I would certainly be using a spiral flute machine tap rather than a straight flute taper tap. The flutes clear the swarf much better.

Look at your tapping fluid – don’t use any old stuff.

Asking quite a lot of a common drill chuck to hold a tap of that size. Hard jaws on a hard & polished shank don’t have a particularly high coefficient of friction.

You’d do better with a proper tap carrier driving via the square. Simple round bar with a suitable length of drilled hole to support the tap and some form of square recess in the end will work although there isn’t going to be much room in a standard chuck for everything. Simpler to have a larger diameter tap carrying end sat outside the chuck with suitable size spigot to hold in by. With flats for the jaws to work on if you want more grip. Grub screws in a pair of tapped holes cross drilled at 180° will do just fine for driving on the square so its all fairly straightforward to make.

Of course a pukka tapping head is best. Whether the simple breed or full on devices like my Pollard set. But I prefer to use them on a pillar drill or milling machine. Always seems to look a bit wrong on a lathe.

It’s arguable that a bit of float in the tap holder so it can follow the hole makes things go easier. Certainly teh pukka heads all have provision for some float.

Clive

You could go to 8.8mm hole, according to Tubal  Cain’s ME Handbook. But probably not going to help much.

There’s a reason for the square shank on taps. That’s a lot of force you are putting on the small key that stops the tailstock barrel turning. I’d use a T tap wrench guided by tailstock centre.

I suppose we should ask what condition is your drill chuck in? If it came with the lathe new back in the 70s then it could have worn jaws and you are not getting a decent grip. I’ve driven M12 x 1.75 into 10.3mm holes without slip using a keyless chuck and spiral flute tap. Though the ability for a chuck to slip may be a worthwhile safety feature if things should jam rather than something else give way or snap the tap.

Not sure of this puts any more strain on the barrel’s keyway than drilling with say a 1″ blacksmiths drill?

EDIT. I found a video of me tapping Hot Rolled steel with M0 x 1.5 into an 8.5mm hole. 16mm deep, keyless chuck, spiral flute

In this sort of situation a drill chuck that doesn’t go right down to “nominal zero” will have a better hold due to the radius on the jaws giving two line contact on each rather than, essentially, one line. I suspect such chucks are often engineered for more grip anyway. Subjectively my 1/8″ to 1/2″ and 3/16″ to 3/4″ Jacobs, in adequate workshop condition, appear to hold better with normal chuck key tightening efforts than the near mint 0 to 1/2″ Jacobs no 34 that i consider part of the lathes standard tooling.

I’ve finally come to the conclusion that its better to spend half and hour or an hour making simple tooling for this sort of thing rather than pushing your good tooling a bit beyond what its comfortable doing. With 60 to do sensible tooling is almost a no-brainer.

I’m impressed that Jason was able to hold his 12 mm tap in a keyless chuck. Machine tool keyless chucks generally rely on significant endwise pressure to generate extra grip to improve tool security. I’ve tried couple of times but never gotten reliable results using an Albrecht chuck to hold a tap. The moment end pressure falters the tap comes properly loose and simply slips back rather than restoring grip when pressure is applied. Given the £££ investment associated with an Albrecht I’m reluctant to risk abuse.

Clive

using a standard drill type chuck on taps above M6 ithink is being a bit abusive to tools that have cost you good money, so I tend to use taping chucks and ER tapping collets. I have also made various square drive things so the taps are driven positively. Oh and rocol every time!!

As Charles says, a mandrel handle is a great help, and youncan use it to back off, to break the swarf..

Also, YOU control the speed, and can tell when the torque required is approaching the point where the tap is lable to break.

Impressive. You did better than me. 6mm was about as big as I managed with the Albrecht without slippage.

I found that once the tap started slipping it would slide back without regaining a solid grip. Perhaps I wasn’t pushing hard enough in the first place so things started off underheld.

Big risk with a keyless chuck when things start sliding back is that they end up pushing hard on the back of the chuck innards resulting in a comprehensive jam up needing very careful work to unstick without damage.

Despite some success with the Albrecht keyless on smaller taps I decided that two failures was good reason to retire an expensive piece of kit from doing jobs it wasn’t explicitly designed for. Shifting over to the drill and fitting a tapping head is a pain but it all works just as Mr Pollard intended. Spendy tho’.

Clive

The danger is sliding back inside the chuck.

A keyless chuck requires some clearance behind the drill (or tap) for the self tightening action from inline forces to behave itself. If the drill slides right in to contact the back before it becomes sufficiently tight everything jams up good and solid. Presumably the self tightening action is able to continue despite the lack of clearance behind.

Something I’d rather not have had experience with! Firm push on an 18″ lever attached to the chuck by a very carefully made and shaped, theoretically minimum crush, clamp around a significant length of shell to release the offending 1/2″ drill. I absolutely wasn’t going to compound the disaster by distorting the outer shell. Lord knows what Albrecht charge for those. Probably a 100% stupidity loading too.

Certainly not the usual return to only a bit more hold than needed to stop things falling out when end pressure is related.

Clive

All the machinists keyless chucks self tighten by rotation if the drill tries to spin.

Basically there is an internal threaded spindle with a “pusher” on top sitting against the bottom of the jaws. If the chuck body turns faster than the drill shank, ie the drill slips, that spindle moves forward shifting the jaws touch further up the taper inside the hood so they grip harder.

Fundamentally the same mechanism as a screwed shank Clarkson type end mill uses to self tightens in a Clarkson chuck under cutting forces. Just a different arrangements of components an chuck jaws rather than a collet.

The clever bit is arranging things so that the chuck doesn’t stay tightened up really hard allowing release by a simple hand action. I imagine the patent will reveal all

German Patent no. 588386, 1933.

but that is Michael’s department.

My guess is that there are differential threads involved so turning the hood anti-clockwise drives the inner spindle back faster than the hood allows the jaws open up so the internal tension immediately releases. If the drill pushes in so far that it contacts the internal pusher everything self tightens up solid so nothing can move and the differential threads don’t come into play. Effectively it’s now acting like a Clarkson chuck which needs a spanner to release.

Page 26 at

https://www.albrecht-germany.com/fileadmin/Medien/Pdfs/Kataloge/2025/1st/Albrecht_Drill_Chucks_90_years_2024-min.pdf

shows the Albrecht innards.

No doubt there is room for considerable subtle variations in design governing how much tightening force is generated and how quickly along with how much torque it takes to open the chuck. I’m little surprised that you expected to need a spanner to help. My Albrecht is always releasable by hand. There is a distinct difference in feel between it and the other, larger and rarely used, keyless chuck I have whose brand I don’t recall offhand.

Clive