Author Topic: Scraping the vertical ways on the knee fo a mill - perpendicularity!!  (Read 1161 times)

Offline mm289

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Hi all,

I am about to start on scraping in the knee on the Centec. I remember Richard mentioning about making sure the knee is perpendicular to the cutter (it's a horizontal mill as well as vertical).

SO question is - how do you do that, I remember him mentioning about putting a shaft in the horizontal arbor and measuring from this but can't figure out what I am meant to be measuring  :doh:

Any suggestions gratefully received :)

Cheers,

Paul.

Offline Mover

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #1 on: December 23, 2017, 05:55:10 AM »
Hi Paul,

If I remember correctly, with it being a horizontal mill you need the knee square to the spindle in two directions.

The top of the knee needs to be parallel to the horizontal arbour and also square to the arbour. The squareness wouldn’t matter on a vertical only machine as long as the x and y where square to each other.

First of I think you need to rig a dti in the spindle to assess the relationship bettwen the spindle and the verticals ways on the column.

Offline HughF

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #2 on: December 23, 2017, 08:32:39 AM »
Isn't this documented in the e-book that Graham uploaded to the dropbox account? I think it is the 'rebuilding machine tools' book

Offline PekkaNF

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #3 on: December 23, 2017, 10:54:28 AM »
Any link to that?

Usually there are two very different measurement modes:

A) Testing (new) machine, bit like 16.4.9. (a) Column ways of knee square with table et.al.
http://what-when-how.com/metrology/alignment-tests-on-milling-machine-metrology/

B) WHEN REBUILDING - you need to find first primary reference and then work from there.

I.E. you have very limited means to spindle axis you need firts to check that spindle is fine, no use to measure from the spindle if it droops 0,1 mm down due to shot bearings. When you are positive that spindle is fine, you can hook an arm to it and have a dial indicator from it. If the column is pretty close to upright (dial indicator reading is not efffected gravity bending the arm) then you can have readings on that swing arc - that will establish that those two points are in a line that should be pretty damn near perpenticular to spindle axiss.

You need to find two points near spindle and two from bottom - secret is to use area the is not worn, then assume that it was originally right, establish a plane and measure how much worn areas differ from that plane. It's way too easy to make something straigh, even planar while it is grossly skewed from the original plane. Important step is to avoid it from the start. You establish the plane and you need to down with that plane and ressist temptation of just making a flat surface on any random plane.

I think it is best first to check the upright column to spindle axiss and then knee to column/spindle and last the table.

It is fine to measure table and all the to spindle, but that just tells how much it is off from ideal with that load whatever you have on the table. Very little where the error is.

Is this any use (it is somewhat CNC stff, but carcass is manual machine):
http://www.practicalmachinist.com/vb/general/small-mill-reconditioning-conversion-234739/

Pekka

Offline mm289

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #4 on: December 23, 2017, 02:09:50 PM »
Great, thanks guys - Page 316 of the E F Connelly seems to cover it nicely, although it may take me a year to read  :palm:

Its a bit too big to try and upload a copy here as the PDF is 99Mb but will see if I can cover some of the principles on my rebuild thread when I get round to it.

Cheers,

Paul.


Offline PekkaNF

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #5 on: December 23, 2017, 03:06:46 PM »
You have Connelyn. If you can read it without falling asleep you should be able to measure and scrape the right bits.

You have the paper book? How much it set you back?

Bit more simple book on measurement (and bit more easy reading) is Testing Machine Tools, Schlesinger. Very good reading.

Pekka

Offline mm289

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #6 on: December 23, 2017, 04:53:26 PM »
Hi Pekka, I have access to a PDF version I found a few years back, and also one of the guys from the scraping course had one - it does take a bit of reading!!

Cheers,

Paul.

Offline Graham Stabler

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« Last Edit: December 24, 2017, 06:16:36 AM by Graham Stabler »

Offline PekkaNF

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #8 on: December 24, 2017, 07:44:12 AM »
Pretty good read on test arbor droop and practical testing arragement. Isn't it?

Pekka

Offline Pete.

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #9 on: December 24, 2017, 11:35:56 AM »
Hi all,

I am about to start on scraping in the knee on the Centec. I remember Richard mentioning about making sure the knee is perpendicular to the cutter (it's a horizontal mill as well as vertical).

SO question is - how do you do that, I remember him mentioning about putting a shaft in the horizontal arbor and measuring from this but can't figure out what I am meant to be measuring  :doh:

Any suggestions gratefully received :)

Cheers,

Paul.

I'd stick an arbor in the horizontal shaft and a box square on the arbor. Indicate the flat ways to the square and scrape them parallel. If you're worried about droop tip the whole thing on it's back - that's how Herbert used to scrape their 0v's.

Offline Joules

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Re: Scraping the vertical ways on the knee fo a mill - perpendicularity!!
« Reply #10 on: December 24, 2017, 12:21:29 PM »
Paul, not sure if this will give you some ideas.

http://madmodder.net/index.php/topic,11658.25.html

I didn’t need to do much to make a better job of the machine than I got it.  Just take careful measurements before you start to make sure your not making things worse.  I mostly just had to get rid of tight spots and improve the bearing surface contacts to improve sliding fits.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup: