Mini Lathe – Chuck comes out of the MT

[Jim Dalton 1Participant @jimdalton1]

Hi All

While tapping a M6 using tools from my tap set in a keyed drill chuck in the tailstock, I have noticed that the chuck tends to come free from the morse taper when i back out the tap.

Any idea how to fix this? I am sure there is a simple fix, but while on the topic, do people tend to upgrade the chucks that come packaged with the mini lathes from new, or is this futile?

 

thanks

Edited By Jim Dalton 1 on 30/09/2019 20:39:23

[Jim Dalton 1Participant @jimdalton1]

[Howard LewisParticipant @howardlewis46836]

Usually Morse tapers grip well, almost too well at times. I rotate the lathe in reverse to back out the Tap.

Maybe push the chuck harder into the Tailstock?

Having an ejector Tailstock, it often releases the taper, if retracted too far.l

Assuming that both tapers are clean, undamaged and match! If they don't you could try blueing to check, (and check other fittings for the Tailstock, to see which is the better match. Maybe lapping the two together?

Howard.

[old martParticipant @oldmart]

I normally lock the tailstock and its barrel, retract the jaws of the chuck below the nose and give the chuck a rap with a soft mallet, or a copper mallet if large size drilling is to be carried out. Don't hit too hard, especially with a self extracting system.

The MT2 tailstock barrel of the museums' lathe had a poor taper, and I managed to get a new one intended for another model. The important dimensions were the same but instead of a slot for a tapered drift extractor, it was designed for self extraction. We soon milled a new extraction slot in the barrel. I don't trust self extraction with a very tight Morse taper.

 I have a little 7X 12 mini lathe at home, it came with a 1/2" chuck, far too large, it now has a 3/8", 10mm one which is more in keeping with a small machine. I once tried drilling a 1/2" hole in steel, and it tended to stall and blow the fuses.

Edited By old mart on 30/09/2019 21:27:18

[Ian Johnson 1Participant @ianjohnson1]

I've got a Mini Lathe and rapidly found that the 2MT tailstock barrel is not deep enough for a standard 2 morse taper. So I have ground the corners off all the tangs on my standard 2MT tools.

The tang is made to locate in a corresponding slot in the tailstock to allow a taper drift to eject it. The Mini Lathe doesn't have this luxury and has to rely on a self eject system using the tailstock screw, which projects into the rear of the barrel with the annoying result of making the taper stick out about 20mm.

So your 2MT might just be touching or bottoming out in the tailstock barrel. Try grinding the corners off the MT.

Ian

[I.M. OUTAHEREParticipant @i-m-outahere]

It could just be a matter of retracting the tailstock barrel faster than you are unscrewing the tap from the hole , i usually unlock the tailstock and let the tap drive it back as i wind the chuck over by hand -never do this under power or with really small taps ( less than 1/8 or 3mm) as they can break or strip the thread out if the tailstock is fairly hefty .

You may not be setting the morse taper into the tailstock barrel correctly – the way i was taught to do it was to clean both tapers to make sure there is no crud in the female taper and to remove any oil off both tapers then extend the tailstock barrel a little so the taper doesn’t bottom out on the ejector rod (which is usually the end of the tailstock feed screw ) then place the taper into the barrel until it just stops then retract it about 1/2 inch (13mm) and with a sharp flick of the wrist set the taper in .

[Mike PooleParticipant @mikepoole82104]

There are many versions of die holder for the tailstock that just let the die self feed once started. A chuck mounted on the same floating holder will allow the tap to back out without having to push the tailstock and maybe damage small threads.

Mike

[SillyOldDufferModerator @sillyoldduffer]

My approach, like Mike's, is not to hold taps in the tailstock chuck directly. Instead the chuck holds a spring loaded end piece that only keeps the tap straight. No pressure is put on the tailstock chuck in either direction.

As pictures are worth a 1000 words.

Small taps usually come with a male end while bigger taps are female, so two spring loaded tap-holders may be needed. I bought a male holder and made the female myself. Nothing complicated: a plunger working against a small coil spring inside a straight tube small enough to fit in the tailstocks drill-chuck. I used the spring out of an old biro pen.

Set up to cut a thread with a normal tap handle.

Starting with the tailstock pushed to fully compress the spring, I cut threads by holding the handle still while turning the chuck to and fro by hand. The tailstock is keeps alignment and is only moved if the spring doesn't have enough travel.

Not a good idea to cut threads under power with this arrangement. Apart from the danger of getting caught in the works, it's important to break and clear swarf by regularly reversing the tap by half a turn or so.

Dave

[Jim Dalton 1Participant @jimdalton1]

Thanks all. Dave, that arrangement looks interesting.

Will study that closely

[Anthony KnightsParticipant @anthonyknights16741]

Easy to make one from a MT blank.

[Paul LousickParticipant @paullousick59116]

I don't have one of the spring loaded tapping guides but use a centre in the tailstock and apply light pressure to the tap, adjusting the tailstock as you manually cut the thread. Once started just tap the hole without the tailstock as a guide.

Paul.

[Howard LewisParticipant @howardlewis46836]

Having bought a sliding Die Holder to fit into the Tailstock, I made a sliding Tap Holder, using ER collets. If the load get too much, the Tap slip[s in the collet, preventing breakage.

The die holder, and the tap holder, are a loose fit in their arbor, in the Tailstock. This allows them to follow the workpiece, rather than risk cutting off centre, and imposes minimal load on the tap or die as it cuts, being spared the task of dragging the Tailstock along the lathe bed. In particular, 40 tpi threads are not strong enough to do this in many cases; they are only 0.016" (0.4 mm) deep.

For Tapping in the Mill/Drill, I use a spring loaded male or female centre to steady and align the Tap whilst torque is applied with a Tap Wrench. This keeps the Tap aligned with the hole, and steadies it, reducing the risk of a broken Tap.

Howard

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