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Drills bits and Chassis holes


SteveG

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I've found when drilling holes in the chassis for M12 bolts etc that even good quality HSS bits lose their edge after a while. I've been using drilling lube too.

What's best - buy the cheaper HSS bits and throw them away when they are no good or use good quality bits and sharpen them?

If latter - how do you sharpen them/what do you need?

Cheers

Steve

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If latter - how do you sharpen them/what do you need?

I use one of these

nut1037.jpg

If the drill is mullered use the grinder, but the linisher is great for just sharpening the edges.

Pretty much every time I grab a drill, a quick touch on the linisher and its good.

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Steve, make sure you use a variable speed drill, keep the speed down and keep a fair bit of pressure on the drill and they should last quite a while.

Even cobalts will dull pretty quick if used to fast.

Proably using it on too fast a speed - I'll chill out and go slower tomorrow when I use it again! B)

Thanks Col. btw turning the CB on in the way instructed didn't work :rolleyes::rolleyes:

Steve

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Proably using it on too fast a speed - I'll chill out and go slower tomorrow when I use it again! B)

Thanks Col. btw turning the CB on in the way instructed didn't work :rolleyes::rolleyes:

Steve

Steve, are you drilling a Pilot hole about 3mm?

Peter

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  • 3 weeks later...

I have a set of drills called "Turbo Max" that have a center point and then cut from the outside inwards. No pilot hole required but as said, you do need to slow the drill right down.

Rule of thumb, the harder the metal, the slower the drill speed.

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I have a set of drills called "Turbo Max" that have a center point and then cut from the outside inwards. No pilot hole required but as said, you do need to slow the drill right down.

Rule of thumb, the harder the metal, the slower the drill speed.

Long time since I worked on the tools, but I doubt the following has changed:

For typical use with steels, the following formula is considered standard:

CS=1000xS

-------------

3.14 X ø

Where CS = Cutting Speed of tool (required answer).

S = Recommended cutting speed of steel (listed in engineering books like Dormers etc)

3.14 = pie

ø = Diameter of cutting tool.

Or just go slow! with more pressure.

And as Petergg says, just a small pilot hole, as a rule of thumb, the pilot only need to be as big as the none cutting area of the next drill (i.e. the bit in the centre which cannot cut)

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There's not a lot in it between cheap & expensive drills in terms of life if you can sharpen them.

You will save yourself a bundle of cash if you can sharpen them. It's much easier to show you than to describe how to do it, and there are one or two tricks in sharpening, particularly big drills, to make them cut better.

When you are grinding, make sure the tip stays symetrical. Do one or two quick passes on each side (each cutting edge) then swap to the other. Do not let it get too hot. Look down along the shank of the drill from the cutting tip and note the shape of the two cutting edges. If they are straight, the drill will cut well under most circumstances. If they bow in, the drill is too flat (it will still cut, but will tend to chatter). If they bow out, the drill is too pointy and you'll get lots of burrs. (the bowing in or out could be the other way round - it's late & I can't remember!). One way or another, straight is best.

One tip is to colour in the tip with a black marker and drill very briefly. You can see where the marker has been rubbed off. If it's rubbed off anywhere other than a straight line behind the cutting edges & point, you have high spots that you will need to grind down some more.

Experiment a bit when you have some time. Very often if you are drilling something and it is not making much progress even though sharp, changing the pointyness a little will do wonders.

Since I learned to sharpen bits - I only replace broken ones or ones which have been ground down to the point where there is no drill left (6.5mm for example - must buy another one!).

Si

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There's not a lot in it between cheap & expensive drills in terms of life if you can sharpen them.

When you are grinding, make sure the tip stays symetrical.

Si

True, and not to be snubbed, it probably contributes more than anything to the life of the tool, and also provides a more accurate hole, and better surface finish.

Drill grinding is a massive subject, but done right its right. During my apprenticeship, I spent 6 months in the tool room grinding everything from Drills to saw blades.

A very easy way to acheive symetry of the tips is to use a "scratch post".

A very simple fab, but can help on grinding bigger drills and maintaining symetry.

Basically, its a piece of flat bar, say 50 x 8, 300mm long, with a 90° fold say 50mm long, then on the short fold, attach a pin in the centre (something like ø8mm with a point of about 30°). Then paint the 300mm long face thinly and dry.

Look at most quality drills, they have a centre hole at the chuck or morse taper end, this then sits on the pin, you can then scratch the 300mm long face (do it lightly), then revolve the drill 180° and check that the second land (cutting edge) is in line. Then grind to suit if required.

For drills without the centre hole, place them in a quality chuck which usually has them.

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I use these

19853.jpg

Cobalt Drill Bits

Cobalt Drill Bits

Super Duty Cobalt Drill Bits for drilling hard metals. This is the bit for your difficult-to-drill alloy applications.

135-degree split-point for quick penetration and reduced walking . M-35 Cobalt steel for increased heat resistance and longer life. Heavy Duty construction.

There not cheap but worth the money

I had them for the racer when you dont have time to faf about and for drilling out 8.8 bolts

and hub nuts

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Drill grinding is a massive subject, but done right its right. During my apprenticeship, I spent 6 months in the tool room grinding everything from Drills to saw blades.

my dad did that as part of his aprenticeship in the late 50's -early 60's... he's bloody good at sharpening drills though...

...mind you after 6 months you should be.... ;)

........cant quite get my head around it though......... :(

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I agree the subject is massive - but, for most people drilling most materials you can learn everything you need to know in minutes plus half an hour of experimenting.

I used to find it bewildering - but Nick (Rogue Vogue) spent half an hour with me several years back and although I'm not brilliant at it, it took the mystery out of it. As I said, I now only buy bits if I lose, break or grind them to nothing.

Cobalt tools are very good (I have a couple of mill cutters) - but, I'll bet one of my chocolate bits will last ten times as long as any cobalt bit (with the occasional tickle with the grinder), but cost 1/10th as much.

We had a carpenter at work moaning about his drill bits all being blunt and the shops being shut - he'd have to come back in a couple of weeks to finish the job (that needed doing overnight!). We spent half an hour sharpening his bits with a 12" petrol stone-cutting grinder (I think it was past HSE's bed time ;) ). I've never seen anyone look so pleased! A couple of weeks later he said he'd bought a grinding wheel from Screwfix and I must of saved him a fortune!

Si

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Cobalt tools are very good (I have a couple of mill cutters) - but, I'll bet one of my chocolate bits will last ten times as long as any cobalt bit (with the occasional tickle with the grinder), but cost 1/10th as much.

Si

Si, it is material and machine specific, that statement could be very easily turned around. In theory, HSS should not out last a similar cobolt when used properly. Although if you have the machinery, ceramic is the way to go, but dammed expensive, a milling machine I used to run had a massive ripper cutter that used to cost £2,100 just to put tips in. I was very fortunate to serve my apprentiship and work at a big engineering company that machined everything from PTFE to Hardox and the moly's etc. I have used almost every type/material of tool bit and every permissible ground form.

But as mentioned, its not always down to material of drill bit. It is often the quality of grinding, I used to regularly turn, mill and drill TOOL steel with TOOL steel.

It all depends on how happy you are with the bore finish, size and concentricity.

Careful use, slower than you expect speed and strong feed (preasure) and plenty of coolant/cutting oil is the solution to drilling most steels.

The standard 59° (118°) HSS will do for most apps.

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