Sharpened large drillbits not cutting

[Ttrees]

Hello all
I've looked through a few pages here and not found results,so I thought I might as well ask...
Having watched a good few youtube videos, I am managing to properly get the sharpening of drill bits
under my belt.... however,
I am surprised not to stumble across the problems I have encountered.
I am not sure whats going on here, and am looking to find out what the problem is.

Having bought a box of Silverline blacksmiths drills and one or two extras I found them good initially.
I probably overheated these in the past, due to being afraid of grinding them down to nothing when practicing.
So I held it off, and slowly drilled the holes I needed taking hours ....

Recently I have been trying to drill a hole in 40mm thick stock that was welded to a thick plate.
I have been drilling out this hole to 22mm plus (damaged bit)
The hole has to be a tad less than my 24mm bit ...
it is for a sleeve on a motor shaft to fit into a pulley .
Anyway
I spent two hours... or probably far more than that drilling this hole
During this time I managed to get my sharpening skills down and experimented with angle changes,
and was highly critical of my results, so strived for perfection .
End result was very sharp cutting edges , correct relief ground in a single swooping facet .
Still no cutting !
I was going up the bits in stages successfully until I got up to about 16mm and then the cutting stopped.

I don't think the tempering was at fault here, as I managed to cut with an overheated bit from grinding
easily ...evident from the blueing on the edges ,
Plus wouldn't the edge get dull on a bit which was annealed ?
Maybe my 40mm stock got work hardened or changed temper ?
Or was it that I should not be drilling these holes in stages of 2mm at a time, and try and get the drill to
bite into more meat to self feed itself and cut more aggressively.
My bits remain sharp after this drilling ceased .
Could the flutes be the problem here ?

Thanks for any advice
Hope I can get some answers
Tom

 

[Bigdanny]

That sounds like a lot of metal to remove with a drill. I am no expert but I would probably try a decent holesaw, make sure you keep the swarf cleared more or less constantly with an airline. Other methods might be if you have a friend with a plasma torch. I am guessing the hole will be covered by a bearing holder so doesnt need to be too accurate.
Hope this helps a little
D

 

[Ttrees]

Hello Danny
The actual size of the hole is not the problem, I just need to find out why I am having this issue in the first place.

It defiantly needs to be accurate though, as I am making a sleeve for a motor shaft.
This is for a tablesaw, so is a 2 pole motor and as you can see if it does not fit correctly it will wear the keyway.
I have since welded this and filed it, and now I'm just waiting to turn this sleeve on the motor once I get the
hole drilled to an accurate size ... VFD in use so adjustable speed .
I might file this last sub 2mm actually, as my 24mm bit is too large and the motor shaft is not quite 24mm .
I have done this allready with the pulley .

Thanks
Would love to read some link or something describing the issues I've been facing.
I would also like to know if anyone has taken 0.5 mm off a drills thickness also.
From what I've seen this is not possible ...although most are not as stubborn as I .
If my "final cut" cheapo 24mm drill is only a one time deal and is for the bin allready,
then will it cut at all if I reduce the diameter ?, any less than the rest of them ?
Tom

 

[sunnybob]

You mentioned the dreaded "S" word.
Dunp them. Youre just wasting your life trying to cut through metal with them.

Buy some decent drills from a proper engineering shop (ebay works, just not the make you already have) Dont buy gold coloured ones either.

To drill a 24 mm hole through metal should done in at least 4 stages. start at 6 mm and go up another 6 mm each time as an absolute minimum.

 

[Sheffield Tony]

You mentioned welded - are you drilling near the weld ? That can leave the hardness a bit unpredictable.

 

[Bigdanny]

Ah now I see pics it makes more sense what you're trying to do.
On the drilling , sharpening thing not sure what the prob is, I watched a vid on youtube from Ave recently and as long as the flutes are clean and a drop of oil to lubricate then should be ok, if the angles of sharpening are good then its down to loss of temper.
But seeing what you're doing I would talk to a lathist and use a boring bar or fabricate the pulley as one to fit on the shaft of the motor.

Good Luck
Danny

 

[Ttrees]

Yes I have heard of these things being referred to as the dreaded "S"
I want to know why though,
I know they wont cut now, but they did for a time....quite some time ..
Enough for me to get my moneys worth outta them.
The pack cost about 20something quid ...
And a single drill of say, more than 20mm would be in the region of about 30something pounds...

There was no titanium nitride coating or other kind from what I could see.
Why have these ceased to cut ?
Is it the flutes ....
Has there been a taper worn (insert correct terminology here) into the first inch or so ?
I have seen worn flutes on some drillbits on various youtube videos, with no mention of reduced
effectiveness.

Thanks for reading
Hope to get to the bottom of this :roll:
Tom

 

[Ttrees]

Sunnybob
I have been drilling these holes in stages ...
I was worrying that I was doing so in too many stages.

Tony
Possibly you are onto something here
As the larger the hole I cut, the closer to the welds I'm getting ...

