Mini Lathe Cross Slide Ballscrew Solutions

[acondit]

As requested, but don't say I didn't warn you that it is ugly.

Andy,

Thanks, I was guessing that you had cut into the dovetails to get that ballscrew nut to fit. I still like the idea. It at least provides protection for the ballscrew and you don't lose any travel on either side of the saddle. Now if I could just afford a small ballscrew.

Did you have to mill the "tunnel" for the ball screw nut?

Alan

[andypugh]

Thanks, I was guessing that you had cut into the dovetails to get that ballscrew nut to fit.

Indeed, but by definition the area round the nut never goes past the ends of the mating dovetail, so those bits are almost redundant. (I guess they contribute to overall rigidity)

Did you have to mill the "tunnel" for the ball screw nut?

I did mill it,but I didn't need to. The ball nut is a little longer than the original nut, and I didn't want to lose any travel. I also wanted an end-stop which prevented the nut coming off the screw. This could have been achieved by drilling a hole for the ballscrew to fit into in the existing material at the end of the slot. I haven't bothered with a support bearing at the back, just a stopper-block with a generous clearance hole for the leadscrew end.

[andypugh]

Further on this conversion.
For aluminium and mild steel it works nicely, but last night, trying to machine a 16mm ballscrew it all felt a bit weak. I am not sure that the tip I had would ever actually machine an Rc60 ballscrew properly, so that might be part of the issue. I have a CBN tipped tool on order and will see how that goes. For this particular job (manual) I can lock the cross-slide during cuts.

I do have a "Plan C". The ISEL integrated nut/mount units
http://www.techno-isel.com/LMC/Products/BmNuts16a.htm
won't fit in their existing housing, but might conceivably squeeze in an a custom housing if the inner ball-track is slim enough. I suspect that might then require machining of the saddle or cross-slide to make space for a ball return track, but then it might squeeze in on the diagonal.

I want to see if it is actually necessary first, though. After all until a few years ago ballscrews would have been considered fundamentally unmachinable except by grinding.

[LeeWay]

You could try annealing the end you need to machine. Big difference between turning an annealed end and a still hardened end.

[andypugh]

You could try annealing the end you need to machine. Big difference between turning an annealed end and a still hardened end.

I considered this, but none of my heat sources are intense enough to anneal the end without spreading to the working area.

[LeeWay]

I just wrapped a soaking wet rag around the end and used a standard propane torch. Held it on about 20 minutes. It never turned red, but did get hot enough to anneal the crust. The inside of my screws are soft anyway. Just Thompson rolled screws.

It makes the whole end turn just like cold rolled steel. Very nice. You can also tell exactly where the rag was. Still very hard there.

[acondit]

I just wrapped a soaking wet rag around the end and used a standard propane torch. Held it on about 20 minutes. It never turned red, but did get hot enough to anneal the crust. The inside of my screws are soft anyway. Just Thompson rolled screws.

It makes the whole end turn just like cold rolled steel. Very nice. You can also tell exactly where the rag was. Still very hard there.

Lee,

I also wrapped a wet rag around the end leaving about 1" of screw hanging out but I used an oxy-acetylene torch as a heat source. I heated it cherry red and then just let it cool down slowly. It cut very nicely (Nook ballscrew).

Alan

[andypugh]

I heated it cherry red and then just let it cool down slowly. It cut very nicely (Nook ballscrew).

I could probably achieve the same thing with my TIG welder, but I am a gear freak (and materials scientist) , and like the idea of a CBN tipped tool :-)

[andypugh]

I could probably achieve the same thing with my TIG welder, but I am a gear freak (and materials scientist) , and like the idea of a CBN tipped tool :-)

For info, if anyone is still reading this, the CBN tipped tool performed perfectly, cutting the hardened ballscrew like HSS through EN24T.

[whoafat]

Andy,
I had writtent off the thought of doing a mini lathe CNC mod since I did not have a CAM that had a dedicated lathe program. That changed and Bobcad V23 can now does CAM for lathes. However, cost may be deterrent since those 8mm leadscrews are probably very expensive. Can you tell me where you got your 8mm leadscrew and if that was the best deal you could get at time. I apologize for jumping in so late in the game since you must be busy running your CNC lathe,
thanks,
Wilfred

[aminear]

Sorry for jumping in here, I have also done a ballscrew on my mini-lathe X axis. Best upgrade I have ever done, no backlash, works great.

I got my ballscrew on ebay, it is a small 8mm one.

I have pictures on the yahoo group
http://groups.yahoo.com/group/7x12mi...unt=20&dir=asc

The biggest part of the job is to make a new top piece for the cross slide.
The original is just too small to fix a screw into. Mine is about 3/8 to 1/2"
thicker. Once you do that everything else is pretty easy, you have enough room to machine a pocket to mount the nut.

In the pictures it is not shown but I added covers to close the ballscrew from swarf.

Arnie

[andypugh]

Andy,
I had writtent off the thought of doing a mini lathe CNC mod since I did not have a CAM that had a dedicated lathe program. That changed and Bobcad V23 can now does CAM for lathes.

I am using EMC2, and that "understands" lathes. I am using two different config files as mine is a combined mill/lathe. One config calls the longitudinal leadscrew X, and the other calls it Y.

However, cost may be deterrent since those 8mm leadscrews are probably very expensive. Can you tell me where you got your 8mm leadscrew and if that was the best deal you could get at time.

I bought it from eBay. I think the supplier was Marchant Dice. They offer 8mm ballnuts at £62 and then £4.80 per 100mm of screw.
I don't know what shipping to the US would cost, probably very little.
http://www.worldofcnc.com/products.asp?recnumber=69

That compares favourably with the $1288 currently being asked on eBay...

[wildwestpat]

Andy,
................ cost may be deterrent since those 8mm leadscrews are probably very expensive. Can you tell me where you got your 8mm leadscrew and if that was the best deal you could get at time. ............Wilfred

Hi folks

I got my 8mm ballscrews off ebay power seller d_kwa2520 (Thialand). There were a number of these offered a couple of months ago and they are a good fit for the compound slide on the 7xXX lathes. The NSK part number is RMA0801.5C7S - 180 i.e. 180mm x 8 mm dia x 5mm pitch C7 rolled.

I have drawn up the conversion GA but am bogged in domestic chore of house painting so I am not able to get started on fitting the ballscrews.

However think very hard about the need to automate the compound slide. With CNC the tool tip can be driven to follow most tool paths without the compound slide. Even screw cutting can use an advance in index point for the Z axis to match the feed applied for each pass of the tool thus avoiding one of the clasic uses of the compound on small lathes where chatter can be an issue. So think about the parts you are going to make and work out if they can be made with the cross slide instead with CNC. Wish I had thought first! So I will be fitting 8mm BS to the compound when the painting is finished.

Also on the NSK data sheet they suggest using deep grove flanged ball races to make a simple screw mounting. This fits very well with the 7xXX - pity the stepper is so big.

Hope this helps.

Have fun with CNC and stay safe

Regards

Pat