Why didn't the drawbar retain the chuck?

Jason's reading of the cause and nature of separation matches mine.

Although I'm a multiple repeat offender in the flaky setup and edgy toolholding department, I certainly agree that holding any laterally-stressing cutters in a Jacobs-type chuck is a fraught idea – if that's what was done here.

The tool pressure is far enough from the chuck-to-shank taper to exert a lot of leverage, and almost any deformation is enough to lose the lock on the mating tapers.

IMO nevertheless the OP has a point that the grubscrew should have been better secured in original assembly.

I suspect the mill was probably shaking itself to death as milling as using a Jacobs chuck for roughing out doesn’t sound like a gentle operation

I absolutely agree with JasonB. Colin

It is important to remember that we were all new to this once and things that are blatantly obvious now may not always have seemed so.

The milling machine is the only machine in most* model engineering workshops that uses a drawbar.

If you have never ever owned or used a milling machine before the prudent thing to do would be to read the manual before you use it. Helpfully, Machine Mart have the instruction manual on their website and you can download it in pdf format before you buy the machine. ** LINK **

So I had a read and tried to see it as a novice would. I think the instructions are concise and clear so a first-time user should have no problems. However, I can also see where a novice could go down the wrong path due to ignorance.

The instructions do clearly state that before attempting milling the drill chuck should be removed and replaced with a milling chuck. Section 8 ends with "…unscrew the draw bar completely until the chuck can be removed, store removed parts safely." Section 9 states: "IMPORTANT: before plugging in and switching ON, ensure all items such as chuck keys tommy bars etc are removed."

Since the only times the drawbar is referred to in the instructions is when removing or installing a chuck it is conceivable that a total novice may regard it in the same way as the chuck key and tommy bar, i.e. its only function is to install or remove a chuck. They may not realise that the drawbar is supposed to stay in place and that it is the one and only thing that keeps the chuck from falling out while the machine is running and possibly causing injury!

*Yes, I know, 5C collets. But not everyone uses them.

I would love to know how many of us have tried the milling cutter in the drill chuck method.

In my youth I did and with the predictable result.

David.

I have!

Confirmed that milling in my bench-top pillar drill with a Jacobs chuck is high-risk. Lots of vibration and the chuck pops out almost immediately. A hefty pillar drill would probably do better, but…

Milling with a cutter gripped in a lathe's 3-jaw is safer, but still dodgy. Light cuts with the cutter firmly held in good chuck jaws and with the saddle snugged down tight is doable, but likely to go wrong, either by the work twisting, or more likely with the cutter pulling out of the jaws. Proceed with care.

Gentle milling with a Jacobs chuck in my milling machine is also doable, but seriously limited compared with an ER32 and drawbar. The Jacobs is bendier, causes more vibration, and is very prone to pull out or slip in the taper. Also harder to get a good finish. After experimenting with it I decided Jacob Chucks are for drilling, not milling, because at best they slow the work rate down and at worst damage the mill, job or operator.

If I've learned nothing else, it's that using the right tool for the job saves time and trouble on a grand-scale. (In the boy-scouts we tried to open a can of soup with two bricks. Didn't go well…)

Dave

Did it on my lathe in my big 4 jaw and it worked quite well most times, but use collets now because they are much more sensible

A big heavy chuck also has a lot of flywheel momentum and this makes for less speed variation as you mill