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small mill reconditioning and conversion

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
Hello all. I thought this may be of some interest to you. I am a design engineer but in my spare time mess about in my shed making things. I have recently finished reconditioning and converting a little horizontal mill to a cnc vertical.

This is the original mill with the replacement mill in the background that made it a bit redundant.

CameraImport4thJuly2007579.jpg


The small centec mill ways were well worn and the leadscrews had lots of backlash so it was not very useful for accurate work.

The target was to convert this tired mill into a cnc with a part accuracy of +/- 0.001" over a working envelope of about 6"x5"x5". The cost limit for the conversion was £500 ($800) including the original machine, computer, all the materials required for the conversion and electronics for the controller.

This is the finished article after remachining the ways and teflon coating them, scraping the ways to alignment, making the leadscrews and antibacklash nuts adding stepper motors and making a vertical spindle

017.jpg


073-1.jpg


anti backlash nut

013-1.jpg


I realise this is a bit HSM for some of you but if there is interest I will go through the reconditioning and conversion process with pictures of alignment measuring set ups which may be helpful to those trying to recondition a small knee mill.
 

Richard King

Diamond
Joined
Jul 12, 2005
Location
Cottage Grove, MN 55016
A quick thought...you may want to weigh the servo on the X axis and put a counter weight on the right side, bolt on a steel bar on the end of the table...so the table wears evenly. How are you lubricating the ways? Have Turcite on the ways? ? The machine really looks sharp...your day time company is lucky to have you. :-)
 
I realise this is a bit HSM for some of you but if there is interest I will go through the reconditioning and conversion process with pictures of alignment measuring set ups which may be helpful to those trying to recondition a small knee mill.

Over here the iron from an obsolete cnc is generally cheaper than the parts to build or modify a manual machine, so it's all down to the control system, generally. But what you've done would be applicable to any machine rebuild, as well as the cnc & control specific systems. If you've documented it I for one would enjoy learning from the process.

smt
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
re-machining the ways

I surveyed the machine and the z axis was in good shape but the x and y had several thou wear so I decided I did not have the patience to scrape that amount!

The mill was stripped down and the table knee ways were remachined:

DSCN2204.jpg

DSCN2270.jpg


If you look closely at the knee machining pic you can see that the knee is located against a previously trammed precision rod (injet priter guide! Less tha 1/10,000" diametric error and as straight as I could measure on my surface plate)

The smaller dovetails were built up with a filled ptfe sheet. This was purchased acid etched to allow adhesion with epoxy. This was then machined true:
DSCN2337.jpg

DSCN2334.jpg
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
machining gib strips and mods to castings

gibs were replaced with ones faced with same filled ptfe sheet. Machining pics below:
051.jpg


table was modded to open up a space for the larger nuts and screws planned:

012-1.jpg


table lever was removed and casting modified to increase travel:
064.jpg
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
fabricating knee screw assembly

the knee was lowered using a rack and pinion assmbly on the original mill. The position was controlled by threaded end stops. This was not suitable for a cnc machine so I set about making a lead screw assy. The first effort was a bit half baked and did not work to well due to the off centre loading.
273.jpg


the second attempt had the lead screw supporting under the cog of the knee. This is the parts for the assembly

004-2.jpg


and the assembly assembled

001-2.jpg


closeup of the rotating nut spindle

003-3.jpg


assembly mounted on machined surface of base plate

006.jpg

first post show motor fitted
 

cash

Titanium
Joined
Aug 8, 2007
Location
Greendale,WI
Nice work!

Any chance you would move to doing this on larger scale machines?

Taking this idea and doing it on a #2 cincinnati would be great!
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
Sure bring it over! Just a quick wade across the pond.

I warn you though my wife says 'lots of stuff goes into the shed but not a lot seems to come out!' So you may not get the Cinci back :)
 

billmac

Stainless
Joined
Oct 17, 2004
Location
Lancashire, UK
Andrew -

Lovely job on your mill.

You would need a really big mill to remachine the ways on a Cinci No2. The first mill I ever worked on and one of the best.

Bill
 

cash

Titanium
Joined
Aug 8, 2007
Location
Greendale,WI
Sure bring it over! Just a quick wade across the pond.

I warn you though my wife says 'lots of stuff goes into the shed but not a lot seems to come out!' So you may not get the Cinci back :)

How far are you from Sheffield? We have a sister company over there.
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
Andrew -

Lovely job on your mill.

You would need a really big mill to remachine the ways on a Cinci No2. The first mill I ever worked on and one of the best.

Bill

Just to clarify I was joking! That is a bit beyond my meagre facilities! Looks like a bit of a beast.

Cash
I am only about 40 miles from Sheffield. It is a great town with lots of steelmaking and working history have you been?
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
x and y leadscrews

X any Y leadscrews were remade. Ball screws blew the budget so precision trapezoidal stock was used, fixed at one end with preloaded ac bearings. The nuts are homemade anti back lash type:
here is a sketch showing a section through the nut (hopefully you can see it!)
135.jpg


the nut is actually two nuts fixed rotationaly by dowels. The two halves can move axially. the two halves are biased by a steel sleeve that is threaded ont one of the nuts. A torque is applied to this nut using a homemade torsional spring
013-1.jpg


the y leadscrew in position

015.jpg


the x leadscrew nut (without spring and before the wiring was sorted)
133.jpg

making the nuts
DSCN2390.jpg

using my homemade dividing head to castelate nuts
072.jpg

drilling dowel holes
071.jpg
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
scraping the knee

right...scraping time

Note that this is my first attempt at scraping so I do not claim to be anything close to an expert. I did however manage to get things parallel or orthagonal to the magic 0.001" in 18" on most ways.

A bit of light reading first (Connely, and yes the cat did enjoy it)

066.jpg


knocked up a straight edge out of durabar

002-7.jpg


004-4.jpg

A quick tidy up of the z axis way (not very worn)
before
DSCN2207.jpg

After
DSCN2217.jpg


measuring the flat ways of the y axis method 1
003-4.jpg

this turned out not to be repeatable enough so I resorted to method 2
001-3.jpg

002-6.jpg

scraped the remaining two flanks of the dovetail and measured using the following method (trusty printer bar used as precision pins again)
047.jpg


saddle next.....
 

Pete F

Titanium
Joined
Jul 30, 2008
Location
Sydney, Australia
Great job and thank you for putting this information up. It's a terrific learning opportunity for the self-taught like myself to look over somebody's shoulder, at least in a virtual sense, and I always appreciate those who take the time to document what they've done and pass on their experience to others.

Pete
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
scraping the saddle

Thanks for the comments.
After I finished the knee I moved onto the saddle.
The flat ways were scraped to the surface plate, then the dovetail way was scraped to the knee.
The top flat way was scraped to the dovetail and checked for parallelism using an indicator (note the slip used to average out the pockets)
079.jpg
 

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
scraping the table

The table was scraped flat to the surface plate. The front of the table was scraped perpendicular to top of the table and approx parallel to the T slots. Perpendicularity was checked in a similar way to the knee.

The horizontal ways were checked for parallelism to the top of the table then the angled face of the back dovetail was scraped parallel to the table front face. The indicator plunger end was of the elephant foot type rather than the ball type so errors from the curve of the pin were minimised.

032.jpg


The front way was then checked for parallelism to the back one using the pins and mic method.
 








 
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