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View Full Version : Machining Ballscrews with a mini lathe (& ballscrew support questions)



HankMcSpank
31-01-2010, 11:15 AM
Ok, so there comes a time in every CNC builders life where he realises that threaded rod was ok for the first few months, but now it needs some proper ball screw.

So it is with some major reluctance that I blow the cobwebs off my CNC 'kitty' tin & delve inside to find the minimal amount sloshing about.

Firstly, I'd rather not upgrade my mill's end supports (which are SK16 ... http://tinyurl.com/ygk4stf (http://tinyurl.com/ygk4stf) ...these in turn hold some bearings with an ID of 8mm) ...esle this is gonna get very costly.

So to my first question, bearing in mind I have simple needs, my X Axis is about 400mm, my Y Axis is about 300mm ...(I'm not touching my Z axis for now) which would be the most suitable ballscrew for integrating into my present CNC mill (would simple trapezoidal type threaded rod be a better option ...if so which pre made nuts to use ....I've turned my back onnthe DIY nut route - life's for living, not making nuts!:smile:)

Next, I have a Sieg Mini Lathe & an ER32 collet chuck/collet set - would it be possible to use this machine the rods ends down to the aformentioned 8mm diameter?

Many thanks for any input - Hank.

Kn8
31-01-2010, 12:50 PM
Hello Hank
I have two lead screws taken from a cnc measuring machine that was being scraped, and are too small for my requirements. The thread diameter is 11.4mm and the pitch is approximately 12mm, the thread lengths are approximately 880mm and 610mm the nuts are some sort of nylon. The two open ends are machined to 6mm diameter with a 9mm sleeve pushed over them. These are available if you could make use of them.

Ivan.

16741675167616771673

HankMcSpank
31-01-2010, 01:53 PM
Result!

I'll PM you!

Robin Hewitt
31-01-2010, 02:04 PM
I've got some of them, not actually ball screws but they do look interesting :smile:

After you decide to go to ball screws you then realise double nuts are a good idea, then it's sprung double nuts. I even spring the axial bearings together on the Y/Z and hold the X screw in tension. No measurable backlash, not a sausage, or tiny fraction of a sausage even :heehee:

Not sure what comes after that because I haven't got there yet :naughty:

HankMcSpank
11-02-2010, 10:57 PM
A hearty thanks to kn8.....leadscrews duly collected - the longest one of the pair since hacksawed into two bits ...which as luck would have it was exactly the right length to be sufficient for both X & Y planes.

Ends of each lead screw piece now turned down to be 8mm diameter (yes, mini lathes are up to the job, but it takes a while!)...my somewhat creaky DIY CNC is now in bits & I'm making some DIY mounts so I can incoproprate the leadscrew nuts that came with the leadscrew (nut mounts will be made out of acrylic - don't ask! But they'll be solid as a rock!)

Got to say...I'm really looking forward to seeing these puppies turn .....3mm pitch (with nice smooth nuts) - luxury after M8 rod!

Lee Roberts
12-02-2010, 12:06 AM
Great news, im pleased for you Hank was very kind of you Kn8, i would love to see the pics of the mounts your going to be making in the acrylic Hank. A build log for this conversion would be cool to follow as well ! CHOP CHOP ! :heehee:

HankMcSpank
12-02-2010, 12:01 PM
Great news, im pleased for you Hank was very kind of you Kn8, i would love to see the pics of the mounts your going to be making in the acrylic Hank. A build log for this conversion would be cool to follow as well ! CHOP CHOP ! :heehee:

Re photos of the mounts - I'm not sure they'd be up to the std required on here! lol

Basically I've separated those white leadscrew nuts pictured above (there were three small hex head bolts holding them to their mounts) ...my tack here was to source a rectangular piece of 'mount' material deep enough for the leadscrew nuts to insert into (about 30mm deep....and because I didn't have any acrylic that deep, I've glued some sheets together...transparent arylic about 20mm thick & two pieces of blue acrylic sheet about 5mm thick! Very blue peter-esque!) .

The leadscrew nut 'extended' bit is 20mm diameter so it's just a matter of boring a 20mm hole through the middle of the acrylic & then attaching the the lot to the underside of each plane's table.

Sounds awful & I'm sure not up to anything other than hobby standards....but have you seen the price of proper nut mounts :eek:

Lee Roberts
13-02-2010, 12:28 AM
Sounds intresting, the great thing is once your up and running you can always start remaking your own parts as you need to.

