Drilling brass.

As Martin says run the stone up the drill's axis so that the leading edge of the helix becomes vertical. The cutting edge will still be sharp and the helix able to remove the swarf.

Clickspring shows it quite well

Edited By JasonB on 14/12/2021 14:48:53

At the Government Training Centre they taught me to grind a zero-rake 'platform' about 0,5 - 1mm wide to defeat the rake at the cutting lip. It's much like JasonB's recommendation above, but - for me at least - quicker and easier to achieve. It resolves the snatching problem completely. Time spent learning to get the bench grinder to do what you want is never wasted.

At work I drilled lot of aluminium bronze ,as mentioned grinding a negative rake on the drill is the way to go.and reduce the web at the point.

When drilling deep holes the drill tended to tighten and seize up in the hole ,to overcome this I would use a smaller drill and grind the point slightly offset Which worked well, also avoid a poilet hole if possible.good luck

Edited By stuart jones 2 on 14/12/2021 22:10:24

Brilliant! Thanks to all for replies. As a result of this I think I understand the way drills work better than I did. They have always been a bit of a mystery to me, there are so many angles involved.

By luck (or perhaps I'm developing an instinct?) my 'random swipes' on the Screwfix bit were pretty much as in JasonB's pic and the Clickspring video he embedded. I was wrong to say 'blunting' - I probably actually sharpened the bit, but with a different geometry. I certainly noticed the difference in the chips coming out - more like normal brass turnings.

I had heard of dedicated brass bits and assumed they were terribly expensive, but looking at the slow spiral bits from Tracy tools it seems not. Thanks for the pointer MadMike.

I agree that pilot drilling is, in general, not the way to go. I have found that in steel I'm better off going straight through with the final diameter bit (17mm is the largest I have - used to make space for a boring bar) to avoid snagging. But I was at my wit's end and thought I'd give it a go. I accept that it wasn't a good idea.

The problem is solved I think - thanks again for advice.

Robin.

Edited By Robin Graham on 14/12/2021 23:35:32

I'm with Jason B on this one, when drilling brass I nip up the quill lock lightly, drill, mill or lathe, for any size hole other than the smallest sizes.

Saves he need to blunt (sort of) a drill.

John

In my early days at work,the process of "backing off "as we called it,was exactly as Jason shows in his dwg and used on brass and bronze,including gunmetal , and also cast iron where there job involved several hundred holes. Backing off was always carried out on a grindstone,smaller drills by hand using the thin wheel on a cutter grinder, never saw anyone using a stone,unless one is very skilled it is all too easy to round off the edge and produce a blunt drill. When drilling brass and bronze fittings which have stepped holes,eg pipe nipples,dont use a pilot drill ,start by centre drilling a slight impression the get the centre then drill the largest part of the hole first and then drill the smaller hole.When drilling phosphor bronze ,there is the tendency for the drill to jam in the hole,this can be cured by grinding the drill point slightly off centre to increase clearance for the drill.

I suppose the stone or diamond slip is more common in a hobby workshop as many won't have access to a T&CG, nearest to a thin wheel might be a disc in a Dremel.

Should also point out to any beginners that although using no pilot will help stop the drill drawing itself into the hole, you loose all that advantage as it breaks out the end of a through hole so take care when you get to the end as that will be the most likely place for it to grab..

I am for stoning or grinding the edge to give 0° rake and keep the drill separate for brass afterwards, resharpening for steel will soon use up your drill bit. Unless you plan well ahead acquiring a slow helix bit will take a few days as unless you have a remarkably good tool merchant close by it will be need to be delivered. I am in the happy position of having amassed too many drills so modifying one for brass won’t usually compromise my set for steel. If you have to modify a drill bit for brass then mark it and store it separately then order a new one for steel and hope it arrives before you need it. Unless you do an extraordinary amount of brass work then investing in a set slow helix drills may not be a good value for money. I think I have one slow helix drill inherited from my father who worked as a toolmaker for a switchgear company so slow helix would have been used in production applications and readily available.

Mike

It has been interesting to read details on modifying drills for brass. I was taught to reduce the angle of rake at the front part of the drill with a couple of strokes with a fine stone, and no mention was made about reducing the helix of the flutes. I will be trying out the method. As already mentioned, increased friction in the tailstock quill by using a bit of lock can help, especially if the tailstock threads allow backlash, not unlike climb milling. Some lathes have adjustable nuts in the tailstock, the Smart & Brown model A has this.

That's always been all that's needed for me too .... but, as is typical when you get a bunch of guys together (especially here), things tend to get way over-complicated.

The helix rate automatically produces the rake angle, the standard helix produces a rake suitable for steel so will have a tendency to self feed in brass. Slow and quick helix drills are available but probably only get specified for production applications. Backing off the drill by grinding or stoning to alter the rake angle to 0° is a quick and dirty modification to counter the grab or self feed tendency of the standard rake drill used on brass. A tailstock with screw feed does give some control over the grab but I have had the chuck or Taper shank drill pulled from the taper which does risk damage to the taper if the tailstock does not have a tang drive.

Mike

My Super 7 tailstock screw had excessive backlash and I ended up swapping it for lever operation.

Subjectively, I feel I have more control over drilling like this, including being able to hold the tool against grabbing. The through-drilled barrel allows the use of a drawbar.

Years ago I had a job of modifying a lot of primer cups for older John Deere engines. I had to open the hole through the stopcock. I bought half round drills rather than risk twist drills pulling into the work. It worked beautifully. The drills came from MSC. They still offer them.

Interesting further replies. I perhaps didn't make it clear in my original post that the 'self feed' was severe enough to pull the taper from the tailstock bore, so nipping up the quill wouldn't have helped.

Mike Poole - thanks for your explanation of the relationship between helix rate and rake angle. Now you've pointed that out it seems obvious, but for me it was a wood and trees thing. Drills seemed so complicated I couldn't see it.

John Reese - thanks for the pointer to half round bits. I couldn't find them on MSC's UK site. Drill Service do them, but at £50 a pop that isn't going to happen. Are these like D-bits but with a 118 degree tip rather than a round end?

Since reading replies I have stoned the tips of the rubbishy Screwfix drills (which have been sitting on the shelf for 10+ years ) and now they go though brass like butter. No grab even on break though. Never throw anything away!

I'm OK with quick and dirty for now - it works!

Robin

Robin,

half round drills are essentially the same as D bits except for the length of flat.