Drill bits

I bought some 5% Cobalt drill bits to drill out the SS machine screws holding my mast foot down, after six screws all ten drill bits were blunt. Enter stage right this little fellow:

http://www.axminster.co.uk/multi-sharp-multi-sharp-dual-purpose-drill-tool-sharpener

Best £15 I ever spent. Takes some reading to configure right, however, I have now sharpened those Cobalt bits twice (they cost £25 themselves, so I'm long in profit), and it works beautifully to recreate the right geometry.
 
Avocet said:
I wish I could do that! I consider myself a failure as an engineer because I can't (repeatably) get them right. Every now and then I get one right and it works very well, but most of the tim, the results are "variable"! I just have a real blind spot when it comes to drill sharpening!
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I still have failures now and again but just have another go and they are usually good. The secret is to make sure the trailing edge is lower than the cutting edge otherwise the cutting edge can't get at the steel to cut it.
 
Yeah, I know all the theory, I just seem too cack-handed when putting it into practice! I'm notmally quite dextroaus, but just sem to have a real blind spot for sharpening drills by eye... I got my dad one of these a few years ago:

http://www.ebay.co.uk/itm/Drill-Doc...210?pt=LH_DefaultDomain_0&hash=item19d47be2ea

and provided you use the (very expensive) diamond wheels that don't turn hourglass-shaped after the first few drills, it's pretty good (if a bit slow).
 
Lots of good advice being given. From my experience you CANNOT drill stainless using a 7-900 watt hand drill or a light pillar drill. Too fast by far and stalls also when you apply real pressure. You would not believe the difference using a 1400 watt drill with a big speed reduction to an ordinary household drill.
 
Cordless drills are good in that respect. Put an 8mm hole through my stainless pulpit tubes for a wire with ease using a 12V cordless.
 
single said:
Is there a make of drill bits that actually work? I'm doing a load of stainless steel things and whatever i use seems to take forever.
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I've just been doing an awful lot of stainless steel drilling to build a Hebridean wind vane https://tammynorie.wordpress.com/2015/07/21/constructing-the-hebridean-day-2/

And earlier this year I had to do a lot for my rubbing strakes / chain plates https://tammynorie.wordpress.com/2015/06/05/replacing-the-strakes-part-2/

I recommend cobalt steel drill bits. I bought mine from DTC http://dtc-uk.com/ but mainly because they're 10 minutes away. Only the 3mm ones used for pilot holes have blunted or snapped. The 5mm and 6mm ones have lasted and lasted.

You also need a cobalt steel countersink. Others just go blunt very fast. There's the one I got and has been excellent through several hundred holes. http://www.amazon.co.uk/gp/product/B005HVZ1SI

Drill on the slowest speed you can and use plenty of lubricant. I have been using tallow. I am using a fairly light pillar drill (from Lidl!) Small holes (such as pilot holes) can be drilled even with a battery powered hand drill.

I've recently been making 20mm and 50mm holes in stainless with hole cutters too. Also cobalt steel. Same pillar drill, lots of tallow, go slowly.
 
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Given the choice I would always use a pillar drill for stainless but when working aboard it is often not an option. Using a battery drill I have often fashioned a lever, from rope/length of wood, to apply the necessary pressure to the drill bit. I find it almost impossible to apply the necessary pressure by hand alone.
 
alahol2 said:
Given the choice I would always use a pillar drill for stainless but when working aboard it is often not an option. Using a battery drill I have often fashioned a lever, from rope/length of wood, to apply the necessary pressure to the drill bit. I find it almost impossible to apply the necessary pressure by hand alone.
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I've seen drills used on building sites that clamp onto steelwork and automatically feed the bit through the material. I imagine it had a built in lubricant pump.

Stainless can be horrible to machine though. I remember turning a flywheel at school. It squealed horribly. And broke the parting bit.
 
Ruffles said:
I've seen drills used on building sites that clamp onto steelwork and automatically feed the bit through the material. I imagine it had a built in lubricant pump.

Stainless can be horrible to machine though. I remember turning a flywheel at school. It squealed horribly. And broke the parting bit.
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Stainless machines nicely with modern tipped tools, with or without any lube, machining it with old-fashioned carbide tipped tools can be interesting, HSS are nice but you need to keep sharpening then so tipped tools are the way I go.

I think the biggest mistake people make when parting off is not to use plenty of speed and feed particularly with stainless. Not enough feed and it will heat up and harden then it gets difficult, best way is to use a decent thin tipped parting tool and some lube - http://www.rdgtools.co.uk/acatalog/...-x-19mm-blade--12mm-shank--76989.html#SID=578 are very good
 
Ruffles said:
I've seen drills used on building sites that clamp onto steelwork and automatically feed the bit through the material. I imagine it had a built in lubricant pump.
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You are talking about mag base drills. I have one and have used it extensive during the building of my steel boat but marine stainless steel is not magnetic os is limited.

I have used mine on stainless by clamping a sheet of mild steel to the stainless to allow me to drill some 20mm dia holes in my bow roller side plated.
Mine does not have auto feed or built in lubricant pump but more expensive models may have.
Ruffles said:
Stainless can be horrible to machine though. I remember turning a flywheel at school. It squealed horribly. And broke the parting bit.
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Turning stainless can be quite difficult as in most cases carbide tipped tools are used and if there is any vibration or chatter the carbide will chip and become useless
Also a lot of the lathes sold in the DIY market have too small a motor and this makes it easy to stall the lathe which will chip the carbide tipped tools.

I uprated the motors on both my lathe and pillar drill to overcome this problem.
 
Hardening is very noticeable. For example with my countersink if you pause for a moment it becomes very hard to get it to bite again. You need to be bold and do the whole thing in one go.
 
I once had a s/s mast-step fitting made up, for the Leisure 17 I was restoring, but decided to drill it to match existing holes in the coachroof. I drilled a 3mm pilot hole, then used a 6mm HSS bit. I was making slow progress, merely achieving a countersunk 3mm hole, so I stopped to change to a sharper bit. This seemed to be going through quite nicely, but strangely it was still putting a load on the drill. When I stopped to have a look at what was going on, I discovered that, due to case-hardening around the hole, I was actually reducing the diameter of my 6mm drill bit to 3mm!
 
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