Here is a ballnut mount i designed for my new machine, i understand what your saying on pricing for the pre made mounts.

http://www.mycncuk.com/forums/attachment.php?attachmentid=1720

http://www.mycncuk.com/forums/attachment.php?attachmentid=1721

http://www.mycncuk.com/forums/attachment.php?attachmentid=1713

http://www.mycncuk.com/forums/attachment.php?attachmentid=1715

http://www.mycncuk.com/forums/attachment.php?attachmentid=1714

http://www.mycncuk.com/forums/attachment.php?attachmentid=1712

Dont forget you have got a high number of people here who are willing to help each other along, if you needed to you could ask for some parts to be made for you.

HankMcSpank
13-02-2010, 06:41 PM
Yours are good (no, in fact perfect), mine are aesthetically challenged, but functional - and at least they cost nowt (& are more colourful!)

The good thing about acrylic is it's free if you have a signmaker near you! (check their skip!) ...also it's very flat (a bit brittle though).....

One lump of 20mm & two pieces of 5mm (I needed 30mm!)
http://img15.imageshack.us/img15/7914/78335692.jpg (http://img15.imageshack.us/i/78335692.jpg/)

Whoever would have thought a 20mm wood bit would be so useful on a metalworker lathe!
http://img15.imageshack.us/img15/1429/72957339.jpg (http://img15.imageshack.us/i/72957339.jpg/)

20mm bore to take the leadscrew nut that came with the leadscrew (the hole is *meant* to be offset!)...
http://img15.imageshack.us/img15/3298/94830334.jpg (http://img15.imageshack.us/i/94830334.jpg/)


And all assembled ready to be mounded under my machines Y plane table...
http://img15.imageshack.us/img15/8775/32410204.jpg (http://img15.imageshack.us/i/32410204.jpg/)


I'm not worried about the colour scheme or the lack of 'finesse'...like I say this is a hobby machine & besides they're outta sight anyway!

My X axis is finished ...and my Y axis is 70% done (I'm not bothering right now with my Z Axis).....wow what a difference it's making to my rapids - amazing!!!

irving2008
14-02-2010, 10:13 AM
Don't knock them.. does the job, so its a good engineering solution and I'll doubt you'll get close to the tensile strength limits of acrylic.... What did you bond the pieces with?

HankMcSpank
14-02-2010, 11:10 AM
They were keyed a litte then bonded with Cyanoacrylate (which sounds a whole lot better than saying superglue) & clamped in a vice to set...when I spoke of acrylic being brittle earlier, I meant to work with - there' no way on earth those mounts will ever snap in situ!!

steve123
14-02-2010, 12:30 PM
Looking good,what sort of difference did you get on your rapids?.

Steve

HankMcSpank
14-02-2010, 12:57 PM
Hi Steve,

I haven't actually got around to working it out yet - but unscientifically I'd say about 3x what I was getting before...

M8 rod has 1.2mm pitch, whereas this leadscrew has 3mm pitch, so a 2.5X win there...but now the motors aren't turning so fast (operating a the better end of their torque delivery - so I'm reckoning there's win there too!

... to mention way less overall nois and erhm less drive screw 'wobble' - my previous M8 threaded rod was marginally warped! I'm sure I'll have less backlash too versus my crap homemade delrin nuts!

steve123
14-02-2010, 01:19 PM
Sounds good Hank,maybe you can post a video once its all up and running.


Steve.

irving2008
14-02-2010, 01:21 PM
They were keyed a litte then bonded with Cyanoacrylate (which sounds a whole lot better than saying superglue) & clamped in a vice to set...when I spoke of acrylic being brittle earlier, I meant to work with - there' no way on earth those mounts will ever snap in situ!!
I was thinking more of the screws pulling out of their threads... but you're right, its unlikely within the boundaries you are working to..

HankMcSpank
15-02-2010, 11:22 PM
Just to give a bit of closure here - I got around to setting up my machine with the new 'old' leadscrews tonight - they are in fact 1/2" pitch doh...kn8 mentioned a figure close to this when he offered them up, but to my untrained eye they looked like 3mm! (BTW if anyone could look at those pictures above towards ID'ing the likely leadscrew I have, it be useful if I want to source some delrin nuts in the future ...as kn8 said, the leadscrew 'thread' diamater is about 11.8mm ...the pitch is 1/2" pitch....I'm easily confused at the imperial way of describing stuff!)


I'm using 1/8th step on my driver which works out at about 125 pulses per millimetre (& gives me a resoluton of about 0.0078mm :-) )

With respect to rapids, I'm now getting a figure of about 6000 on the motor tuning page (previously about 500!) & my backlash measures 0.06mm - not sure if this is good or bad, but it's very good for my needs!

Thank kn8 matey....you've made my whole CNC experience a whole lot faster, quieter & enjoyable. :dance: