Minimill Leadscrew accuracy

[cliveastro]

Hi
I have a Sieg type minimill but its a model that they only produced for a short while with a 550 watt motor and a longer X axis table.
I want to convert it to a 2 axis CNC machine.
But no one does ballscrew kits for it, so does anyone know what you can get the backlash down to using the leadscrew.
At present the backlash is 0.0055". How much better can I get it.

I realise I can get a ballscrew made but I dont know the cost of a special.
I thought a 12mm dia ballscrew with a 5mm pitch would be about the right size as the the 16mm ones have a huge nut (my X table is 410mm long).
Any ideas about cost and quality.
The machine is a hobby machine.

Clive

[Oldmanandhistoy]

Hi Clive,

Are the nuts on your machine split with screws to adjust backlash; if not that could be something you could do to improve the stock screw backlash.

As for ballscrews take a look here http://cgi.ebay.co.uk/16x5-spindle-B...QQcmdZViewItem he also gives prices for turning them to your requirements if you look in his shop you will find the prices there.

John

EDIT: Just noticed you are looking for 12mm ball screw but he may have them also in his shop.

[cliveastro]

Hi John
Thanks for the reply.
I have not split the nuts as yet.
I made some adjustments last night and managed to get the x axis down to about 0.001" but its really stiff so I might have to back it off a bit. The y axis is really sloppy. I see another strip down coming on.

I had a look at the link you sent me on the ball screws which was really helpful (I am certain I had a look before and couldnt find anything).
My main worry about using the 16 x 5 is the size of the nut, but many people seem to have done it.

The ballscrews on ebay look like they could be conventional machined (ie not ground) the material is 16MnCr5 which looks feasible. Anyone tried?

Clive

[marchantdice]

We can offer 12mm x 4 or 5 mm pitch Class 5 (JIS 0.018/300mm) preloaded / zero backlash ballscrew assemblies with ground journals for the same price as our turned bearing journals?
If your really stuck for room we have 8x2.5 assemblies!
Regards / Kevin.
Marchant Dice Ltd. World of CNC

[Oldmanandhistoy]

Originally Posted by cliveastro Hi John Thanks for the reply. I have not split the nuts as yet. I made some adjustments last night and managed to get the x axis down to about 0.001" but its really stiff so I might have to back it off a bit. The y axis is really sloppy. I see another strip down coming on. I had a look at the link you sent me on the ball screws which was really helpful (I am certain I had a look before and couldnt find anything). My main worry about using the 16 x 5 is the size of the nut, but many people seem to have done it. The ballscrews on ebay look like they could be conventional machined (ie not ground) the material is 16MnCr5 which looks feasible. Anyone tried? Clive

Hi again,

It has recently come to my attention that if you can get away with 16mm ballscrews then you can very likely buy them here http://www.homeshopcnc.com/page3.html at what would probably work out to be half the price of the previous suggested sellers prices.

John

[cliveastro]

Thanks John
I sent them an email a week ago and did not get a reply!

Clive

[Oldmanandhistoy]

Originally Posted by cliveastro Thanks John I sent them an email a week ago and did not get a reply! Clive

Not good news especially as I may buy mine from them. I know others in the UK have.

John

[marchantdice]

Hi Clive, we can supply Class 7 JIS (0.050/300mm) R12x5 ballscrews with zero backlash + ground journals.
Please note the spindle hardness is 60 to 64Hrc and can not be machined using conventional tooling (we use ceramic tips)
Unlike other soft ballscrew spindles on the market, the additional hardness offers longer life.

RSW Ballnut info: http://www.worldofcnc.com/products.asp?recnumber=69
PDF: http://www.worldofcnc.com/images/RSW%20Ballnut.pdf

Regards / Kevin
Marchant Dice Ltd
www.worldofcnc.com

[Oldmanandhistoy]

Originally Posted by marchantdice Hi Clive, we can supply Class 7 JIS (0.050/300mm) R12x5 ballscrews with zero backlash + ground journals. Please note the spindle hardness is 60 to 64Hrc and can not be machined using conventional tooling (we use ceramic tips) Unlike other soft ballscrew spindles on the market, the additional hardness offers longer life. RSW Ballnut info: http://www.worldofcnc.com/products.asp?recnumber=69 PDF: http://www.worldofcnc.com/images/RSW%20Ballnut.pdf Regards / Kevin Marchant Dice Ltd www.worldofcnc.com

Thanks for posting that; I was hoping to be able to turn my own screws which I planned to buy from you. Now I will need to rethink the cost as I would also now need to pay for machining.

John

[marchantdice]

John, We can anneal /soften back the balltrack to allow the use of conventional carbide tooling! or process turn to remove the hard track"