Dangerous Design Failure
|Barry Tattersall||03/12/2020 10:42:15|
|3 forum posts|
Whilst roughing out a brass blank using a 10mm end mill the grub screw locating the handle shaft vibrated loose allowing the handle shaft to disengage from the fine adjustment dog clutch, this resulted in the uncontrolled recoil of the quill shaft and the sudden impact against the upper stop. The shock wave from this caused the chuck c/w cutter to disengage from the mandrel taper and propel itself downwards just missing my foot.
Suggested modification; Loctite grub screw in correct position and check on a regular basis.
Footnote!!! I would think that most of us operate on our own and wear the appropriate protective clothing but do we wear work boots/shoes? Fortunately I do and glad I do with a near miss like this. The only casualty this time being the workpiece.
|Barry Tattersall||03/12/2020 10:48:33|
|3 forum posts|
This machine, I would think, is in common usage by many MEW members and my machine is less than a year old, although does get a lot of use especially during the lockdowns so I thought this matter needs to be addressed urgently, preferably by the manufacturers/suppliers.
22604 forum posts
This is one of the reasons it is not advisable to use the drill chuck for milling, get some finger collets, endmill holders or a collet chuck.
Instructions say "use appropriate accessories" A collet chuck is listed as an accessory in my Machine Mart catalogue.
Instructions also say " insert the cutter to be used into the milling chuck or collet"
Edited By JasonB on 03/12/2020 12:18:46
|Nicholas Wheeler 1||03/12/2020 12:50:47|
|913 forum posts|
Why didn't the drawbar retain the chuck?
22604 forum posts
OP said cutter and (drill) chuck disengaged from the mandrel taper so assume the MT taper is still in place and the chuck came off it's J or B taper loosened by milling loads and the sudden stop finished it off
Edited By JasonB on 03/12/2020 13:07:45
|Mick B1||03/12/2020 13:25:48|
|2162 forum posts|
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.
|Andrew Johnston||03/12/2020 16:11:24|
6577 forum posts
I do; there are a pair of slip-on industrial steel toecap shoes by the workshop door that I put on when machining. They keep my tootsies warmer than slippers too.
|Frances IoM||03/12/2020 16:32:49|
|1250 forum posts|
|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|
|old mart||03/12/2020 18:40:12|
|3728 forum posts|
The only time I would use a milling cutter in a drill chuck would be to produce a counterbore for a SHCS, there is no sideways force.
|colin hawes||03/12/2020 19:03:30|
|557 forum posts|
I absolutely agree with JasonB. Colin
|not done it yet||03/12/2020 19:09:29|
|6748 forum posts|
addressed urgently, preferably by the manufacturers/suppliers.
Unfortunately, the manufacturers/suppliers have little input regarding the safety, or otherwise, of the purchaser/operator. Excessive vibration is a clear indication of an impending problem. Not sure how the manufacturer would be able to check the security of fixings nearly a year after the sale and delivery.
If the correct milling chuck was in use, it is likely it was not secured with the drawbar?
Guessing this is the OP’s first machine.
|Henry Artist||04/12/2020 09:55:07|
121 forum posts
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.
|Martin Dowing||04/12/2020 10:06:12|
355 forum posts
They are just those things which every novice need to learn on his own skin.
Here was an example and leaving key in lathe chuck is another one.
Also: Pay attention to slow moving power driven parts like leadscrews etc.
They are rather unforgiving once they get you, even on small machine.
|David Colwill||04/12/2020 10:12:59|
|774 forum posts|
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.
|Michael Gilligan||04/12/2020 10:28:38|
20112 forum posts
Interesting, and encouraging, to see this reasonable discussion taking place ... unlike the bravado that was apparent on the recent thread about the Lidl ‘wood lathe’
8513 forum posts
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...)
|Andrew Johnston||04/12/2020 11:04:08|
6577 forum posts
Yes, but only for spotfacing or counterboring, never for milling. I also use milling cutters in the lathe tailstock for creating none critical flat bottom holes or rough drilling brass and bronze where I don't have a suitable slow helix drill.
5069 forum posts
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
|Barry Tattersall||04/12/2020 13:02:56|
|3 forum posts|
REF; Micro milling/drilling machine CMD10.
Many thanks for all the constructive advice. I should have known better having been a timed served Marine Engineer apprentice some 60 years ago when, if I remember correctly, vertical mills were fitted with Clare collet chucks. That aside, the problem was caused by an insecure locating grub screw failure that initially caused the chuck to come adrift [ as previously explained] & I have not experienced a previous problem using a Jacobs chuck for milling, that said, I have today ordered a MT2 collet chuck for future use. Lesson learnt! Many thanks for all the prompt replies & advice.
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