small mill for machining steel. Max spend £500 including computer

[Andrew Wilding]

looks like an interesting solution. Looks like it was well covered in the thread so I will not regurgitate that here, but how would that work with large pitch (high lead) screw like the one fitted to your mill. You may only end up with one or two line contacts per bearing? I guess it is not an issue with the type of duties our mills see. Obviously you will have to post results when you get onto manufacture!


Nice job on the refurb by the way.

[Andrew Wilding]

I tried the new x axis nut out last night. Backlash was very similiar to the previous nut at about 0.0007" and did not reduce even if I cranked the nut up tight so I suspect that I need to look at the preload on the AC bearings or check for movement of the bearing in its housing.

Rapids have gone up from about 30" min to 150" min (+ acceleration increase) without lost steps so nut drag is much reduced.

I am happy with the solution. Now to make the y axis (Z does not have a fancy nut as gravity is working in the same direction ad the cutting force so eliminating lash naturaly)

[Andrew Wilding]

I have had a busy week as my second child was born on Friday! All is well and Lydia is starting to become a bit more aware of her surroundings. It does mean that I have some paternity leave and so in between changing nappies and winding I have had a bit of shed time.

I have rebuilt the mill and painted it. Here are some pics of the z assembly showing rotating nut (not pressed in in the photos)

[Andrew Wilding]

Here is a picture of the newly painted mill part assembled


Jobs I am hoping to do in the next couple of weeks:

tidy up wiring with conduit and built swarf protection for limit switches
screw and way protection
Modify spindle ratio
guards and machine mounted E stop

[M250cnc]

Hi Andrew,

Looking good

How long did it take to design and build the Z axis ?

Phil

[Andrew Wilding]

Hi Andrew,

Looking good

How long did it take to design and build the Z axis ?

Phil

Cheers. Design was carried out during daydreaming on the train and manufacture two or three saturdays of pottering in the shed plus a bit on the computer to purchase belts and bearings etc.

[Andrew Wilding]

I had my spindle running at 3500rpm and it was seriously heating up. Tried all the usual things, preload lubricant etc but to no avail. Thread on it here:

http://www.mycncuk.com/forums/showth...2074#post22074

Long story short I have rebuilt the spindle with better bearings and different seal system.

Rubber seal replaced with alu labyrinth (shaft clearance 0.0015")




I have also made a perspex guard over the pulleys. It is smoked rather than black so you can see which pulley has the belt on



without guard



I am running the bearings in and will post progress when I next get a chance

[Andrew Wilding]

I fancied a change of tack so I have started checking and improving the geometry of the axes.

First check is the perpendicularity of the knee. This is the set up for the first method




This was the second method which I was planning on checking the first method with, however the results of this method were not very consistent so I abandoned it.



The results show an error of about 0.001" out of plane using the first method which can be improved with a bit of judicious scraping.



I has previously used the gound side surface of a parallel as my reference. This was not a very good reference so the next task is to scrape a reference surface. Oh joy - blue fingers over the weekend then! Once the horizontal surfaces are complete I will then check the other two surfaces of the dovetail are parallel.

[Andrew Wilding]

I have made a straight edge to fully scrape in my dovetails. Before I used a piece of round plate which was not that good.



after scraping to 20-25 spots per inch

[Andrew Wilding]

some more scraping updates:

dovetails on the knee were scraped parallel



Horizontal ways on table were scraped parallel to top of table (measured with mic)

Back way scraped to front face.



front way scraped parallel to back way using smae method as the knee.

old rack and pinion spindle bearing removed to increase travel by 1"



saddle scraped to knee by blueing knee ways.

x horizontal ways scraped parallel to y horizontal ways. Gauge block used to measure tops of undulations (indicator tip is too small and waviness was being measured)


table to knee perpendicularity checked and scraped etc. Precision pin and blocks used to provide reference to compare table way direction.



The scraping reference book that I managed to find in the library, interesting but by the time I had found this I had done most of the work! The cat did not think much of it.








nearly finished the scraping! I will be glad when I have a fully square and straight mill.