Stupid question but
|Colin Jacobs 1||03/05/2011 19:07:21|
|69 forum posts|
Is this cos they are cheap, used c ten times drilling BMS 3mm thick it is a 7mm and 4mm bits. Can I re sharpen them? I had a go but alas no cutting they just either make sparks, go blue/ black or overheat.
Sorry to be a pain.
|Clive Farrar||03/05/2011 20:55:43|
119 forum posts
I may be because they are cheap but most likely is you are not getting the cutting angle right.
May I suggest if you are hand grinding only that you do the following.
Get a largeish 10mm + new drill and line it up with the staionary wheel so that the cutting edge is across the face of the wheel. Mark that angle on your rest with a marker or something.
Take your blunt drill start the whhel and offer the drill up at the desired angle and with the drill cutting edge hoizontal.
touch the drill lightly to the wheel and imediately start rotating it clockwise. As you rotate slow down slightly untill you have done the full face. cool the drill in water and repeat with the other face.
The idea of slowing down as you rotate is that slight extra time is allowing it to grind more and give you the secondary clearance.
Not a perfect way of doing it and probbably not the best explanation but they should cut a bit better than your current attempt.
|1017 forum posts|
What sort of revs are you using these bits at?
If they are not of great quality, then it might be wise, once you have them sharpened/replaced, to use one of the cutting goops - Trefolex RTD etc to try to keep them cool. I use a goop on all drill bits.
If they were cheap, then probably the best thing to do is throw them away and buy good ones. If you are on a budget, then still throw them away and buy good ones. If you are desperate, then buy a drill sharpening tool and an off hand grinder. You'll get them sharp and buy time so you can throw them away later - but you will have acquired sharpening kit which you can use on a variety of tools.
There is no such thing as a useful cheap drill bit. Sorry.
|Clive Hartland||03/05/2011 21:41:42|
2820 forum posts
Colin, there are some cheap old drills on the market and its no good buying those little boxes of black drills you find on market stalls.
I have seen some reasonably priced TIN coated drills in metric sizes in Wilkinsons, in fact I bought some and they are OK.
When you buy drills make sure they are High Speed steel drills, there are other types for cutting hardened steel and other types for drilling brass and such like.
Best get a book or a catalogue and study it.
Regarding sharpening, its practice, practice and do it again until its second nature. You will soon learn whats good and be able to drill clean holes.
The smaller the drill the faster it goes, bigger drills slower.
|Ian S C||04/05/2011 12:20:19|
7468 forum posts
Before youbin the drills, use them for practice sharpening them. Then when you'v had a go at that put them aside, and use them for wood working, but they might be OK, just cut the speed by a half of what you are using now. It sounds that they may be carbon steel, so be even more careful about not over heating them either when sharpening or drilling. Ian S C
|Colin Jacobs 1||04/05/2011 18:13:37|
|69 forum posts|
Just bought some jobbers again and they spin and spark and smoke in the hole, not drilling at all, what have I done??? I drilled the holes part way then the older drills stopped cutting has the heat hardened the BMS?
Sorry if those questions seem foolish.
|Andrew Johnston||04/05/2011 19:11:41|
6602 forum posts
There are no foolish questions; even the most knowledgable know only an insignificant fraction of what is known.
If the material is BMS then it will not have been hardened by the heat, as it doesn't contain enough carbon. So, first question; are you sure it is BMS? Give us some numbers; what size drill, what rpm are you using? Where did you get the drills, ie, are they quality drills or 'DIY' level?
|1017 forum posts|
No the heat hasn't hardened the BMS - as Andrew indicates you won't heat treat BMS unless you add carbon.(At which stage it stops being BMS)
It sounds as if you are running at high revs and not applying cutting pressure. Thus you get a lot of banging and sparking and heat. The heat then affects the temper of the drill bit, it goes blunt, fails to cut and then rgets really hot.
Slow down, apply pressure, and use a cutting compound - and a decent drill bit. Don't forget that while cutting generates heat, it also gets rid of it in the chips and swarf, so don't let the bit rub - MAKE it cut.
Actual speed depends up to a point on the size of the machine and how rigid it is. For a lightish hobby drill press, and a 7 mm bit, 500RPM tops, more like 350? You are far better running slower, and leaning on the work, than poncing about with high revs and a low feed rate.
Are you sure these bits are HSS? Sound like monkey metal woodworking bits to me???
Edited By mgj on 04/05/2011 19:48:49
|Steve Wan||05/05/2011 04:04:28|
|131 forum posts|
Small diameter drill bits is best sharpened by hand grinder though you may need some practise but the result is rewarding. The shape of the drill tip is not much affected by hand grinding and the properties are not affected either.
If you want to get an even grind a perfect angle for mild steel and maintain an even cutting edge bothside one can use the drill gauge to check.
I have successfully made a drill grinding jig of Tormek grinder design. I'm able to get the so call 4 facet cutting faces. When tested, I got an even flow of chips both ends and the drill simply sucked into the hole at ease during drilling, ending a mirror wall finish. of course its better to make pilot holes for larger dia. usually I drill 3mm first after a spot drill by a hand drill.
11 forum posts
Can old HSS drills be ground into tooling for small lathes?
|Andrew Johnston||13/05/2011 11:12:47|
6602 forum posts
.....the shank of HSS drills is often left soft, so unless you have a means of hardening it, they won't be of much use.
11 forum posts
As Mutley would say......"Ssassa-nassa-frassa"
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