Countersinking stainless steel

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ricardio

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My grp boat has at some point had a plywood bridge deck fitted which I have now removed as it was beginning to rot. As a result I have to replace the external stainless steel strips which hold the washboards in place with slightly longer ones.

I would prefer to use countersunk rather than say pan headed screws to fix the new strips in place. I can find lots about drilling but not much about countersinking stainless. Does anyone have any tips?
The only countersinks I can find are HSS -will this do or should I look around for cobalt or more exotic versions?
Also is there a quick way to make sure all the holes are countersunk to the correct depth?
 
I think if I was in your position, rather than invest in a tool I would probably never use again, I would be tempted to just take it to a small engineering workshop and ask them to do it for me. Probably cost less than the tool and be done more accurately. I hate working with stainless!
 
Whats wrong with panhead as it can be difficult drilling stainless as it work hardens
so if your gonna drill it don't Hang around and apply lots of pressure or it will work harden and your in trouble!
 
HSS will be fine - but cooling is the key.

If you have cutting oil then use it copiously in large quantities. If not, any oil in large quantities too. Old engine oil is fine.

Failing that, running water will work pretty well.

The main thing is that there is enough cooling. Which rules out just dipping the drill and workpiece occasionally. It has to stay cold.

Be careful with the electrical side of the drill.
 
A decent HSS countersink will be quite expensive, and won't be brilliant on SS. If you can use a grinding wheel, I suggest sharpening an ordinary HSS drill bit to a 90 deg. point and using that at low speed and reasonably heavy pressure, preferably in a bench drill.
 
It would require a more than ordinary degree of skill to do this well with a pistol drill. With a bench drill you will be fine with a reliable HSS bit... as others have pointed out.
A cheapo Chinese bench press is fine but don't rely on the stop to contol the depth of cut, they are rarely up to it, with care you can do it by eye.
Slow speed and firm pressure is the key and use some of this stuff:

http://www.lawson-his.co.uk/scripts/details.php?cat=Metal Cutting Lubricants&product=1790

If things start to smoke, stop right away and cool things down. If you dont hold your workpiece firmly enough/run the bit too fast, it will chatter.
 
As said slow speed and plenty of coolant pistol drill is perfect for the job keep it at right angles to the workpiece use a HSS countersink they are reasonably cheap a few quid each in fact buy a couple countersink to the same diameter as the screw head as a guide remember tosecure the workpiece******simples?
 
ricardio said:
My grp boat has at some point had a plywood bridge deck fitted which I have now removed as it was beginning to rot. As a result I have to replace the external stainless steel strips which hold the washboards in place with slightly longer ones.

I would prefer to use countersunk rather than say pan headed screws to fix the new strips in place. I can find lots about drilling but not much about countersinking stainless. Does anyone have any tips?
The only countersinks I can find are HSS -will this do or should I look around for cobalt or more exotic versions?
Also is there a quick way to make sure all the holes are countersunk to the correct depth?
Click to expand...

Countersinking to look good must be done correctly, stating the obvious but it will look a mess otherwise.
Use a HSS drill the same diameter as the screw head so that it will sit level with or just below the surface being countersunk.
Cutting fluid is essential with a new drill or one properly ground, I can recommend your own spit as a cutting agent, keep the swarf clear and go slowly with a good speed on the drill.
One tip, it helps if the hole your going to countersink is smaller than you need but can be opened later to required size, it prevents drill 'chatter' as you countersink, particularly with SS. s to depth it is easy to see the shoulder depth which the screw head thickness will fill.
I would not recommend a countersink all size tool as you will have different countersinks at each one and doesn't look good.
Finally use a pedastal drill as a hand drill will make it more difficult to control.

Hope this helps
 
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