Is it me or is it the drills I buy

[MG David]

I have been having problems with drills bits that I buy.
The sizes I have been using are 3mm, 4mm, 7.5mm and 8mm and I have been drilling holes for plug welds.
The drills seem to go blunt and get blackened at the tip very quickly, especially in the larger sizes.
In the larger sizes these have included ones with a goldy coloured coating I got in Halfords, a "bullet" style one I got in Homebase and a blue coloured one I already had. All were sold for metal.

I start with a hole punch, I then use the 3 or 4mm drill followed by either the 7.5 or 8mm drill. As I am doing the plug weld holes on a foot well there are dozens to do.

The 4mm drill has held up best. It is of a shiney silver appearance.

With the larger drills I have tried sharpening them using my cheap drill powered sharpener but it does not do much good. Could this be because they have been over heated?

My drill has a maximum speed of 3000rpm is that to fast?

Should I be buying my drills somewhere else?

 

[Shox Dr]

The drill you are buying are most likley crap.
The blue one you had has been killed by over heating it. hence the "blue" colour

3k is whey too fast

Dormmer. Presto etc are good makes

 

[Hitch]

Sounds like you may be going too fast, and probably questionable drill bit quality.

Pull the trigger on and off to get the drill to run slower.
Somewhere between about 600- 800rpm should do it.

 

[Cal]

For a High Speed Steel (HSS) drill bit drilling a hole in mild steel (MS) I go for the following approx speeds

3mm - 3000rpm
4mm - 2400rpm
7.5mm - 1275rpm
8mm - 1200rpm

If you are using a hand drill with a maximum of 3000rpm then the amount you are pressing down is slowing the motor, so as your 4mm is lasting the longest then that's probably why.

Are you drilling out spot welds? They tend to be harder than the surrounding MS, but you can buy specialist cutters google zipcutters

 

[mrcheese]

You sound like me when it comes to drills. I have bought cheap and expensive.
Not tried a sharpener yet. Are they worth it?

 

[PhillipM]

Those cheap sharpeners are usually pretty shocking - better off doing it by hand on a grinding wheel - for a cheap HSS bit, jobber length, in a wobbly fixture (hand drill), with no lubrication and uncontrolled you want to be around 1500rpm even for the little 4mm drill to keep it alive for any length of time.

Personally I'd go around this:
3mm - 2000rpm
4mm - 1500rpm
7.5mm - 1100rpm
8mm - 1050rpm

I know it sounds slow, but you'll find a sharp drill ran slow with plenty of pressure cuts a lot faster than a drill dong a million rpms with a melted tip...
You can bump those speeds up 10-15% if you're using a good moly cutting lube on the tips.

 

[mrcheese]

I did read somewhere that older drill bits (>15 years) are generally of better quality than newer stuff. So buying old drill bits from boot sales and sharpening them is a good bet. Any truth in that?

Sounds like getting a variac to control the speed of my electric hand drill would be a good idea.

 

[PhillipM]

Well, I've seen plenty of the cheap chinese ones sharpened the wrong way lately, so...

 

[Simon-]

Branded names means usually better quality control. slower speeds, positive feed rate and a dash of coolant/tapping fluid will help a fair bit to combat wear

 

[beetlejac]

Hi l was drill sharpener champion 5 years on the trot,hahaha,there's not a lot lm good at but sharpening drills l am good at.What l always go on when drilling is for a 12mm drill 280rpm,any bigger go slower and any smaller go faster thats worked for me the last 20 years.

 

[PhillipM]

That sounds pretty slow even for a dry bit and a skinny bloke with the shakes holding the drill

 

[langy]

x 2, as soon as you mentioned Halfords it was a giveaway

The drill you are buying are most likley crap.
The blue one you had has been killed by over heating it. hence the "blue" colour

3k is whey too fast

Dormmer. Presto etc are good makes

 

[PhillipM]

I like the guhring cobalt stub drills for general hand use/fab shop stuff, little more than a cheap set but as you can buy them individually just get the most common sizes you use and a cheap HSS set for the rest.

 

[Rick]

I drill really slow, usually 400rpm's or so in mild steel with lots of pressure 8mm drill, drills last ages and it gets through pretty quick as your removing a bigger cut.

 

[hareng]

I just get a feel for it and alter the feed and speed rate to suit, but yeah 3k way too fast.

Made the mistake some years ago with them gold Homebase drills, i topped up and replaced the good ones for junk.

The only drils i will buy are reputable from Titex, Guhring or Dormer A002, A102 but each has different grades etc.
Prefer cobalt stuff but very dear.

Best drills found to date for all round use on soft to hard materials are the three flute Titex and they last http://www.ebay.co.uk/itm/150488801139

 

[MG David]

Thanks for your comments everyone.

I went home last night and sharpened the 7.5mm freehand on my grind wheel instead of using the sharpener. The result was not very beautiful but it was sharp! I turned the drill speed down to 1/3rd and it cut well.

I may try getting a drill sharpening jig for the bench grinder. I think Machinemart do one. Any good?

 

[Luke]

I wouldn't waste any money on any of the cheap drill sharpening 'tools'. Instead, I found it more worthwhile to practise on the bench grinder. These two pages are useful info.

I sharpen any/all drill bits by hand now and sometimes get the odd one wrong, but on the whole, I have no issues. Once you know what you're doing it takes 10 seconds to get a drill sharp again.

 

[jugs]

Welding 2 nuts (M12 ish) together side by side on the flats, gives you a rough gauge for the point angle = 120° (close enough to 118° )

 

[PhillipM]

I grind mine to 135*, better find some funny shaped nuts

 

[jugs]

I grind mine to 135*, better find some funny shaped nuts

Mrs jugs says I've got some