tube requires a brand new or newly sharpened bit. Usually three or four. Drilling holes in thin stainless is different then sheet or plate - because of it's structure and thin-ness. Of course it's the type of stainless, 304, 316 - thickness of wall - but also how the tube was made.

You might also find a larger tube drilling jig made out of two opposing right angle pieces of aluminum that you clamp around the work. It might be around the same $50 whack. It could be used, maybe, to get holes in stainless stanchion bases since they are fabricated usually with tube. If cast stainless bases, no experience here. But to drill em you probably have to immobilized em and use a drill press.

Imco the set holes in the stanchion base should be in the fore-n-aft position, parallel to the toerail, so that pushing or pulling on the tube won't tear or perhaps break the set screw in the base - which might happen if the screw was on the 'cabin' side of the stanchion.

Here is an exquisite DRILL & TAP CHART from steven henderson's cutting edge designs (have to give him full credit!) www.shender4.com/thread_chart.htm.
Here you will see clearly that to drill for a 10-24 or 10-32 or 1/4-28 set screw you need the correct number drill, and a tap of the correct size to thread the hole.

www.icscuttingtools.com is probably the only website you possibly get cobalt bits for s.s. in size
25-20 or 21-18 for the #10 set screw - 1/4-28 set screw wants number 3 or 1 - depending on the alloy of the base and depth of thread.
Had a preliminary conversation by phone with ICS about adding number and letter bits to a sweet 40pc HSS hex die and tap set found on their site... for a bunch of $$. Imco if taps & dies are going to last for any time on stainless they have to be HSS. Same for using cobalt bits.
I don't know if ICS will sell a specific die or tap, die or tap handle, and set of bits - but it may well be worth a try. It seems to be a generational mom-n-pop outfit with a knowledgable person on the phone! The site is beautifully set up, it's a gas to cruise!


Drilling tube, I'd make a jig from a thick piece of wood that has the OD of the tube size drilled thru it. Then cut the piece in half to clamp it around the tube. This ought the keep the tube from crushing - and with a predrilled hole of the correct size will make a steady for drilling. Depth of wood around hole would make it easier to control the variable speed drill. Friction here would be helpful (but also heat up the bi!)
A bench press would allow the drill speed to be at DEAD SLOW. With a NEW bit. You have to feel for the amount of pressure needed, and for the sudden let-go when you drill thru. Right befor you drill thru is where a bit catches on thin steel still attached to the unfinished hole - and snap goes the bit. You have to keep raising the bit out of the block to clear chips. And squirt in coolant.
Also important is not letting ANY HEAT build up. It'll harden the steel and dull the bit immediately. This will probably happen no matter what you do - have extra bits. We see various liquids used for cooling and lube. Imco cooling is way more necessary than lube: cutting oil, WD-40, condensed milk out of the can.
For COOLING especially with cobalt: I've been lucky with plenty of denatured alcohol dispensed with a restaurant vinegar bottle, or just plain water.

All the way thru base and tube with a pin is the way to go! No threads. Easy to remove.
__________________________________________________ __________________________________________________ __________
NO DOUBT for a short job HSS split point drill bits should surfice.

Sorry about the load here. And I began the post not knowing that Jerry was going to get posted befor me.
So my thoughts are an effort to respond to Mike's post. Sorry for any confusion.

[bill@ariel231]

All of Jerry and Ebb's points are well taken, oil is always a good idea drilling thru stainless.

On the boat Alyce and I race (A friend's Frers 40) the stanchion bases are thru drilled and fastend with an 8-32 machine screw. No problems with these in years of inshore and offshore racing.

For A-231 I followed a similar path but replaced the set-screws with 8/32 machine screws that engage the stanchion pipes (these are drilled thru on just one side, at the point that the set-screw formerly bore against the stanchion).

No doubt thru bolting is stronger but i did not need to modify the stanchion bases. It is stronger than set screws (I can pull on the lifeline up without worry about removing the stanchion from the stanchion base).

Offshore thru bolting is a good idea. In-shore just about anything goes, but thru drilling one side of the stanchion and leaving the stanchion base un-modified worked for me (and they are still easy to remove for the winter cover).

cheers,
Bill@ariel231