King Midas mill conversion

[diy-john]

The XY screws appeared much too long until it was all together, have a pic...

Robin, that is one sweet looking machine. One can tell, a lot of planning has gone into it. Like the kind of contrast with the big, sturdy, used Warco mill, and then the precise CNC -parts. Very cool.

King Midas conversion last couple of days has been measuring + and thinking how/where conversion related components will be. From all your comments, I have realized how distant my thoughts have been from this project. Feel one has been watching this project sort of from cloud -level, but now there is need for much closer look. Exciting.

1) Y-axis ballscrew -related
1.1) Ballnut would be attached to "lower", "stationary" bed of the mill. (view from front of the mill)



1.2) Y-axis ballnut would be attached to "lower", "stationary" bed of the mill. (side -view, from right hand -side of the mill)
- white box, height is 55mm, width is 18mm (for reference only)


1.3) Overview / sketch of Y-axis ballscrew (side view, from LEFT -hand side of the mill)
- colours have no specific meaning, just different colours for different components
- length of ballscrew is now at 508mm. (note how it has grown, initially one was going to buy a 346mm screw...LOL)



1.4) A challenge in Y-axis ballscrew is a 35mm vertical space here
- thought initially there is 40mm space, since the "cave" bottom looked like level with "outside" (see picture attached)
- need to make DIY "slim" ballscrew floating end-mount. Haven't found a slim-enough ready made mount.
- SKF 7200 BEP bearing outer diameter, for a 16mm diameter screw, is 30mm
- Would mount screw to "moving upper deck".




I haven't got a lathe yet. Tool/workshop -wise I am in the wrong league. Looking to do premier league, but my skills/tools are only 5th division. But thanks to this forum and careful planning, maybe this game is possible..

[Robin Hewitt]

You will need to get the ends of the 16mm screws turned down to 12mm and partially threaded 1mm pitch.

Watch out, 12mm single row, angular contact bearings don't have dust shields, you will want to bury them in grease.

You can't use double row bearings with shields because they aren't crushable.

This is how I built up my Y screw assembly...

I put on one bearing
the aluminium mount that bolts to the machine
then another bearing
then a pair of Belleville washers
then the pulley
then a stepped iron sleeve to carry the indicator dial and the handle
then a 12mm half nut

I nipped in flat ended grub screws through the iron sleeve and pulley, flats cut on the screw shaft.

I wound the 12mm nut in one turn to preload the Bellevilles and crush the bearings.

Then I added another 12mm half nut to lock the first one.

Then I tightened the grub screws.

There was no need for a bearing at the far end of the Y screw, it simply isn't long enough to whip.

[diy-john]

Robin, tried to understand how things would go on the ball screw. Now, this is getting to the far edge of my knowledge, this is all new.

Made a sketch of how I have understood:




So, starting from the right hand side, in the picture, requirements for machining screw:

- Machine 12mm length of screw to 10mm diameter (if want a bearing at the far end of the screw). Moving further from right to left, add

I put on one bearing <--- 1 bearing, shaft=12mm, OD=32mm, W=15.9mm, like this http://3.bp.blogspot.com/_3D8MX6Q_YG...G_0326+sml.jpg so machine ballscrew width=15.9mm diameter=12mm
the aluminium mount that bolts to the machine <--- For this, machine 3mm length of ballscrew diameter=12mm. Bearings will go mostly inside this mount(?)
then another bearing <--- machine ballscrew width=15.9mm diameter=12mm
then a pair of Belleville washers <--- like this http://www.trakar.com/spring-trainin...rings/disc.jpg machine 2mm length of ball screw to diameter = 12mm
then the pulley <--- machine total width of pulley (eg. 25mm) diameter = 12mm + flat spot
then a stepped iron sleeve to carry the indicator dial and the handle <--- machine total width of pulley (eg. 25mm) diameter = 12mm + flat spot
then a 12mm half nut <--- machine a thread M12 x 1mm to the end of the screw, perhaps for a length of 10mm

OR: machine the screw like this:
http://www.slidesandballscrews.com/images/machining ball screw-1100mm.jpg
- Except no.1 : that there would be a longer piece of screw machined to 12mm diameter (perhaps 35.8 mm length instead of 23mm in picture, to allow 2 x bearings (30.8 mm) + bearing housing (3mm) + belleville washers (2mm) = 35.8mm
- Except no.2 : Make a 12mm "flat spot of 50mm length" (to take pulley and handwheel)


For now, this project focus is trying to understand requirements: how / to what specification machine ballscrews.

Please comment!

Thanks!

[Robin Hewitt]

Can you read an AutoCAD .dwg or .dxf? My drawing is a bit chaotic but it's al there if you look hard enough. I draw to get the dimensions then draw individual pieces for cutting.

I have lots of 12mm Belleville washers left, the minimum order was generous. I can send you half a dozen for the three screws if you PM an address, may take a while to find them though. I may have some 16mm I used for the ballnuts, spec is at www.bellevillesprings.com

[diy-john]

Robin, your offer is very generous, thank you very much. Will send you a PM.

Did not realize how critical these ballscrews are to the build, and how much thinking has to go to them.

The X-axis, which I have so far thought as being "the piece of cake" in this project, and hence did not really think about it much.

Today thought better still check available space for X-axis ball screw.

- X -axis ball screw would have to go through this hole:



- The hole height is equal to 28.66mm, which sounds great when you think it is only a 16mm ballscrew to put in there.


- However it comes so close, because the ball nut height = 40mm, and the nut must clear the moving "top deck" (which slides over the ball-nut).


Think there will be only 0.66mm of air underneath the screw, if one will go for 16mm screw. (and if the screw really is 16.00 mm). Challenge is, that one can not move the ballscrew higher, because then the ball nut would not clear the sliding "top deck".

A bit frustrating perhaps to just measure and measure, when one wants metal chips and sparks to fly. But guess you really don't want buy ballscrews that are only good to post to classifieds section... so slowly it goes. :)

[Robin Hewitt]

Did not realize how critical these ballscrews are to the build, and how much thinking has to go to them

If you get the ballscrews right you never notice them. Get them wrong and you will be for ever adjusting and compensating.

I can export that drawing as a PDF if you think it might help, I have never exported anything as a PDF so I don't know.

[Gary]

In most conversions of machines of this size that i have been involved with the ballnut between the X and Y needed to be the FSI of DFI type that has two fixing holes either side of the flange and 2mm lower profile than the standard FSU type.
This will get over you space problem.

[diy-john]

FSI of DFI type that has two fixing holes either side of the flange and 2mm lower profile than the standard FSU type.

Thanks Gary - Please do you know the "height" of the lower-profile ballnut, for a 16mm diameter screw (1605)?
- Have used 40mm in my calculations, thinking might have by coincidence already used a lower profile version(?)
- If one could get 2mm lower than 40mm, then it would be great yes.

With a bit of help from Robin, latest draft -version for X -screw is here:


Total length of screw now is 871mm. (it has grown an extra 290mm from the original plan).

Hope that "custom" screw would not break the bank. (don't know how much extra cost that machining will add on top).
- Have prepared to go "conventional" cuttings, too, if it becomes really dear.
- One facet: want to get the screws as good as possible
- Another facet: being a newbie at this, would be very, very surprised if one gets it right first time round. Not sure how much point there is in paying top money for ballscrews, only to want something else next month. Of course trying very hard to get it right first time, but have to be realistic.

Slowly forward..