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Grinding brad points on long series hss drills

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jon hill 324/07/2022 00:21:42
128 forum posts
24 photos

I tried deep drilling wood on the drill press and the drill always wonders off on the far end with hss general purpose drill bits. I have heard that the brad point grind is better for wood so may help with deep drilling...

Has anyone any experience with grinding brad points on general purpose 300mm drills? I have a bench grinder and a tormek if that narrows my options.

Jon

Peter Krogh24/07/2022 00:27:20
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223 forum posts
20 photos

300 mm is a very large drill!

peak424/07/2022 01:42:54
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1776 forum posts
193 photos

Is this the sort of grind you are contemplating.
Not the best video presentation, but still illustrated the point quite well

Bill

Speedy Builder524/07/2022 07:04:23
2642 forum posts
217 photos

this is a good video on brad points. Brad Point

Clive Foster24/07/2022 08:26:59
3172 forum posts
113 photos

That brad point sharpener technique looks pretty amenable to a jig or two to ensure the angles are equal and the grind central. I'd think a look at Howard Halls methods would be inspirational.

The presentation seems classic apprentice instructor style. Show and tell then walk round correcting the trainees technique as they try for themselves. I rather like the lack of flash but it doesn't really translate well to the modern YouTube age. If only thre were a way to link print out pictures to do the equivalent of teachers blackboard in a classroom.

Clive

DC31k24/07/2022 08:27:22
725 forum posts
2 photos

Brad point drill are alternatively called 'lip and spur' drills, so that could be a useful term when searching.

There is another good video by JSK-koubou, called 'convert a drill bit to brad point' where he shows the actual angles he uses: 77 degrees (or 13 degrees from the axis of the drill) to form the lips, with 10 degrees relief angle. Rotate the drill slightly once the lips are formed to finish the point. Looks like a reasonably sharp corner on the bench grinder wheel is helpful.

Clive Foster24/07/2022 08:40:16
3172 forum posts
113 photos

Further to my earlier post here is a video showing how to make a wooden jig to do brad points using the same technique. The method of cutting the point is sligtly different and, possibly, more accurate. Metal version could be smaller.

https://www.youtube.com/watch?v=U0jGbXY3rUY

Can't make the embed thing work!

PS That is the video referenced by DC31K who posted whilst I was struggling.

Clive

Edited By Clive Foster on 24/07/2022 08:46:39

larry phelan 124/07/2022 09:19:34
1190 forum posts
15 photos

Peter, Perhaps the 300mm refers to the length of the drill, not to the dia ?frown

Hopper24/07/2022 09:22:04
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6616 forum posts
347 photos

They are very easy to grind freehand on a bench grinder. Woodworkers do it all the time. Get some old drill bits and practice on them. You grind the standard pointed drill bit down flat across the end first and then hold the cutting edge on the corner of the wheel to put the angle on each side, leaving the "tit" in the middle, which can be finely shaped to a point agan on the corner of the wheel. You grind the OD tips down so the tit in the middle sticks out a little further than the the OD tips. That way the tit in the middle acts as a sort of centre drill as you go.

This type of drill point is also very good for drilling thin sheet metal. Just lay the sheet on a piece of wood first so the centre tit goes through into it and then the two OD tips cut out the outer circle to a nice hole with no grabbing and burring like you get with a 118deg point on thin sheet. It's a sort of trepanning action.

It's a very handy skill to develop. Worth wasting a few old drill bits on to learn.

Edited By Hopper on 24/07/2022 09:23:16

Mike Poole24/07/2022 09:34:22
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Moderator
3374 forum posts
76 photos

Hopper you have just said exactly what I was going to say as I was reading down the thread, including how useful they are for sheet metal. I found them very useful for drilling holes for security switches in situ on a car, that was a long time ago when cars didn’t have alarms.

Mike

Calum Galleitch24/07/2022 11:50:22
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194 forum posts
65 photos

The purpose of a brad point is to create a clean entry hole in soft material; it has no bearing on straightness and I'd guess probably makes it worse.

Drilling an accurate hole in 300mm of wood is a challenge; some more information about the workpiece and setup might be helpful. Generally, though, the advice would be to start off with a stub drill one size under, ream to size, then step up drill lengths. The drill will still wander but it will get progressively worse instead of veering off sideways from the start.

If that isn't sufficient, you will need to leave the world of twist drills behind and investigate things like D-bit drills and gun drills.

Trevor Drabble24/07/2022 12:52:32
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287 forum posts
5 photos

Jon , You have not said what diameter you are drilling . Have you seen the Fisch long series auger bits at Axminster Power Tools ?

Clive Foster24/07/2022 14:06:41
3172 forum posts
113 photos

Hafta disagree with Calum as to the action of brad point drills.

Correctly ground they cut from the outside edge inwards. The actual cutting edge should be slightly concave. Good quality commercial ones have a very shallow lip on the circumference projecting slightly forwards of the cutting edge.

As the brad point stabilises the centre the cutting forces on flat material will be balanced at the outside diameter of the drill so there should be no net deflection forces. Unlike a conventional drill where the cutting edges are offset from the centre creating a net deflection force. The deflection force remains even when the cutting edges of a conventional drill are fully engaged but generally they are overwhelmed by the stabilising effects of cully engaged cutting edges and, on deeper drillings the hole walls. If the deflecting forces are not fully overcome the drill wanders.

As with a conventional chisel point a brad point doesn't properly cut. Its more ore less forced into the material. Hence the general restriction to softer materials. The concave shape of the cutting edge means a brad point drill is much worse than a conical point at clearing the extruded material produced when the point is forced into the material being drilled. Another reason for the restriction to soft or thin materials. Generally if the material is thicker than the brad point lenght things start getting iffy on more resistant materails.

Clive

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