This round stock that you can see is 40mm tall, and was welded to the plate in the same orientation as shown,
Plate was underneath ..It was some kind of prop ...
Big beefy 10 or 15mm plate with heavy round bar welded to it and a champfer on the top.
It might have got hotter again with me cutting it with an angle grinder

If this were the case though, would the start of each size bit used not be much faster cutting,
as the weld was on the bottom of the stock .

Danny
I'm the only machinist I can afford :lol:

Thanks for the input guys
Tom

 

[Phil Pascoe]

I needed a 16mm blacksmiths and got it on ebay from UKDrills for £2.56 inc. P&P. Sometimes their stuff is cheaper on ebay than straight from them. 15/16" would give you a minute amount under 24mm if you could find one.

 

[Ttrees]

Thanks Phil
Will try and look for one
It will save me thinking about possibly reducing the size of the 24mm one
Gonna go searching
Cheers

 

[lurker]

What sort of speed (rpm) are you drilling at?
It needs to be really slow

If the bit is not visibily cutting then all thats happening is you are case hardening the workpiece via friction

 

[Ttrees]

Lurker
I have not been adhering to this rule.
My drill press is not equipped to run that slow.
I have been using loads of coolant and the drill is not hot, but the workpiece is very warm
You seem to be correct.
I take it it's still possible though, as I think I have experienced a dull drill getting quite hot
eventually getting through the hole, and then change to a bigger drill and it sails through the work.
I think a new bit would sail through this ...
I could be wrong though ?
Tom

 

[lurker]

If you sure its not getting hot you could still be work hardening it.
A very common failing when drilling stainless steel (I realise you are not drilling SS)

 

[CHJ]

.....If the bit is not visibily cutting then all thats happening is you are case hardening the workpiece via friction

+1 for that. It was my first reaction.

Too high a cutting speed. (you probably need to be able to watch the flutes rotate)
Too little feed pressure.
Too little cooling/cutting lubrication.


The very fact that you are quoting such long times to drill the holes indicates the above to me.

Drill swarf should be hot, possibly Blue, Drill itself should be warm with no discoloration.

What HP and size of Pillar drill are you trying to do the job on? in my last shop to drill holes in steel plate of those dimensions we used a radial arm drill weighing several tons with power feed.

Sorry but personal reaction is to cringe at making a shaft sleeve that way, for something that is going to run at those RPM and requiring good balance. I'd seriously recommend asking for help from someone with a lathe.

 

[wallace]

My drill was too fast for doing large holes in metal so I found it worked better doing them free hand in a variable speed hand drill. If you can clamp the item on the floor and work above it exerting a reasonable amount of pressure whilst keeping the speed down.

 

[Phil Pascoe]

24mm holes in steel with a hand drill, Popeye? :lol: Really?

 

[Ttrees]

Thanks guys
I managed to find a set of drills on eBay with a 15/16" one up to an inch.
I might go this route.
I have managed to drill steel up to 25mm with these Silverlines before ...
I think I might be able to get it done again.
I can always drill for a second and let it cool off and repeat.
Its not like I'm drilling multiple holes and am doing this to a deadline.

I might check what the shaft diameter is before I choose to go this route
If the 15/16" hole proves too large, I will have to make another marking tool to file to

Here is everything at present
Was planning to bore the aluminum out now that the hole is centered ...
Either that or use the sleeve as a marking tool ...

Still curious if anyone disagrees with me about a new drill cutting this a LOT faster ?
Tom

 

[Inspector]

I would just hunt down a steel reducer bushing, shaft adaptor or shaft sleeve in your area. Or have a machinist turn it on a metal lathe. You've work hardened the steel (see if a file skates across your sleeve) because you can't remove the metal fast enough and if you get a quality new bit it may be dulled in seconds when it hits the hardened area. That would be better turned to size and then bored out on a metal lathe plus it would have the advantage of being concentric. what you will end up within a wobbly pulley that will wear out, possibly wrecking the shaft. You don't want wobbly pulleys on a table saw.

https://www.grainger.com/product/DAYTON ... ?$smthumb$

https://inverterdrive.com/group/Gearbox ... r-to-19mm/

https://www.fastenal.com/products/power ... pters%22|~

Pete

 

[pcb1962]

You really should find someone with a lathe. If you tell people where you are perhaps someone will offer. If you're anywhere near me I can make you a reducer bush in 20 minutes. Cutting the keyway may take slightly longer.

 

[Ttrees]

So it seems theirs mutual agreement that the piece is work hardened ...

It wont bother me as its only less than 2mm to remove ....
It wont bother me regrinding the bit being dulled either...I've sussed that part.
I can make another center marking tool for the sleeve OD
and I can rig up an angle grinder and turn the workpiece on the motor spinning at a low RPM and get it close
And follow up with a file being jigged up or something similar.

I wont have a wobbly pulley and I can't see how I would destroy shaft as I can just weld it up again.
]I like challenges anyway
Its the best way to learn
Thanks
Tom