Author Topic: Measuring acceptable deflection on a mill.  (Read 8393 times)

Offline trevoratxtal

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Measuring acceptable deflection on a mill.
« on: September 26, 2010, 11:49:09 AM »
Please assist me in finding out what deflection your mill shows when pressure is applied downward on the head.
The reason is I would like to find what is acceptable to users  and what type of mill you use.
The measurement is taken with a clock gauge between the head and table , not the quill or chuck. motor not running!
My mill an old very heavy type shows 0.001 (one thou) with 50 pound pressure.
I  feel this is excessive or maybe I am not seeing the bigger picture.
The interest come about when taking a thin skim with a 8 tooth 2 inch cutter, I applied pressure to the drive cover to check it was in place, there was a distinct change in cutter swish, it also showed a a faint difference on the finish! this surprised me so I took further checks, hence my interest.
Many thanks folks.  :D

Trev

Offline kwackers

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Re: Measuring acceptable deflection on a mill.
« Reply #1 on: September 26, 2010, 12:20:33 PM »
Mines in about the same ballpark. I can change the amount of overhang though, more overhang would obviously make it worse, less better.

All machines move when you apply force, usually more than you'd think. Even some enormous machines have measurable deflection when you apply moderate forces. IIRC the relationships between mass and rigidity are complex and non-linear.

Offline John Stevenson

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Re: Measuring acceptable deflection on a mill.
« Reply #2 on: September 26, 2010, 01:13:37 PM »

My mill an old very heavy type shows 0.001 (one thou) with 50 pound pressure.
I  feel this is excessive or maybe I am not seeing the bigger picture.


Trev

I think you are very lucky, my Bridgeport moves two post codes when the door is left open on a windy day.

Throw the dial gauge away it's only worrying you.
John Stevenson

Offline kwackers

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Re: Measuring acceptable deflection on a mill.
« Reply #3 on: September 26, 2010, 01:19:30 PM »
 :lol:

I think you are very lucky, my Bridgeport moves two post codes when the door is left open on a windy day.

Throw the dial gauge away it's only worrying you.

Offline Bogstandard

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Re: Measuring acceptable deflection on a mill.
« Reply #4 on: September 26, 2010, 04:28:13 PM »
I remember watching a machinist pulling his hair out while doing a very long facing job on the lathe, truing up a 2ft diameter lapping plate. The surface finish went to pot every so often across the cut, and he just couldn't fathom it out. This was on a large Triumph lathe.

You could have timed his smoke breaks by the surface finish. Every so often, he would park his a**e against the lathe drip tray and roll himself a smoke, and light it up. Once he went back to check the cut, it was cutting perfectly, but the previous few minutes it had been cutting crap.

As John said, forget about checking, just don't lean on the machine while it is in action.


Bogs
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Offline rleete

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Re: Measuring acceptable deflection on a mill.
« Reply #5 on: September 26, 2010, 05:29:49 PM »
That's funny, Bogs!

I have a Seig micro mill.  One step above a hammer and chisel.  If I get repeatable accuracy within .002, I consider myself lucky.  Leaning on the workbench the mill is mounted to probably changes the deflection.  I take very light cuts, and hand finish the surfaces.

It was cheap (as am I), it does what I want most of the time, and I'm not pushing any boundaries. 
Creating scrap, one part at a time

Offline trevoratxtal

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Re: Measuring acceptable deflection on a mill.
« Reply #6 on: September 27, 2010, 03:42:45 AM »
Many thanks folks for your observations.
I gather it is something to live with and be great full.  :beer:
Had I not had MadModers to turn to I would have had sleepless nights. :(
Again many thanks. :bow:
Trev
Ps I will stop putting my pint/can'y/Jar/Tube, on the machines!

Offline Stilldrillin

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Re: Measuring acceptable deflection on a mill.
« Reply #7 on: September 27, 2010, 03:45:35 AM »
Apprentice shop. A long time ago. Leaning on the table, watching the cutter. In me own little world......  ::)

Instructor walloped me head. "Gerrofff!!".......  :bugeye:

Then he pointed out the changes in finish, coinciding with the actions....  :scratch:

"Let the machine do it's job, and don't interfere while it's doing it".  :D

David D



David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!